Layout & Special Features Of GT46MAC 1. Lay Out

1 2 3 6 7 21 8 9 10 11 12 13

19 14 5 16 20 4 15 17 18 1. DRIVERS CAB 12. COOLING FANS 2. #1 ELECTRICAL CONTROL CABINET 13. RADIATORS 3. DYNAMIC BRAKE GRIDS & FANS 14. AC TRACTION MOTOR 4. #1 TCC 15. BATTERY BOX 5. #2 TCC 16. FUEL TANK 6. DUST BIN BLOWER 17. UNDER FRAME 7. TRACTION MOTOR BLOWER 18. DRAFT GEAR 8. EXHAUST MANIFOLD 19. COUPLER 9. ENGINE 20. AIR BRAKE RACK 10 EQUIPMENT RACK 21. TRACTION ALTERNATOR 11 AIR COMPRESSOR • AC-AC locomotives hitherto manufactured by GM have been only for the

North American market which does not impose any major constraint on the layout primarily because axle loads are in region of 30t are permitted on North American Railroads. Development of the layout for GT46MAC the axle load for which is restricted to around 20.5 t , was therefore, a major exercise in locomotive design.

• The locomotive has been designed on the ‘platform’ concept i.e. the layout

and the mounting of equipment is arranged in such a manner that retrofitment of equipment developed in future on existing locomotives as well as equipment changes/upgradation of the existing design of the locomotive can be implemented without any major change in the underframe, superstructure and even layout.

2 GT46MAC is provided with the following special features- • 710G3B fuel efficient engine is a low maintenance high fuel efficiency

diesel engine. The fuel efficiency of this locomotive is 11 % better than the existing WDM2 locomotive. The engine has many modern features like :

• Laser hardened cylinder liners, • Unit fuel injectors which eliminate the problematic HP tube • Inconel valves and Hydraulic valve adjuster • Durable crankcase and piston structure

• AC-AC transmission has the following features / advantages -

• High adhesion and Tractive effort • Maintenance-free traction motors • No limitation of minimum continuous speed • High reliability and availability • Lower rolling resistance and higher energy efficiency

• Computer Control, a 32 BIT computer control for locomotive controls

having, following advanced features -

• Trouble Shooting and Self -Diagnostics • Alpha Numeric display • Archive memory and Data logging • Radar based super series Wheel Slip/Slide Control system

• High adhesion HTSC bogies, which have traction bar arrangement with

unidirectional traction motors resulting in low maintenance, longer wheel life and higher adhesion.

• Improved mechanical systems, the notable being -

• microprocessor based engine cooling system • High lube oil sump capacity • Self-cleaning inertial type primary filter • Efficient secondary air filtration

• Improved Miscellaneous Electrical Systems, the notables being:

• Wide range dynamic brakes effective down to near standstill • Maintenance-free roller suspension bearings having lower rolling

resistance • Efficient filtration for electronic cabinet

5. Locomotive Design There have been significant changes in locomotive technology during past 10-15 years. Modern electric and diesel-electric locomotives have sophisticated control systems that allow precise control for power application to the rails. These locomotives, therefore, have the ability to significantly out-perform older technology locomotives. Introduction of AC-AC technology ensures that the locomotives are dispatched to gain the maximum benefit of the increased dispatchable adhesion. The following mechanical principles and mathematical formulas that govern locomotive power application need to be clearly defined: 5.1 Locomotive Horsepower There are four different horsepower ratings on a locomotive: 5.1.1 Brake horsepower.

Brake horsepower is measured at the engine crankshaft and is a measure of the TOTAL horsepower available for conversion to electrical energy at the main generator plus the power required for driving accessory loads. 5.1.2 Traction Horsepower Traction horsepower = Brake horsepower - Accessory loads GT46MAC locomotive has the following accessory horsepower

demands:

• Auxiliary Generator.

• Traction Motor/Main Generator Blower. • Air Compressor - mechanically driven by engine, but has a zero

horsepower load when unloaded and is disengaged. GT46MAC has a clutch which disengages when no compressed air is required.

• Inertial Filter Blower Motor. • Radiator Cooling Fans - electrically driven by the companion

alternator. GT46MAC utilises two speed-cooling fans to lessen the horsepower demands for engine cooling when full cooling is not required.

• AC Inverter Blowers - electrically driven by the companion

alternator.

Traction HP rating is the most commonly used rating when quoting locomotive horsepower. When railroads dispatch loads on hp/ton basis, they in almost all cases use traction hp for calculations.

5.1.2 Net Traction Horsepower Net Traction Horsepower = Traction Horsepower x Generator Efficiency In case of GT46MAC locomotive, 0.94 is the efficiency of the main generator. 5.1.3 Rail Horsepower Rail horsepower, the power delivered by the locomotive wheels at the rails, can be expressed by Rail Horsepower = Traction Horsepower x Transmission Efficiency Transmission efficiency is through: • Main Generator • Switch Gear • Cables • Traction Motors • Traction Motor Axle Gears. • Inverters 5.1.4 Draw Bar Horsepower The power developed at the draw bar called Draw Bar Horsepower and is the actual horsepower used to pull a trailing load. It is the engine to generator horsepower minus electrical transmission losses minus horsepower necessary to move the locomotive only. Drawbar Horsepower =

{(Engine to Generator H.P. x Transmission Efficiency) - (Loco weight x locomotive resistance x kmph)}

270 kg km per hour Due to the fact that the formula includes "locomotive resistance" and kmph, it is necessary to specify the grade and curve condition as well as the speed of movement to obtain draw bar hp value. The resistance for each one percent of grade requires an additional 9.2 kg/t. Each degree of curvature requires and additional about 0.37 kg/t. The influence of Rolling Resistance on DB

horse power will be explained later. It should be clear that the Draw bar horsepower decreases with increased speed. 5.1.5 Horsepower Required to Pull a given Train Load The calculations to find the Drawbar horsepower to pull a given train up a specified grade and curvature can also be made. Drawbar HP required = Resistance X Wt. of Freight Car X No. of Freight Cars X kmph 270 Draw bar horsepower requirements will increase with increased speed. 5.2 Resistance 5.2.1 Rolling Resistance The rolling resistance of a train can be determined by formula is generally is taken from tables and curves based on formula. The most widely used of such formulae is the "Davis Formula". Rolling resistance is generally expressed in kg/t and is summation of Flange Resistance, Journal Resistance and Air Resistance. Other things being equal, total Rolling Resistance increases as speeds increase. 5.2.2 Grade Resistance Grade resistance, expressed in kg/t , is independent of and unrelated to train speed. It is due to the force of gravity. It is always equal to 10 kg/tonne for each percent of grade as illustrated in the calculations below. 1 m rise

1% Grade = 100 m distance when Weight, W = 1 tonne = 1000 Kg RG = 1/100 x 1000 Kg = 10 Kg Grade resistance = 10 Kg per 1 % of grade. Rise in elevation x 100 x RG (10 kg/t) Total Grade Resistance =

Distance travelled .

Comment [D1]:

5.2.3 Curve Resistance

A one degree curve is a curve whose central angle extends to a chord of 30.48 m (100 feet). A 30.48 m (100 feet ) chord is 1/360 of a complete circle, the radius of a 1' curve is 1746.5 m (5730 feet). Curve resistance is expressed in kg / t / degree.

Degree of curvature = 5730 / Radius in feet or 1746 / Radius in m 5.3 Tractive Effort

Tractive effort is defined as the turning force produced at the rails by the driving wheels. Tractive Effort can be expressed mathematically as follows for an AC locomotive.

Tractive Effort = Traction Horsepower x 315 mile-Ibs/hr / Speed in miles per hour or Traction Horsepower x 230 km-kg/hr / Speed in km per hour a. Tractive effort depends on five major factors:

I. Horsepower of the diesel engine. II. Ability of the main generator. III. Ability of the traction motors. IV. Gear ratio. V. Adhesion

• Weight on driving wheels. • Rail condition. • Wheel Slip Control System. • Inverter System.

b. The effect of the above factors on tractive effort is explained below:

i) Horsepower of the Engine HP of the diesel engine primarily determines the possible TE a locomotive can develop at the rims of the driving wheels. T.E calculations use the Traction HP for calculation purposes. With an increase in the horsepower of the engine, either T.E. of the locomotive will increase for the same speed or speed will be increase with the same T.E. ii) Ability of the Main Generator

The main generator is the first step in the transmission of engine horsepower to the wheels. The main generator converts the mechanical power into electrical energy, referred to as kW. This electrical energy is then used by the traction motors to turn the locomotive wheels. kW are measured by the following formulas : Main Generator Voltage x Main Generator

Current Main Generator Kilowatts = 1000 W per kilowatt Tractive Horsepower = Main Generator Kilowatt /0.746 HP per kilowatt The generator can produce any combination of amperage and voltage within the rated power range of the locomotive. iii) Ability of the Traction Motors Traction motors transform the electrical energy of the main generator into mechanical force to turn the locomotive wheels. At low speeds, the traction motors must be capable of operating at their thermal limit. Maximum locomotive speed is limited by the safe rotational speed of the armature. In a DC motor, the armature windings limit the maximum speed of the armature to approximately 2400 RPM. In an AC motor for the GT46MAC, the induction rotor allows the operating RPM to increase to 3600 RPM. The ratings of the traction motors also affect the "Minimum Continuous Speed" of a DC locomotive, as well as the tractive horsepower available for transmission to the motors. With an AC locomotive, however, "Minimum Continuous Speed" is not a consideration. With AC traction motors, the locomotive can be put to full throttle at standstill without any damage to the motors. iv) Effect of Gear Ratio At full load, a given power output will produce a corresponding rotor speed regardless of gear ratio. The effect of changing gear ratio is to change the train speed at which full load can be applied continuously without thermal damage to the motors. Therefore: 1. Increasing the gear ratio reduces the minimum speed (hence

increases tonnage) at which a given locomotive can operate without heat damage to the motors.

2. Reducing the gear ratio, the maximum speed at which a given

locomotive can operate without mechanical damage to the motors.

v) Adhesion

Adhesion can be defined by the following locomotive formula: % Adhesion = Tractive Effort (kg) X 100/ Locomotive Weight There are three classes of adhesion:

• Required (Train Weight and Grade dependent) • Available (Operation under a given set of rail conditions) • Developed (Locomotive capability through enhancements-wheel

slip control)

The adhesion rating of a locomotives depends upon confidence level. This means that at a confidence level of 98%, the user can count on the locomotive developing the given adhesion factor 98% of the time. This is also termed as "All Weather Adhesion". There are cases where trains can be dispatched with a lower confidence level and a higher adhesion requirement. For example, trains may be dispatched during the summer months at a lower confidence level i.e. the user is counting on higher adhesions because of good weather conditions. Under inclement weather conditions, the locomotives can be dispatched at a higher confidence level of making a successful trip as the rail conditions deteriorate. There is a large gain in dispatchable adhesion as the confidence level drops to say 80 %. This means that if one counts on the locomotive to produce 43% adhesion, it will probably make the run successfully only 80% of the time without help.

• Weight on Driving wheels The weight on the driving wheels is that portion of the entire weight supported by the wheels driven by traction motors. The weight on driving wheels is in an important factor in the locomotive's "adhesion". Adhesion is the grip produced by friction between the steel wheels and steel rails. Adhesion is required to keep the wheels from slipping. In the modern locomotives which allow "wheel creep" (controlled wheel slip), however, the maximum tractive effort can be much higher due to the precise control of the wheel creep systems. • Rail Conditions With a given weight on rails, adhesion depends on rail conditions. Dampness, water, leaves, rust, ice, frost, and oil cause rails to be slippery. With GT46MAC locomotive, the adhesion may TEMPORARILY reach as much as 45% (with ideal rail conditions). Practical year round adhesion factor may be as low as 33 %. • Wheel Slip Control System

The wheel slip control system used on a locomotive can have a dramatic effect on the adhesion level achieved. Until the introduction of the "Super Series" wheel slip control system, all wheel slip control systems were "corrective" type systems. In other words, they operated under the principle that all wheel slip is bad and would reduce power to traction motors to control the slip. The introduction of "Super Series" improved dispatchable adhesion. The "Super Series" wheel creep control system allows the wheels to exceed ground speed by a certain percentage, depending on rail conditions, to improve adhesion. Super Series is activated automatically through the control system. The introduction of AC technology also improves the wheel creep control system due to its rapid response. In a DC locomotive, power is modulated by varying the DC field current of the main generator. There is an inherent lag time as the main generator's magnetic field requires time to collapse. With the AC locomotive, the wheel creep corrections are far more rapid as the devices that control the power output to the AC traction motors (called Gate Turn Off Thrystors, or simply GT0s) can have their switching sequence changed almost instantaneously. Power corrections are much more rapid and smoother with the AC traction equipped locomotive. • Inverter System

GT46MAC locomotive utilizes a system called "truck control", where one inverter controls all of the axles within a truck unlike GE which uses single axle inverter system i.e. one inverter per axle. While "truck control" system has less number of physical components to maintain, this has the disadvantage of the power reduction in the event of an inverter failure.

5.4 Dynamic braking effort

Dynamic braking effort may be considered as negative tractive effort. It is useful for controlling train speed. Dynamic Brakes are normally not used to stop a train but are used to assist deceleration.

Dynamic Brakes are the preferred tool to control train speed on, many railroads for the following reasons:

i) It saves considerable brake shoe wear, the subsequent reduction in air brake use minimizes the chance of stuck brakes on the train.

ii) It eliminates the fuel inefficient practice of 'Stretch braking' a train

with air brakes.

5.5 Brake Effort Braking effort for a train can be calculated by the Following formula: Brake Effort = (-GR r+ CR + CarR) x (Trailing load in tonne + Locomotive Wt. in tonne) where GR = Grade resistance CR = Curve resistance

CarR = Car resistance 5.6 Comparison Between Four Axle & Six Axle Locomotive

Six axle locomotive has 50% more Traction Motors than a four axle locomotive resulting in:

• Six axle locomotive has about 50% more tractive effort than a four axle locomotive.

• Six axle locomotive weighs about 50% more than a four axle

locomotive. • Six axle locomotive's minimum continuous speed is approximately

40% more than a four axle locomotives with equal horsepower.

With equal trailing tonnage, six axle locomotive's running time on a given run over the railroad is slightly longer than the four axle locomotive. This is because of the increased rolling resistance with the additional two motors / axles.

As a general rule, if the locomotive's primary mission is to haul trains at high speeds (intermodal use), four axle locomotive is better suited. If the locomotive's primary responsibility is heavy service over terrain with grades and curves, six axle locomotive is better suited.

1

Locomotive Design There have been significant changes in locomotive technology during past 10-15 years. Modern electric and diesel-electric locomotives have sophisticated control systems that allow precise control for power application to the rails. These locomotives, therefore, have the ability to significantly out-perform older technology locomotives. Introduction of AC-AC technology ensures that the locomotives are dispatched to gain the maximum benefit of the increased dispatchable adhesion. The following mechanical principles and mathematical formulas that govern locomotive power application need to be clearly defined: 1 Locomotive Horsepower There are four different horsepower ratings on a locomotive: 1.1 Brake horsepower.

Brake horsepower is measured at the engine crankshaft and is a measure of the TOTAL horsepower available for conversion to electrical energy at the main generator plus the power required for driving accessory loads. 1.2 Traction Horsepower Traction horsepower = Brake horsepower - Accessory loads GT46MAC locomotive has the following accessory horsepower

demands:

• Auxiliary Generator.

• Traction Motor/Main Generator Blower. • Air Compressor - mechanically driven by engine, but has a zero

horsepower load when unloaded and is disengaged. GT46MAC has a clutch which disengages when no compressed air is required.

• Inertial Filter Blower Motor. • Radiator Cooling Fans - electrically driven by the companion

alternator. GT46MAC utilises two speed-cooling fans to lessen the horsepower demands for engine cooling when full cooling is not required.

• AC Inverter Blowers - electrically driven by the companion

alternator.

2

Traction HP rating is the most commonly used rating when quoting locomotive horsepower. When railroads dispatch loads on hp/ton basis, they in almost all cases use traction hp for calculations.

1.3 Net Traction Horsepower Net Traction Horsepower = Traction Horsepower x Generator Efficiency In case of GT46MAC locomotive, 0.94 is the efficiency of the main generator. 1.4 Rail Horsepower Rail horsepower, the power delivered by the locomotive wheels at the rails, can be expressed by Rail Horsepower = Traction Horsepower x Transmission Efficiency Transmission efficiency is through: • Main Generator • Switch Gear • Cables • Traction Motors • Traction Motor Axle Gears. • Inverters 1.5 Draw Bar Horsepower The power developed at the draw bar called Draw Bar Horsepower and is the actual horsepower used to pull a trailing load. It is the engine to generator horsepower minus electrical transmission losses minus horsepower necessary to move the locomotive only. Drawbar Horsepower =

{(Engine to Generator H.P. x Transmission Efficiency) - (Loco weight x locomotive resistance x kmph)}

270 kg km per hour Due to the fact that the formula includes "locomotive resistance" and kmph, it is necessary to specify the grade and curve condition as well as the speed of movement to obtain draw bar hp value. The resistance for each one percent of grade requires an additional 9.2 kg/t. Each degree of curvature requires and additional about 0.37 kg/t. The influence of Rolling Resistance on DB

3

horse power will be explained later. It should be clear that the Draw bar horsepower decreases with increased speed. 1.6 Horsepower Required to Pull a given Train Load The calculations to find the Drawbar horsepower to pull a given train up a specified grade and curvature can also be made. Drawbar HP required = Resistance X Wt. of Freight Car X No. of Freight Cars X kmph 270 Draw bar horsepower requirements will increase with increased speed. 2 Resistance 2.1 Rolling Resistance The rolling resistance of a train can be determined by formula is generally is taken from tables and curves based on formula. The most widely used of such formulae is the "Davis Formula". Rolling resistance is generally expressed in kg/t and is summation of Flange Resistance, Journal Resistance and Air Resistance. Other things being equal, total Rolling Resistance increases as speeds increase. 2.2 Grade Resistance Grade resistance, expressed in kg/t , is independent of and unrelated to train speed. It is due to the force of gravity. It is always equal to 10 kg/tonne for each percent of grade as illustrated in the calculations below. 1 m rise

1% Grade = 100 m distance when Weight, W = 1 tonne = 1000 Kg RG = 1/100 x 1000 Kg = 10 Kg Grade resistance = 10 Kg per 1 % of grade. Rise in elevation x 100 x RG (10 kg/t) Total Grade Resistance =

Distance travelled .

Comment [D1]:

4

2.3 Curve Resistance

A one degree curve is a curve whose central angle extends to a chord of 30.48 m (100 feet). A 30.48 m (100 feet ) chord is 1/360 of a complete circle, the radius of a 1' curve is 1746.5 m (5730 feet). Curve resistance is expressed in kg / t / degree.

Degree of curvature = 5730 / Radius in feet or 1746 / Radius in m 3 Tractive Effort

Tractive effort is defined as the turning force produced at the rails by the driving wheels. Tractive Effort can be expressed mathematically as follows for an AC locomotive.

Tractive Effort = Traction Horsepower x 315 mile-Ibs/hr / Speed in miles per hour or Traction Horsepower x 230 km-kg/hr / Speed in km per hour a. Tractive effort depends on five major factors:

I. Horsepower of the diesel engine. II. Ability of the main generator. III. Ability of the traction motors. IV. Gear ratio. V. Adhesion

• Weight on driving wheels. • Rail condition. • Wheel Slip Control System. • Inverter System.

b. The effect of the above factors on tractive effort is explained below:

i) Horsepower of the Engine HP of the diesel engine primarily determines the possible TE a locomotive can develop at the rims of the driving wheels. T.E calculations use the Traction HP for calculation purposes. With an increase in the horsepower of the engine, either T.E. of the locomotive will increase for the same speed or speed will be increase with the same T.E.

5

ii) Ability of the Main Generator The main generator is the first step in the transmission of engine horsepower to the wheels. The main generator converts the mechanical power into electrical energy, referred to as kW. This electrical energy is then used by the traction motors to turn the locomotive wheels. kW are measured by the following formulas : Main Generator Voltage x Main Generator Current

Main Generator Kilowatts = 1000 W per kilowatt Tractive Horsepower = Main Generator Kilowatt /0.746 HP per kilowatt The generator can produce any combination of amperage and voltage within the rated power range of the locomotive. iii) Ability of the Traction Motors Traction motors transform the electrical energy of the main generator into mechanical force to turn the locomotive wheels. At low speeds, the traction motors must be capable of operating at their thermal limit. Maximum locomotive speed is limited by the safe rotational speed of the armature. In a DC motor, the armature windings limit the maximum speed of the armature to approximately 2400 RPM. In an AC motor for the GT46MAC, the induction rotor allows the operating RPM to increase to 3600 RPM. The ratings of the traction motors also affect the "Minimum Continuous Speed" of a DC locomotive, as well as the tractive horsepower available for transmission to the motors. With an AC locomotive, however, "Minimum Continuous Speed" is not a consideration. With AC traction motors, the locomotive can be put to full throttle at standstill without any damage to the motors. iv) Effect of Gear Ratio At full load, a given power output will produce a corresponding rotor speed regardless of gear ratio. The effect of changing gear ratio is to change the train speed at which full load can be applied continuously without thermal damage to the motors. Therefore: 1. Increasing the gear ratio reduces the minimum speed (hence

increases tonnage) at which a given locomotive can operate without heat damage to the motors.

6

2. Reducing the gear ratio, the maximum speed at which a given locomotive can operate without mechanical damage to the motors.

v) Adhesion

Adhesion can be defined by the following locomotive formula: % Adhesion = Tractive Effort (kg) X 100/ Locomotive Weight There are three classes of adhesion:

• Required (Train Weight and Grade dependent) • Available (Operation under a given set of rail conditions) • Developed (Locomotive capability through enhancements-wheel

slip control)

The adhesion rating of a locomotives depends upon confidence level. This means that at a confidence level of 98%, the user can count on the locomotive developing the given adhesion factor 98% of the time. This is also termed as "All Weather Adhesion". There are cases where trains can be dispatched with a lower confidence level and a higher adhesion requirement. For example, trains may be dispatched during the summer months at a lower confidence level i.e. the user is counting on higher adhesions because of good weather conditions. Under inclement weather conditions, the locomotives can be dispatched at a higher confidence level of making a successful trip as the rail conditions deteriorate. There is a large gain in dispatchable adhesion as the confidence level drops to say 80 %. This means that if one counts on the locomotive to produce 43% adhesion, it will probably make the run successfully only 80% of the time without help.

• Weight on Driving wheels The weight on the driving wheels is that portion of the entire weight supported by the wheels driven by traction motors. The weight on driving wheels is in an important factor in the locomotive's "adhesion". Adhesion is the grip produced by friction between the steel wheels and steel rails. Adhesion is required to keep the wheels from slipping. In the modern locomotives which allow "wheel creep" (controlled wheel slip), however, the maximum tractive effort can be much higher due to the precise control of the wheel creep systems. • Rail Conditions With a given weight on rails, adhesion depends on rail conditions. Dampness, water, leaves, rust, ice, frost, and oil cause rails to be slippery. With GT46MAC locomotive, the adhesion may

7

TEMPORARILY reach as much as 45% (with ideal rail conditions). Practical year round adhesion factor may be as low as 33 %. • Wheel Slip Control System The wheel slip control system used on a locomotive can have a dramatic effect on the adhesion level achieved. Until the introduction of the "Super Series" wheel slip control system, all wheel slip control systems were "corrective" type systems. In other words, they operated under the principle that all wheel slip is bad and would reduce power to traction motors to control the slip. The introduction of "Super Series" improved dispatchable adhesion. The "Super Series" wheel creep control system allows the wheels to exceed ground speed by a certain percentage, depending on rail conditions, to improve adhesion. Super Series is activated automatically through the control system. The introduction of AC technology also improves the wheel creep control system due to its rapid response. In a DC locomotive, power is modulated by varying the DC field current of the main generator. There is an inherent lag time as the main generator's magnetic field requires time to collapse. With the AC locomotive, the wheel creep corrections are far more rapid as the devices that control the power output to the AC traction motors (called Gate Turn Off Thrystors, or simply GT0s) can have their switching sequence changed almost instantaneously. Power corrections are much more rapid and smoother with the AC traction equipped locomotive. • Inverter System

GT46MAC locomotive utilizes a system called "truck control", where one inverter controls all of the axles within a truck unlike GE which uses single axle inverter system i.e. one inverter per axle. While "truck control" system has less number of physical components to maintain, this has the disadvantage of the power reduction in the event of an inverter failure.

4 Dynamic braking effort

Dynamic braking effort may be considered as negative tractive effort. It is useful for controlling train speed. Dynamic Brakes are normally not used to stop a train but are used to assist deceleration.

Dynamic Brakes are the preferred tool to control train speed on, many railroads for the following reasons:

i) It saves considerable brake shoe wear, the subsequent reduction in air brake use minimizes the chance of stuck brakes on the train.

8

ii) It eliminates the fuel inefficient practice of 'Stretch braking' a train

with air brakes. 5 Brake Effort Braking effort for a train can be calculated by the Following formula: Brake Effort = (-GR r+ CR + CarR) x (Trailing load in tonne + Locomotive Wt. in tonne) where GR = Grade resistance CR = Curve resistance

CarR = Car resistance 6 Comparison Between Four Axle & Six Axle Locomotive

Six axle locomotive has 50% more Traction Motors than a four axle locomotive resulting in:

• Six axle locomotive has about 50% more tractive effort than a four axle locomotive.

• Six axle locomotive weighs about 50% more than a four axle

locomotive. • Six axle locomotive's minimum continuous speed is approximately

40% more than a four axle locomotives with equal horsepower.

With equal trailing tonnage, six axle locomotive's running time on a given run over the railroad is slightly longer than the four axle locomotive. This is because of the increased rolling resistance with the additional two motors / axles.

As a general rule, if the locomotive's primary mission is to haul trains at high speeds (intermodal use), four axle locomotive is better suited. If the locomotive's primary responsibility is heavy service over terrain with grades and curves, six axle locomotive is better suited.

15. Locomotive Testing And Painting 15.1 Locomotive Test General Motors adheres to following concept/philosophy:

⇒ All individual assemblies and components are tested during the locomotive assembly either at the GM works or at the supplier end.

⇒ All electronic and air brake equipment are to be left unplugged during assembly.

15.2 Testing should verify/ audit integration of all locomotive system and sub-system. A very elaborate test procedure for the complete locomotive is followed by EMD before the locomotive is put on line. The test procedure is based on the relevant Engineering Test Instructions, defects found on previous units and reports from the service department. In case of GT46MAC, which would be a prototype even as it is electrically similar to SD70MAC, the procedure for the first locomotive is a more exhaustive and stringent test protocol. After completion of testing, the test records are scrutinised. As test checks are completed or at the end of the shift, they are to be initialled by the test personnel opposite to the test numbers.

After the preliminary inspection, Hi Pot Test for power & control circuits including Dynamic brake is done to ensure that no damage has been done during production assembly. It is followed by continuity check on various sub-system and installation of EM2000 modules. All the connections to other electronic system are completed and power-up & self-tests done. During testing the following safety procedure are taken into consideration.

The second stage of testing starts with pre-lube of engine. The engine is started and all mechanical and electrical checks including Siemen’s Commissioning checks are completed. A pre-load test is done to confirm that other systems are ready for load test, e.g., Inertial blower and also customer specific feature, if any. During the load test, the locomotive power output is dissipated in the dynamic grids to confirm the integrity of the cabling of Dynamic brake system. The locomotives not having self load Test feature, are connected to external grids. During the Load Test, measurement of cab noise and vibrations at few selected locations are also done.

Finally, in the last stage, the locomotive is prepared for Track Test. Air brake

system is checked to ensure its integrity, besides any other specific feature which remains to be checked. The track test is done on a test track of 1/2 miles length approx. with maximum permissible speed of 35 kmph.(located in Diesel Division). it is done for single unit as well as multiple unit. The functioning of speed indicator, ground relay and pneumatic controls checked, besides push pull test for Dynamic brake Drag operation.

A pre-delivery inspection is carried out by down-loading all the fault/unusual

message encountered during testing of the loading and a final inspection carried out before dispatching the locomotive.

♦ On microprocessor units whenever a module is installed or removed, power supply

to the computer is switched off. A wrist grounding strap is used. ♦ All the electronic system should be disconnected prior to megger and hi-pot testing. ♦ To check the continuity and test point voltage, only digital type meter should be used ♦ Under open circuit condition, the main generator should not be excited. ♦ The meter leads and jumpers should not touch the carbody ground from 15V

circuits. ♦ Test points in 15 Volt supply should not be jumpered. ♦ Engine blow-out must be performed before starting the engine if the engine has

been down for eight hours or more. Some preliminary tests like checking of hand brakes, wheels, air compressor, engine oil, dust etc. are done before starting the actual testing. The testing consists of the following well defined steps sequentially -

⇒ Hi Pot test ⇒ Trainline continuity ⇒ Lighting circuit ⇒ Blower/Fans operation ⇒ Power contactor operation ⇒ EM2000 module application and computer preliminary test ⇒ EM 2000 system integration ⇒ Dynamic brake signals ⇒ Sanding ⇒ TM blower shutter ⇒ Engine run ⇒ Engine start ⇒ AG checks ⇒ Air compressor control, low air engine speed up & air system safety valve ⇒ TCC phase module temperature control ⇒ TCC power supplies, systems and operations test ⇒ Excitation test ⇒ Preload ⇒ Load test ⇒ Track test ⇒ Traction inverter cut-out ⇒ Multiple unit operation ⇒ Pre delivery test

15.3 Locomotive Painting:

The locomotive after complete testing is brought to specially designed painting booth. The painting is done as per the following sequence:

⇒ Preparatory booth

The locomotive is washed, degreased and deburring of all external welded joints completed. The appropriate areas e.g., consoles in the cab, TG fan, valves & pipes, rubber side bearer etc. are masked.

⇒ Painting Booth There are two painting booths where the following activity are done:-

• The external is coated with the epoxy primer.

• The cab and long-hood exterior surfaces are given polyurethane paint coat.

• The polyurethane masked stickers as per the painting style ( pertaining to rail road name, road number and longitudinal strips) are affixed at the appropriate locations. The masks are removed after the final painting.

• The external surfaces including underframe & bogies are then given one coat of polyurethane paint. Two hours drying time is given before applying another coat of the same paint. The dry & wet gauges are used to measure the paint thickness . Normally the paint thickness is of the order of 6 thou and its uniformity over the surface is maintained by the experience of the painter.

EMD also have separate painting booth for small piece parts and underframe.

The underframe assembly after fabrication is given one coat of epoxy paint before & after piping and cabling. Similarly assembled equipment rack is also given one coat of epoxy paint.

16. Visits To Various Facilities 16.1 Visit To M/S Atchison Castings/Kansas -USA

Atchison Castings Corporation (ACC) was re-organized in 1991 with the purpose

of becoming a broad based foundry company. ACC products are iron and steel castings ranging in size from 1 to 120, 000 lb. ACC customers are leaders in their own field and include General Motors, Caterpillar, General Dynamics, Rockwell International, Westinghouse, John Deere, General Electric, Morrison Knubsen, Bombardier, ABB etc.

The company was founded in Atchison, Kansas in 1872 to supply iron castings to

the Railroads. In 1956, the facility was acquired by Rockwell International. In 1991, ACC acquired Rockwell’s Foundry in Atchison, Kansas and Machine Shop in St. Joseph, MO.

All the castings are electronically analysed in the design development process

and create modifications using solidification software techniques, which optimise quality and cost without adversely affecting functional performance. M/s Atchison Casting is using their proprietary bonding agent. They have also very excellent sand recovery system.

All the casting ranges produced by ACC Castings are machined in fully finished

condition at St. Joe division (Atchison Castings Machine Shop) which is a separate unit.

The casting of truck requires one piece thin walled, high integrity, frame

castings. With solidification and mould filling simulation on computer, the company is able to achieve excellent quality. Bogie frame for HTSC truck have been developed as U-section in place of traditional Box-section. This design eliminates use of cores. The use of cores increase the cost of production and decrease the quality of castings. M/s GM/EMD and M/s Atchison Castings have collaborated for development of this design.

It is learnt that for future supplies of cast steel HTSC bogie frames to DLW, M/s

Atchison Casting has entered into a TOT contract with M/s Simplex Engg. & Foundry Works/Bhilai.

16.2 Visit To M/S Lord Corporation/ Erie/ PA - USA

Lord Corporation have facilities for designing, manufacturing and testing of metal

bonded rubber components as per customer requirements. Main component supplied to EMD is metal bonded rubber spring used in

secondary suspension and metal bonded rubber bushes for various joints. The design of metal bonded rubber spring is done on FEM package to optimise

the profile of rubber to avoid stress concentration. Lord Corpn. have modern manufacturing facility for manufacture of metal

bonded rubber components. Transfer moulding process is followed for moulding the rubber. For bonding between metal and rubber, they use special type of chemical developed for this purpose.

M/s Lord corporation have extensive fatigue testing facilities. Company has set

up new testing shop which is equipped modern fatigue testing machines, vibration shaker which are controlled by computer various data are recorded and analysed further. since major percentage of their products are supplied to aircraft industry, so they have installed three axis machines by which they can conduct all modes of testing simultaneously. The locomotive components are required to be tested for one million cycle at varying frequency.

17. Computer Aided Design By Unigraphics EMD uses Unigraphics package which is a completely integrated software and is used for drawing-drafting and modelling. The underframe, car body, cab, bogie frame and other bogie components such as wheels, axles, axle box, traction motors, suspension and brake rigging components are generated by solid modelling and assembled together. The package is very useful for preparation of layouts and study of infringement/clearances between different components of bogie. The package also enables calculation of weights, moment of inertia and centre of gravity which are required for vehicle dynamics studies. The models prepared by Unigraphics can be

transferred to ANSYS for finite element analysis. The package is supported by standard library of components such as nuts, bolts, screws, etc.; the components most commonly used can be generated and can also be included in the library.

Sizing of various cross section was done by keeping section modules of this bogie frame same with a similar bogie frame with box section. Afterwards optimisation of sections were carried out by FINITE ELEMENT ANALYSIS by applying load cases. 18. Recommendations 18.1 DLW should install Unigraphics system and ANSYS FEM package not only to fully assimilate EMD technology but also develop expertise in design of new locomotives of horse power ranging from 3000 to 5000 hp with EMD 12 cylinder and 20 cylinder engines. 18.2 DLW should follow EMD project management and design review process in design and manufacture of locomotives and assemblies.

GT46MAC LOCOMOTIVE Specification Track Gauge 1676 mm Total Weight on Rails 126 t Design Speed 100 kmph Wheel Arrangement Co-Co Height (top of rail to top of cooling fan) 4,120 mm Overall Length Over Buffers 21, 245 mm Fuel Capacity 6,000 L Cooling Water Capacity 1144 L Performance Specification

TCV 4,000 Starting Tractive Effort 540 kN Braking effort capability 270 kN

Engine 16-71OG3B

Turbocharger High Efficiency Fuel Injection Unit Fuel Injection

Traction Technology AC-AC

No. of invertors One/truck

EM2000 Advanced Computer

32-bit microprocessor Reduction in modules and components compared to Dash-2 series controls Improved reliability and performance Information can be downloaded to a laptop computer Flexible and expendable to accommodate future system enhancements Complete self-diagnostics Archived unit history data,

HTSC Bogie

No wearing surfaces extends bogie overhaul intervals to 1.6 million km Dual high adhesion and high speed Available gear ratios for heavy haul and passenger operation

Cab Features

Air operated windshield wipers Dual desk type control console - optional Multi-resettable vigilance controls - optional

Air System Direct drive air compressor Brake System Electronic Air Brake System Reliability and Serviceability

90-day maintenance intervals AC motors doubles traction motor life No running maintenance required

* No brushes, commutator, or rotor insulation * No flashovers

Bogie Inverter Control * High level of reliability with fewer parts

1.6 million kilometre overhaul with HTSC Bogie 6-year engine overhaul period

Safety Aspects

Increased Crashworthiness Provision of Anti-climber

WDG4 loco DESCRIPTION OF BOGIE

1. WDG4 loco is provided with HTSC (High Tensile Steel Cast) Bogies. 2. This is a three-axle bolster-less bogie with two-stage suspension with helical coil springs in primary

stage and rubber compression springs in secondary stage of suspension. 3. The locomotive car body weight is transferred directly to the bogie frame through four rubber

“Compression” spring assemblies.

4. The lateral stiffness of rubber springs is utilized to provide lateral guidance at the secondary stage and provide the yaw stiffness for stability.

5. Lateral spacing of rubber springs affords stability of locomotive on curves and damping provided by rubber springs and yaw dampers prevents nosing at high speed.

6. The bogie frame is supported on axles through “soft primary” suspension consisting of twelve single helical coil springs, two springs mounted on each axle box, to provide ride quality and equalization of wheel-set loads.

7. Shims of different thickness are provided above the outer and inner rubber “compression” spring assemblies for axle load equalization.

8 Centre pivot does not take any vertical load and is used only for transfer of traction and braking forces.

9.. The bogie is fitted with lightweight asynchronous, axle hung, nose suspended traction motors.

10. All traction motor nose positions are oriented to the same side of each axle within the bogie frame.

11. The relatively stiff secondary suspension, uni-directional arrangement of traction motors and low

center pivot limits the weight transfer between axles during adhesion. 12.. For wheel-set guidance in longitudinal mode, guide link fitted with rubber bush is provided between axle box and bogie frame to cushion the longitudinal thrust.

13.. Traction and braking forces are transmitted from wheel-set to bogie frame through these guide

links.

14. Axle boxes are fitted with tapered roller bearings with integrated bearing adapter.

15. Six vertical hydraulic dampers are provided in primary stage between axle and bogie frame, one with each nest of primary springs on the axle box.

16. Two hydraulic yaw dampers are provided in secondary stage between bogie frame and the loco under frame to supplement the damping provided by rubber springs.

17. The yaw dampers are oriented in such a way that they provide damping both in lateral and yaw modes.

18 Safety links are provided at the lateral stop locations between bogie frame and the under frame. 19 These links serve to prevent separation of the bogie from the locomotive car body in case of

derailment and also provide means of lifting the bogie along-with the locomotive car body.

20 Safety “hoops” are installed between each axle interlock bracket. 21. The locomotive is provided with conventional brake gear arrangement with single composition brake

shoe per wheel.

Ride Characteristics of WDG4 locomotive • Designed for 110 km/h • Axle load of 21.0t • Maximum Lateral force 4t • Derailment coefficient <1 • Lateral and Vertical acceleration 0.3g preferred ( 0.35g max.) • RI in Lateral & Vertical 3.75 preferred (max. 4.0) Ride and stability Performance • Oscillation test was carried on Main Line track (Lucknow - Sultanpur) speed of 115 km/h • Max. Lateral force observed was 2.9t • Derailment Coefficient was 0.30 • RI Vertical at 115 km/h was 3.65 • RI Lateral at 115 km/h was 3.83 • Acceleration in Vertical and Lateral mode were within limit. Some special features of bogie • Cast “U” type frame-High strength. • Unidirectional TM- High Adhesion. • Use of Guide links-Low flange force. • TM suspension through nose links-maintenance free. • Four bar mechanism centre pivot arrangement-maintenance free. • Soft primary helical springs-better load equalisation. • Stiff secondary rubber springs-controls pitching.

WDP4 loco Design features of WDP4 bogie

• Basic design is similar to that of WDG4 bogie the differences are highlighted • Axle load 19.5t • AA1 (B1) wheel arrangement • Lighter bogie frame (reduction of section of end transom). • Softer Primary helical springs. • Axle size is smaller of axle 3 & 4. • Secondary rubber lateral stiffness made softer • Different shimming due to difference in axle load. • Stiffer guide links. • Use of happy pads. • Different Damper capacity. Performance observed • Tested at Pueblo USA • On standard gauge • Tested up to Max speed of 180km/h • Lateral force, Derailment coefficient, Acceleration/RI (Vertical & Lateral) were measured. • Curving performance was checked. Design parameters • Speed potential of 180 km/h • Lateral force 3t • Derailment coefficient < 1 • RI Vertical & Lateral < 4.0 • Acceleration Vertical & Lateral mode < 0.35g • For track standards maintained to C&MI Vol-1 Ride Characteristics of WDP4 locomotive • Oscillation test was carried on at Pueblo(USA) speed of 180km/h • Max. Lateral force observed was 1.5t • Derailment Coefficient was 0.18 • RI Vertical at 180 km/h was 3.66 • RI Lateral at 180 km/h was 3.42 • Acceleration in Vertical and Lateral mode were within limit(less than 0.19g/0.15g)

LUBE OIL SYSTEM INTRODUCTION The complete engine lubrication system is a combination of four separate systems. They are the main lubricating system, the piston cooling system, the scavenging system and the soak back or turbo lube system. Each system has its own oil pump. The main lube oil pump and piston cooling oil pump (although individual pumps) are contained in the same housing and driven from a common drive shaft. There are separate pumps for scavenging and turbo lube oil system also. The main lube, piston cooling and scavenging pumps are driven mechanically from engine through accessory gear train at the front of the engine. The turbo soak back pump is driven electrically by an AC motor. System lube oil capacity: 950 Litres/ 1450 Ltrs, The oil level is checked by an oil gauge (Dip Stick). The oil level should be between low and full marks when the engine is at idle and the oil is hot (66°C) The system lube oil pressure is 125 psi. (LOPS setting: 8-12 psi at idle and 25-29 psi at full speed) The filter by pass valve is set at 40 psi. The turbo soak back oil pressure is 50 psi. Main lubricating system The main lubricating oil system supplies oil under pressure to most of the moving parts of the engine. It takes oil from strainer housing and sends it to main oil manifold, located above the crank shaft. System oil pressure is limited upto 125 psi by a relief valve situated in the passage between the pump and the manifold. Oil tubes at the center of each main bearing “A” frame conduct oil from the main manifold to the upper half of the main bearings. Drilled passages in the crankshaft supply oil to the connecting rod bearings, torsional damper and accessory drive gear at the front of the crank shaft. Leak off oil from adjacent main bearings lubricates the crank shaft thrust bearings. Oil from manifold enters the gear train at the rear of the engine, at the idler gear stub shaft. Oil passages in the base of the stub shaft distribute the oil. One passage conducts oil upward to the left bank camshaft drive gear stub shaft bracket through a jumper, and downward to the lower idler gear stub shaft and bearing. Another passage conducts oil to the right bank camshaft drive stub shaft bracket and on to the turbocharger oil filter supply line. After passing through the filter, the oil enters the return line, returning to the upper idler gear stub shaft bore and bearing. Filtered oil enters the turbocharger oil system from upper idler gear stub shaft. An oil pressure line connects to the top of turbocharger oil manifold, adjoining the filter. This oil pressure line goes to the low oil pressure device in the governor. Oil enters the hollow bore camshafts from the camshaft drive stubshafts. Radial holes in the camshaft conduct oil to each camshaft bearing. An oil line from one camshaft bearing

at each cylinder supplies oil to the rocker arm shaft, rocker arm cam follower assemblies, hydraulic lash adjusters and injector rocker arm button. Leak off oil returns to the oil pan. Passages in the turbocharger conduct oil to the turbo charger bearings, idler gear, planet gear assembly and auxiliary drive bore. Piston cooling oil system Piston cooling oil system pump receives oil from a common section with the main lube oil pump and delivers oil to the two piston cooling oil manifolds extending the length of the engine, one in each side. A piston cooling oil pipe at each cylinder directs a stream of oil through the carrier to cool the underside of the piston crown and the ring belt. Some of the oil enters the grooves in the piston pin bearing and the remainder drains out through holes in the skirt to the sump.

Scavenging oil system The scavenging oil system pump takes oil from the oil pan sump through the scavenging oil strainer. The pump then forces the oil through the oil filters and cooler, which are located at the equipment rack near the engine. Oil then returns to the strainer housing to supply the main lube oil pump and piston-cooling pump with cooled and filtered oil. Excess oil spills over a dam in the strainer housing and returns to the oil pan.

Soak back oil system To ensure lubrication of the turbo bearings prior to engine start, and the removal of residual heat from the turbo after engine shutdown, a separate lube oil pressure source is provided, called soak back system. The working of this system is controlled automatically by the locomotive control system. The motor is timed to operate 35 minutes after each time it is started. Oil circulation through the turbocharger is necessary prior to starting the engine and during the period when the engine oil pressure is building up to provide proper lubrication.

Turbo lube pump timing after shut down is based on the throttle position. Throttle position is logged by the computer. If throttle remains in position for 2 minutes or more the timing is as follows: Throttle position Time

1 15 Mins 2 20 Mins 3 25 Mins 4 30 Mins 5 (or higher) 35 Mins

An AC motor driven pump draws lube oil from oil pan, pumps the oil through a filter and head of the turbocharger oil filter directly into the turbocharger bearing area. The motor driven pump and the filter are mounted on the side of the oil pan on the Right Bank of the engine. A 55 psi relief valve, located in the head of the filter, controls the system pressure. A bypass valve set at 70 psi is also located at the filter head. This valve will open to permit oil from the soak back pump to bypass the filter element, if clogged. So that, lubrication can be supplied to the turbocharger to prevent turbo damage. SYSTEM COMPONENTS Lube oil strainer housing Lube oil strainer housing is situated at the accessory end of the crank case It contains one strainer (coarse) at the suction side of the scavenging pump and two strainers (fine) at the suction side of the main lube and piston cooling pump. An oil level is maintained in the strainer housing up to the bottom of the overflow opening by the scavenging system. This oil serves as the supply for the main lube and piston cooling system. Excess oil not used by these systems returns to the engine sump. A spring-loaded valve is provided to drain the oil from the strainer housing into the engine sump for strainer maintenance. Both of these valves are located under the filler cover. Normally oil is added to the engine by strainer housing.

STRAINER

The scavenging oil strainer (coarse) is installed in the housing at the suction side of scavenging pump. All oil for the scavenging system is drawn through it. Its duty is to protect scavenging pump from foreign materials. Main and piston cooling oil strainers (Fine): They are two in numbers, installed within the housing by a crab and hand wheel on the stud between the holes. Each strainer is sealed at the top by a “O” ring seal to arrest leakage. Each strainer consists of an element of pleated perforated metal core covered with mesh screening, and a metal cylinder that encloses the element. Cylinder prevents collapse of the element in the event of high pressure drop. The element is attached to the cylinder by a through bolt in the cylinder, which runs through the base of the element and is secured with a lock nut. The unperforated outer cylinder provides a constant head of oil since suction is from the bottom only and not through the entire length of the screen. Oil flow is from the bottom of the strainer between the cylinder and the mesh screen, through the mesh screen and the perforated metal core into the center of the element, then out the top of the strainer. Main Lube Oil and Piston Cooling pump The main lube oil and piston cooling pumps are positive displacement helical gear type pumps contained in one housing. A spacer plate separates the two pumps between the sections of the pump body. Each has individual oil inlet and discharge opening. The lube oil and piston cooling pump assembly is mounted in the center of the accessory drive housing, and driven by the accessory drive gear. Discharge capacity of main lube oil pump: 229 GPM at 900 rpm Discharge capacity of piston cooling pump: 109 GPM at 900 rpm Scavenging Oil Pump The scavenging oil pump is a positive displacement helical gear type pump, exactly similar to main and piston cooling pump except for the spacer between them. The scavenging pump is mounted on the accessory housing in line with, and to the left of the crankshaft, and is driven by accessory drive gear. The pump body, split transversely for ease of maintenance, contains sets of mated pumping gears. The driving gears are retained on the pump drive gear shaft by woodruff keys. The idler shaft is held stationary in the housing by a setscrew, and the driven pump gears rotate on this shaft on bushings pressed into the gear bores. The drive shaft turns in bushings pressed into the pump body. Pump discharge capacity: 405 GPM at 900 rpm.

Lube oil Filter Tank Lube oil filter tank is situated at the equipment rack in the front side of the engine. It consists of 05 Nos. pleated paper type filter elements. Filter elements must be renewed if filter tank pressure reaches 25 psi. at 8th notch and 7 psi at idle.at 66°C lube oil temperature. A bypass valve is provided in the filter tank to bypass the filter during cold start or plugged filter element. The bypass valve works at 40 psi differential pressure. Lube Oil Cooler The lube oil cooler assembly is positioned at an angle in the equipment rack at the front side of the engine. The external construction of the cooler consists of a fabricated steel oil tank surrounding the oil cooler core. The cooling water returning from the radiators enters the cooler through flange connection at the top side, flows down through the cooler tubes and is discharged through flanged connection at the bottom of the cooler. The lubricating oil enters the shell space through a flanged connection near one end of the cooler, flows transversely around the tubes and around the end of the baffles, and leaves the shell through a flanged connection near the opposite end of the cooler. The coolant and the oil flow through the cooler in opposite directions to produce the maximum cooling effect.

LUBE OIL COOLER

Lube Oil Pressure Relief Valve The lube oil pressure relief valve is installed on the lube oil cross over manifold, inside the accessory gear train housing on the left side of the engine. This valve is accessible for inspection and service by removing the Engine Protection Device. The purpose of the valve is to limit the maximum pressure of the lube oil entering the engine oil system. When the lube oil pump pressure exceeds the spring tension on the valve, the valve will be lifted off its seat and relieve the excess pressure. This oil drains into the accessory housing and then into oil pan. Turbocharger oil filter The turbocharger oil filter provides additional protection for the high speed bearings and other lubricated areas of turbocharger, by filtering the oil just before it is admitted to the turbocharger. Oil enters the filter through a cast manifold and, after passing through the filter, returns to the upper idler gear stubshaft and into the turbocharger. The filter element is of pleated paper construction, and is disposable. The filter is mounted on camshaft drive housing at the right bank of the engine. Some engines have disposable spin on type turbo lube filter. The filters should always be filled with clean oil before installing on the engine.

FORCED AIR SYSTEM This is a centralised system for storing and providing clean air for all-purpose engine requirement like cooling, combustion air and pressurisation of compartments etc. Its location is in between the TCCs and engine compartment. It is properly sealed so that unfiltered air should not rush into it. Entry of air is done through inertial filters located at either side of the locomotive car body and dirt blower expels separated dirt, out to the atmosphere through the roof of the locomotive. Air that is drawn into the compartment is primarily to supply: • Combustion air for the diesel engine • Cooling air for MG, companion Alternator and rectifier bank • Cooling air for Traction Motors • Cooling air for Traction Inverter equipments • Pressurisation of engine room and electrical cabinets BLOWERS Various blowers used in this system are: 1. M G BLOWER

Mounted on Aux. Generator on the front side closest to the Main Generator. Both MG Blower and TM Blower are mounted on the same housing separated by a partition. It supplies air for: • Cooling Main Generator Rectifier bank, Main Generator, Companion Alternator

and finally to Engine Room. • Maintain slight positive pressure in the engine room • Part of this air is used by Air Compressor and thus reduces the load of its filter

assembly 2. TM BLOWER

Mounted on Aux Generator on the front side away from the Main Generator. It supplies air for: • Traction Motor cooling • Generator pit operator operation • Main electrical cabinet pressurisation • Traction computer cooling

3. TCC ELECTRONIC BLOWER Mounted at Central Air compartment. It is driven by AC motor powered by Companion Alternator. This air is further filtered by paper filter located under each filter cabinet. Used for: • Cooling and pressurising a part of the Inverter Cabinet containing DC Link

Capacitors, gate units and Traction Computers 4. TCC BLOWERS

There are two TCC Blowers, one for each cabinet. It’s a 3 phase AC motor driven blower powered by Companion Alternator. Initial command for blower operation comes from TCC Computer and finally executed by EM 2000. They draw air directly from the ambient across the modules and expel it across the R-2 snubber resistor. They are used for supplying air for cooling phase module and cabinet.

ENGINE AIR INTAKE FILTER (FIBER GLASS BAG) Additional filtration is required for the air used by the engine. For this a fiberglass bag filter element is used for engine intake air filter. It is equipped with pressure switches to sense the pressure difference between turbocharger inlet and ambient. The switches are located inside the electrical cabinet and connected by tubes to the turbo inlet side of engine air filter and to ambient. They work as follows: • If pressure difference exceed 356 mm/ 14″ of water column Filter Vacuum Switch

(FVS) will trip closed and display message will read (FILTER VACUUM SWITCH TRIPPED)

• If pressure difference reaches 610 mm/ 24″ of water column Engine Filter Switch (EFS) trip close and EM 2000 will reduce engine speed and load to 6th notch with the display message (ENGINE AIR FILTERS ARE DIRTY- CHANG OUT REQUIRED, POWER MAY BE LIMITED TO 6TH NOTCH).

Hose stems are provided on the front of the electrical cabinet to take the manometer reading of pressure drops across the inertial air filter, the engine plus inertial air filters and the electrical cabinet filters.

14. Electrical Systems & Traction Alternator Design & Aux. System Design

14.1 Locomotive Electrics- Basic AC-AC System: The system basically uses diesel engine, alternator, rectifier, d.c. link, invertor(s) and asynchronous motors. The alternator is directly coupled to the diesel engine. The frequency of the alternator output varies with the speed of diesel engine. The voltage is rectified and the power is fed through a d.c. link to the invertor of the tractive system. Drive system uses asynchronous motors. Asynchronous motor when used on railway vehicle has to be supplied variable alternating voltage of variable frequency (VVVF). This is accomplished by the invertor the input to which is d.c. voltage through d.c. link. All AC-AC diesel locomotives employ this principle. The number of invertors and the size of the alternator depends on the amount of energy to be converted. ENGINE GENERATOR INVERTOR TRACTION MOTOR G = M 3 ~ 3~ 3 ~ The electronic control system ensures that the correct control inputs are given to the invertor. It also controls and monitors the diesel engine, the alternator and the other auxiliaries of the locomotive. It is the central control unit which ensures that the locomotive operates optimally. 14.2 Main Alternator and Companion Alternator Alternator is foot mounted with flange coupling with the engine. Alternator TA17 is a 3 phase, 10 pole machine equipped with two independent and interwoven sets of stator winding. It is basically two generators in one - two sets of stator windings, permanently connected in series, work with a rotating field common to both the windings in order to provide a higher generator output voltage, which is a basic requirement of a low current high voltage generator used on AC-AC locomotives.

The main alternator has a companion auxiliary generator CA 6 for power supply to large auxiliaries. It is also the main excitation source for the main alternator. The companion alternator is an electrically independent machine and is mechanically coupled on the main shaft of the traction alternator. The companion alternator rotor field is excited directly by auxiliary supply of the locomotive (74+4 VDC). It receives the excitation current from the auxiliary generator through slip rings located adjacent to the slip rings of the main generator. The output voltage is directly proportional to the speed of rotation but varies to some extent with change in alternator temperature and load.

Both these alternators are forced air cooled. A dedicated blower coupled to the engine crankshaft provides cooling to the Alternator / Rectifier system. The air flow pattern has been depicted below. Axial & Radial Cooling In EMD Alternator AIR FLOW STS CORE STACKS AIR FLOW

COMPANION ALTERNATOR

RECTIFIER

ALTERNATOR MAIN WINDING

14.3 Rectifier

AC output from the main alternator is supplied to air cooled rectifier. The rectifier assembly consists of high current, high voltage silicon diodes connected in 3 phase full wave bridge rectifier circuits. RC circuits are connected to suppress the transients signal.

14.4 Traction Motor The asynchronous motor with a squirrel cage rotor is the simplest of all electrical machines. When fed by a 3- phase alternating voltage, a magnetic field rotates in the stator. The speed of rotation of this field is directly proportional to the frequency of the A.C. voltage. The rotating magnetic field causes the rotor to turn at a slightly lower speed due to electric slip. This difference in speed is responsible for the development of the torque. The only winding fed with voltage in the asynchronous motor is housed in stator. To prevent hot-spot developing in winding overhang, it is directly ventilated. The winding is impregnated under vacuum. There are no exposed

metallic parts, so that excellent protection is assured. The rotor is squirrel type, i.e. it consists of un-insulated copper bars joint to sturdy short-circuiting rings. There is no commutator, sliprings, Brushgear or anything similar. Following aspects are given primary importance while designing AC traction motors :

♦ Vibrations and shocks from track ♦ Envelope dimensions - more torque packed in small space ♦ Reliability - TM subjected to different elements like movement of

locomotive, dirt heat & humidity ♦ Presence of transients ♦ Requirement of starting and road characteristics

14.5 Electrical Control Cabinet No. 1 (HVC)

Electrical control cabinet is for mounting of the following main equipment :-

• Main Control Panel • DC Link switch gear • Braking contactors • Circuit breakers • EM2000 computer chassis • EM2000 support hardware • GFC, GFD & IMGF • SCR bridge • Power supply for GTO1 & GTO2 • TCC blower contactors - six numbers • IB1 ,IB2 , IBKBL1 , IBKBL2 transducers • Display Screen on ECC#1 door • Engine Control Panel • TMA transducer • 74 V receptacles • The routine testing of HVC is an elaborate process . There is a

dedicated test station which is microprocessor controlled and has the facility to check the important aspects related with performance and reliability, viz., continuity of all the wires on the cabinet and actual operation of the relays, switches and contactors. All the test data is logged, abnormalities identified and a printout is taken for undertaking the rectification work.

• The software for the test station is written in HP Basic. EM

2000 Modules, which are not mounted at this stage, are therefore not tested at EMD. The cabinet complete is despatched to DD , London, OT.

14.5.1 Design Aspects Of ECC#1

• Ventilation Engineering of the cabinet has been done based on

the cooling requirements of major components, e.g. power chassis , EM2000 , SCR Bridge Assembly. Main duct has been constructed along the wall sided which branches to supply air to the components.

• The panel is modular so as to facilitate quicker assembly. • The cabinet is pressurised to avoid ingress of dust etc. A

pressure of 2 to 3” of water gauge is maintained. • No electro pneumatic contactors are used on this cabinet. • Components and cables of a common electrical circuit are

grouped together (e.g. GFC, GFD, RE2 , RE32, CA32 and the SCR Bridge) in order to reduce EMC interference.

14.5.2 Electrical Cabinets 2 & 3

Electrical cabinet number two and three are smaller cabinets than the HVC. These cabinets consist of the following components: Cabinet# 2. ♦ Auxiliary Generator circuit breaker ♦ ST & STA contactors - for starting of engine. ♦ RE11 & RE12 ♦ BCASM - Battery Charging assembly ♦ Provision for Shunt DC ♦ DVR - Digital Voltage Regulator ♦ Inductor L4,5,6 ♦ Air Filter Cabinet# 3 (AC Cabinet) ♦ Cooling fan contactors -six numbers ♦ Terminal Boards ♦ MRPTs- Main reservoir pressure transducer ♦ DIP80 - Diode Panel and CMUX hardware for multiplexing ♦ Air Filter

146 EM 2000

EM2000 is a modern locomotive computer control system. The system, has effectively replaced the outdated electronic and IC-based control systems used earlier. Some of the basic features of the system, inter alia, are- • Significant reduction in number of control modules • Better fault detection of components • Self diagnostics and self tests to aid in troubleshooting • Memory archive and data snap shot

The main computer chassis contains the following modules

• One CPU module which uses a 32 bit Motorola 68020 16 Mhz microprocessor

• Three Digital Input/Output (I/O) modules ( DIOs) • One communication module (COM) • One Analogue to digital and digital to analogue module ( ADA) • One memory module ( MEM ) The computer chassis is split in the middle by a metal partition. The right houses the high speed data modules, CPU, MEM and COM. The left side houses the I/O handlers, i.e., ADA and DIOs. On the front of all the above modules, Fault LEDs are mounted on the face plate. These LEDs illuminate for a couple of seconds as part of the ‘power up’ diagnostic routine. These are tripped by watchdog timer faults, database errors or through certain other conditions satisfied in the software.

14.6.1 CPU Module

• CPU Module is the brain of the entire computer system. which processes all incoming locomotive parameters and controls locomotive responses to derive the operating characteristics. It contains the following hardware

• 32 bit Motorola 68020 16.5 Mhz microprocessor with a math co-processor for enhancing the speed and efficiency of information processing

• Motorola 68881 floating point co-processor running at 16.5 M Hz • 512 KB ‘flash prom’ memory storage which can be easily

reprogrammed in the field with the aid of laptop computer communicating through an RS 232 port or through special module called MMB. While the time required to load a programme from MMB is approximately 15 seconds, the same through laptop computer is 15 minutes. The programme storage can be upgraded to 1 MB.

• 128 KB static RAM for data storage, which can be upgraded to 1 MB

• 64 K B static dual port RAM for inter processor communication . • 6840 Programmable timers which are use for periodic inputs and

out puts. • RS232 Serial port with programmable baud rates. • RS422 Serial port with programmable baud rates. One of these

port is dedicated to the display unit.

CPU module plays a very active role in SCR gating sequence as it sends the weak gate signals to the FCD and receives information from the zero cross detection circuit on the FCF so that it knows what phase angle to fire at to achieve desired alternator excitation.

14.6.2 Digital Input /Out Put (I/O) Modules

Comment [D1]:

The digital inputs and output to and from EM2000 are handled by three such modules. Each module has 24 input channels and 26 output channels. This module works as an interface between locomotive’s 74 VDC control system and the computer’s 5 VDC system.

The DIO input channels are either +74 VDC or 0 VDC signals

depending upon the relay/contactor status, picked up or dropped out. The DIO output channels, in turn, depend upon the logic built-up, either +74 or 0 VDC, so as to pickup or drop out the relay/contactor by supplying the gating power to the field effect transistor.

Multiplexing is a selective monitoring process through which several

inputs may be monitored through the use of only one input channel. In other words not all inputs need be monitored constantly.

14.6.3 Communication Module

All the computers on board i.e. EM2000, Sibas 16, electronic brake computer etc. need communication with each other. The two traction computers SIBAS 16 communicates to each other and to EM2000. The link carries all sorts of the information which, inter alia, could be data ranging from torque requests, feed backs to contactor requests and acknowledgements to fault annunciation etc.

14.6.4 Analogue To Digital And Digital To Analogue Module

It is responsible for converting analogue input signals to digital signal for processing the data and digital information from the CPU into an analogue signal that is required by the receiving device (external ammeters). It has within it -

• Differential analogue inputs • Hall effect transducer current inputs • General purpose frequency inputs for period & frequency

measurements 14.6.5 Memory (Archive Memory) Module

This module holds dynamic locomotive parameters and archive data that are required to remain intact even in case of power failure. It has one 128 KB battery backed static RAM . which can be upgraded. The amount of data stored with each fault is substantial. For selected faults such as ground relay, data is stored from each of the 5 seconds before the occurrence of the fault.

14.6.6 Panel Mounted Modules

Many other modules, called panel mounted modules, belonging to the EM2000 control are directly mounted to the rear panel of the HVC. These modules are-

• Analogue signal conditioner modules- ASC 300- scales and filters

analogue signals. • Firing control driver - FCD 300 - amplifies SCR gate signals to control

the CA6 output for main alternator field. • Firing control feedback - FCF 300 - scales three phase companion

alternator frequency feedback • Voltage amplifying module- VAM 300- trainline 24 T interface for slow

speed pace setter control ( optional for GT46MAC) • Trainline filter - TLF 300- scales and filters digital data from trainline

signals. 14.7 Power Supply

EM2000 control system requires different power supply and conditioner modules which are mounted in the Power Chassis. These modules are-

• PSM 300 module for Power supply of +5V DC - the main power supply for EM2000

• PSM310 module for +12VDC - • PSM 320 module for Power supply of +15VDC - for feed back circuits

like hall effect transducer devices & analogue circuits viz. magnetic speed pickup

• PRG300 power regulator is the power conditioner for the PSM modules and functions properly even with the voltage variation within 20-95 VDC. It regulates the output voltage between 64-77 VDC when the input voltage is between 25-68VDC. If the input is beyond this range, there is a variation in the output within the acceptable limit.

14.8 Development Of Software The software for EM2000, or any sophisticated computer system, is developed by EMD in the following steps-

Development of Sales Specification Finalization of System Specification Development of Software Specification Actual Software Code Writing Software Test

A locomotive characterisation report, which identifies the exact type of the equipment used, defines all the functions and indicates the value of all the parameters, is issued by the Product Engineering group. This report forms the basic locomotive document and the foundation on which the entire software of the locomotive is built up. 14.9 Locomotive Performance & Train Run Simulation

EMD has developed versatile computer simulation programme for train run simulation and offers this service to all its customers on commercial basis. 14.10 Thyristors, GTOs And AC Motor Control The thyristor offers immense advantages like compactness, high reliability, excellent time response and low loss. An added advantage of using thyristors in power converters for drive control is the easy manner in which they can be adopted for sophisticated feed-back schemes. As a result, microprocessor control of thyristor-drive systems can provide great operational flexibility. GTO thyristor or the ‘gate turn-off thyristor’ is referred to briefly as ‘GTO’. It is a four-layer silicon semiconductor device and is an improvement over the normal, slow devices used in line commutated converters into increasingly faster devices with better dynamic characteristics by refining the gate geometry. GTO allows fast turn-off with a negative current impulse by means of the gate alone, which is not possible with the conventional thyristor. This results in simplification of the converter circuitry. A three-phase inverter system with variable voltage and frequency output, is achieved by using GTOs for speed/torque control of 3-phase asynchronous motor. 14.11 Pulse-Width Modulation Six load carrying thyristors and six free wheeling diodes are the basic ingredients of three phase bridge inverter circuit. A DC-link capacitor is added for stabilising the DC-link voltage and supplying of magnetising reactive power required for induction motor.

+ + +

+ + +

I N P U T C O N V E R T E R

V O L T. - S O U R C E I N V E R T E R

D C

L

I N

K C

A P

.

M3 ~

PWM INVERTER CIRCUIT FIG-7

Amplitude and frequency setting take place solely by the principle of pulse width modulation (PWM). The max. possible amplitude of the phase-to-phase output voltage Uv depends on the magnitude of the DC link voltage Ud such that,

Uv = 0.78 Ud This method of voltage control of an inverter is known as pulse-width modulation. 14.12 Locomotive Cables, Wire Running And Layout

GT46MAC locomotive employs mainly the Exxon cables. The cables used on this locomotive are classified into following categories:

♦ Category 0 - These are used in the circuits with extremely high

potential requiring increased creepage distances.(DC link cables) ♦ Category 1- These are used in the circuits of high potential and high

current levels ( Generator , Traction Motors and Battery Trunk Lines to be routed through cleats)

♦ Category 2 - These are used in the circuits of AC voltage and high current DC voltage (conductors larger than AWG#12, not including traction circuit)

♦ Category 3 - These are used in locomotive control logic wiring (typically 74 V DC including all electro mechanical devices)

♦ Category 4 - Low voltage and energy control signal lines ( shielded multi conductor cables, and signals below 24 V)

♦ Category 5 - Specific conductors requiring independent routing (communication radio antenna cabling, or high energy unfused conductors)

14.13 Locomotive Cabling: ♦ All the cables which are to be laid out on the underframe are performed

with end lugs, connectors, sockets provided. For this purpose there is a separate section consisting of the wire measuring and cutting table, end shearing machine for preparing the ends and crimping of the lugs. The bigger size lugs are made in house using metallic tubes on a lug making machine, others are bought out from trade.

♦ The cabling on the underframe is done in the belly up position (in the over-turned position)

♦ The cable layout has been so planned that all the cables are planned to run on only one side of the underframe i.e. on the left side in the belly up position looking from the short hood side.

♦ Brackets for the rubber cleats are welded to the underframe before the laying of cables is started and are located through out the length of the underframe.

♦ The power cables are laid first followed by the control cables. For the control wires running between EM2000 and Traction Control Cabinet use is made of special channel having EMI protection and runs on the top corner through out the length of U/frame.

♦ The cleats used are of BUNA-N rubber. Special clamps for smaller diameter cables are used which have a rubber lining to prevent the damage of insulation of cable due to vibrations and prevention from grounding.

♦ Splicing of the power cable going into the traction motor is done to avoid running of large number of cables from TCC and the exposed joints are covered using heat shrinkable silicon rubber boots.

♦ Cutouts on the underframe are already provided for the cables and no oxy cutting of the underframe is done at all during the cabling stage.

A separate wire running list as per zone, wire category and wire tag is prepared and circulated to the shop to give details of wire running from source to destination. The wire running list is derived from the locomotive schematic as soon as the same is ready. 14.14 Electrical Schematics

The schematic of GT46MAC consists of two major parts - EMD schematics and Siemens schematic. The schematic conventions followed by EMD and Siemens are different.

The major equipment covered by the two sections of schematic are as

under- EMD schematic - EMD manufactured or vendor supplied equipment

viz. alternator - rectifier, locomotive computer, electrical control cabinets including all switches, contactors and relays, auxiliary machines, safety and alarm circuits, third party equipment like radar etc.

Siemens schematic - Siemens manufactured equipment viz. inverter

and inverter control equipment, traction computer and traction motors. The EMD schematic is built around the main block diagram of the

electrical equipment of the locomotive. The schematic is a representation of the hard wiring along with the connection/termination details of the equipment. All the computer/microprocessor modules, which control the operation of the hardware like relays, contactors etc., have been represented as a block. The logic used by EMD is not known.

All the electrical sub-assemblies like ECCs, control consoles etc. have

been allocated a zone identification. This schematic also explains the various wiring nomenclature used in the EMD schematic. For locating any item, the equipment locator chart provided in the schematic can be used which

identifies location based on the zone in which the equipment in question lies on the locomotive and schematic sheet no. along with the location on the schematic sheet. Similarly, the circuit for any function like engine cooling control, engine governor control, traction motor bearing temperature probe etc. can be located easily in the schematic by using an alphabetical index. In addition, locator charts based on digital & analogue input/output functions employed on EM 2000. A chart detailing the location of various switches and circuit breakers as well as the sequence of operation of main interlock contact of the switches is also provided in the schematic.

The schematic is very versatile and the category, size and specification

of any wire can be read straightaway from the connecting points. In addition, details of all plugs and receptacles are also provided clearly indicating the used & potential free pin numbers. Details of terminal boards are also given with internal & external connections with locomotive wire numbers.

The schematic can be divided into three strings of control viz. Battery

(i.e. on battery side & past battery knife switch), local control (PA / NA string) & control (13T/4T string). The schematic shows the interfacing with the inverter cabinet (TCC1 & TCC2) and other third party.

The Siemens schematic has been drawn by Siemens and is annexed

to the EMD schematic. As indicated earlier, this schematic is meant largely for inverter and inverter control equipment, traction computer and traction motors. The schematic gives the details of the arrangement of GTOs along with other devices like anti parallel diodes, snubber capacitors and resistors etc. The protection circuits including the hard and soft crowbar circuits for protection of GTOs, have been shown in the schematic. The interface and connections to the SIBAS traction computer have also been shown.

14.15 Integration Of Electrics With Engine And Other Mechanical

Systems

The following mechanical aspects which are closely linked or interfaced with the electrics of the locomotive are -

• Coupling of alternator with engine • Torque requirement of the engine and starter motor requirement • Engine cooling system interface with EM 2000 • Engine cooling fan design and air circuit

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FUEL OIL SYSTEM OBJECTIVE • Understand the Fuel Oil System of WDM2 Locomotive. • Learn the function of individual components of Fuel Oil System. • Learn the concept of Fuel Feed System and Fuel Injection System. • Check the efficiency of fuel feed system on full load condition • Learn the purpose of fuel efficient kit application on diesel engine STRUCTURE 1. Introduction 2. Fuel Feed System and it's associate components 3. Functioning of fuel feed system 4. Fuel Injection System ( fuel injection pump & nozzle ) 5. Orifice test of fuel feed system 6. Calibration of fuel injection pumps 7. Phasing of fuel injection pumps 8. Fuel injection nozzle test 9. Nozzle valve lift 10. Fuel efficient kit 11. Summary 12. Self Assessment

INTRODUCTION

All locomotive units have individual fuel oil system. The fuel oil system is designed to introduce fuel oil into the engine cylinders at the correct time, at correct pressure, at correct quantity and correctly atomised. The system injects into the cylinder correctly metered amount of fuel in highly atomised form. High pressure of fuel is required to lift the nozzle valve and for better penetration of fuel into the combustion chamber. High pressure also helps in proper atomisation so that the small droplets come in better contact with the fresh air in the combustion chamber, resulting in better combustion. Metering of fuel quantity is important because the locomotive engine is a variable speed and variable load engine with variable requirement of fuel. Time of fuel injection is also important for better combustion. FUEL OIL SYSTEM The fuel oil system consists of two integrated systems. These are- FUEL FEED SYSTEM. FUEL INJECTION SYSTEM.

FUEL FEED SYSTEM AND ITS ASSOCIATE COMPONENTS The fuel feed system provides the back-up support to the fuel injection pumps by maintaining steady supply of fuel to them at the required pressure so that the fuel pump

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can meter and deliver the oil to the cylinder at correct pressure and time. The fuel feed system includes the following:- • Fuel oil tank

A fuel oil tank of required capacity (normally 5000ltrs), is fabricated under the superstructure of the locomotive and located in between the two bogies. Baffle walls are used inside it to arrest surge of oil when the locomotive is moving. A strainer filter at the filling plug, an indirect vent, drain plug, and glow rod type level indicators are also provided. • Fuel primary filter

A filter is provided on the suction side of the fuel transfer pump to allow only filtered oil into the pump. This enhances the working life of the fuel transfer pump. This filter is most often a renewable bleached cotton waste packed filter, commonly known as socks type filter element. These socks type filters are coarse filters and have a greater ability to absorb moisture, and are economical. However, in certain places, it has been replaced by paper type filter, which have longer service life. • Fuel transfer pump or booster pump

The fuel feed system has a transfer pump to lift the fuel from the tank. The gear type pump is driven by a dc motor, which is run by storage batteries through a suitable circuit. The pump capacity is 14 ltrs per minute at 1725 rpm at pressure 4 to 4.8 kg/cm. sq. • Fuel relief valve

The spring- loaded relief valve is meant for by passing excess oil back to the fuel tank, thus releasing excess load on the pump and on the motor, to ensure their safety. It is adjusted to a required pressure (normally 5 kg/cm2), and it by- passes the excess fuel back to the oil tank. It also ensures the safety of the secondary filter and the pipe lines. • Fuel secondary filter

The fuel secondary filter is located after the booster pump in the fuel feed system. The filter used is a paper type filter, cartridge of finer quality, renewable at regular intervals. This filter arrests the finer dirt particles left over by the primary filter and ensures longer life of the fuel injection equipments. • Fuel regulating valve

The fuel-regulating valve is spring-loaded valve of similar design as the fuel relief valve. It is located after the secondary filter in the fuel feed system. This valve is adjusted to the required pressure (3 kg/cm2), and always maintains the same pressure in the fuel feed system by releasing the excess oil to the fuel oil tank. There is no by-passing of oil if the pressure is less than the adjusted level. Functioning of fuel feed system The fuel booster pump or transfer pump is switched on and the pump starts sucking oil from the fuel oil tank, filtered through the primary filter. Because of variable consumption by the engine, the delivery pressure of the pump may rise increasing load on the pump and its drive motor. When the rate of consumption of the fuel by the engine is low, the relief valve ensures the safety of the components by releasing load, by- passing the excess

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pressure back to the tank. Then oil passes through the paper type secondary filter and proceeds to the right side fuel header. The fuel header is connected to eight numbers of fuel injection pumps on the right-bank of the engine, and a steady oil supply is maintained to the pumps at a pressure of 3 Kg./ sq. cm. Then the fuel oil passes on to the left side header and reaches eight fuel injection pumps on the left bank through jumper pipes. The regulating valve remaining after the left side fuel header, takes care of excess pressure over 3 Kg/cm Square by passing the extra oil back to the tank. A gauge connection is taken from here leading to the driver's cabin for indicating the fuel oil feed pressure. Thus the fuel feed system keeps fuel continuously available to the fuel injection pumps, which the pumps may use or refuse depending on the demand of the engine. FUEL INJECTION SYSTEM When diesel engine is started, all fuel injection pumps start functioning. According to firing order all F.I. pumps start discharging fuel oil at high pressure to there respective nozzles through high pressure line tube. Fuel injection nozzle injects fuel oil to combustion chamber at 4000 psi. The internal function of F.I. pump and nozzle are described below. 1. FUEL INJECTION PUMP It is a constant stroke plunger type pump with variable quantity of fuel delivery to suit the demands of the engine. The fuel cam controls the pumping stroke of the plunger. The length of the stroke of the plunger and the time of the stroke is dependent on the cam angle and cam profile, and the plunger spring controls the return stroke of the plunger. The plunger moves inside the barrel, which has very close tolerances with the plunger. When the plunger reaches to the BDC, spill ports in the barrel, which are connected to the fuel feed system, open up. Oil then fills up the empty space inside the barrel. At the correct time in the diesel cycle, the fuel cam pushes the plunger forward, and the moving plunger covers the spill ports. Thus, the oil trapped in the barrel is forced out through the delivery valve to be injected into the combustion chamber through the injection nozzle. The plunger has two identical helical grooves or helix cut at the top edge with the relief slot. At the bottom of the plunger, there is a lug to fit into the slot of the control sleeve. When the rotation of the engine moves the camshaft, the fuel cam moves the plunger to make the upward stroke. It may also rotate slightly, if necessary through the engine governor, control shaft, control rack, and control sleeve. This rotary movement of the plunger along with reciprocating stroke changes the position of the helical relief in respect to the spill port and oil, instead of being delivered through the pump outlet, escapes back to the low pressure feed system. The governor for engine speed control, on sensing the requirement of fuel, controls the rotary motion of the plunger, while it also has reciprocating pumping strokes. Thus, the alignment of helix relief with the spill ports will determine the effectiveness of the stroke. If the helix is constantly in alignment with the spill ports, it bypasses the entire amount of oil, and nothing is delivered by the pump. The engine stops because of no fuel injected, and this is known as ‘NO-FUEL’ position. When alignment of helix relief with spill port is delayed, it results in a partly effective stroke and engine runs at low speed and power output is not the maximum. When the helix is not in alignment with the spill port through out the stroke, this is known as ‘FULL FUEL POSITION’, because the entire stroke is effective.

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Oil is then passed through the delivery valve, which is spring loaded. It opens at the oil pressure developed by the pump plunger. This helps in increasing the delivery pressure of oil. it functions as a non-return valve, retaining oil in the high pressure line. This also helps in snap termination of fuel injection, to arrest the tendency of dribbling during the fuel injection. The specially designed delivery valve opens up due to the pressure built up by the pumping stroke of plunger. When the oil pressure drops inside the barrel, the landing on the valve moves backward to increase the space available in the high-pressure line. Thus, the pressure inside the high-pressure line collapses, helping in snap termination of fuel injection. This reduces the chances of dribbling at the beginning or end of fuel injection through the fuel injection nozzles. FUEL INJECTION NOZZLE The fuel injection nozzle or the fuel injector is fitted in the cylinder head with its tip projected inside the combustion chamber. It remains connected to the respective fuel injection pump with a steel tube known as fuel high pressure line. The fuel injection nozzle is of multi-hole needle valve type operating against spring tension. The needle valve closes the oil holes by blocking the oil holes due to spring pressure. Proper angle on the valve and the valve seat, and perfect bearing ensures proper closing of the valve. Due to the delivery stroke of the fuel injection pump, pressure of fuel oil in the fuel duct and the pressure chamber inside the nozzle increases. When the pressure of oil is higher than the valve spring pressure, valve moves away from its seat, which uncovers the small holes in the nozzle tip. High-pressure oil is then injected into the combustion chamber through these holes in a highly atomised form. Due to injection, hydraulic pressure drops, and the valve returns back to its seat terminating the fuel injection, termination of fuel injection may also be due to the bypassing of fuel injection through the helix in the fuel injection pump causing a sudden drop in pressure. ORIFICE TEST This test is a rough and ready method to ascertain the efficiency of the fuel feed system under full load condition. The procedure of testing is as under: 1. An orifice plate of 1/8 inch is fitted in the system before the regulating valve. 2. A container to be placed under the orifice to collect the oil that would leak through it

during the test. 3. The fuel booster pump to be switched on for 60 seconds. The rate of leakage should be about 9 lt. of fuel per minute through the orifice ( with the engine in stopped condition ). The system should be able to maintain 3 kg /cm.sq pressure with this rate of leakage, which simulates approx. the full load consumption by the engine. In the event of drop in pressure the rate of leakage would also be less indicating some defect in the system reducing its efficiency to meet the full requirement of fuel during peak load. The above test is easy, reliable and also saves time. CALIBRATION OF FUEL INJECTION PUMPS

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Each fuel injection pump is subject to test and calibration after repair or overhaul to ensure that they deliver the same and stipulated amount of fuel at a particular rack position. Every pump must deliver regulated and equal quantity of fuel at the same time so that the engine output is optimum and at the same time running is smooth with minimum vibration. The calibration and testing of fuel pumps are done on a specially designed machine. The machine has a 5 HP reversible motor to drive a cam shaft through V belt. The blended test oil of recommended viscosity under controlled temperature is circulated through a pump at a specified pressure for feeding the pump under test. It is very much necessary to follow the laid down standard procedure of testing to obtain standard test results. The pump under test is fixed on top of the cam box and its rack set at a particular position to find out the quantum of fuel delivery at that position. The machine is then switched on and the cam starts making delivery strokes. A revolution counter attached to it is set to trip at 300 RPM or 100 RPM as required. With the cam making strokes, if the pump delivers any oil, it returns back to the reservoir in normal state. A manually operated solenoid switch is switched on and the oil is diverted to a measure glass till 300 strokes are completed after operation of the solenoid switch. Thus the oil discharged at 300 working strokes of the pump is measured which should normally be within the stipulated limit. The purpose of measuring the output in 300 strokes is to take an average to avoid errors. The pump is tested at idling and full fuel positions to make sure that they deliver the correct amount of fuel for maintaining the idling speed and so also deliver full HP at full load. A counter check of the result at idling is done on the reverse position of the motor which simulates slow running of the engine. If the test results are not within the stipulated limits as indicated by the makers then adjustment of the fuel rack position may be required by moving the rack pointer, by addition or removal of shims behind it. The thickness of shims used should be punched on the pump body. The adjustment of rack is done at the full fuel position to ensure that the engine would deliver full horse power. Once the adjustment is done at full fuel position other adjustment should come automatically. In the event of inconsistency in results between full fuel and idling fuel, it may call for change of plunger and barrel assembly. The calibration value of fuel injection pump of WDM2 engines as supplied by the makers is as follows at 300 working strokes: 9 mm (Idling) 34 cc +1/-5 30 mm (Full load) 351 cc +5/-10 The calibration values for YDM4 engines are as under.

9 mm (idling ) 45 cc +1/-5 28 mm (full load) 401 cc +4/-11

Errors are likely to develop on the calibration machine in course of time and it is necessary to check the machine at times with master pumps supplied by the makers. These pumps are perfectly calibrated and meant for use as reference to test the

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calibration machine itself. Two master pumps, one for full fuel and the other for idling fuel are there and they have to be very carefully preserved only for the said purpose. PHASING OF FUEL INJECTION PUMPS Every fuel injection pump after repair / overhauling and testing needs phasing while fitting on the engine. In course of working the drive mechanism of the FIP suffers from wear and causes loss of motion. This may also cause shorter length of plunger stroke and lesser fuel delivery. The pump lifter is adjusted individually for all the FIPs. An adjustment is provided in the valve lifter mechanism to adjust the markings between the guide cup and the sight window so that they coincide with each other after positioning the engine. This adjustment is known as phasing of the pump to make up the wear loses. FUEL INJECTION NOZZLE TEST The criteria for good nozzle is good atomization, correct spray pattern and no leakage or dribbling. Before a nozzle is put to test the assembly must be rinsed in fuel oil, nozzle holes cleaned with wire brush and spray holes cleaned with steel wire of correct thickness. The fuel injection nozzles are tested on a specially designed test stand, where the following tests are conducted. SPRAY PATTERN Spray of fuel should take place through all the holes uniformly and properly atomized. While the atomization can be seen through the glass jar, an impression taken on a sheet of blotting paper at a distance of 1 to 1 1/2 inch also gives a clear impression of the spray pattern. SPRAY PRESSURE The stipulated correct pressure at which the spray should take place 3900-4050 psi for new and 3700-3800 psi for reconditioned nozzles. If the pressure is down to 3600 psi the nozzle needs replacement. The spray pressure is indicated in the gauge provided in the test machine. Shims are being used to increase or decrease the tension of nozzle spring which increases or decreases the spray pressure DRIBBLING There should be no loose drops of fuel coming out of the nozzle before or after the injections. In fact the nozzle tip of a good nozzle should always remain dry. The process of checking dribbling during testing is by having injections manually done couple of times quickly and check the nozzle tip whether leaky. Raising the pressure within 100 psi of set injection pressure and holding it for about 10 seconds may also give a clear idea of the

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The reasons of nozzle dribbling are 1) Improper pressure setting 2) Dirt stuck up between the valve and the valve seat 3) Improper contact between the valve and valve seat 4) Valve sticking inside the valve body. NOZZLE CHATTER The chattering sound is a sort of cracking noise created due to free movement of the nozzle valve inside the valve body. If is not proper then chances are that the valve is not moving freely inside the nozzle. NOZZLE LEAK OFF RATE A very minute portion of the oil inside the nozzle passes clearance between the valve and the valve body for the purpose of lubrication. Excess clearance between them may cause excess leak off, thus reducing the amount of fuel actually injected. The process of checking the leak off rate is by creating pressure in the nozzle up to 3500 psi and holds the pressure till it drops to 1000 psi. The drop of pressure is due to the leak off and higher the leak off rate the pressure drop is quicker. In the event of the leak off time recorded below stipulation the nozzle valve and the valve body have to be changed for excessive wear and clearance between them. CHECKING OF NOZZLE VALVE LIFT The valve and the valve seat are surface hardened components. Any attempt to work them beyond the hardened surface is restricted. The amount of wear on the valve face and the seat is measured with the help of a dial gauge and the process is known as checking of valve lift. FUEL EFFICIENT KIT Certain modifications carried out on WDM2 locomotive engine to improve specific fuel consumption by over 6%, ruduction in existing exhaust gas temperature by over 100 deg.-C and reduction in lube oil consumption. These modifications are considered as fuel efficient kit. Modifications are given below:

1. Modified water connection to after cooler: - Water inlet of the after cooler is connected from outlet of the radiator, to provide water at minimum possible temperature into the after cooler. Previously it was connected from water pump discharge side.

2. 17 mm fuel injection pump:- 15 mm pumps are being replaced by 17 mm pumps, to have sharper fuel injection. For this, modified fuel pump support with wider fuel cam roller, shall be used on fuel efficient engine. The maximum rack opening with 17 mm pump is restricted to 28+_ 0.25 mm instead of existing 29.5+-0.25 mm. Changes will have to be made in the lever/ linkage of the governor for this.

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3. Modified cam shaft with 140 degree over lap:- The cam shaft has been modified to increase the over lap from 123 degree to 140 degree to improve the scavenging.

4. Large After Cooler: Large After Cooler with higher effectiveness has been introduced to provide cooled air to engine. For this Turbo mounting bracket and certain pipe line connections will need to be changed.

5. Steel capped pistons: In the fuel efficient engine, peak firing pressure likely to exceed 1800 psi and thus steel cap pistons are required to be used. Use of steel cap pistons will also result in lower lube oil consumption.

6. High efficiency Turbo Charger: Existing 720 turbo chargers being replaced by high efficiency ABB VTC 304/ NAPIER NA 295 turbo chargers having capacity to develop 2.2kg/cm2 air pressure/ booster pressure.

SUMMARY Fuel Feed System is responsible for supply of clean oil with adequate quantity at required pressure to Fuel Injection System, to meet the requirement of fuel oil of the engine at rated output. In Fuel Feed System, Fuel tank acts as reservoir of HSD oil of the engine; Primary and Secondary filters maintain cleanliness of oil in the system. Fuel Booster Pump works for generating pressure and maintaining adequate supply of fuel in the system; Relief and Regulating Valves maintain constant pressure in the feed system. Fuel Injection System comprises of mainly two components (a) Fuel Injection Pump (b) Fuel Injection Nozzle. Fuel Injection Pump is a plunger type Pump having constant stroke with variable delivery. The quantity of fuel delivered is decided by the position of the helix groove, that varies with the twisting of the plunger according to the fuel rack position. Hence it is responsible for supplying correct quantity of pressurized fuel upto the nozzle. Nozzle is responsible for delivering pressurized fuel in atomized form into the combustion chamber. The breaking pressure i.e. the final pressure at which fuel is released into the combustion chamber is decided by the setting of Nozzle Valve Spring pressure. SELF ASSESSMENT

1. What are the functions of Relief Valve and Regulating Valve in fuel feed system?

2. Draw a neat sketch of the Fuel Feed System of WDM2 type locomotive and label it

3. How quantity of fuel delivery varies in Fuel Injection Pump? 4. What are the functions of Fuel Injection Nozzle? 5. Describe the function of fuel injection nozzle. 6. How can you check the efficiency of the fuel feed system under full load

condition? 7. What is fuel-efficient kit?

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CHARGE AIR SYSTEM OBJECTIVE

The objective of this unit is to make you understand about :- • the need for supercharging • various methods of supercharging • Turbo Supercharging as applied in WDM2 type Locomotive • various components of Turbo Supercharger and their duties. • Lubricating, Cooling and Air Cushioning of Turbo Supercharger Components. • Cooling of supercharged air STRUCTURE 1. Introduction 2. Advantage of supercharging 3. Turbo Supercharger and its working principle 4. Main components of Turbo Supercharger 5. Lubricating, Cooling and Air Cushioning 6. After cooling of Charge Air 7. Summary 8. Self Assessment

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INTRODUCTION The diesel engine produces mechanical energy by converting heat energy derived from burning of fuel inside the cylinder. For efficient burning of fuel, availability of sufficient air in proper ratio is a prerequisite. In a naturally aspirated engine, during the suction stroke, air is being sucked into the cylinder from the atmosphere. The volume of air thus drawn into the cylinder through restricted inlet valve passage, within a limited time would also be limited and at a pressure slightly less than the atmosphere. The availability of less quantity of air of low density inside the cylinder would limit the scope of burning of fuel. Hence mechanical power produced in the cylinder is also limited. An improvement in the naturally aspirated engines is the super-charged or pressure charged engines. During the suction stroke, pressurised stroke of high density is being charged into the cylinder through the open suction valve. Air of higher density containing more oxygen will make it possible to inject more fuel into the \same size of cylinder and produce more power,, by effectively burning it. ADVANTAGES OF SUPER CHARGED ENGINES. A super charged engine of given bore and stroke dimensions can produce 50 percent or more power than a naturally aspirated engine. The power to weight ratio in such a case is much more favourable. Charging of air during the suction stroke causes better scavenging in the cylinders. This ensures carbon free cylinders and valves, and better health for the engine also. Higher heat developed in a super charged engine due to the burning of more fuel, calls for better cooling of the components. The cool air charged into the cylinders has better cooling effect on the cylinders, piston, cylinder head, and valves, and save them from failure due to thermal stresses. Better ignition due to higher temperature developed by higher compression in the cylinder. Better fuel efficiency due to complete combustion of fuel by ensuring availability of matching quantity of air or oxygen. METHOD OF SUPERCHARGING Different methods of pressurising air for supercharging in engines are adopted. Using a reciprocating type of air compressor. These are unsuitable for locomotive engines, because of their large size, and higher power demand. Moreover, The system does not maintain proper air to fuel ratio. Specially designed roots blower or centrifugal blowers. These have the same drawbacks as the reciprocating compressors. Most efficient and economical method of supercharging is by a centrifugal blower run by the exhaust gas driven turbine. In the system, energy left over in the exhaust gas, which would otherwise have been wasted, is used to drive the gas turbine in the turbo super charger. The turbine in turn drives the centrifugal blower, which sucks air from atmosphere and pressurises it. This does away with the need for an additional power required for driving the blower, thus saving energy. Moreover, this system can maintain more favourable air and fuel ratio at all speed and load conditions of the engine than any other system.

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TURBO SUPERCHARGER AND ITS WORKING PRINCIPLE The exhaust gas discharge from all the cylinders accumulate in the common exhaust manifold at the end of which, turbo- supercharger is fitted. The gas under pressure there after enters the turbo- supercharger through the torpedo shaped bell mouth connector and then passes through the fixed nozzle ring. Then it is directed on the turbine blades at increased pressure and at the most suitable angle to achieve rotary motion of the turbine at maximum efficiency. After rotating the turbine, the exhaust gas goes out to the atmosphere through the exhaust chimney. The turbine has a centrifugal blower mounted at the other end of the same shaft and the rotation of the turbine drives the blower at the same speed. The blower connected to the atmosphere through a set of oil bath filters, sucks air from atmosphere, and delivers at higher velocity. The air then passes through the diffuser inside the turbo- supercharger, where the velocity is diffused to increase the pressure of air before it is delivered from the turbo- supercharger. Pressurising air increases its density, but due to compression heat develops. It causes expansion and reduces the density. This effects supply of high-density air to the engine. To take care of this, air is passed through a heat exchanger known as after cooler. The after cooler is a radiator, where cooling water of lower temperature is circulated through the tubes and around the tubes air passes. The heat in the air is thus transferred to the cooling water and air regains its lost density. From the after cooler air goes to a common inlet manifold connected to each cylinder head. In the suction stroke as soon as the inlet valve opens the booster air of higher pressure density rushes into the cylinder completing the process of super charging. The engine initially starts as naturally aspirated engine. With the increased quantity of fuel injection increases the exhaust gas pressure on the turbine. Thus the self-adjusting system maintains a proper air and fuel ratio under all speed and load conditions of the engine on its own. The maximum rotational speed of the turbine is 18000 rpm for the 720A model Turbo supercharger and creates 1.8 kg/cm2 air pressure in air manifold of diesel engine, known as booster pressure. Low booster pressure causes black smoke due to incomplete combustion of fuel. High exhaust gas temperature due to after burning of fuel may result in considerable damage to the turbo supercharger and other component in the engine. MAIN COMPONENTS OF TURBO-SUPERCHARGER Turbo- supercharger consists of following main components.

• Gas inlet casing. • Turbine casing. • Intermediate casing • Blower casing with diffuser • Rotor assembly with turbine and rotor on the same shaft.

GAS INLET CASING The inlet casing of the latest type of turbo are of CH 20 stainless steel which is highly heat resistant. The function of this casing is to take hot gases from the exhaust manifold and pass them through the nozzle ring, which is bolted to the casing face. This assembly is fitted on the turbine casing with cap screws. TURBINE CASING

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The turbine casing houses the turbine inside it, and is cored to have circulation of water through it for cooling purposes. It has an oval shaped gas outlet passage at the top. It is fitted in between the inlet casing and the intermediate casing. It is made of alloy cast iron or fabricated. INTERMEDIATE CASING This casing is also water-cooled and have cored passage for water circulation and is made of alloy cast iron or fabricated like the turbine casing. It is placed between turbine casing and the blower casing. It separated the exhaust and the airside and also supports the turbine rotor on the two tri-metal bearings, which are interference-fit in the intermediate casing. BLOWER HOUSING ASSEMBLY This houses the blower and is in two parts, namely the blower inlet, and the blower housing. Air enters through the blower inlet axially, and discharged radially from the blower through the vane diffuser. The vane diffuser is a precision alluminium casting and screwed on the blower casing. ROTOR ASSEMBLY The rotor assembly consists of rotor shaft, rotor blades, thrust collar, impeller, inducer, centre studs, nosepiece, locknut etc. assembled together. The rotor blades are fitted into fir tree slots, and locked by tab lock washers. This is a dynamically balanced component, as this has a very high rotational speed. LUBRICATING, COOLING AND AIR CUSHIONING LUBRICATING SYSTEM One branch line from the lubricating system of the engine is connected to the turbo- supercharger. Oil from the lube oils system circulated through the turbo- supercharger for lubrication of its bearings. After the lubrication is over, the oil returns back to the lube oil system through a return pipe. Oil seals are provided on both the turbine and blower ends of the bearings to prevent oil leakage to the blower or the turbine housing. COOLING SYSTEM The cooling system is integral to the water cooling system of the engine. Circulation of water takes place through the intermediate casing and the turbine casing, which are in contact with hot exhaust gases. The cooling water after being circulated through the turbo- supercharger returns back again to the cooling system of the locomotive. AIR CUSHIONING There is an arrangement for air cushioning between the rotor disc and the intermediate casing face to reduce thrust load on the thrust face of the bearing which also solve the following purposes.

• it prevents hot gases from coming in contact with the lube oil.

• it prevents leakage of lube oil through oil seals.

• it cools the hot turbine disc.

Pressurised air from the blower casing is taken through a pipe inserted in the turbo- supercharger to the space between the rotor disc and the intermediate casing. It serves the purpose as described above. TURBO RUN –DOWN TEST

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Turbo run-down test is a very common type of test done to check the free running time of turbo rotor. It indicates whether there is any abnormal sound in the turbo, seizer/ partial seizer of bearing, physical damages to the turbine, or any other abnormality inside it. The engine is started and warmed up to normal working temperature and running at fourth notch speed. Engine is then shut down through the over speed trip machanism. When the rotation of the crank shaft stops, the free running time of the turbine is watched through the chimney and recorded by a stop watch. THE minimum time allowed for free running is90 seconds and maximum 180 seconds. Low or high turbo run down time are both considered to be harmful for the engine. AFTER COOLER It is a simple radiator, which cools the air to increase its density. Scales formation on the tubes, both internally and externally, or choking of the tubes can reduce heat transfer capacity. This can also reduce the flow of air through it. This reduces the efficiency of the diesel engine. This is evident from black exhaust smoke emissions and a fall in booster pressure. Fitments of higher capacity turbosupercharger- following new generation turbosuperchargers have been identified by RDSO for 2600/3100HP diesel engine. ABB VTC 304, NAPIER NA-295, GE 7S1716, HISPANO SUIZA HS 5800 NGT, ABB TPL61 SUMMARY Supercharging is the method of pressurizing the induced air to increase the efficiency and performance of the engine. This can be achieved by any of the methods, like, engine crankshaft driven Centrifugal / Roots Blower, exhaust gas driven Turbo Supercharger etc. Exhaust gas driven Turbo Supercharger being more economical and scientific, it is applied in WDM2 Locomotive Engine. In this system, the streamlined exhaust manifold collects the exhaust gas of all cylinders and directs it to Turbine through a Fixed Nozzle Ring. The Rotor Shaft comprises of Turbine and Compressor unit integral on it, which is supported by two Nos. Trimetal Bearings, housed in the intermediate casing. Thus exhaust gas driven turbine drives the compressor, being the integral part of the rotor shaft. The discharge of the compressor gets pressurized at diffuser and finally the hot compressed air after getting cooled at Aftercooler is stored in the Inlet Manifold of the engine, which in turn goes into the cylinder as per the working cycle. SELF ASSESSMENT

1. What are the advantages of supercharging? 2. What are the various methods of supercharging? Which method is considered

to be more scientific and why? 3. What is the importance of air cushioning? How is it done? 4. Describe the wdm2 loco charge air system with neat sketch.

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LUBE OIL SYSTEM OBJECTIVE

To understand about: - • the function of lubrication system in diesel engine • the lube oil system of WDM2 locomotive engine • the function of Relief & Regulating valve • the purpose of by passing arrangement of lube oil • the factors affect the low lube oil pressure & contamination in lube oil • the factors affect high lube oil consumption STRUCTURE 1. Introduction 2. Lube Oil system of WDM2 Locomotive 3. Problems in lube oil system 4. Lube oil quality observation by laboratory 5. Summary 6. Self assessment

INTRODUCTION The lubricating system in a diesel engine is of vital importance. The lubricating oil provides a film of soft slippery oil in between two frictional surfaces to reduce friction and wear. It also serves the following purposes.

1. Cooling of bearing, pistons etc. 2. Protection of metal surfaces from corrosion, rust, surface damages and

wear. 3. Keep the components clean and free from carbon, lacquer deposits and

prevent damage due to deposits. The importance of lube oil system is comparable to the blood circulation system in the human body. Safety of the engine, its components, and their life span will largely depend upon the correct quality of oil in correct quantity and pressure to various location of diesel engine.

LUBE OIL SYSTEM OF WDM2 LOCO The diesel engine of WDM2 class locomotives has full flow filtration lube oil system with bypass protection. The system essentially consists of the following components.

1. Gear type lube oil pump driven by the engine crankshaft. 2. Spring loaded relief valve, adjusted to 7.5 kg/cm2. 3. Lube oil filter tank accommodating eight nos. of filter elements. 4. Differential bypass valve set at 1.4 kg/cm2 differential pressure across the

filter tank.

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5. Lube oil cooler, which has a bunch of element tubes through which cooling water circulates and circulation of lube oil takes place around the tubes.

6. Regulating valve, which is a spring loaded valve adjusted to 4kg/cm2. 7. Lube oil strainer, which is a wire mesh type filter reusable after cleaning. 8. Oil pressure switch (OPS), which is meant to automatically shut down the

engine in case of a drop in lube oil pressure below 1.3 kg/cm2. 9. Oil pressure gauge, which indicates the main oil header pressure. 10. Oil sump having capacity 1260 lt. RR606 multigrade oil.

The lube oil pump on the free end of the engine is driven by the engine crankshaft through suitable gears and keeps it running along with the engine. When the engine is started the pump draws oil from the engine oil sump and delivers it. The delivery pressure of the pump has to be controlled as the pump is driven by an engine of variable speed and would often have higher delivery pressure or load on it than actually required. This would mean loss of more power from the engine for driving the pump. Higher pressure may also endanger the safety of the filters and the pipelines and its joints. The relief valve releases the delivery pressure above its setting and bypasses it back to the oil sump. Oil then flows to a filter tank containing eight nos. of paper type filter elements. The filter has a bypass valve across it set a differential pressure of 1.4 kg/cm2. Due to the choking of the filter elements, if the pressure differential between the inlet and the outlet of the tank is more than 1.4 kg/cm2, then the differential bypass valve opens up to bypass a part of oil without filtration, and thus reduces the pressure on the filters. Although allowing unfiltered oil into the engine is not advisable, but there is another filter at later stage through which oil has to pass before entering the engine. Moreover, higher pressure on the filters may cause damage to the filters, and cause greater damage to the engines. After the filtration, the oil passes to the coolers, gets cooled by transferring heat to water, and regains its lost viscosity. At he discharge side of the cooler, a regulating valve adjusted at 4 kg/cm2 is provided to regulate the pressure. Excess pressure is regulated by passing the oil back to the engine oil sump. The oil then finds its way to the main oil header after another stage of filtration in the strainer type filter from which it is distributed for lubrication to different places as required. Direct individual connections are taken from the main oil header to all the main bearings. Oil thus passes through the main bearings supporting the crankshaft on the engine block, passes through the crank pin to lubricate the connecting rod big end bearing and the crank pin journals. It reaches the small end through rifle drilled hole and after lubricating the gudgeon pin and bearings enters into the pistons. The Aluminium alloy pistons are provide with spiral oil passage inside them for internal circulation of lube oil. This is done with the purpose of cooling the pistons, which are highly thermally loaded components. After circulation through the pistons, the oil returns back to the oil sump, but in this process, a part of the oil hits the running connecting rod and splashes on the cylinder liners for their lubrication. The actual lube oil pressure is a function of lube oil pump, temperature of oil, engine speed and regulating valve setting. A line from the main oil header is connected to a gauge in the driver's cabin to indicate the pressure level. If lube oil pressure drops to less than 1.3 kg/cm2, engine will automatically shut down through a safety device (OPS) to protect it from damage due to insufficient lubrication. From the main oil header, two branch lines are taken to the right and left side secondary headers to lubricate the components on both banks of the V shape engine. Each branch

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line of the secondary header lubricates the camshaft bearings, fuel pump lifters, valve lever mechanisms, and spray oil to lubricate the gears for camshaft drive. A separate connection is taken to the turbo super charger from the right side header for lubrication of its bearings. After circulation to all the points of lubrication, the oil returns back to the sump for recirculation through the same circuit. Problems in lube oil system There are four factors, which effect the lube oil system pressure directly that is lube oil pump discharge capacity, diesel engine temperature, pressure setting value of Relief & Regulating valve and quality of lube oil. Some other factors like choking of filters / strainer, low oil level in c/case, contaminated lube oil, low idling speed and excessive wear/ clearance in bearings also effect the system pressure. During running of diesel engine it is observed that lube oil contaminated with water and oil level in c/case is increasing, which indicates water leakage inside the c/case. The sources are leakage of cylinder liner bottom gasket & sleeve, cracked cylinder liner, cracked cylinder head etc. Sometimes it is observed that lube oil contaminated with fuel oil, which indicates nozzles dribbling or fuel leak off gallery cracked. It is also observed that some engines consume high rate of lube oil, which indicates clearance between valve and valve guide is more, engine piston rings worn out or turbo oil seal damaged. Lube oil quality observation by laboratory To maintain sound health of the engine, control on quality of oil is as much necessary as the pressure. Every maintenance depot/diesel shed is equipped with a laboratory, which keeps strict watch on the quality of lube oil of each individual loco. Contamination in any form i .e. by fuel oil, cooling water, soot, dirt etc. in service is immediately reported for corrective action in maintenance. Change in other properties like viscosity, PH value, TBNE etc. are also watched at regular intervals. Lube oil changing in locos are normally done on condition basis. Spectrographic analysis at regular schedule is also done to ascertain the extent of concentration of wear metal particles in the oil. This can indicate the wear pattern of the engine components or ensure longer service life. SUMMARY The Diesel Engine of WDM 2 Locomotive has full flow filtration lube oil system with bypass protection. RR-407 is the Lube oil used in the system. Engine crankshaft driven, gear type lube oil pump sucks oil from the engine sump and delivers it into the system. A relief valve, set at 110 psi, is fitted just after the pump to save the pump from excess loading. Pumped oil then passes through filter tank, containing 8 Nos. of filter elements, for filtration. A bypass valve, set at 20 psi differential pressure, is fitted across the filter tank to maintain the continuity of flow, in case the filter gets choked.. Lube oil cooler fitted in the system maintain operating temperature of lube oil, by dissipating excess heat through water, circulating around it. Regulating valve, set at 75 psi, maintains the pressure of the whole system. The oil then passes through a strainer and finally gets stored into main and secondary headers, from where it is distributed to various components of the engine for lubrication. Cooling of Piston is done by circulation of lube oil through it. For this, lube oil from main header reaches to main bearing through S-pipes. Again from main bearing, through internal drill passages of crankshaft and con.rod, oil reaches to piston. After circulating inside the piston, the oil flows down to sump through an opening provided in the piston. While flowing down the oil gets splashed by crankshaft for

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lubricating liners. Finally the oil drops down to sump after lubricating all the components of the engine. SELF ASSESSMENT 1. What are the various factors that affect the low lube oil system pressure? 2. Draw a neat sketch of WDM2 engine Lube Oil system and label it. 3. What are the various factors that affect the high lube oil consumption? 4. What are the sources for fuel contamination in lube oil? 5. What are the sources for water contamination in lube oil?

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COOLING SYSTEM OBJECTIVE

To understand about • the need for cooling system in a diesel engine • the benefit of water cooling system • harmful effects of natural water in cooling system • the method of water treatment and the quality of treated water • the water cooling system of WDM2 Locomotive STRUCTURE 1. Introduction 2. Cooling water and its treatment 3. Cooling water system of wdm2 locomotive engine 4. Water pump 5. Modifications in cooling system 6. Summary 7. Self assessment

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INTRODUCTION After combustion of fuel in the engine, about 25-30 % of heat produced inside the cylinder is absorbed by the components surrounding the combustion chamber like piston, cylinder, cylinder head etc. Unless the heat is taken away from them and dispersed elsewhere, the components are likely to fail under thermal stresses. All internal combustion engines are provided with a cooling system designed to cool the excessively hot components, distribute the heat to the other surrounding components to maintain uniform temperature throughout the engine, and finally dissipate the excess heat to atmosphere to keep the engine temperature within suitable limits. Different cooling systems, like air cooling, water cooling are adopted, depending on the engine design, working conditions and service etc.. The advantage of having a water cooling system is that it maintains a uniform level of temperature throughout the engine and by controlling the water temperature, the engine temperature can be controlled effectively. COOLING WATER AND ITS TREATMENT Although natural water can meet the basic requirement, its use is prohibited for the cooling of the engine because it contains many dissolved solids and corrosive elements. Some of the dissolved solids may form scales on the heat exchanger surface and reduce the heat transfer coefficient. It also accelerates corrosion. Other minerals get collected in the form off sludge at an elevated temperature. This sludge may get deposited at the low-pressure zone and choke the passage of circulation. The insulation caused by the scale deposits results in unequal expansion and localized stress, which may eventually rupture the engine block, cylinder block, cylinder heads etc. to eliminate all of these, distilled or de-mineralized water is used in the cooling system of the diesel locomotive. The water sample is tested for chromate concentration, hardness, pH value, and chloride content. In case Chromate concentration is found lower than the required quantity, mixture is added. Water is changed if hardness and chloride is higher than the recommended limit. Water is also changed if found contaminated with oil etc. When water is changed due to contamination etc. the system is cleaned by adding Tri-Sodium Phosphate, and circulating water for 45min, this water is drained out, and fresh distilled water with chromate mixture is filled in the locomotive.

COOLING WATER SYSTEM The WDM2 class locomotives have a closed circuit non-pressurised water cooling system for the engine. The system is filled in by 1210 ltrs. Of distilled water or demineralised water treated with nonchromate corrosion inhibitor (Borate nitrite treatment) to maintain a concentration of 4000 PPM. The pH value is '8.5-9.5'. The water circuit has two storage tanks in two segments known as expansion tanks on top of the locomotive. Apart from supplementing in case of shortage in the system, these interconnected tanks have some empty space left at the top to provide expansion to the water when it is hot. A centrifugal pump driven by the engine crankshaft through a gear sucks water from the system and delivers it through outlet under pressure. The outlet of the pump has three branch lines from a three-way elbow. The branching off leads water to the different places as follows- 1. To the turbo-supercharger through a flexible pipe to cool the intermediate casing, bearings on both sides of the rotor and the turbine casing. After cooling the components in the turbo-supercharger, water return to the inlet side of the pump through a bubble collector. The bubble collector with a vent line is a means to collect air bubbles formed

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due to evaporation and pass it onto the expansion tank, so that thy cannot cause air lock in the water circulatory system. 2. The second line leads to the left bank of the cylinder block and water enter the engine block and circulates around the cylinder liners, cylinder heads on the left bank of the engine, and then passes onto the water outlet header. Individual inlet connections with water jumper pipes and outlet water riser pipes are provided to each cylinder head for entry and outlet of water from cylinder head to the water outlet header. Cooling of cylinder liners, piston rings, cylinder heads, valves, and fuel injection nozzles are done in this process. Water then proceeds the left side radiator for circulation through it, and releases its heat into the atmosphere to cool itself down before recirculation through the engine once again. 3. The third connection from the three-way elbow leads to the right side of the cylinder block. After cooling the cylinder liners, heads etc. on the Right Bank the water reaches the right side radiator for cooling itself. Before it enters the radiator, a connection is taken to the water temperature manifold where a thermometer is fitted to indicate the water temperature. Four other temperature switches are also provided here, out of which T1 is for starting the movement of radiator fan at 60O C slowly through the eddy current clutch. The second switch T2 picks up at a water temperature of 64O C and accelerates the radiator fan to full speed. The third switch is the ETS3 (Engine Temperature Switch),set at 90 degree calcius protection against hot engine, which gives bell alarm and red lamp indication. The fourth switch is ETS4 (set at 95 degree calcius) which brings the engine back to the idling speed and power cutoff also takes place to reduce load on the engine. In this situation the GF switch is cut off and engine is notched up to full notch. It helps in bringing down the cooling water temperature quickly with the radiator fan moving at full speed. Water temperature is controlled by controlling the movement of the radiator fan. Cooling water from the left side radiator passes through the lube oil cooler, where water circulates inside a bunch of element tubes and lube oil circulates around the tubes. Thus passing through the lube oil cooler and cooling the lube oil, it unites with the suction pipe for recirculation through the cooling circuit. Cooling water from right side radiator passes through after cooler, where water circulates inside a bunch of element tubes and cooling the charge air, it unites with the suction pipe for recirculation. Apart from hot engine protection, another safety is also provided by way of low water switch (LWS). In the event of cooling water level falling below one inch from the bottom of the tank, the LWS shuts down the engine through the governor with warning bell and alarm indication to ensure the safety of the engine. Vent lines are provided from the after cooler, lube oil cooler, radiators. Turbo-supercharger vent box and bubble collectors etc. are provided to maintain uninterrupted circulation of cooling water by eliminating the hazards of air locks in the system. Cooling water is subjected to laboratory tests at regular intervals for quality controls. Contamination, chloride contents, and hardness etc.. are checked to reduce corrosion and scaling. The concentration of anti-corrosive mixture is also checked and laboratory advises corrective action in case of contamination. Proper quality control of cooling water and use of proper quantity of nonchromate corrosion inhivitor prevents scaling and corrosion in the system, and ensures longer life of the components. Normally 8.2kg is added for new water in WDM2 locomotive. WATER PUMP

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MODIFICATIONS PERTAINING TO COOLING WATER SYSTEM OF WDM2 LOOMOTIVE Louvred fin radiator: - The radiator core has been redesigned by providing louvred fins thereby increasing the cooling capacity by 14% due to improved air flow pattern through the radiator. High efficiency turbochargers:- High efficiency turbochargers has been provided on the fuel efficient version of wdm2 locos. This has resulted in lowering of the exhaust gas temperature by around 15% with modified after cooler. Large after cooler & water connection:- Large after cooler & water connection has been provided on the fuel efficient locos. This has reduced the heat input to the cooling system. Revision of ETS setting :- The setting of ETS3 is raised to 90 deg.C from 85 deg.C in order to avoid frequent hot engine alarms. Subsequently, with the introduction of pressurised cooling water system, one more ETS is added with the idea of providing only hot engine alarm through ETS3 at 90 deg. C and bringing the engine to idle by ETS4 at 95 deg. C. This change not only reduces the occurrences of hot engine alarm but also increases the heat transfer potential of the radiator at high temperature. Revised setting of OPS:- The setting of low lube oil pressure switch on WDM2 locos used to be 1.8 kg/ cm2 with a view to obviate the problem of engine shutting down due to operation of OPS while suddenly easing throttle from higher notches to idle, particularly during summer season, the OPS setting has been revised to 1.3 kg/ cm2. Pressurisation of cooling water system:- The cooling water circuit has been pressurised upto 7 psi thereby increasing the boiling point by 11 deg. C. This has not only increased the margin before the cooling water gets converted to steam but has also increased the temperature differential acrossed the radiators at peak engine temperature, thereby increasing the rate of cooling in radiators. This has been achieved by providing a pressure cap assembly on the water tank. Flexible water inlet elbow:- Rubber hose type flexible water inlet elbow has been developed in place of the rigid one piece metallic water inlet elbow for obtaining better leakproofness even in face of mislignments between the engine block and the cylinder head. Digital water temperature indicator cum switch:- This has been developed to replace the existing water temperature gauge as well as the four engine temperature switches whose performance was quite unreliable. This aims at ensuring operation of radiator fan and alarm at proper temperature. Electronic water level indicator cum switch:- This has been developed to replaced the existing water level gauge as well as the low water switch. This indicator shall give precise and reliable information regarding the water level to the driver in the cab itself. Improved type pipe joints:- This has been improved to replace the existing pipe joints viz. dressers victaulics by superior rubber hoses along with double wire stainless steel clamps and by stainless steel bellows. SUMMARY In the process of combustion, about 25% to 30% of the total heat developed is absorbed by the components of the engine forming the combustion chamber. Hence an effective cooling system is essential to dissipate the accumulated heat. Amongst the various

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methods of cooling the water cooling system is the most effective method of cooling, as it maintains the uniformity of temperature through out the engine. In WDM2 type engine water cooling system is being used with 1200 ltrs system capacity. Dimeneralised water treated with chromium compound is used as coolant water. In this system a centrifugal pump, driven by engine crankshaft is being used to deliver water into the system with pressure. The outlet of the pump is being divided into main three heads- one for cooling turbo charger and after-cooler and the other two for cooling the engine components situated at left and right bank of the engine. Finally the water gets collected at headers and sent to radiator for cooling. An induced draft radiator fan is used to blow air through the radiators for cooling. The radiator fan takes drive from the engine crankshaft through ECC (EDDY CURRENT CLUTCH). A temperature switch controls the clutching effect of ECC and hence radiator fan rpm. Safety devices are provided both for hot engine and low water conditions of the engine. SELF ASSESSMENT 1. What type of water is used in cooling water system of locomotive? How water treatment is done? 2. What are the harmful effects of using natural water in cooling system? 3. Draw a neat sketch of the cooling water system and label it. 4. How does Radiator Fan get drive? How its rpm is controlled? 5. What is the purpose of providing vent box and bubble collector in cooling water circuit? 6. What are the modifications carried out in cooling water system?

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UNIT M2- DIESEL ENGINE COMPONENTS

OBJECTIVE The objective of this block is to make you understand about the major components of the Diesel Engine as per the following details:

• Construction

• Manufacturing process

• Salient features and required dimensional accuracy in the key areas

• Assembling technique and their inspection procedure.

• Failure analysis of components

STRUCTURE

Introduction

Engine base

Engine Block

Crankshaft

Camshaft

Cylinder Head and valves

Liner

Piston, Piston Rings & Con Rod

Failure analysis of components & Failure investigation.

Summary

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Key words

Self-assessment

INTRODUCTION

This unit contains, in brief, the essential details in respect of design, construction, working principle and maintenance procedure of the Diesel Engine components. The discussion has been kept confined to standard locomotives of Indian Railways that is WDM2..

The Diesel engines consists of following major components & assemblies: -

1.Engine base 2.Engine block 3.Crank shaft

4.Cam shaft

5.Cylinder head and Valves

6. Liner 7.Piston, Piston rings and Connecting rods.

ENGINE BASE :- When diesel engines were of low speed and low horse power the engine base and blocks were made of heavy cast iron casting. In older types engines one of the main functions of the base was to take the crank shaft. In the modern engines the crank shaft is underhung from the engine block. With the development in diesel engines and with the change in design, fabricated engine blocks and bases are finding favour though in some small horse power engines cast iron blocks are still in use. The engine ;base of ALCO Locos WDM2, WDM4 are made from weldable quality steel to specification IS-2062 with 0.2% of carbon. The engine bases of ALCO Locos have following functions. It has to - a) Support the engine block b) Serve as oil sump c) Accommodate lube oil mainheader d) Take lub oil pump and water pump at the free end e) Allow openings for crank case inspection f) Take fitment of crank case explosion cover

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g) Foundation pads are provided for transmitting load to the chassis and also to take lower blots of the main generator magnet frame.

A perforated screen is fitted to the base to prevent foreign matter like pieces of metal etc. getting access to the sump. The top face of the base which takes the engine block is machined smooth and a sealing compound is applied before fitting the block to make the crank case air tight so that crank case vacuum can be maintained. Except for the size and sump capacity the engine base of YDM4 Locos is same as that of WDM2 in respect of material and manufacturing technique. In case of WDS4B Engines there is no separate base. The function of oil sump is performed by fabricated steel sheet fitted at the bottom of the block with gasket in between.

ENGINE BLOCK The engine block is the most important and very highly stressed structure on

which are fitted a number of important fittings like crank shaft, cam shaft, cylinder heads, cylinder liners, pistons, Con. Rods, fuel injection pumps and cross-head, turbo support, governor etc to form a complete Power pack.

Manufacturing Process

This structure is fabricated from low carbon steel to specification IS-2062. The saddle, however, is a forging out of steel to specification IS-1875. The fabrication is done in a definite sequence to minimize distortion and build up of stresses. In order to ensure that best quality of fabrication is done in all cases down hand welding is resorted to. For this purpose extensive use of positioners are made. Wherever possible, continuous welding is done in the process of automatic submerged arc welding. To make sure that there is no defect in the welding, X-ray testing of welding is done liberally.

After fabrication by welding stress relieving and shot blasting is done and then hydraulic test of water chamber is done so that no water leakage can take place. Finally the block is taken to the marking table for marking and then machining. After marking, the engine blocks are placed on the planning machine for machining the sides and the top faces, all the faces being machined at a time. While setting up for machining, it is ensured that the side faces are at right angle to the end face. The bottom face and the saddle faces are also machined in the same machine.

The blocks are then taken for serration milling of saddle faces. In continuation with serration of saddle faces the serration milling of bearings caps are done. This is to avoid error caused due to wear and tear to the milling cutter. Each bearing cap is marked for the location so that the bearing cap cannot be pooled about or wrongly fitted. After the milling operation the depth of serration, and distance between two consecutive pitches are

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measured with the help of special dial gauges.

After the inspection the bearing caps are assembled and they are tightened to the specified torque value. Subsequent to fitting of the caps to the block the engine block is placed on the horizontal boring cum milling machine. On this machine, end face milling is done and boring of main bearing housing and camshaft bearing is done in one setting with the help of a fixture. This is done to ensure that the distance between crankshaft to camshaft is exactly equal throughout and the central line is perfectly parallel to each other. The maximum possible misalignment permitted in main bearing housing bore are as follows: -

Horizontal misalignment:

1. Between adjacent bores. 0.002"

2. Between any to any bore. 0.004"

Vertical misalignment:

1. Between adjacent bore 0.0015"

2. Between any to any bore. 0.003"

This sort of misalignment can be checked with the help of mandrel and feeler gauge. But this is considered to be rather crude method. It is advisable to make such checks with the help of optical instruments like collimators to give accurate results.

After the boring of crank and camshaft bearing housing, the work of machining top & middle decks of cylinder liners is taken up. The two bores, the chamfers and facing of the top face are all done simultaneously with the help of machine with two boring bars fixed at an angle of 45O.

The engine blocks have been found to show signs of distortion after a life of 12 to 15 years or as an after effect of crankshaft seizure or major accident. In order to cope with such defects, capacity has been created in DLW for reclamation of blocks.

The method of construction, manufacture, inspection and maintenance of YDM4/WDS6 engines base and block is almost the same as WDM2 block except for dimensional difference and except for the fact that WDM2 are 16 cylinder "VEE" blocks and YDM4 are with 6 cylinder in line engine blocks.

Maintenance & Inspection Schedule: POH

Details of Inspection:

• Visual Inspection: To check about the physical damages in the block and take decision about its reuse or reclamation.

• Examination of threads and renewals of threads, if essential.

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• Measurement of top and bottom deck to select liner as well as to change liner sleeve, if necessary.

• Measure cam bearing dimension and change bearing, if necessary.

• Main Bearing Inspection: 1. Check serration of saddle and M/ Bearing cap by serration gauge.

2. Fit main bearing cap and elongate properly upto .040" as per laid down procedure.

3. Measure each bore at two different planes ½" away from both sides and in each plane at 3 different locations, vertical and at 45°angular position at both sides of it.

Difference in readings at a particular plane gives the value of ovality (limit 0.003")

Difference in vertical readings gives the value of vertical taper (limit 0.001"}.

*Difference in angular readings gives value of angular taper (limit 0.003")

Concentricity of Main Bearing bore should be maintained within the following limit:

Horizontal misalignment: 1) between adjacent bores: 0.002"

2) Between any to any: 0.004"

Vertical misalignment: 1)Adjacent 0.0015"

2)Between any to any 0.003"

Misalignment is checked with the help of Mandrel and filler gauge.

• While assembling, block and base should be perfectly aligned within the limit (Gen end: 0.000", side ways: 0,002" max).

• Hydraulic test: Hydraulic test conducted at 2.5 kg/cm² at normal temperature to check whether any leakage exists between block and liner. If so, liner O-rings are changed or other corrective measures are taken accordingly. This is done after assembling liners during assembly stage.

CRANKSHAFT The engine crankshaft is probably the singular costliest item in the diesel engine. It

is the medium of transforming reciprocating motion to rotary motion. The crankshaft may be assembled type or two pieces bolted type or may be single piece forging. Balance weights can be either bolted up or welded. The standard Locomotives of Indian Railways

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are with single-piece crankshaft with welded counter weights. In case of CLW/MAK engines the counter weights are bolted.

The ALCO crankshafts are manufactured from chrome-molybdenum steel equivalent to SAE 4140. The process of forging is such that continuous grain is maintained. In manufacture of crankshaft, following sequence of operation is generally followed: -

a) Forging and forming operation

b) Rough machining

c) Drill of oil holes.

d) Ultrasonic & Mechanical testing

e) Welding of counter weights & their X-ray test.

f) Stress relieving & shot blasting

g) Final machining & for giving fillet radius at crank journal corners and making oil holes.

h) Nitriding

i) Grinding Lapping

j) Static & dynamic balancing

k) Final inspection

There are two processes of surface hardening with details given below:-

Method of hardening Hardness Depth of hardness

Induction hardening C-40 0.124"

Nitriding C-60 0.012 to 0.015"

Generally for low HP engines the first process is preferred, as depth of case is more and the crank journals and man bearing journals can be ground down to next step size. In case of high HP and high-speed engines, the preference is for the second process as it gives long life, the rate of wear being negligible.

Maintenance & Inspection Schedule: POH

Procedure: After cleaning thoroughly, Dye penetration / Magnaflux test is conducted to detect surface crack. Measure the following dimensions:

Crank pin: Positioning it vertically check dimension at two locations just beside two oil holes (at two right angular planes in each location) to check ovality and taperness.

Nominal Dia: 6", Limit upto 5.996"

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Ovality: .002"(max) Taperness: .001"(max)

Main journal: Position the crankshaft, keeping No 1 crankpin in vertical location, measure the dimension as that of crank pin.

Nominal Dia: 8.5", Limit upto 8.496"

Ovality:002" (max) Taperness: .001" (max)

Fillet Radius: Checked through a special gadget. (.0005" filler gauge should not pass between the gadget and the fillet)

Eccentricity checking: Eccentricity is checked between any three consecutive main journals (1,2,3) is given by the distance between the center points of journal 2 and the mid point of the line joining the center points of journals 1 & 3. The limit of eccentricity is .001". Eccentricity is checked by the following way:

• Place the crankshaft horizontally on a "V" block supported at No3 and No 7 Main Journals, keeping No 1 crank pin in vertical position.

• Mark Dial of a clock at the free end flange in this position, to understand angular location of the maximum deviated zone.

• Record the readings of maximum deviation of every main journal along with their angular location.

• An example of calculating the eccentricity (For No 1,2,3 Main Journals) is given below:

- Highest total indicator reading (TIR) for:

No 1 M.J.0.0015" at 3 o'clock location. No 2 M.J. 0.004" at twelve o'clock

No 3 M.J. 0.0015 at 1-30 o'clock

- Plot the graph according to deflection and o'clock location, with suitable scale.

- Connect TIR position of No1 and No3 with a straight line.

- Mark the midpoint of the above straight line and connect it with the TIR of No 2. This is the relative runout of No 1,2,and 3 main journals.

- Divide the runout by 2. This is the eccentricity and must not exceed .001". (This case it is .00175" and not acceptable.)

- Repeat the above case for each group of three consecutive main journals

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12 0'CLOCK

2 .0035 TIR

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1 3 O'CLOCK

Crank web deflection: Checking of crank web deflection is one of the major works while assembling engine.

Main generator is coupled at one end of the crankshaft, whose other end is supported on a bearing housed at the magnet frame. As such, due to mislocation of magnet frame, if axis of armature does not completely align with the axis of the crankshaft, the unbalanced mass of armature will cause uneven loading on crank web at different angular positions during rotation. This causes deflection on crank web, which will be changing at various positions of crankshaft during rotation. Such kind of continuous cyclic variation of load leads to main bearing seizure and breakage of crankshaft.

The crank web deflection can be measured by fitting a deflection gauge at the located punch mark on the 8th crank web, nearer to TG and rotating the crankshaft in both the directions

The permissible limit of deflection on each side is ±. 0008", TIR ±. 0016".

Correction is made by adding or subtracting shims at the mountings of magnet frame with engine block. The magnet frame is mounted at two locations with the engine block and at two locations at the base. Adjustable shims are provided at the mountings of the magnet frame with the block. The shims of the magnet frame with the base are fixed and normally not disturbed during crankshaft deflection.

CAM SHAFT In diesel engine the cam shaft performs the vital role of opening and closing inlet

and exhaust valves and allowing timely injection of fuel inside the cylinder. Usual practice is to provide 3 cams for each cylinder the two outer cams being for exhaust and inlet valves and the central cam being for fuel injection.

Like most of the Diesel engine manufacturers, ALCO engines have cams integral with camshaft. Each camshaft section takes care of two cylinders. After profile milling of the cam lobes the cams are given for induction hardening. Subsequent to this the cams are put on profile grinding machine. The individual camshafts are joined together by bolting.

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The location of dowel hole is of importance as it determines the relative angular position of one camshaft section with respect to the adjacent one.

In order to avoid wrong assembly respective catalogue Nos. of camshaft sections are punched onto the shaft. Care has to be taken to see that the correct section is fitted in correct location. The rifle hole is made in the center of the shaft for lubrication of cam bearings. Lubrication to cam lobes is provided by oil coming from valve lever mechanism via the push rod.

Material composition: The ALCO camshafts are made from AISI specification 1050 with following metallurgical composition.

Carbon 0.48 to 0.53%

Manganese 0.60 to 0.90%

Chromium 0.15 to 0.30% Max.

Phosphorus 0.025% Max.

Sulphur 0.025% max.

Assembly & Inspection Schedule: POH

Inspection: Check cam profile through profile gauge.( If damaged or worn out the cam segment is changed.)

Setting of Cam shaft & Valve/ FIP timing:

(a) Timing Mark & Pointer

• Timing Marks are provided on Timing Disc (Main Generator fan) fitted with Main Generator armature, mounted on crankshaft. (Relation between crank shaft, armature and armature fan are maintained through dowels, provided)

• TDC, INJ Pointer is mounted on the block to read the relative position of cylinder corresponding to pointer and timing disc. (Pointer needs to be calibrated during engine overhauling by finding TDC with the help of dial indicator or trammel gauge.)

(b) Setting of cam shaft

• Assemble the cam segments as per correct sequence and order (Part Number indicates the sequence and dowels fix their angular relation). Thus left and right side camshafts are formed.

• Position the crankshaft to 1R TDC. Match both side cam gears with crankshaft gear in such way that cut marks (line mark) on cam gear should perfectly match with block edges.

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• Now fit both camshafts matching with the key holes of cam gears.

• Secure the camshafts finally on cam gear by tightening it properly through locknut.

(c) Valve Timing

• Rotate the crankshaft and bring the corresponding cylinder to compression stroke (ensure compression stroke by feeling free rotation of push rods.)

• Check the gap between the valve stem and yoke. It should be 0.034". If not adjust it through valve lever adjustment nut and yoke adjustment nut.

(d) FIP Timing

• Rotate the engine to bring the injection point against the corresponding cylinder.

• Match the body cut mark of FIP at inspection window with the given line mark on guide cup .If not, adjust it through timing allenscrew provided at the bottom of the FP lifter.

CYLINDER HEAD

The cylinder head is held on to the cylinder liner by seven hold down studs or bolts provided on the cylinder block. It is subjected to high shock stress and combustion temperature at the lower face, which forms a part of combustion chamber. It is a complicated casting where cooling passages are cored for holding water for cooling the cylinder head. In addition to this provision is made for providing passage of inlet air and exhaust gas. Further, space has been provided for holding fuel injection nozzles, valve guides and valve seat inserts also.

In cylinder heads valve seat inserts with lock rings are used as replaceable wearing part. The inserts are made of stellite or weltite. To provide interference fit, inserts are frozen in ice and cylinder head is heated to bring about a temperature differential of 250°F and the insert is pushed into recess in cylinder head. The valve seat inserts are ground to an angle of 44.5° whereas the valve is ground to 45° to ensure line contact. (In the latest engines the inlet valves are ground at 30° and seats are ground at 29.5°). Each cylinder has 2 exhaust and 2 inlet valves of 2.85" in dia. The valves have stem of alloy steel and valve head of austenitic stainless steel, butt-welded together into a composite unit. The valve head material being austenitic steel has high level of stretch resistance and is capable of hardening above Rockwell –34 to resist deformation due to continuous pounding action.

The valve guides are interference fit to the cylinder head with an interference of 0.0008" to 0.0018". After attention to the cylinder heads the same is hydraulically tested at 70 psi and 190°F. The fitment of cylinder heads is done in ALCO engines with a torque value of

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550 Ft.lbs. The cylinder head is a metal-to-metal joint on to cylinder.

The cylinder head castings are made from special alloy cast iron as per specification given below: -

Material composition: Total carbon 3.00 to 3.40%

Silicon 1.80 to 2.20%. Sulphur 0.12% to 0.8%.

Phosphorous 0.15 Max..

Manganese 0.65% to 90%

Chromium 0.20% to 0.40%

Nickel 1% Min.

Molybdenum 0.35% to 0.45%

ALCO 251+ cylinder heads are the latest generation cylinder heads, used in uprated engines, with the following feature: -Fire deck thickness reduced for better heat transmission.

-Middle deck modified by increasing number of ribs (supports) to increase its mechanical strength. The flying buttress fashion of middle deck improves the flow pattern of water eliminating water stagnation at the corners inside cylinder head.

-Water holding capacity increased by increasing number of cores (14 instead of 11)

-Use of frost core plugs instead of threaded plugs, arrest tendency of leakage.

-Made lighter by 8 kgs (Al spacer is used to make good the gap between rubber grommet and cylinder head.)

-Retaining rings of valve seat inserts eliminated.

Benefits:-

-Better heat dissipation

-Failure reduced by reducing crack and eliminating sagging effect of fire deck area.

Maintenance and Inspection Schedule: Yearly

• Cleaning: By dipping in a tank containing caustic solution or ORION-355

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solution with water (1:5) supported by air agitation and heating.

• Crack Inspection: Check face cracks and insert cracks by dye penetration test.

• Hydraulic Test: Conduct hyd. test (at 70 psi, 200°F) for checking water leakage at nozzle sleeve, ferrule, core plugs and combustion face.

• Dimensional checks : (a) Face seat thickness: within 0.005" to 0.020"

(b) Interference:

I. Valve seat insert to housing: 0.0015" to 0.0035" (Stellite)

0.003" to 0.005" (Weltite)

II. Valve Guide: 0.0008" to 0.0018"

III. Yoke Guide: 0.0015"

(c) Projected Height:

I. Valve Guide: 2.25"

II. Yoke Guide: 3.210" to 3.272"

(d) Clearance between valve and guide: 0.004" to 0.007"

(e) Thickness of valve disc & Insert: 5/32" (new) 3/32" (min)

(f) Straightness of valve stem: Runout should not exceed 0.0005"

(g) Free & Compressed height (at 118 lbs.) of springs: 3 13/16" & 4 13/16"

• Checks during overhauling:

(a) Ground the valve seat insert to 44.5°/29.5°, maintain run out of insert within 0.002" with respect to valve guide while grinding.

(b) Grind the valves to 45°/30° and ensure continuous hair line contact with valve guide by checking colour match.

(c) Ensure no crack has developed to inserts after grinding, checked by dye penetration test.

(d) Make pairing of springs and check proper draw on valve locks and proper condition of groove and locks while assembling of valves.

(e) Lap the face joint to ensure leak proof joint with liner.

(f) Blow by test:

I. On bench blow by test is conducted to ensure the sealing effect of cylinder head.

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II. Blow by test is also conducted to check the sealing efficiency of the combustion chamber on a running engine, as per the following procedure:

a) Run the engine to attain normal operating temperature (65°C)

b) Stop running after attaining normal operating temperature.

c) Bring the piston of the corresponding cylinder at TDC in compression stroke.

d) Fit blow-by gadget (Consists of compressed air line with the provision of a pressure gauge and stopcock) removing decompression plug.

e) Charge the combustion chamber with compressed air.

f) Cut off air supply at 70 psi. through stop cock and record the time when it comes down to zero.

g) 7 to 10 secs is OK., if less check the leakage.

h) To check leakage, charge continuously at 70 psi

-Leakage through TSC indicates head defective.

-Leakage through Sump indicates defect in Piston or Liner.

(g) Tale-tell hole checks: Tale tell hole in cylinder head tells about the condition of cylinder heads in running condition as per the following:

I. No leakage: OK

II. Fuel droplets: Upto 2 drops/min OK.

If more, Nozzle leak off rate is high.

III. Fuel Mist: Nozzle seat defective.

IV. Water leakage: Nozzle Sleeve cracked.

V. L/Oil leakage: Rubber ring on Nozzle perished.

LINERS

Liner forms the wall of the combustion chamber as well as it also guides the movement of piston inside it. Liners are mainly of two types i.e. (a) Dry liner (b) Wet liner.

(a) Dry liners are those, which does not come in direct contact with coolant but fits in as a sleeve inside an already complete cylinder. The temperature of the inside surface of dry liner is higher than corresponding wet liner. Dry liners are in use in only very small engines.

(b) Wet liners are those, which not only form the cylinder wall, but also form a part of the

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water jacket. ALCO Locomotives are fitted with wet liners, which have slight interference fit on upper and lower decks. In addition to this, synthetic rubber seals of suitable qualities are to be used, one on the upper deck groove and two on middle deck. Lack of interference or defect in gaskets may result in water leakage causing water contamination of crank case oil. The liner bore has chrome-plated surface and is honey combed by electrolytic process. ALCO liners have no step size in the bore. It has got only one standard size permitting a wear of 0.009 inch.

The General Motor cylinder liners are fabricated type embodying the water jacket. In General Motor Locomotives, instead of liner bore being chrome plated the piston rings are chrome plated.

The ALCO cylinder liners are made of high strength close-grained alloy cast iron heat-treated to relieve stresses. The liner metal composition of a typical ALCO engine is given below: -

COMPOSITION

(Unalloyed cast iron grade 17)

Carbon 3.00 -0 3.50%

Silicon 1.70 to 2.30%

Sulphur 0.12% Max (mandatory)

Phosphorus 0.15% Max (mandatory)

Manganese 0.60 to 0.90%

Chromium 0.25 to 0.60 %

Molybdenum 0.35 to 0.70% (mandatory)

Maintenance & Inspection: Yearly inspection, 3 yearly & POH renewal

The cylinder liners suffer from the following major defects:

(a) Wear in the bore (Nominal bore 9”.Max allowed 9.009”)

Max ovality: .003”(max) Max taperness: .002”(max)

(b) Loss of interference in the top & bottom decks.

In the bottom deck portion, in between Liner and block a sleeve is used, made of spheroidal cast iron. Hence in case of losing interference or any other defect the sleeve is renewed.

Interference between block to sleeve: .004” to .008”

Int. between sleeve to liner: .0005”to .0015”

As the liners form water jacket with the engine block, hence for proper sealing one rubber

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ring of Si- rubber and two rubber rings of Viton rubber are used at the top and bottom deck respectively. It is essential to change the rubber rings while renewing or removing liners.

(c)Cavitation erosion of outside circumference particularly near the location of fuel injection pump side and also opposite to fuel injection pump side.

• The cylinder liners can be reclaimed by re-chrome-plating in case of wear in the bore up to a certain limit. In case of cavitation and erosion, if the cavity is more than 1/8" deep then the liner has to be taken out of use.

PISTONS, PISTON RINGS AND CONNECTING ROD PISTON

The piston is the most important component in the diesel engine as it takes direct part in transmission of power. It is, therefore, necessary that the designers and users must know the essential details about the piston. The combustion of fuel results in large amount of heat being developed. Out of this about 18% of the heat is absorbed by piston only.

The functions of the piston are: -

(a) It compresses the air to required pressure & temperature.

(b) It receives the thrust of expanding gases and transmits the force through connecting rod (for rotating crankshaft).

(c) It forms the crosshead through which side thrust due to angularity of connecting rod is transmitted to the cylinder wall.

(d) With the help of piston rings it prevents leakage of gas from combustion chamber to crank case.

Guiding factors for dimensions are as follows: - (a) The top portion of the piston is in contact with direct heat of combustion. Inspite of cooling arrangement, it takes up more expansion and as such the need for more clearance at this location.

(b) Relief has to be provided at the piston pin located area to prevent seizure of piston due to bulging of material at this location in course of working.

Ring Grove Insert The top most ring bears the maximum burnt of high pressure hot gases. This result in heavy wears in the upper ring groove. In order to over come this problem, Ni-resist ring insert is fitted in the uppermost ring groove. Ni-resist rings apart from being dove tailed in Aluminium casting/forging, are molecularly bounded to the Aluminium body by AI-FIN-process.

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Piston material: In many ways cast iron is best-suited material for manufacture of piston. The reasons are as follows: - (a) Co-efficient of expansion matches with cylinder liner whereas Aluminium has got twice the co-efficient of cast iron.

(b) Heat conductivity is 3 times better than Aluminium.

(c) Compression strength is much more than Aluminium at high temperature.

(d) Wear is less than Aluminium.

But the two main disadvantages with cast iron piston are: - (a) Weight of Aluminium is 0.097 1bs. per cubic inch in place of cast from which is 0.284 1bs. per cubic inch. Thus cast iron pistons are about 3 times heavier than Aluminium piston in weight.

(b) Possibilities of cylinder liner being scored are more in case of cast iron piston.

The factor of weight has become more over riding in view of the high speed of the modern diesel engines and hence Aluminium alloy pistons are favoured. ALCO 251 engines pistons are of Aluminium alloy with composition given below-

COMPOSITION

Copper 5.8 to 6.8%

Zinc 0.10% max.

Manganese 0.20 to 0.40

Titanium 0.02 to 0.10

Vanadium 0.05 to 0.15 %

Zirconium 0.10 to 0.25 %

Silicon 0.20% Max.

Iron 0.30% Max.

Magnesium 0.02% Max.

Other 0.15% TOTAL

Aluminium - remainder

These pistons are in two parts i.e. the piston body (or skirt) and the ring carrier having interference fit. The joint between the ring carrier and piston is welded at the crown by inert gas welding.

Mahle has developed single cast Al alloy piston, reducing the chances of dislodging of ring carrier during working.

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Steel cap pistons are used in Fuel efficient and upgraded engines.

PISTON RINGS The main functions of piston rings are: - a) Sealing of combustion chamber and thus prevents blow by of air and high temperature combustion gasses from getting access to crank case.

b) Scraps down excess lube oil from walls of cylinder liner and thus prevents reaching lube oil into combustion chamber.

Piston rings are made of malleable grey cast iron with open graphite structure and a hard pearlitic matrix. The piston ring operates during a part of its life under conditions of marginal lubrication hence material composition has important role in this regard.

Piston rings are used in combination to perform the above functions. They are either 5 ring combination or 6 ring combinations. Now a days 5 ring combinations are in use.

Compression Rings: 1. Square Face 1. Square Face

2.Taper Face 2. Taper Face

3. Taper Face 3. Taper Face

Oil scrapper Rings: 4.DoubleTaper face 4.DoubleTaper Face

5. Conformable 5.Double Taper face

6. Conformable

In the latest fuel efficient engines barrel faced piston rings are used in place of square faced compression rings and both the oil scrapper rings are conformable rings.

CONNECTING ROD

Connecting rod is a member connecting piston and crankshaft and is a medium for converting the reciprocating motion to rotary motion. In four stroke engines during the compression and power stroke the connecting rod is subject to high compressive load. In suction stroke it undergoes high tensile stresses. In case of two-cycle engine the connecting rod is only subject to compressive load. Connecting rod length is usually about 4 to 5 times of the crank radius. They are I beam sections of fine-grained, fully killed alloy steel forging. Connecting rods are having a fine-drilled hole from the big end to the small end for transporting oil for lubrication at small end bearing and piston pin and for cooling of piston.

The connecting rod assembly consists of: - (i) Connecting rod, (ii) Connecting rod cap (iii) Piston pin bushing (iv) Bearing Shell upper (v) Bearing Shell lower (vi) Connecting rod bolts and nuts.

During assembly the bolts are to be tightened with specified torque value and elongation

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upto .015” to .018”. Connecting rods are mostly made of carbon steel or alloy steel forging. The metallurgical composition of connecting rod is given below in percentage.

COMPOSITION

Carbon 0.43

Manganese 0.75%

Phosphorous 0.025% Max.

Sulphur 0.025% Max.

Silicon 0.20 %

Nickel 0.40 %

Chromium 0.40 - 0.60%

Molybdenum 0.15 - 0.25%

Boron 0.5% Min.

Maintenance & Inspection: Schedule: Yearly

Cleaning: Solution of ORION 516 in HSD Oil is used for Piston cleaning.

Checks: Zyglo test for checking surface cracks.

Visual checks for checking damages in piston crown, Ring grooves, circlip groove and Ni- resist insert

Dimension checks:

a) Piston crown, skirt and bottom

b) Piston pin hole dia: ( Tolerance : +0.001”, Ovality : 0.0005”)

c) Con rod to Piston side clearance: 0.013”to 0.024”

d) Piston to pin Dia clearance: 0.0005 to 0.0025”( max 0.0035”)

e) Bushing to pin dia. clearance 0.0025 to 0.004” (max 0.006”)

Piston ring checks during assembly:

a) Proper sequencing

b) Maintaining proper side ( top and bottom)

c) Ring Gap check:

Compression Ring: 0.045 to 0.055” (max 0.200”)

Oil Scrapper Ring: 0.030 to 0.040” ( max 0.125”)

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d) Side clearance

Compression Ring: 0.006 to 0.0085”(max 0.012”)

Oil Scrapper Ring: 0.002 to 0.0045” (max 0.006”)

e) Maintain 180° interval between two consecutive ring gaps.

Con Rod checks: a) Measure big end bore dia, ovality (max 0.003”)

b) Twist: 0.002”, bend 0.001”(max)

c) Length of Con Rod bolt 11±.005”

FAILURE ANALYSIS OF COMPONENTS & FAILURE INVESTIGATION A part or assembly is said to have failed under one of the three conditions-

When it becomes completely inoperable-occurs when the component breaks into two or more pieces.

When it is still inoperable but is no longer able to perform its intended function satisfactorily- due to wearing and minor damages.

When serious deterioration has made it unreliable or unsafe for continuous use, thus necessitating its complete removal from service for repair or replacement-due to presence of cracks such as thermal cracks, fatigue crack, hydrogen flaking.

GENERAL PRACTICE OF FAILURE INVESTIGATION The objective of failure investigation, and subsequent analysis is to determine the primary cause of failure, and based on this determination, decide on corrective measures, which should be initiated to prevent similar failures. The principal stages of investigation are-

Collection of background data and collection of sample-

All available information regarding the manufacturing, processing, and service history should be collected. Particulars and condition of other affected components should also be noted. Details about operating conditions must also be noted meticulously. Selection of the sample should be done prior to starting the examination.

2. Visual examination of failed components-

After the receipt of the broken and affected components in a metallurgical lab, each sample is registered against a particular sample number. The fracture face is cleaned with K oil. And soft metallic brush. Location of the fracture must be done in relation to some fixed corner or side depending upon the specimen. Examine the fracture face with a

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magnifying glass to determine the type of fracture. Nature of stress raiser can also be determined. Examination can be done for the presence of welding or reclamation marks, wearing etc., and if possible, photographs may be taken.

To determine the nature of fracture and stress raiser-

On the basis of visual examination, fractures may be classified as:

Ductile fractures: it involves a reduction in area and neck formation at the location of the fracture. Overloading is the main reason of this type of fracture. Generally found in tough materials

Brittle fractures: the entire fracture face is crystalline without any origin. Sudden shock or loading is the main cause of this type of fracture. There is no reduction in area of cross section at the point of fracture. Generally occurs in fragile materials. However, sometimes a part made of tough material, can sometime fracture in a brittle manner if that part contains a large enough flaw or if there is sufficient elastic or plastic constraint.

Fatigue fractures. They result from the application of repeated or cyclic stresses, each of them may be substantially below the normal yield strength of the material. Fatigue fracture face has two distinct zones. It is comparatively smooth and huge concentric circles or marks originating from a single nucleus are present. They generally show slight roughness as the crack grows. The remaining portion is crystalline in nature due to the sudden fracture.

3. Non-destructive testing:- These tests include magnetic particle inspection, ultrasonic testing, liquid penetrant inspection, and radiography. These tests are done to find out surface and sub-surface defects. The magnetic particle inspection is done on Ferro-magnetic components, while penetrant tests, ultrasonic tests, and radiography tests can be done on all the components.

Mechanical testing:- Mechanical tests include hardness tests, UTS, elongation, bend tests, izod-charpy tests etc. They help ascertain whether the component conforms to the physical properties mentioned in the drawing. Nick break test is done on non-ferrous materials to see segregation and oxidation.

Chemical testing:- Drillings of the component are taken to determine its chemical composition.

Macro examination:- Two types of macro examination are done:

Deep etch test to determine the grain flow and to decide whether the component is forged, rolled, or cast. It gives indication of inclusion, segregation, rolling seam etc.

Sulphur print: this test gives the indication of Sulphur segregation, and is done by pressing

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Silver Bromide paper dipped in 5% sulphuric acid on the polished surface of transverse cut section.

Micro-examination:- This determines the microstructure, inclusion, and mode of heat treatment given to the component. This also tells about the presence of micro-cracks, welding, structural changes due to working etc. a small piece of fractured material is cut, including the region of fracture, and is polished. The final polishing of longitudinal section is done on the polishing disc. Unetched micro-examination is done on the polished surface after etching the micro-piece with suitable chemicals under bench microscope, at magnification from 100 to 1000.

Analysis of all the evidence, formulation of conclusion on the basis of all the previous steps.

Recommendations are made on the basis of findings, and remedial measures are suggested to minimize such failures. SUMMARY

This unit mainly deals about the Diesel Engine of WDM2 type Locomotive, the standard Diesel Locomotive, in use, in Indian Railways. Diesel Engine is the power unit of the Locomotive, hence it is also called power pack assembly. It is a V shaped 16 cylinder Engine. Engine Block, made of fabricated steel, forms the structure of the Engine. Various components are housed in it to form the complete Engine assembly. Cylinder Liner, Cyl Head and Piston form the combustion chamber of the engine. Cylinder head forms the lid of the combustion chamber. It houses inlet and exhaust valves to provide passage for incoming air and outgoing gas. It also accommodates Nozzle for supply of fuel in atomized form into the combustion chamber. Cylinder Liner is made of cast iron with honey combed chromeplated bore. They are basically wet type liner. Piston, made of Al alloy, in combination with special malleable grey cast iron Piston Rings seals the combustion chamber. Con Rod, made of forged steel, connects the movement of piston with Crankshaft. Crankshaft, made of forged steel with hardened surface, converts the reciprocating motion of Piston into rotating motion as the output power. It also gives drive to camshaft, water pump, lube oil pump, Expressor, Radiator Fan, main generator and many other auxiliaries of the engine. Camshaft operates inlet & exhaust valves and Fuel Injection pump of different cylinders as per their firing order. Each piece of camshaft takes care of two Nos. of cylinder, hence, there are total 8 Nos. of cam pieces to form left and right bank camshaft. Cam shaft is made of forged steel and surface hardened to reduce wear and tear. Camshaft and Crankshaft are supported with bi-metal and tri-metal bearings at their housing to reduce wear and tear, which are further assisted by lubrication system to do so. Different methods of failure investigation and their analysis help to detect the failures and to decide corrective measure to save the components from premature failure in service.

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KEY WORDS

Saddle: The portion of the engine block, which houses the crankshaft.

Mandrel: Gauge (straight iron bar) for checking alignment of main bearing bore.

SELF ASSESSMENT

1. What are the main components housed in the Engine Block to form the complete Diesel Engine.

What is crank web deflection? How it is adjusted?

What are the duties of a Camshaft? Each section of camshaft serves how many cylinders? Describe briefly the procedure of installation of camshaft in the Engine block.

What are the common defects noticed in the liners in course of service?

What are the guiding factors for selecting the dimensions of the piston?

What checks and measures should be done during fitment of piston rings?

What checks and measurements are required to be done during overhauling of Cylinder heads?

What are the various types of fracture? How do you detect them?

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UNIT M5-WOODWARD GOVERNOR OBJECTIVE The objective of this unit is to make you understand about • the principle of governing

• duties of governor in locomotive engine and their types

• features of woodward governor

• hydraulic circuits pertaining to different activities of governor

• testing of governor

• trouble shooting of governor

STRUCTURE • Principle of governing

• Introduction to Woodward Governor

• Basic governing section

• Speed setting section

• Load control section

• Fuel limiting section

• Load control override

• Lube oil pressure shutdown and alarm

• Testing of Governor

• Trouble shooting

• Summary

• Self assessment

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PRINCIPLE OF GOVERNING There is a particular RPM at which the efficiency of the engine is highest. This Rpm is guided by the pre assigned load to the engine. But the RPM of engine gets varied if the load on the engine gets changed. Hence to maintain the RPM constant, Governor is applied in the engine. The Governor basically makes the correction of engine speed by changing the amount of fuel supply into the engine, they are called speed governors. In the locomotive engine where fixed throttle system exists, Governor is required to maintain both the RPM and HP constant at any specific notch (throttle position). As such in the locomotive besides fuel correction, correction is made on the load also. Depending upon how the Governor recognises the engine RPM and actuates for its correction the governors are classified as mechanical, hydraulic or electric. Sometimes they work in combination like mech-hydraulic, electro-hydraulic etc. In all the diesel electric locomotive of Indian Railways either GE (electro hydraulic) or Woodward (hydraulic) governors are used.

INTRODUCTION The Woodward governor for locomotive applications is a standard hydraulic governor which regulates engine speed with a number of special devices for locomotive and train operation. It senses engine rpm mechanically from cam gear through a set of gear train constituted in the base unit. It includes an electro-hydraulic speed setting mechanism for remote control of engine speed, a mechanical-hydraulic load control device for automatic regulation of engine load to maintain a specific power output at each speed setting, and a single acting spring return hydraulic power servo. The power servo has a reciprocating or linear output. The governor usually has both a servomotor and a rheostat as an integral part of the governor to adjust the generator exciter rheostat. SPECIFICATIONS OF A TYPICAL GOVERNOR Mounting Attitude : Vertical Drive Shaft Keyed 1 1/8" - 48 Serrations Maximum speed Range 200 to 1600 RPM Drive Power 1/2 hp at maximum drive speed and normal hydraulic fluid viscosity. Hydraulic Fluid Petroleum base-lubricating oil

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Recommended Viscosity Range 100 to 300 SUS (Minimum of 50 to a maximum of 3000 SUS for wide range applications) Recommended oil temperature 140 to 200 deg F. range Supply Self contained (2.25 litres capacity approx.) Useful work capacity 8.0 foot pounds Maximum work capacity 12.0 foot pounds Stroke linear 1 inch reciprocating output Weight 105 to 130 pounds depending on optional features. The basic Woodward locomotive governor has three functional sections, a basic governing section, a speed setting section and a load control section.

BASIC GOVERNING SECTION (FIG-1) This section consists of an oil pump, two accumulators, a speeder spring, a flyweight head and bushing assembly, a thrust bearing, a pilot valve plunger, a buffer compensation system, and a power cylinder. The governor drive shaft passes through the governor base and engages the flyweight head and bushing. The pump supplies pressure oil for operation of the basic governor section, the speed setting section, the load control system (except where engine oil is supplied to the control system), and all other auxiliary features or devices. A spring loaded accumulator and relief valve system maintains the governor oil operating pressure at 100 psi. Where the operating pressure is reached, the spring pressure is overcome and the oil is released to sump. The four check valves in the pump result in the same direction of flow regardless of the direction of rotation of the pump. The governor drive rotates the oil pump and the flyweight head and bushing . A thrust bearing rides on top of the flyweight head toes permitting the rotational motion between the downward force of the speeder spring and the upward force of the

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flyweights. The relative motion between the bushing and plunger minimises static friction. A "spring driven" ballhead assembly is used to lessen vibration from the engine. These vibrations may originate from a source other than the drive itself. But reach the governor through the drive connection. Unless minimised or eliminated, these vibrations are sensed as speed changes and the governor will continually adjust the full rack in an attempt to maintain a constant speed. The greater of two opposing forces moves the pilot valve plunger up or down. Flyweight force tends to lift the plunger while speeder spring force tends to lower the plunger. When the engine is onspeed at any speed setting, these forces are balanced and the flyweights assume a vertical position. In this position, the control land on the pilot valve plunger is centred over the regulating port(s) in the rotating bushing. A change in either of these two forces will move the plunger from its centred position. The plunger will be lowered. (1) When the governor speed setting is unchanged but an additional load slows the engine and governor (thereby decreasing Flyweight force), or (2) When engine speed is unchanged but speeder spring force is increased to raise the governor speed setting. Similarly, the pilot-valve plunger will be raised. (1) When the governor speed setting is unchanged but load on the engine is reduced causing a rise in engine and governor speed (and hence, an increase in flyweight force), or (2) Where engine speed is unchanged but speeder-spring force is reduced to lower the governor speed setting. When the plunger is lowered (an underspeed condition) pressure oil is directed into the buffer compensation system and power cylinder to raise the power piston and increase fuel. When lifted (an overspeed condition)oil is permitted to drain from these areas to sump and the power piston moves downward to decrease fuel. The buffer piston, springs and needle valve in the hydraulic circuits between the pilot-valve plunger and power cylinder make up the buffer compensation system. This system functions to stabilise the governing action by minimising overshoot or undershoot following a change in governor speed setting or a change in load on the engine. It establishes a temporary negative- feedback signal (temporary droop) in the form of a pressure

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differential which is applied across the compensation land of the pilot valve plunger. The flow of oil into or out of the buffer system displaces the buffer piston in the direction of flow. This movement increase the loading on one spring while decreasing the load on the other and creates a slight difference in the pressure on either side of the piston with the higher pressure on the side opposite the spring being compressed. These pressure are transmitted to the opposite sides of the plunger compensation land and produce a net force, upward or downward which assists in recentring the plunger whenever a fuel correction is made. SPEED SETTING OR LOAD INCREASE Increasing the speed setting or increasing load on the engine at a given speed setting have an identical effect. In either case, the flyweights move inward (underspeed) due to the increase in speeder-spring force or due to the decrease in centrifugal force caused by the decrease in engine speed as load is added. The movement of the flyweights is translated into a downward movement of the pilot valve plunger. This directs pressure oil into the buffer system, causing the power piston to move upward in the increase fuel direction. The oil pressures on either side of the buffer piston are simultaneously transmitted to the plunger-compensation land with the higher pressure on the lower side. The net upward force thus produced is added to flyweight force and assists in restoring the balance of forces and recentring the pilot valve plunger. In effect, this enables the governor to control the additional fuel for acceleration by stopping the power piston when the differential pressure across the buffer piston reaches a level which causes enough net upward force on pilot valve plunger to recentre it. It will, therefore, be seen that the first correction to fuel, thus applied, is directly dependant on the amount of speed error (or the difference in the speeder spring force and the centrifugal force). As the engine continues to accelerate towards the set speed, the compensation force is gradually dissipated to offset the continuing increase in flyweight force. This is done by equalising the pressures on each side of the compensation land through the needle valve at a rate proportional to the continued rate of acceleration. If the rate of dissipation is the same as the rate of increase in flyweight force, the pressure differential is reduced to zero at the instant flyweight force becomes exactly equal to speeder spring force. This minimises speed overshoot and permits the governor to quickly re-establish stable operation. The needle valve setting determines the rate at which the differential pressure is dissipated and allows the speed rise to be "matched" to the leakage rate set with the needle valve. If the rate of speed rise does not correspond to the leakage rate the pilot valve plunger is uncentred again and another fuel correction (increase or

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decrease depending on the direction of unbalance of pilot valve plunger) is applied to bring the rate of speed rise in line with that corresponding to the set leakage rate. The speed recovery rate can thus be controlled to prevent overshoot or hunting. Closing the needle valve is thus analogous to increasing the damping on the governor speed maintaining action. The compressed buffer spring returns the buffer piston to its centred position as the pressure differential is dissipated. Wherever large changes in speed setting or load are made the buffer piston will move far enough to uncover a bypass port in the buffer cylinder. This limits the pressure differential across the buffer piston and permits oil to flow directly to the power cylinder. Thus, the power piston is made to respond quickly to large changes in speed setting or load. SPEED SETTING OR LOAD DECREASE Decreasing the speed setting or decreasing load on the engine at a given speed setting also are identical in effect, and cause a reverse action to that described above. The flyweight move outward (overspeed), lifting the pilot valve plunger and allowing all to drain from the buffer compensation system. The buffer piston moves away from the area under the power piston which then moves downward in the decrease fuel direction. The differential pressure acting across the compensation land produce a net downward force tending to assist the speeder spring in recentring the pilot valve plunger before the engine has fully decelerated. This stops power piston movement when the differential pressure across the buffer piston reaches a level which causes enough net downward force on pilot valve plunger to recentre it. As before, it will be seen that the first correction is related to the speed error. Dissipation of the compensation force occurs in the same manner as previously described and, in this instance, controls the rate of reduction of speed. COMPENSATION CUTOFF With large decreases in speed or load, the power piston will move to the "no fuel" position and block the compensation oil passage between the power cylinder and needle valve to prevent normal equalisation of the compensation pressure. This holds the buffer piston off centre and the compensation force remains at a high level as the pressure differential cannot decay with the compensation oil passage blocked. The higher pressure differential, added to the effect of the speeder spring, temporarily increases the governor speed setting. The governor brings corrective action as soon as engine speed drops below the temporary speed setting and starts the power piston upward to restore the fuel supply in sufficient time to prevent a large underspeed transient. The above action is sometimes referred to

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as "compensation cut-off". When the upward movement of the power piston again uncovers the compensation oil passage, normal compensating action will resume and start regulating the rate of approach to the target speed. NOTE :- Due to the location of the compensation cut-off portion the power cylinder wall, the governor/fuel rack linkage must be designed so that the power piston"gap" does not exceed 1.03 inches at idle speed no load.

SPEED SETTING SECTION FIG1 This section consists of a speed setting piston, a speed setting pilot valve plunger housed within a rotating bushing,four speed setting solenoids, a triangular plate, and restoring linkage mechanism. GENERAL The speed setting section provides a method of changing compression (force) of the speeder spring which opposes flyweight centrifugal force. It does this by controlling the position of the speed setting piston in the speed setting cylinder, when control oil is admitted to the cylinder, the piston moves downward, compressing the speeder spring and raising the speed setting. When oil is allowed to drain from the cylinder, the piston spring forces the piston upward, reducing speeder spring force and lowering the speed setting. The flow of oil in or out of the speed setting cylinder is regulated by the speed setting pilot valve plunger in the rotating bushing. The plunger is controlled by the solenoids which provide incremental control of speed in equally spaced steps. An integral gear on the governor flyweight head drives the bushing through a splined mating gear on the lower end of the bushing. The rate of movement of the speed setting piston over its full downward stroke (idle to maximum speed) is usually retarded to occur over some specific time interval to minimise exhaust smoke during accelerations. This done by admitting governor pressure oil into the rotating bushing through an orifice which registers with the main supply port once in every revolution of the bushing. This retards the rate at which oil is supplied to the control port in the bushing and, thus, the rate of oil flow to the speed setting cylinder. The diameter of the orifice determines the specific time interval which may be anywhere within a nominal range of 1 to 50 seconds. Typical engine acceleration period for switching and suburban service is approximately 5 seconds, for freight or passenger service about 15 seconds and for turbo supercharged engines the timing may be

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as much as 50 seconds to permit the supercharger to accelerate with the engine. On turbo supercharged units. the rate of movement of the speed setting piston over its full upward stroke (Maximum to idle speed) also is retarded to prevent compressor surge during decelerations. This timing may be anywhere within a nominal range of 1 to 15 seconds. In this case, a vertical slot in the drain land of the pilot valve plunger registers with a drain port in the rotating bushing once each revolution. This retards the rate at which the oil is allowed to drain from the speed setting cylinder. SPEED SETTING Three of the four speed setting solenoids A, B and C actuate the speed setting pilot valve plunger by controlling the movement of the triangular plate which rests on top of the floating lever attached to the plunger. The fourth solenoid D controls the position of the rotating bushing with respect to the plunger. Energising the A, B and C solenoids, singly or in various combinations, depresses the triangular plate a predetermined distance. The movement of the plate is transmitted through the floating lever to uncentre the speed setting pilot valve plunger and oil is sent to the speed setting cylinder, forcing the speed setting piston downward to increase the governor speed setting. Energising the D solenoid pushes the rotating bushing downward and opens the control port to drain oil from the speed setting cylinder and thus decrease the speed setting. An identifying letter is found on the solenoid bracket adjacent to each solenoid. Table 1 - Typical Engine Speed Chart THROTTLE SOLENOIDS ENERGIZED SPEED (RPM) POSITION A B C D GOVERNOR ENGINE ---------------------------------------------------- STOP * 0 0 IDLE 430 400 1 430 400 2 * 522 485 3 * 613 571 4 * * 708 657 5 * * * 798 743 6 * * * * 890 829 7 * * 962 914 8 * * * 1074 1000 -----------------------------------------------------

Advancing or retarding the throttle control from one step to the next energises or de-energises the solenoids in various

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combinations to increase or decrease engine speeds in approximately equal increments. A common solenoid energising sequence in relation to engine speed is given in Table 1. In the arrangement shown all solenoids are de-energised at IDLE and first notch. Energizing A increases speed by one increment, B adds four increments, C adds two increments and D reduces speed two increments when used in combination with A, B and C. When the throttle is moved to the STOP position, solenoid D only is energised. Whenever a change in speed setting is made, the movement of the speed setting piston, downwards or upward, is transmitted or fed back through the restoring linkage and floating lever to recentre the pilot valve plunger. This stops the flow of oil into or out of the speed setting cylinder at a position corresponding to that speed setting. SPEED SETTING INCREASE When one or more of the solenoids is energised by the movement of the throttle, the solenoid plungers move downward and depress the triangular plate and in turn the floating lever. Since the right end of the lever is attached to the lower end of the restoring link, the left end of the lever is forced downward to uncentre (lower) the pilot valve plunger. This directs intermittent pressure oil to the speed setting cylinder which forces the piston downward to further compress the speeder spring and thereby increase the speed setting. The downward movement of the piston is transmitted through the restoring linkage to right end of the floating lever and causes it to move downward a proportional amount. This allows the loading spring under the pilot valve plunger to raise the plunger, with the floating lever pivoting about the triangular plate. This action will continue until the plunger is again recentred, stopping the flow of oil in the speed setting cylinder at the instant the piston reaches the new lower position corresponding to the increased speed setting. SPEED SETTING DECREASE Moving the throttle to a lower step de-energizes (or energizes) one or more of the solenoids and causes a reverse action to that of speed setting increase. The triangular plate moves upward, being held in contact with the solenoid plungers by a loading spring. This allows the loading spring under the pilot valve plunger to uncentre (raise) the plunger which allows oil to drain from the speed setting cylinder. The upward movement of the speed setting piston is transmitted through the restoring linkage

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to recentre the plunger.

Table 2 - Solenoid Adjustment for ALCO Engine Order of Throttle Energised Item of Adjustment position Solenoids Setting 1 6 ABCD Base speed setting nut 2 8 ABC D 3 7 BC A 4 4 AC B 5 Idle or 1 None C NORMAL SHUTDOWN (See Fig.1) Under normal operating conditions, the engine is shut down by moving the throttle to the STOP position. This energizes the D solenoid pushing the rotating bushing down and opening the control port to drain the oil from the speed setting cylinder. The speed setting piston then moves up lifting the shutdown nuts and shutdown rod in the process. This lifts the governor pilot valve plunger, draining oil from the buffer compensation system and allowing the power piston to move down to the shutdown (no fuel) position. The upward movement of the speed setting piston is limited by the stop screw. The speed setting piston stop screw limits piston rod travel. due to this the restarting of the engine is easier because less oil volume is required to move the speed setting piston down. LOW IDLE FEATURE With a view to achieve fuel economy the Indian Railways adopted the low idle feature under which the engine runs at 340 rpm at idle. This low idle setting is reached by energising the A and D solenoids together. A look at Table 1 will indicate that this should ordinarily result in a speed setting of 315 rpm; i.e. idle speed minus the 85 rpm step ;between notches. Since the desired low idle speed setting is 340 rpm, it would appear that this is unattainable. However, the objective is achieved by

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making use of the tolerances for speed setting at various notches. While carrying out the experimental trials for getting the low idle speed of 340 rpm M/s Woodward faced difficulties in achieving the close tolerance of 4 rpm at normal idle. Accordingly this tolerance has been raised to +8 rpm. Even with this it may not be possible to achieve low idle speed within specified tolerance in one pass through the setting sequence. According to the RDSO report "it may be necessary to repeat the governor speed setting sequence once again/few number of times by varying the position of base speed setting nut (forward/backward) every time in small increments (however by maintaining 6th notch speed within tolerance limits) followed by remaining sequence of adjustments in the specified order until the low idle speed is achieved within specified limits of tolerance." The recommended speed setting sequence for WDM2 and YDM4 locos is given in Table 3.

Table 3 Speed setting sequence for LOW IDLE feature STEP SOL. WDM2 WDM2 YDM4 YDM4 ADJUST Nominal Gov.RPM Nominal Gov.RPM (seq) Eng.RPM Eng.RPM ------------------------------------------------------------------ Low Idle AD 340 365+4 340 307+4 - Idle/ 1 - 400 430+8 400 361+8 C (5) 2 A 486 522+15 500 452+15 - 3 C 571 613+15 600 542+15 - 4 AC 657 706+4 700 633+4 B (4) 5 BCD 743 798+15 800 723+15 - 6 ABCD 829 890+4 900 813+4 Base Nut(1) 7 BC 914 982+4 1000 904+4 A (3) 8 ABC 1000 1074+4 1100 994+4 D (2) ------------------------------------------------------------------

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LOAD CONTROL SECTION FIG1 In most governor applications, the primary function of the governor is to automatically maintain a specific engine speed under varying load conditions by controlling the fuel flow to go to the engine. With the locomotive governor, a secondary function is included to maintain a constant engine power output at each specific speed setting. Thus, for each throttle setting, there is both a constant engine speed and a predetermined rate of fuel flow required. To satisfy both conditions, the load on the engine must be adjusted as the locomotive operating conditions (speed and locomotive auxiliaries) vary and it is the function of the load control mechanism in the governor to do this. NOTE :- It should be kept in mind that maintaining a constant engine speed does not mean that locomotive road speed also will be constant. Control of engine-load is achieved by regulating engine speed and fuel setting. This is done by adjusting the generator field excitation current through the use of a vane servo controlled variable resistance in the generator field circuit. The vane servo is controlled by the load control pilot valve and related linkage in the governor. The load control linkage is so arranged that for each speed setting there is only one fuel setting (engine power output) at which the load control pilot valve plunger will be centred. An increase or decrease in either governor speed setting or engine load will change fuel flow. The power piston moving in either the increase or decrease fuel direction will (through the floating lever linkage) move the load control pilot valve up or down, respectively. The vane servo decreases or increases field excitation and in turn engine load. The vane servo is a rotary type, and in usually integral with the governor using governor oil for its operation. It consists of a commutator about which a set of moveable brushes rotate to change the value of the resistance in the generator field excitation circuit. The brushes are driven by the servomotor which, in turn, is controlled by the load control pilot valve. The integral vane servo is used with low wattage pilot or amplifier type excitation systems. Drain oil from the vane servo is circulated through the cover of the unit to provide necessary cooling for the resistor pack.

The load control pilot valve plunger is suspended from the load control floating lever. The lever is connected to the power piston tailrod at one end and to the speed setting piston rod at the other end. Any movement of either or both pistons causes a corresponding movement of the plunger which is housed within a

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non-rotating bushing. Pressure oil is supplied to the plunger either externally from the engine lubricating oil system or internally from the governor oil pump. Two lands on the plunger control the flow of oil to or from the vane servo. Whenever the the load control pilot valve in the governor column is uncentred, pressure oil is directed to one or the other side of the vane servo while the opposite side is opened to drain. This causes the vane to rotate which, in turn, rotates the contact brush assembly about the commutator. When internal governor oil issued for operation of the vane servo, a supply (cut-off) valve is provided in the oil supply passage to the load control pilot valve. The supply valve is closed during starting so that all available oil from the governor oil pump is delivered to the speed setting and power pistons to quickly open the fuel racks and thus minimise cranking time. After the engine starts, the increase in governor oil pressure opens the supply valve and restores normal load control system operation. This valve also serves secondary function, reducing the oil pressure in the load control system to control the vane servo response rate (timing). OPERATION WITH LOAD INCREASE Assuming that the train is in motion and that the electrical load is balanced with the desired engine fuel (power output)at the existing governor speed setting, the load control system will be stationary with the LCPV plunger centred. When a compressor turns or ( or any situation increasing load) the engine speed decreases and the governor increases fuel flow to bring the engine back to the preset speed while still carrying the added load. The power piston moves upward simultaneously raising the right end of the load control floating lever, which in turn, lifts the LCPV plunger above centre. This directs pressure oil through the upper control port in the bushing to the decrease excitation side of the vane servo while opening the lower port in the bushing to drain. With a reduction in load, the engine will overspeed and the governor will then act to reduce fuel. The reduction in the field excitation current and engine fuel will continue until the power piston and floating lever have returned to their original positions. The recentres the LCPV plunger and stops the servomotor. Consequently, the electrical load is reduced sufficiently to bring the engine power output (fuel flow) to the original level. At this point, the engine will have also returned to an on speed condition. OPERATION WITH LOAD DECREASE Under the same conditions as stated above, a decrease in any load will causes the engine to decrease fuel and , in the process, lower the right end of the floating lever. This moves

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the LCPV plunger below centre and directs pressure oil through the lower control port in the bushing to the increase excitation side of the vane servo. With an increase in load, the engine will underspeed and the governor will act to increase fuel. This increase in field excitation current and engine fuel will continue until the power piston and floating lever have returned to their original positions. This recentres the LCPV plunger and stops the servomotor. Consequently the electrical load is increased sufficiently to again bring the power output (fuel flow) to the original level. OPERATION WITH SPEED SETTING INCREASE Advancing the throttle to a higher step causes the speed setting piston to move downward. This lowers the left end of the below centre. Pressure oil is directed to the increase excitation side of the vane servo. The governor acts to increase fuel to compensate for both the increase in speed setting and the simultaneous increase in electrical load. As the power piston moves upward, it raises the right end of the floating lever to return the LCPV plunger to its centred position. This stops the servomotor as the power piston reaches its new higher position corresponding to the increased speed setting. At this point, the electrical load has been sufficiently increased to balance the increase in engine power output. OPERATION WITH SPEED SETTING DECREASE Moving the throttle to a lower speed setting causes the speed setting piston to move upward. This raises the left end of the load control floating lever and lifts the LCPV plunger above centre. Pressure oil is directed to the decrease excitation side of the vane servo. The governor acts to decrease fuel to compensate both for the decrease in speed setting and the simultaneous decrease in electrical load. As the power piston moves downward. It lowers the right end of the floating lever to return the LCPV plunger to its centred position. This stops the servomotor as the power piston reaches its new lower position corresponding in the decreased speed setting. At this point, the electrical load has been sufficiently decreased to balance the decrease in engine power output. VANE SERVO TIMING The rate of vane servo movement (timing) must be controlled to effect a controlled rate of load application and to provide stability of the overall system. Several methods are commonly used to provide a balanced action and are identical in that they restrict the flow of oil to and from the vane servo and thus determine its rate of movement. The timing valve assembly consists of two adjustable ball

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check valves in series (See inset E Fig.1). The ball valves are individually housed and internally installed in the top of the governor column. The valves are individually adjustable to provide the desired maximum rate of movement over the full travel of the servomotor in either the increase or decrease-excitation direction. MINIMUM OR MAXIMUM FIELD START ADJUSTMENT The load control system in the governor may be set up for either "Minimum" or "Maximum" field start. MINIMUM FIELD START builds up engine load slowly, providing a smooth take-up of slack in the train. The LCPV plunger is mechanically set above centre with the throttle in IDLE position. Field excitation is retarded due to the retarded position of the LCPV plunger. The vane servo rheostat remains in the minimum- excitation position until the throttle is moved in the increase- speed direction. This lowers the LCPV plunger to the recentre position and beyond to increase excitation. MAXIMUM FIELD START enables the engine load to build up immediately for rapid acceleration. The LCPV plunger is mechanically set below centre with the throttle in IDLE position. LCPV plunger. The vane-servo rheostat remains in the maximum- excitation position until the throttle is moved in the increase- speed direction to raise the LCPV plunger. LOAD CONTROL OVERRIDE Under certain condition of locomotive operation, (transition, maximum field start and wheel slip), it is sometimes desirable or necessary to override the normal action of the governor load-control mechanism to cause a reduction in generator-excitation current when it would normally respond by increasing excitation current. The load-control-override mechanism in the governor consists of an overriding solenoid (ORS), a two-position overriding control valve, and an overriding piston within a cylinder which surrounds the upper end of the load-control pilot-valve plunger. See Fig.1. Energising the ORS pushes the overriding valve plunger down closing the drain to sump and all lowing pressure oil to flow into the overriding cylinder. The overriding piston moves upward, contacting the spring collar on the stem of the LCPV plunger and lifting the plunger above its centred position. The slot in the link connecting the LCPV plunger to the floating lever permits the plunger to rise independently of the lever. This directs pressure oil to the decrease-excitation side of the vane servo, thus reducing generator output. When the ORS is deenergized, the overriding valve plunger moves upward, closing

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the pressure port and allowing the oil to drain from the overriding cylinder. This restores normal load-control system operation. TRANSITION is a condition where the electrical circuits between the generator and traction motors are automatically changed, as road speed changes, to provide more efficient transmission of electrical power. Overriding is used in these circumstances to protect the switchgear from arcing which would occur during transition if high current existed in the traction motor circuits. WHEEL SLIP is a condition when rail and load conditions cause drive wheel slip, and an immediate decrease in load occurs at the traction motors and generator. The resulting increase in engine speed would normally cause the load-control system to respond by increasing generator output at a time when it should, in fact, be reduced. Overriding is used in these circumstance in conjunction with wheel slip relays to cause a reduction in generator output until wheel slippage ceases. FUEL SCHEDULE AND LOAD CONTROL ADJUSTMENTS It has been explained that the load control system has the characteristic of keeping the engine power (fuel rack) constant at any notch. This is achieved provided the load control rheostat end limits are not reached before the load (fuel rack) is brought to the programmed level. For every speed setting there is a unique fuel position which will balance the LCPV plunger. It will be readily seen that for a higher notch (speed setting) the lower position of the speed setting piston will result in higher fuel rack balancing position. Thus the load control will tend to fix the fuel rack position for each notch (speed setting) according to the Fig.2. FUEL RACK ENGINE RPM Fuel Schedule (Fig: 2)

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The characteristic in Fig. 2 can be adjusted according to the design by suing the range adjustment and eccentric screws at the top end of the LCPV suspension. This characteristic is referred to as the fuel programme or fuel schedule. Ordinarily it is a straight line with a slope as shown but on some locos considerations of notchwise power level spacing may require a two slope characteristic. This may be achieved by using the optional two slope pickup screw arrangement (not described in this handout). RACK SETTING When a calibrated governor is installed on the engine it is necessary to adjust the fuel rack linkage so that specified governor power piston gaps result in specified fuel racks. A well adjusted fuel schedule on the governor is meaningless unless rack linkage is aligned carefully on the engine. This process of alignment is commonly referred to as rack setting. After mounting the governor on the engine the spacer block corresponding to notch 8 power piston gap (0.220" in case of WDM2 and YDM4 Locos) is applied and the output shaft jacked up to make this spacer tight. (CAUTION- MAKE SURE THAT NOBODY STARTS THE ENGINE IN THIS CONDITION) Now the individual FIP racks are adjusted so that they are at the specified notch 8 setting (29mm for WDM2). The jack is taken out and the racks are checked to see that they satisfy the condition for stopping the engine. This is merely a check and the rack setting must be done only with the notch 8 spacer as described.

FUEL LIMITER (Optional) GENERAL The fuel limiter is an auxiliary system designed primarily for use on Woodward governors installed on turbo super charged locomotive engines. It is used with absolute manifold air pressure as a reference. During acceleration on turbo supercharged engines, it is possible to supply more fuel to the engine than can be burned with the available air. This results from the normal lag of supercharger speed. The fuel limiter restricts the movement of the governor power piston towards the increase-fuel direction, limiting engine fuel during acceleration, as a function of manifold air pressure (an approximation of the weight of air available at any instant). Fuel limiting improves the air to fuel ratio and during

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acceleration, allows complete combustion. This improves acceleration and reduces smoke. Fuel limiting also protects the engine if the turbo supercharger fails or reductions in engine air supply occur due to other causes. Fig. 4 illustrates the unlimited, limited and steady state fuel schedules for a typical engine together with a typical acceleration transient from one steady state condition to another. DESCRIPTION The fuel limiter is essentially consisting of a floating lever, a bellcrank, a pressure sensor and cam, and a hydraulic amplifier together with a feedback lever and a fuel limit lever. The right end of the floating lever is connected to the tailrod of the governor power piston and pivots about one leg of the bellcrank. The left end of the floating lever rests on the right end of the hydraulic amplifier feedback lever. The position of the bellcrank, and therefore the position of the floating lever pivot point is determined by the position of the fuel limit cam. Raising the floating lever pivot as manifold air pressure increases, allows the governor power piston to move upward a proportionally greater distance before fuel limiting occurs. The pressure sensor is a force balance device consisting of an inlet check valve, an orifice pack restriction, a piston and cam assembly, a restoring spring, a bleed valve and either a gauge pressure or an absolute pressure bellows arrangement. The sensor establishes a corresponding piston ( and cam) position for each different manifold air pressure. The relationship between manifold air pressure and governor power piston position (fuel flow) where limiting occurs is determined by the profile and angular tilt of the cam. Cam profiles are either linear or non linear depending on engine and turbo supercharger characteristics. The hydraulic amplifier is a pilot operated single acting hydraulic cylinder. The amplifier provides the force necessary to overcome the resistance of the speeder spring, and lift the shutdown rod and the governor pilot valve plunger when the fuel limit is reached for a given manifold air pressure. Pressured oil enters the fuel limiter through the inlet check valve. Oil is directed to the upper side of the sensor piston and through the orifice pack restriction to the under side of the sensor piston. The inlet check valve prevents siphoning of the oil from the limiter housing during shutdown periods and omits the time lag to refill the orifice pack and piston cylinder. This prevents the sensor piston from going to maximum fuel position during start up. The bleed valve regulates the rate of oil flow from the area under the sensor piston to sump.

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The sensing element of the absolute pressure type fuel limiter consists of two opposed, flexible metallic bellows of equal effective area. The upper bellow is evacuated and the lower bellow senses manifold air pressure. A spacer joins the bellows at the centre while the outer end of each bellow is restrained to prevent movement. Manifold air pressure acting internally on the sensing bellow produces a force causing the spacer to move toward the evacuated bellow. The evacuated bellow force is directly proportional to the absolute manifold air pressure. Movement of the bellows spacer is transmitted through an output strap and a bleed valve pin to the bleed valve diaphragm. The bellows force tends to open the bleed valve while the restoring sparing force tends to close the valve. When these opposing force balance, the bleed valve diaphragm floats just off of its seat bypassing oil to sump. This rate of oil flow maintains a constant volume of oil in the area under the sensor piston. ACTION ON INCREASE OF SPEED SETTING Assume that the governor speed setting is increased. The governor power piston moves upward supplying the additional fuel required for engine acceleration. Since manifold air pressure lags engine acceleration, the fuel limiter cam and bell crank initially remain stationary until manifold air pressure rises. As the governor power piston moves upward increasing fuel, the fuel limit floating lever pivots about the upper leg of the bellcrank and depresses the right end of the feedback lever on the hydraulic amplifier. This pushes the amplifier pilot valve plunger below centre allowing pressured oil to flow into the area under the amplifier piston, causing the piston to rise. As the piston rises, it simultaneously lifts the left ends of both the fuel limiter lever and the feedback lever. When the fuel limit contacts the fuel limit nut on the shutdown bushing, it begins lifting the shutdown rod to recentre the governor pilot valve plunger. The upward movements of the fuel limit and feedback levers continue until the left end of the feedback lever raises far enough to recentre the amplifier pilot valve plunger stopping the upward movement of the governor power piston. This limits the amount of fuel to provide a proper air/fuel ratio for efficient burning. Although the governor flyweights are in an underspeed condition at his time, the power piston remains stationary until manifold air pressure rises. As engine speed and load increase, manifold air pressure rises after a short time lag. The increase in manifold air pressure produces a; proportionate increase in the sensing force. The increased sensing force, causes the bleed valve diaphragm to move further off its seat. This allows a greater flow of oil to

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sump. The increased flow rate results in greater drop of pressure across the orifice pack and the pressure in lower chamber falls. This disturbs the equilibrium of sensor piston and it starts moving down. The downward movement increases the restoring spring force and the bleed valve diaphragm moves closer to the seat. The oil leakage rate falls and the pressure in the lower chamber recovers. The downward movement increases the restoring spring force and the bleed valve diaphragm moves closer to the seat. The oil leakage rate falls and the pressure in the lower chamber recovers. The downward movement of the sensor piston, therefore, stops when the restoring spring force and oil pressure acting upwards again balance the force due to governor oil pressure above the sensor piston. Thus for every value of manifold air pressure there is a corresponding equilibrium position of the sensor piston and the cam. As the sensor piston and cam move downward in response to a rise in manifold air pressure, the bell crank rotates in a cw direction. This allows the floating lever pivot point, the left end of the lever and in turn the hydraulic amplifier pilot valve plunger to rise. The loading spring under the pilot valve plunger maintains a positive contact between the plunger levers, bellcrank and cam. When the pilot valve plunger rises above centre, the oil under the amplifier piston bleeds to sump through a drilled passage in the centre of the plunger. The passage in the plunger restricts the rate of oil flow to sump and decreases the rate of movement of the amplifier piston to minimise hunting. As the amplifier piston moves downward. The left end of the fuel limit lever also moves downward. This lowers the shutdown rod which in turn lowers the governor pilot valve plunger and increases engine fuel. The sequence of events described above occurs in a continuous and rapid sequence. Normal governor operation is overridden during an acceleration transient and engine fuel is scheduled as a function of manifold air pressure, regardless of governor speed setting. To prevent interference with normal governing action during steady state operation, the fuel limit piston and cam, therefore, continue their downward movement until sufficiently below the effective limiting point. ACTION ON DECREASE IN MANIFOLD AIR PRESSURE A drop in manifold air pressure rotates the bellcrank to a ccw direction. This lowers the fuel limit floating lever, depressing the pilot valve plunger and releases pressured oil to the underside of the amplifier piston. The shutdown rod and governor pilot valve plunger are raised, releasing oil from the power piston cylinder to sump, and decreasing fuel to the engine. The left end of the fuel limit floating lever pivots upwards

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releasing the hydraulic amplifier pilot valve plunger upward. As the control land of the pilot valve plunger opens the port from the piston cylinder, oil is bled to sump through a hole in the pilot valve plunger shaft. The shutdown rod is lowered, allowing the governor pilot valve plunger to recentre.

LOAD CONTROL OVERRIDE LINKAGE (Optional) The load control override linkage consists of an overriding lever which connects the left end of the fuel limit lever to the load control overriding solenoid through a pin and a yield spring combination. The overriding solenoid adjustment set screw must be adjusted to fully depress the overriding solenoid plunger completely, at a point just before the fuel limit lever contacts the fuel limit nut. Pressurised oil is released to the underside of the overriding piston, lifting the load control pilot valve plunger in the decrease load direction. During acceleration transients when fuel limiting occurs, the integral vane servomotor begins to unload prior to an acceleration lag reducing overload and poor acceleration. Depending on engine and turbo- supercharger characteristics, premature unloading can permit the engine to pressure rapidly enough to prevent any fuel limiting to take place. As engine speed nears the new setting and manifold air pressure rises, a downward movement of the fuel limit lever permits the overriding solenoid plunger to rise. Oil is released from under the load control overriding piston to sump, lowering the load control pilot valve plunger. The load control pilot valve plunger moves down, releasing pressured oil to the vane servomotor and increases excitation. This restores load on the engine according to normal load control settings. ADJUSTMENTS Fig. shows the typical fuel limit obtained by the fuel limiter. The fuel limit curve has to be adjusted by using various adjustments in the linkage and the pressure sensor. The steps involved are given below. 1. Pressure Sensor Calibration :- With zero gauge pressure the eccentric adjustment screw is turned till the sensor piston is a specified distance (say 0.165 inch) below its topmost position. 2. Linkage Adjustment :- Adjust fuel limit nuts so that the fuel limit lever is nearly horizontal (determined visually) when it just touches the bottom of fuel limit nuts. 3. Fuel Limit Low End Setting :- Adjust the fuel limit

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adjustment screw till the specified fuel limit is obtained at zero gauge pressure. 4. Fuel Limit High End Setting :- Adjust the fuel limit cam angle till the specified fuel limit is obtained at the high end of the fuel limit schedule. Repeat steps 3 and 4, if necessary.

Fig. 5 illustrates the interrelationship and individual effects of the fuel limit adjustment screw and the fuel limit cam angle (tilt) on fuel limit schedule. Adjustment of the fuel limit screw raises for (or lowers) the schedule a like amount over its entire length. Adjustment of the fuel limit cam alters the slope of the schedule with the greatest change occurring at the high end. The contour of the schedule is a reflection of the cam profile and may be non-linear as illustrated or linear. LUBE OIL PRESSURE SHUTDOWN AND ALARM Engine oil pressure is directed to the oil pressure diaphragm. The shutdown valve plunger is connected to the diaphragm which has three forces acting on it. Load spring and engine oil pressures act to move it to the right while governor speed setting servo oil pressure acts to move it to the left. Normally, load spring and engine oil pressures hold the diaphragm and shutdown valve plunger to the right, permitting oil to the left of the shutdown piston to drain to sump. When engine lube oil pressure drops below a safe level, speed setting servo oil pressure (which is dependent on the speed setting and on the rate of the speed setting servo spring) overcomes the load spring and engine oil pressure forces and moves the diaphragm and shutdown valve plunger to the left. Governor pressure oil is directed around the shutdown valve plunger to the shutdown piston and ;moves it to the right. The shutdown piston moves the inner spring and the shutdown plunger to the right. The differential piston with two diaphragms (Fig.11) allows a high engine lube oil pressure trip point without a corresponding increase in the speed setting servo oil pressure. The engine lube oil pressure required to initiate shutdown is increased. When the shutdown plunger moves sufficiently, it trips the alarm switch. In addition oil trapped above the governor speed-setting servo piston flows at down the smaller diameter on the left end of the shutdown plunger and drains to sump. This action allows the speed setting servo spring to raise the speed setting servo piston. When the piston moves sufficiently, the piston rod lifts the shutdown nuts and rod. The shutdown rod lifts the governor pilot valve plunger. When it is lifted above its centred position oil trapped below the power

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piston drains to sump and the power piston moves to the no fuel position. ANTI-BLOCKING VALVE "Blocking" the shutdown mechanism by pushing the plunger back or by stopping its outward movement will not prevent a shutdown. A spring loaded ball valve within the shutdown plunger is normally held on its seat and has no effect on the operation of the shutdown mechanism. However, in the event of a blocking action as described, the action of the shutdown piston pushing on the valve pin, will move the ball valve off its seat and the oil from the speed setting piston will drain through the shutdown plunger and out to the governor sump. This will shut the engine down as previously explained. BYPASS VALVE Governor pressure oil is supplied to the shutdown piston in one of two ways, depending on the speed setting. At 2nd notch and above, the bypass valve is moved down off its seat by the triangular plate. Governor pressure oil passes directly to the shutdown piston and immediately initiates engine shutdown in the event of lube-oil failure. When starting and at idle speeds, the bypass valve is closed (due to the higher position of the triangular plate) and governor pressure oil travels through an intermittent flow orifice in the rotating bushing. With each rotation of the bushing, a slot in the bushing registers with an oil supply passage in the governor column and a hole in the adjustment sleeve. Thus intermittent pressure oil is passed to the shutdown valve plunger. The adjustment sleeve may be turned (by readjusting the time delay pointer) so that the cross sectional area of the oil passage is increased or decreased. Thus the volume of oil supplied with each rotation of the bushing is increased or decreased. Turning the pointer cw increases volume and decreases the time required to pass sufficient oil to initiate shutdown. SHUTDOWN PRESSURE LEVEL Since the speed setting servo oil pressures are higher at higher notches, the pressure of engine oil required to keep the shutdown valve plunger to the right will be higher. This means that with this device the operating point (engine oil pressure) will be higher at higher notches. This matches with the normal design considerations for the safe operation of the engine.

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GOVERNOR TEST The need or maintaining test charts for every Woodward governor leaving the test room cannot ;be over emphasised. Well designed test charts given the setting sequence and briefly indicate the method of setting. When carefully followed they serve to remind the workman of what he must do. Ignoring the importance of these charts could be an unnecessary invitation to trouble. It must be mentioned that there is nothing like a universally applicable test chart for all governor models employed even on one class of locos. Ensure that the test room staff has sufficient copies of the relevant test charts for all the models being tested or calibrated by them. These charts can be obtained from DLW, RDSO and M/s Woodward. A typical test chart for particular model in use on WDM2 Locos is given in Table 4. Table 4 - TEST RECORD OF WOODWARD ELECTRO-HYDRAULIC GOVERNOR Shed - Model No.8573-463 Date of Removal - Gov.Sl.No. - From Loco No.- To Loco No. - Cause of Removal - Tested on Dt. - Tested By Date Fitted - 1. Tested with SAE30 oil at 170 - 190 deg F case temperature. YES/NO 2. Governor oil pressure at 150 rpm. ......psi (Range 100-110 psi) 3. Close compensating needle valve and back off 2 to 3 turns to reduce damping while following the adjustment procedures. 4. Apply 60" of Hg. gauge pressure to the pressure sensor in order to ease the fuel limit.

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5. Speed Adjustment Not- Sol. Nominal Tolerance Adj. Seq. Actual Speeds ch Test Std Bracket Increasing Decreasing rpm rpm ------------------------------------------------------------------- 1 - 430 426-434 C 5 .... .... 2 A 522 507-537 .... .... 3 C 613 598-628 .... .... 4 AC 706 702-710 B 4 .... .... 5 BCD 798 783-813 .... .... 6 ABCD 890 886-894 Base 1 .... .... 7 BC 982 978-986 A .... .... 8 ABC 1074 1070-1078 D .... .... ------------------------------------------------------------------- 6.Speed Setting Timing Notch l to notch 8 (Range 11-21 sec.) .......sec 7.Normal Shutdown a. Adjust the shutdown bushing to have 0.032 + 0.005 inch (0.8 + 0.1 mm) clearance above speed setting piston at idle. b. Adjust speed setting piston stop screw by turning it in till it makes contact with the speed setting piston and then backing it out by two turns. 8. Lube Oil Shutdown a. Tripping pressure at notch l (Range 28-32 psi).....psi b. Tripping pressure at notch 8 (Range 55-59 psi).....psi c. Adjust bypass screw to just obtain ;instant trip at notch 1 then back up screw 1/2 turn. d. Time delay at idle (Range 35-45 sec). .....sec e. Trips instantly at notch2. YES/NO f. Shuts down if shutdown plunger is pushed or pulled YES/NO G. Signal switch operates. YES/NO

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9.Load Control Schedule Align the load control pointer to the`O' mark when the LCPV plunger is in the balanced position as indicated by the indicator dot remaining stationary at any point other than the minimum or maximum positions. With60" of Hg gauge pressure applied on the bellows, adjust the eccentric and range adjustment screws to obtain the following fuel schedule. a. At notch 8 and with the 0.220 inch spacer tight in the piston gap, adjust the eccentric screw so that the load control indicator is stationary but not at extremes. b. At notch 1 and with the 0.820 inch spacer tight in the piston gap, adjust the range adjustment screw so that the load control pointer points to`O' mark. c. Repeat steps a and b till the fuel schedule is obtained. 10. Manifold Pressure Fuel Limiting. a. Adjust valve seat eccentric so that sensor piston is down 0.165 inch from its top at zero gauge pressure. b. Adjust cam angle and fuel limit adjusting screw to obtain the following schedule with speed bogged 7 - 13 rpm at notch 8. Absolute Press. Gap (Inches) at Limiting Actual Gap in inches of Hg Normal Tolerance inches ----------------------------------------------------------- 30 0.795 0.790-0.800 ........... 34 0.615 0.600-0.630 ........... 50 0.375 0.360-0.399 ........... 65 0.222 0.207-0.237 ........... ----------------------------------------------------------- 11. Overriding Solenoid a. Loosen lock nut on ORS and turn the adjustment screw down till armature bottoms. Back off screw by 2.5 turns and secure by lock nut. b. Adjust override trip lever so that the mechanical override takes place 0.005 - 0.015 inches (of tail rod movement) prior to the fuel limiting. c. Check that ORS functions normally when energised.

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12. Vane Servo Timing a. Check timing with the load control indicator pointing to maximum or minimum marks. b. With ball valves open the timing to be within 6 - 10 sec. c. Adjust the ball valve to set the timing from maximum to minimum position (Range 9-11 sec) ........sec d. Adjust the ball valve to set the timing from minimum to maximum position. (Range 28-32 sec) ........sec 13. Excitation Resistor a. Resistance with the vane servo at maximum. ........sec (should be less than 0.1 ohms) b. Resistance increases uniformly without indication of open or short as the vane servo moves from maximum to minimum. YES/NO c. Resistance at minimum position of servo (Range 27.5 to33.5 ohms) ........ohms 14.General a. Speed setting servo scale aligned at idle and scribed at notch 8. YES/NO b. Gap scale on tail rod set at 1/2" with0.500" gap block. YES/NO c. Governor free of leaks. YES/NO d. Solenoids Operate at 64 volts or less. YES/NO e. Reset needle valve to 1/4 turn open (or according to experience). Final setting must be done on the engine. f. Governor cover sealed with the authorised seal. YES/NO Signatures of the Mechanic Signatures of the Supervisor

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TROUBLE SHOOTING INTRODUCTION It is impossible to anticipate every kind of trouble that is encountered in the field. This covers the most common troubles experienced. Poor governing may be due to faulty governor performance, or it ;may be due to the governor attempting to correct for faulty operation of the engine or turbine auxiliary equipment. The effect of any auxiliary equipment on the overall control requirements of the governor also must be considered. A carefully maintained test chart will assist in trouble shooting. OIL Fill the governor with oil to the mark on the oil level gauge with the engine idling. Oil must be VISIBLE IN THE GAUGE GLASS during all other conditions. Dirty oil causes approximately 50% of all governor troubles. Use clean new or filtered oil. containers should be perfectly clean. Oil contaminated with water breaks down rapidly, causes foaming and corrodes internal governor parts. COMPENSATING NEEDLE VALVE The compensating needle valve must be correctly adjusted with the governor controlling the engine, even though the compensation may have been previously adjusted at the factory or on governor test equi9pment. Although the governor may appear to be operating satisfactorily because the unit runs at constant speed without load, the compensation may still not be correctly adjusted. High overspeeds and low underspeeds , or slow return to speed after a load change or speed setting change, are some of the results of an incorrect setting of the compensating needle valve. DEFINATIONS Use the chart on the following pages to determine the probable causes of faulty operation and to correct these troubles. Terms used in the chart are defined as follows :- HUNT A rhythmic variation of speed which can be eliminated by blocking governor operation manually but which will recur when returned to governor control.

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SURGE A rhythmic variation of speed always of large magnitude, which can be eliminated by blocking governor action manually and which will not recur when returned to governor control, unless speed adjustment is changed or the load changes. JIGGLE A high frequency vibration of the governor fuel rod end (or terminal shaft) and fuel linkage. do not confuse this with normal controlling action of the governor. PRELIMINARY INSPECTION Governor troubles are usually revealed in speed variations of the prime mover, but it does not necessarily follows that such variations are caused by the governor. When improper speed variations appear the following procedure should be performed. 1. Check the load to be sure the speed changes are not the result of malfunctions in the vane servo generator control circuits, switchgear etc. 2. Check engine operation to be sure all cylinders are firing properly and that the fuel injectors are in good operating condition and properly calibrated. 3. Check linkage between governor and fuel racks to be sure there is no binding or excessive backlash. 4. Check setting of governor compensation needle valve. 5. Check speed setting circuits for voltage level and sequencing. 6. Check for fuel pressure changes. 7. Check governor oil pressure. a test port is provided in two sides of the governor power case for this purpose. 8. The source of most troubles in any hydraulic governor stems from dirty oil. Grit and other impurities can be introduced into the governor with the oil, or form when the oil begins to break down (oxidise) or become sludgy. The internal moving parts are continually lubricated by the oil within the unit. Valves, pistons and plungers will stick and even "freeze" in their bores. due to excessive wear caused by grit and impurities in the oil. If this is the case erratic operation and poor response can be corrected by flushing the unit with fuel oil or kerosene. The use of commercial solvents is not recommended as they may damage seals or gaskets.

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9. Check drive to governor for any evidence of misalignment, roughness, excessive backlash etc. 10. Remember that no repair should be attempted on the governor while it is installed on the engine. The only acceptable place for internal adjustments of a Woodward governor is the test stand. It is a good practice to permit the opening of governor cover only in the dust free test room. Table 5 - Troubleshooting TROURBLE CAUSE CORRECTION 1. Engine A. Needle valve adjustment Adjust needle valve. hunts incorrect or surges B. Lost motion in engine Repair linkage, fuel pumps. C. Low oil level. No harm Add oil slowly to the will be done if top of correct level in gauge. oil is visible in gauge glass. E. Dirty oil, foaming oil Drain oil, flush governor in governor. to clean and refill with proper clear oil bleed air and adjust the needle valve F. Governor worn or not a. Check flyweight pins correctly adjusted and bearings for wear. b. Check flyweight toes for wear and flat spots. c. Check flyweight head thrust bearing. d. Pilot valve plunger may be sticking. Clean and polish if necessary. (CAUTION - Do not break corners of control land.) e. Check vertical adjustment of pilot valve plunger and correct, if necessary f. Clean and polish all moving parts to ensure smooth and free operation.

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2. Fuel A. Low oil pressure in a. Check governor pump pump governor gears and gear pockets racks for excessive wear. No do not correction except to open replace worn parts. quickly b. Flush governor and when refill with clean oil cranking to remove dirt in pump engine check valve. B. Cranking speed too low Correct condition C. Shutdown nuts not Adjust correctly adjusted correctly. 3.Jiggle A. Rough engine drive Inspect drive mechanism at Governor a. Check alignment of rod end or gears. terminal b. Inspect for rough gear shaft. teeth, eccentric gears, or excessive backlash in gear train. c. Check gear keys & nuts or set screws holding drive gears to shafts. d. check engine vibration damper. e. If governor has serrated drive shaft, check for wear of shaft and serrated coupling

B. Failure of flexible Remove, dissemble and clean drive in fly-weight flyweight head parts. head. Check spring and install new spring coupling assembly if necessary. Centre the coupling for equal travel in opposite directions. C. Governor not bolted Loosen screws, disconnect down evenly on engine fuel linkage and turn mounting pad. governor 45 degree cw and ccw.Tighten screws.

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4.Engine A. Low Governor oil See item 2-A of this is slow pressure Table. to reco -ver from a speed B. Fuel supply restricted Clean fuel filters and deviation Fuel supply lines. from a change in load C. Engine may be Reduce the load or slow overloaded to res- pond to D. Supercharger does not Overhaul the turbo. change come to new speed quick- in speed ly to supply sufficient setting air to burn the added fuel. 5.Engine A. Fuel racks do not open a. Check rack stops & does enough adjust as necessary not b. Check linkage between pick governor and fuel pumps up and adjust if necessary. rated c. Gov.oil pressure may be full too low. See Item 2-A load of this Table. B. Supercharger does not Overhaul supercharger. supply sufficient air 6. Engine A. Governor action Adjust needle valve over- underdamped opening. speeds on starting 7. Engine A. Governor action Adjust needle valve stalls underdamped. opening. on decel -eration to minimum B. Compensation not being Check rack linkage speed. cut off at idle. setting.

Fuel limiter troubles such as erratic operation or slow response to changes in manifold air pressure are usually the result of oil contamination. Correct this type of trouble by flushing the governor with fuel oil or kerosene.

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8. Hard The fuel limiter's sipho- Replace check valve. starting ning check valve leaking and/or Sensor piston goes to excessive max fuel position at smoke start-up then returns to for short min fuel position as duration housing refills with oil. during starting after a rela- tively long shutdown period. 9. Excessi- A. Fuel limiter orifice Drain governor oil, flush ve smoke pack clogged sensor gov. with fuel oil or during piston goes to and kerosene. Refill with acceler- remains at max fuel clean oil, operate for a ation position. short time, drain and refill. If necessary remove fuel limiter orifice pack disassemble and clean. B. Fuel limiter not Adjust as instructed. adjusted. C. Restoring spring Replace restoring fatigued. spring. 10. Engine Load control override Adjust as instructed. bogs linkage improperly during adjusted. Acceleration. 11. Erratic A. Contaminated or foamy Drain oil, flush with fuel operat- oil, sludge formation oil or kerosene. Refill ion. with clean oil, operate for short time, drain and refill. If necessary, remove fuel limiter, disassemble and clean. B. Low governor oil level Add oil to correct level due to air entrapment indicated on sight gauge glass. Check for leakage, particularly at governor drive shaft oil

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seal. Check manifold air pressure line for presence of oil which would indicate leakage at fuel limiter bellows. C. Leakage in manifold Repair leaks air pressure lines or fittings D.Fuel-limiter bellows Replace bellows leaking. 12. Dead band Fuel limiter-sensor Adjust as instructed at low or piston travel not

high end properly calibrated of fuel with manifold air- limiting pressure change. schedule

SUMMARY The duty of a governor in an engine is to maintain the engine RPM constant. The correction of engine RPM is made by increasing or decreasing the fuel supply. In a locomotive engine the duty of governor is to maintain both the RPM and HP constant at different notches. This is maintained by correcting both the fuel and the load on generator (correction of field excitation of generator). Generally there are two types of governor used in diesel electric locomotives. They are GE (Electro hydraulic) and WOODWARD (hydraulic). The sensing device of engine RPM in GE governor is electrical, through Tacho-generator taking drive from cam gear. Woodward governor senses engine RPM mechanically from cam gear through a set of gear trains situated in the base unit. In Woodward governor there are various hydraulic circuits to perform different functions of the engine. The basic governing section consists of flyweight assembly, speeder spring, pilot valve plunger and bushing, buffer compensation device and power piston assly. The duty of basic governing section is to maintain engine RPM constant with the correction of fuel supply. The responsibility of speed setting section is to set the speeder spring force according to the notch position. In this, there are 4 solenoids, which are energised, in different combinations according to the throttle position as set by the driver. They cause movement of speed setting plunger and bushing to increase or decrease fluid supply at the top of speed setting piston, responsible for varying speeder spring force, according to notch position. The duty of load control section is to increase or decrease the field excitation of

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generator in order to correct the HP output of the engine to remain constant. It consists of a resistance pack, the resistance of which is varied through a vane servo, which is controlled by a pilot valve plunger. In addition to the above functions this governor has the additional facility to shut down the locomotive in case of low lube oil pressure of the engine. The fuel limiter section regulates the fuel supply according to booster air pressure. The over riding solenoid reduces the power output by reducing excitation in case of wheel slip, transition etc.

SELF ASSESSMENT 1. What is the duty of Governor in a locomotive? 2. Explain the buffer compensation system in basic governing

section. 3. Explain the speed setting action of the governor. 4. Explain the load control function of the governor. 5. What do you understand by min field start and max field start? In

which locomotive do they have? 6. What is the duty of over riding solenoid? How does it work? 7. Explain the function of low oil pressure safety device in the

governor. 8. What is the function of fuel limiting section? How does it work?

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EXPRESSOR

(6 CD, 4 UC COMPRESSOR EXHAUSTER) Objective • To learn the requirement of expressor in locomotive. • To learn the function of exhauster. • To learn the function of compressor. • To learn the loading-unloading arrangement of compressor. • To learn the function of air governor. Structure 1 Introduction 2 Construction and description 3 Working of exhauster 4 Working of compressor 5 Loading – unloading of compressor 6 NS-16 Air governor 7 Lubrication of expressor 8 Expressor crank case vacuum 9 Alignment of expressor 10 Summary 11 Self assessment • INTRODUCTION In Indian Railways, the trains normally work on vacuum brakes and the diesel locos on air brakes. As such provision has been made on every diesel loco for both vacuum and compressed air for operation of the system as a combination brake system for simultaneous application on locomotive and train. In ALCO locos the exhauster and the compressor are combined into one unit and it is known as EXPRESSOR. It creates 22" of vacuum in the train pipe and 140 PSI air pressure in the reservoir for operating the brake system and use in the control system etc. The expressor is located at the free end of the egine block and driven through the extension shaft attached to the engine crank shaft. The two are coupled together by splined flexible coupling (Kopper's coupling). Naturally the expressor crank shaft has eight

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speeds like the engine crank shaft and runs between 400 RPM to 1000 RPM range. • CONSTRUCTION AND DESCRIPTION The expressor consists of the following components mainly; (1) Crank case (2) Crank shaft (3) Four Nos. of exhauster cylinders with cylinder heads (4) One low pressure compressor cylinder with cylinder head (5) One high pressure cylinder with cylinder head (6) Six nos. of pistons with connecting rods (including one LP, one HP and four exhauster). (7) Lube oil pump. Each of two crank journals support three connecting rods. The crankshaft is supported at the both ends by double row ball bearings. Outside the ball bearings are located oil seals to prevent the leakage of oil from inside the crank case and air from out side into it. The specific features and data are given below:- Details Compressor(LP) Compressor(HP) Exhauster 1. No.of cylinders 1 1 4 2. Cylinder bore 7.750" 4.250" 7.250" 3. Stroke 5.625" 5.625" 5.265" 4. Piston rings 2+2 2+2 2+2 (Comp.& oil scrapper) 5. Normal working pressure - 140 PSI or 10 Kg/cm.sq. 6. Rated speed - 1000 RPM 7. Compressor displacement - 153.5 CFM / 4350 LPM at rated speed. 61.4 CFM / 17400 LPM at rated speed. 8. Exhauster displacement - 614 CFM / 17400 LPM at rated speed.

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246 CFM / 6960 LPM at idling. 9. H.P consumed - 115 H.P max. 10. Lube oil pressure - 25 PSI to 60 PSI. 11. Oil sump capacity - 21 Lts. 12. Weight in assembled condition - 982 Kg. • WORKING OF EXHAUSTER Air from vacuum train pipe is drawn into the exhauster cylinders through the open inlet valves in the cylinder heads during its suction stroke. Each of the exhauster cylinders have one or two inlet valves and two discharge valves in the cylinder head. A study of the inlet and discharge valves as given in a seperate diagram would indicate that individual components like (1) plate valve outer (2) plate valve inner (3) spring outer (4) spring inner etc. are all interchangable parts. Only basic difference is that they are arranged in the reverse manner in the valve assemblies which may also have different size and shape.The retainer stud in both the assemblies must project upward to avoid hitting the piston. The pressure differential between the available pressure in the vacuum train pipe and inside the exhauster cylinder opens the inlet valve and air is drawn into the cylinder from train pipe during suction stroke. In the next stroke of the piston the air is compressed and forced out through the discharge valve while the inlet valve remains closed. The differential air pressure also automatically open or close the discharge valves, the same way as the inlet valves operate. This process of suction of air from the train pipe continues to create required amount of vacuum and discharge the same air to atmosphere. The VA-1 control valve helps in maintaining the vacuum to requsite level despite continued working of the xhauster. • COMPRESSOR The compressor is a two stage compressor with one low pressure cylinder and one high pressure cylinder. During the first stage of compression it is done in the low

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pressure cylinder where suction is through a wire mesh filter. After compression in the LP cylinder air is delivered into the discharge manifold at a pressure of 30 / 35 PSI. Working of the inlet and exhaust valves are similar to that of exhauster which automatically open or close under differential air pressure. For inter-cooling air is then passed through a radiator known as inter-cooler. This is an air to air cooler where compressed air passes through the element tubes and cool atmospheric air is blown on the out side fins by a fan fitted on the expressor crank shaft. Cooling of air at this stage increases the volumatric efficiency of air before it enters the high- pressure cylinder. A safety valve known as inter cooler safety valve set at 60 PSI is provided after the inter cooler as a protection against high pressure developing in the after cooler due to defect of valves. After the first stage of compression and after-cooling the air is again compressed in a cylinder of smaller diameter to increase the pressure to 135-140 PSI in the same way. This is the second stage of compression in the HP cylinder. Air again needs cooling before it is finally sent to the air reservoir and this is done while the air passes through a set of coiled tubes below the loco superstructure. • LOADING AND UNLOADING OF COMPRESSOR To avoid the compressor running hot due to overloading and also to avoid the wastage of engine horse power, arrangements are provided to unload the compressor when a particular pressure is reached. In other words the compessor cylinders are not required to compress air any further when the main reservoir pressure reaches 10 kg/sq.cm. So the compressor stops loading the main reservoir. Due to no further compression being done, reservoir pressure naturally falls due to normal consumption and leakages. When the M.R. pressure comes down to 8 kg/sq.cm. the compressor resumes loading of the M.R. again. Basically in these compressors unloading is effected by the unloader plunger prongs pressing down the inlet valves of both L.P. & H.P. cylinders to keep them in open position as soon as 10kg pressure is reached in the M.R.

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It continues to be so till the pressure comes down to 8 kg/sq.cm. Thus the compressor remains unloaded or releived of load in the range between 10 to 8 kg/sq.cm. M.R. pressure. In this case,the L.P. cylinder air drawn in through the intake filter is thrown out in the same direction. In case of the H.P. cylinder air is pushed back to the inter cooler and L.P. discharge manifold. This is achieved through the function of the unloader plunger in conjuction with the air governor. • NS - 16 AIR GOVERNOR The function of the air govornor is to transmit main air reservoir pressure to the top of unloader plunger as soon as the MR pressure reaches 10 kg/sq.cm. With the fall of pressure to 8kg. the same supply is discontinued and existing pressure in the unloader valve is vented out. This actions keep the suction valve open when loading of MR is not required any more and again allow the compressor to work normally for loading when needed. The NS-16 air govornor consists of govornor body in two pieces of bronze castings and a pipe bracket with a number of air passages. It also incorporates (1) wire mesh filter (2) cut out cock (3) cut out adjusting stem (4) cut out valve spring (5) cut out valve spring adjusting nut (6) cut in tail valve (7) cut in valve (8) cut in valve adjusting stem (9) cut in valve spring (10) cut in valve adjusting nut. When MR pressure gets access into the air governor through pipe A, it passes through the filter (1) to passage B and then bifurcates in the pipe bracket. A part of this air passes through the passage C at the bottom of the cut out valve. The other portion of the air passes through passage D and work on the cut in tail valve. Once the MR pressure reaches 10 kg. the pressure acting at the bottom of the cut out valve overcomes the cut out valve spring tension and lifts the valve to get access to passage E. The air pressure acting on cut in tail valve lifts the cut in valve thereby opening the passage from E to F which leads to the top of the unloader plunger. At the same time the exhaust passage G of the casting is blocked by the upper lips of cut in valve.

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Once the MR pressure goes below 10kg. but remains above 8kg.the cut out valve spring forces the cut out valve to be seated and the passage from C to E is blocked. But the cut in valve is still kept up with the help of pressure between 10kg to 8kg and the amount of air passing through the cut in tail valve keeps on supplying air to the unloader valve top. As soon as the MR pressure drops to 8kg., or below the cut in valve spring closes the valve and thereby block the passage to F and no further air is supplied to the top of unloader. Further, whatever air is there in the pipe line is exhausted as soon as the cut in tail valve upper lips move down opening the connecting passage G to exhaust port. • LUBRICATION The lube oil system of the expressor is a seperate system indipendent of the lube oil system of the engine. Lubricating oil of SAE 30 or SAE 40 grade is filled in the sump of 21 lts. capacity. A gear type pump under hung from the crank- shaft journal and is driven through sproket and chain. The sump oil is sucked through a strainer filter screen by the pump and then circulate the same to the journal bearings at a pressure between 45 psito 60 psi. It also lubricates the small end bush of the connecting rods and the cylinder liners. A connection is taken from the pump housing to the stem valve , lift of which indicates adequacy of oil pressure. A relief valve is also provided to release oil pressure in case the pressure in the system is beyond its usual limit. • EXPRESSOR CRANK CASE VACUUM The expressor crank case must have some vacuum to prevent oil throw over through the exhaust by preventing development of pressure in the crank case. Crank case vacuum is maintained by connecting the vacuum pipe to the crank case by a pipe connection through the crank case vacuum maintaining valve. Normally in well maintained expressors a differential of 5" of vacuum is considered ideal. In other words when train pipe vacuum is 22", the crank case vacuum should be 17".

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It has been experienced that oil throw over and sticking of expressor valves (with its consequential adverse effects) are inversely proportional to the amount of crank case vacuum. It is advisable to take expressor for attention, once the crank case vacuum drops below 15". • ALIGNMENT OF EXPRESSOR Though the expressor is coupled up with the engine extension shaft through the medium of flexiable splined coupling, special care has to be taken for ensuring proper alignment at the time of installation. The following checks are required to be made :- (1) SHAFT SEPERATION - While installing the expressor it is to be ensured that a gap is left between the expressor crank -shaft and the engine crank- shaft ends. A maximum of 9/16" is recommended to be maintained between the two ends. Similarly distance of maximum 3.3/8" and minimum of 3.1/8" is required to be maintained between the two hubs which are shrunk fitted on to the taper ends of engine extension shaft and expressor crank shaft. To determine the correct hub seperation and shaft seperation, as mentioned above, the distance from from the end of each sleeve to the end of the hub is to be measured without dismantling the expressor. The distance should be between 2.1/2" to 2.3/4" (2) ANGULAR MISALIGNMENT - During installation of the expressor it can suffer from angular misalignment in vertical plane, horigental plane or may be a combination of both. In order to ensure that there is no angular misalignment the distance between the two hubs should be kept equal all round the circumference of the hub face. A tolerance of + 0.006 only is permissible. This measurement is to be taken at the outer circumference of the hub-face with the help of micrometer at every 90 degree. (3) OFF-SET MISALIGNMENT - There may not be any angular misalignment, but there may be off-set misalignment. For checking off-set misalignment use a dial indicator, fitted on the expressor crank shaft nut with suitable clamping arrangement. While the crank -shaft is manually rotated with the help of expressor cooing fan and the limit of 0.0008" is to be maintained.

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Judicious use of jack screws is to be made for insurting or removing shims at the base for correction of misalignment and also for lateral shifting of the expressor. (4) BACK - LASH - In view of the facts that the couplings are splined type flexible couplings, some amount of clearance between the male and female couplings are provided. Back -lash of 0.024" at 3.1/2" radius is to be maintained when new. Thus, when two sleeves are coupled together a total back- lash of 0.50" should be there. The maximum limit permitted after use is 0.001" at 3.1/2" radious. The back -lash mesurement is also done with the help of a dial indicator while moving the sleeve by hand. • SUMMARY The expressor is located at the free end of the engine bloke and driven through the extension shaft atteched to the engine crank -shaft. Expressor is a combind unit of exhauster and compressor. The main function of exhauster unit is to create vacuum 22'' in train pipe. Air from vacuum train pipe is drawn into the exhauster cylinders through the inlet valves during its suction stroke and that air is thrown out to atmosphere during compression stroke through descharge valves. The main function of compressor unit is to create air pressure in main reservoir of locomotive upto 10kg/cm2. Atmospheric air is drown into the compressor LP cylinder through the open inlet valves during suction stroke and same air is descharged to HP cylinder through descharge valves and delivery pipe. The HP cylinder compress the air at high pressure and descharges it in main reservoir of locomotive for the use of brake system. • SELF ASSESSMENT 1 Describe the function of exhauster unit? 2 Describe the function of compressor unit? 3 Describe the function of loading-unloading arrangement of compressor unit? 4 Why crank case vacuum is provided in expressor? 5 Describe lube oil system of expressor?

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DIESEL LOCOMOTIVE TWIN PIPE DUAL BRAKE SYSTEM A9 AUTOMATIC BRAKE VALVE The A9-Autometic Brake Valve is a compact, self-lapping, pressure maintaining brake valve.It is capable of graguting the application or release of locomotive and train brakes. THE a9 AUTOMETIC BRAKE VALVE HAS FIVE POSITIONS:

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DIESEL LOCOMOTIVE

TWIN PIPE DUAL BRAKE SYSTEM

Introduction Diesel locomotives of Indian Railways are equipped with brake system designed by either M/S WABCO/ USA or M/S KNORR Germany or IRAB-1 Indian Railways or M/S KNORR Brake (NYAB). Initially locomotives were equipped with M/S WABCO, USA designed 28LV-1 Brake system for use in vacuum brake train only. In 80's locomotives were switched over to 28LAV-1 Brake system for use both in vacuum and air braked Trains. In 90's some of the locomotives were equipped with IRAB-1 brake system, which are suitable for only air-braked trains. Recently acquired WDG4 and WDP4 locomotives are equipped with CCB (computer control brake) system designed by KNORR BRIMSE (NYAB), which are suitable for air braked train only.

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Over view of Diesel locomotive Brake System Type of brake system - Designed by – Fitted on 6SLAV-1 air & vacuum WABCO/USA WDM1 brake System 28LV-1 air & vacuum ,, WDM2, WDM4, WDM6, brake System WDM3, YDM3, YDM4, YDM5, WDS5, WDS6 28LAV-1 twin pipe dual ,, WDM2A, WDP1, WDP2, brake System WDG2, WDM2c KNORR air & vacuum M/S KNORR WDM3, WDS2, WDS3, brake System Germany WDS4, YDM1, YDM2, ZDM1, ZDM3 ,, hydro pneumatic ,, ZDM4, ZDM5 IRAB-1 brake system RDSO WDM2C, WDP2, WDG2 CCB System KNORR BRAKE WDG4, WDP4 (NYAB)

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Air circuits of 28 LAV-1 brake system 1. Independent brake system (Loco brake) 2. Vacuum train brake system 3. Brake pipe system (Air train brake) 4. Feed pipe system 5. Proportionate brake system 6. Safety devices 7. Multi unit operation

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Important feature of the 28LAV-1 brake system

1.Locomotive brakes may be applied with any desired pressure between the minimum and maximum. This pressure will be maintained automatically in the locomotive brake cylinders against normal leakage from them. 2. The locomotive brakes can be graduated on & off with either the automatic or the independent brake valve. 3. It is always possible to release the locomotive brakes with the independent brake valve, even when automatically applied. 4. The maximum braking position emergency, ensuring the shortest possible stops distance. 5. It is always possible to haul both vacuum / air brake trains. 6. Automatic brake application and power cut off with idle rpm of engine is always possible during train parting. 7. Multiple unit operation is also possible.

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Independent Brake system (Loco Brake)

Objective

- Understand the loco brake system - Learn the concept of requirement of loco brake - Learn the function of SA-9 Valve - Learn the roll of MU2B Valve in loco brake - Learn the function of C2-Relay Valve

Structure

- Introduction - Purpose of this system - Loco Brake valves - Description of independent brake system

Introduction Loco brake system is provided to stop the Locomotive, whenever it runs as light engine. It is purely compressed air brake system known as independent brake system. For this separate air circuit is provided in 28LAV-1 & IRAB-1 Brake system which is independent to other air circuit. SA9 Independent brake valve is provided in driving control stand for application & release of loco brake. Valve has three positions ie. quick release, release and application. Purpose of this system Independent Brake System is designed to apply and release brake on locomotive. When locomotive is moving itself Independent Brake is applied. Loco brake valves System consists SA9 Independent Brake valve, Double check valve and C2-Relay valve. Description of loco brake (Independent brake) system The SA9 Valve handle is kept normally in release position (right side). MR air is always available at port no.30 of SA9 valve. When handle is brought in application potion (left side) than SA9 port 30 connects port 20 and starts supplying pilot air to C2-Relay air valve. The pilot air passes through MU2B Valve port no. 2&20 and inters to C2-Relay at port no.2. See the line diagram of loco brake system. The pilot air pressure

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depends upon the handle position, at maximum it is 3.5kg/cm2. The C2-relay air valve actuates after getting pilot air and connects MR pressure to brake cylinders of locomotive through port no.1&3. The brake cylinder pressure depends upon pilot air pressure, supplied into C2-Relay chamber through port no.2. For full brake application SA9 handle is moved to maximum travel position. In this way independent brake/loco brake is applied. There is a gauge line taken from front truck of locomotive to driver’s cabin control stand for indicating brake cylinder pressure. When SA9 handle is placed in release position, loco brakes are released. How MR air is reduced to 3.5kg/cm2 see internal function of the SA9 valve & C2-Relay valve. SA9 Brake valve handle is normally kept in release position. Loco brake can be applied through SA9 Valve handle. It can be applied any desired pressure between the minimum and maximum. This pressure will be automatically maintained in the locomotive brake cylinders against normal leakage from them. The locomotive brake can be graduated on and off with either the automatic (A9) or the independent brake valves (SA9). It is always possible to release the locomotive brakes with the SA9 valve.

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VACCUM BRAKE SYSTEM Objective

- Understand the vacuum Brake train - Understand the train brake application and release - Roll of A9 automatic brake valve - Roll of VA1B control valve - Roll of HS4 control air pressure valve

Structure

- Introduction - Purpose of this system - Vacuum Brake System valves - Description of vacuum brake system

Introduction Indian Railway runs both the trains vacuum and air brake. In vacuum brake train brakes are controlled through vacuum of train pipe. After coupling the locomotive to the vacuum brake train the vacuum is obtained in train pipe. An exhauster unit is provided to create the vacuum in the train pipe as well as the Vacuum cylinders of each coach/wagon. A9 automatic brake valve is provided in driving control stand through which vacuum is controlled. Normally valve handle is kept in release position. Purpose of this system This system is designed to apply and release brakes on vacuum brake train. Which is achieved through A9 Automatic Brake valve. Vacuum brake system valves System consists A9 Automatic Brake valve, VA1B Control valve and HS4 Control valve. Description of Vacuum Brake system Locomotive and train has a long vacuum brake pipe, in which 56cm vac. is maintained through an exhauster unit. There is a VA1B control valve in between train pipe and exhauster unit, which controls 56cm vac.in train pipe. A9 automatic brake valve is provided in driving control stand to apply vacuum brake on train. When A9 handle is placed in application zone, train pipe vacuum drops and brakes are applied through vacuum cylinders of coaches.

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The function of A9valve is to supply control pressure to Add.C2-Relay valve. The function of VA1Bcontrol valve is to maintain 56cm vac. in train pipe. The function of HS4 valve is to supply 1.7kg/cm2-air pressure to bottom chamber of VA1B control valve at port no.1. Other valves are provided in this circuit for MU operation. See line diagram of vacuum brake circuit. Charging of system Air at 8 to 10kg/cm2 pressure is charged at different valves through MR-2. See the line diagram of vacuum system. Port no.30 of A9 valve, port no.1 of Add.C2-Relay valve and port no.1 of HS4 control pressure valve. A9 valve handle is kept at release position normally. Simultaneously A9valve will supply control pressure to Add. C2-Relay valve, through MU2B valve. After getting supply of control pressure, Add.c2-relay valve will supply 5kg/cm2 pressure to BP pipe. BP pipe is connected to VA1B control valve top chamber at port no.3. At port no.1 control pressure at 1.7kg/cm2 is supplied through HS4 control valve. VA1-B control valve maintains 56cm vacuum in train pipe. Application of brake A9 handle is moved in application zone for brake application. A9 reduces Control pressure to Add.C2 Relay valve. Add. C2 Relay reduces BP pressure in proportion to control pressure dropage. BP pressure may be zero if A9handle moved at over reduction position. If handle is placed at emergency position BP will drop to zero immediately within 3 sec. After dropping BP pressure brakes are applied. Releasing of brake When handle is moved to release position, A9 valve starts supplying full control pressure to Add. C2 Relay valve causing BP pressure start increasing to 5kg/cm2 and brakes are released. Vacuum trouble in train Following test are recommended:- 1. BLOCKAGE TEST: Remove one end of the vacuum hose pipe and raise it upwards.

If more than 8cm vacuum is created, there is a blockage in the system. 2. EFFICIENCY TEST: Against an 8 mm leak disc, the loco should create 53 cm

vacuum. 3. LEAKAGE TEST: Vacuum on dummy and on leak disc should be not vary by more

than 3 cm.

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The Board has therefore standarised the vacuum level in engine and brake van for all Railways both the traction. Type of service Engine Brake van Average M/E 53 47 50 Passenger 50 44 47 Goods 46 38 42

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Proportionate brake system

Objective

- To learn about the proportionate brake - To learn about proportionate brake valve - How the prop/brake is isolated - Why prop/brake is isolated

Structure - Introduction - Prop/system valves - Purpose of this system - Description of system

Introduction In prop/brake system locomotive brake works in proportion to train brake. If train brake is partially applied to slow down the train in proportion to that loco brake will be applied. This work is done through proportionate brake valve. Proportionate brake system valves

Proportionate brake system consists SA9valve, MU2Bvalve, Proportionate brake valve, C2 Relay valve, Double check valve.

Purpose of this system

System is designed for Locomotive brake application during train brake application through A9 handle. This is known as synchronising brake system also.

Description of the system

In this system proportionate valve is connected to vacuum pipe and MR pipe, when vacuum is dropped to zero for train brake application, at the same time vacuum of prop/valve chamber A is also drops to zero. See the line diagram of proportionate brake system. Then Prop/valve supplies control /pilot air pressure to C2-Relay air valve and loco brakes are applied.

To avoid loco brake, in SA9 valve Quick Release position is provided. If handle is moved to Quick release position then loco brake will not take place. Prop/valve has two vac./chambers, which are connected to SA9 valve port no.1&7. At Q/Rel. position both ports are connected causing both chamber of prop/valve equalized. So there is no action inside the valve. In IRAB-1 Brake system C3W-Distributor valve is provided in place of proportionate brake valve, which senses the BP pressure.

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Brake Pipe System

Objective - To learn about air brake train

- To learn about Additional C2-Relay valve - To learn about Air Flow Measuring valve - To learn about R-6 Relay Air valve - To learn about Air Flow Indicator

Structure

- Introduction - BP system valves - Purpose of this system - Description of BP system

Introduction BP system is introduced to run Air Brake train, where train brake is controlled through BP pipe instead of vacuum pipe. Additional C2-Relay valve is introduced in this system to supply sufficient air to BP system. BP system valves BP system consists A9 Automatic brake valve, MU2B valve, Add./C2-Relay valve, Air flow measuring valve,R-6 Relay air valve and Air flow indicator. Purpose of this system This system is introduced to run air brake train. Air Brake system can sustain better brake power and can haul a long train. Description of BP system MR air is connected to A9valve at port 30 and Add./C2-Relay valve at port 1. Normally A9 handle is kept at release position and maintains 5kg/cm2-air pressure in brake pipe. In this position brakes are found released position. When A9handle is moved to application zone, B P pressure drops through Add. C2-Relay valve, port 3 is connected to exhaust. In this condition brakes are applied. Brake release When A9 handle is moved to release position, Add. C2-Relay valve port3 is connected to port1 and B P pipe is charged to 5kg/ cm2 and brakes are released.

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Feed pipe system

Objective

- To learn about Feed Pipe system - To learn about the Feed Valve - To learn about the Duplex Check valve - To learn about the double pipe system

Structure

- Introduction - FP system valves - Purpose of this system - Description of the system

Introduction Air Brake system has two brake pipes, BP pipe and FP pipe. BP Pipe is provided for brake application and release where as FP Pipe is provided to help in release time. FP system valves System consists Feed valve and Duplex check valve, which are connected from MR-1. Purpose of the system Feed Pipe system is introduced to reduced the release time after brake application in air brake trains. Description of the system FP System is charged 6kg/cm2 through MR pipe and Feed valve. Air flows from MR-1 to Duplex check valve, which allows air to outlet when MR pressure becomes more than 5kg/cm2. Air reaches directly to Feed valve through cut-out cock. Feed valve supply air to feed pipe at 6kg/cm2. How Feed valve reduces the MR pressure to 6kg/cm2 see the internal function of the valve.

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Safety devices

Objective - To learn about the safety device of brake system - To learn about the function of H5 Relay valve - To learn about the function of HB5 Relay valve - To learn about the function of D1 Emergency brake valve

Structure - Introduction - Safety valves - Purpose of this system - Description of safety valves system

Introduction Locomotive and Train brake system is designed to apply brake automatically during emergency situation. When driver applies brake suddenly without notching down the engine during emergency situation safety valve functions. System valves System consists H5-Relay air valve, HB5-Relay air valve and D-1 Emergency brake valve. Purpose of these valves These valves work in train parting. Description of safety valve system H5-Relay valve is connected to BP system, Which senses the 5kg/cm2 pressure. When pressure drops below 2.5kg/cm2 then H5valve starts supply of MR pressure to POWER CUT OFF SWITCH (PCS). PCS brings the engine to idle notch rpm with power cut off. See the line diagram of safety devices system. HB5-Relay air valve is connected to vacuum pipe through VA1B Control protection valve. When vacuum drops 15cm below the requisite vacuum, VA1B control valve bottom diaphragm follower hits the protection valve stem. Pro/valve moves down connecting HS4 pressure 1.7kg/cm2 to HB5-Relay valve chamber. The HB5 valve supplies MR pressure to PCS unit. PCS brings the engine to idle notch rpm with power cut off. See the line diagram of safety devices system. When D-1 Emergency brake valve is opened, train pipes vacuum/air suddenly drops, which actuates H5/HB5 Relay air valves.

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Multiple Unit Operation

Objective - learn the function of multi unit locomotive - learn about multi unit pipe connections - learn about multi unit testing - learn about multi unit advantage

Structure - Introduction - Purpose of multi unit - Multi unit valves - Multi unit pipe connections - Multi unit valves & cut out cock position - Multi unit testing - MU advantage - Description of MU system

Introduction When two or three locomotives are coupled together in multi unit service, called multi unit operation. In multi unit locomotive one set of crew is provided to run the train and look after the other locomotives. It can haul a long train. Purpose of multi unit The scope of multi unit operation is provided in all brake system. Which can haul a long load with one-set of driver. Multi-unit operation is beneficial for Railways. Multi unit valves There are four valves, which works in MU operation, MU2B valve, F1-Selector valve, VA1 Release valve and A1 Differential pressure valve.

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Multi unit pipe connections Attach the following air & vac. pipelines: Multi unit for Multi unit for Air brake train Vacuum brake train BP to BP √ √ FP to FP √ × BC to BC √ √ MR Eq.to MR Eq. √ √ Vac. hose to Vac.hose × √ Multi unit cable should be connected between two locos. Multi unit valves and cut out cock position The locomotive operating as a lead/control unit, all valves and cocks are set as in a single unit locomotive operation. Locomotive operating as a trailing unit, the MU2B valve is set in ``Trail or dead” position. Lead loco: no change Trail loco: MU valve in trail position ¾”COC of BP in close position A9 & SA9 handle in release position A1-deferential pressure valve handle in open position.

Multi unit testing First the loco should be tested individually for its Independent Brake/Train Brake application and release. Then trail loco to be placed in trail position and both the locos to be tested through lead loco for Independent Brake application & release. It should be performed as a single unit. Secondly the trail loco position should be changed in lead position and lead loco in trail position. Now again the Independent Brake application & release to be tested through lead loco. It should be performed as a single unit. Multi unit locos should be examined for Train Brake also through A9 valve. It should maintain the drop of pressure in both the locos simultaneously according to notch position. BP system is also examined through this test. For FP system Feed Valve cut out cock is opened, both the locos should maintain the same pressure. MU advantage - The Multi Unit locomotives can haul a long load.

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- One set of crew is required for Multi Unit locomotives.

Description of MU system In MU system, when MU2B valve knob is placed in trail position, it changes its port connections and supplies MR pressure to F1-Selector valve. After getting MR pressure F1-Selector valve changes its port connections. See the internal function of MU2B valve and F1-Selector valve. A1- Differential Pressure valve is connected to BP pipe and VA1 Release valve. Trail Locomotive exhauster unit is isolated in MU operation. Only during release of brakes after application, A1 Differential Pressure valve supplies BP air pressure to VA1-Release valve to connect train pipe. See the internal function of VA1 Release and A1 Differential valve.

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Modifications Automatic switching `ON’ of flasher light Introduction At present, Driver of the train is required to switch ON flasher light in emergency situation. Some time it is over looked by the Driver, so RDSO developed an automatic switching ON of flasher light circuit by modification in locomotive brake system. BP pressure drop is linked to operate flasher light. Objective

- To operate flasher light automatically during train parting - Not to operate flasher light during normal brake application and release

Modification 1 BP pressure is charged through MR airport of Additional C2-Relay valve with ¾” opening normally. A magnet valve with ¾” opening and a 5mm dia. Choke is provided in MR line of Additional C2 Relay valve in this modification. When A9 Valve handle is moved to release position (after application), Magnet valve push button is pressed to provide ¾” opening to charge BP system. This position is known as `RELEASE’ position. When BP system is charged and brakes are released then Magnet valve opening is closed, only 5.5mm choke is connected to BP system to maintain normal leakage of the train. This position is known as `RUN’ position. See the diagram of modification 1. Modification 2 See Fig.2, for pure air brake IRAB-I system locomotive. In this modification two pressure switches provided on BP circuit, designated as P1 between A9valve & MU2B valve on Additional C2-Rlay valve control pressure and P2 on loco BP pipe. Pressure settings of P1&P2 are as under:- P1 to close at pressure below 4.6 kg/cm2 P1 to open at pressure above 4.9 kg/cm2 P2 to close at pressure below 4.5 kg/cm2 P2 to open at pressure above 4.8 kg/cm2

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During train parting on air brake trains, due to restricted charging, BP drops. Pressure just below 4.5 kg/cm2, P2 will close, which energises electrical circuit connected with P2 to bring Diesel Loco to idle rpm, to give audio & visual indications, also to switch ON flasher light automatically. However, BP also drops during normal brake application while the above mentioned may take place, to avoid this situation, an additional pressure switch P1 is provided there. The P1 pressure switch closes when pressure in the Additional C2-elay control line is below 4.6 kg/cm2 which pressure drop, is faster than the drop in BP pipe of loco. Therefore, P1 closes earlier than P2 and deactivates electrical circuit of P2. But there is a possibility of loco coming to idle rpm during release of brake by A9valve, control pressure of Additional C2-Relay builds up faster than BP on loco, to avoid this situation an OFF delay relay has been provided in series with electrical contact of pressure switch P1. This relay provides time delay in activation of P2 electrical circuit. Time delay relay is set to introduce a time delay of 60 seconds. During this time delay relay period BP builds up 4.8 kg/cm2 and P2 opens. In this way automatic switching ON of flasher light, audio-visual indications, loco coming to idle rpm during normal brake release, is avoided. For dual brake 28LAV-1 system locomotive See Fig.2a for vacuum brake train, the flasher light functions discussed above, remains same while working in air brake train. However, while working vacuum brake trains the flasher light function achieved by connecting the flasher light circuit to the existing PCS. It has been observed that during normal operation and control of vacuum brake train, BP pressure goes below the H5 Relay valve setting, thereby operating PCS. This will also happen when emergency brake is applied through A9valve, in both vacuum and air brake trains. Therefore, the flasher light may gets witched ON repeatedly during normal train operation also. To avoid this, the modification ensures that the flasher light will not get switched ON when emergency brake is applied on train through A9 valve. For this purpose, in modified scheme two pressure switches designated as PCS1 and PCS2 have been provided. PCS2 is directly mounted on the brake pipe of locomotive. It is a replacement of H5 Relay air valve. PCS-1 is connected to HB5 Relay air valve similar to the existing system and will operate during train parting on vacuum brake train. On pure air brake loco only PCS-2 will be there. On dual brake loco, both PCS-1 and PCS-2 will be there. H5 Relay air valve and double check valve will be removed on both pure air brake and dual air brake locomotives. The pressure setting of PCS-1 and PCS-2 are as under: PCS-1 to close at pressure below 6.5 kg/cm2

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PCS-1 to open at pressure at above 7.5 kg/cm2 PCS-2 to open at pressure above 4 kg/cm2 PCS-2 to close at pressure below 2.8 kg/cm2

FLASHER LIGHT Conventional Flasher Light Modified Auto Flasher Light Train Train Air Brake Vac. Brake Air Brake Vac. Brake . Switching ON of flasher Light Manual Manual Automatic Automatic P2 PCS-1 . Engine speed to idle rpm H5 + HB5 + PCS-2 HB5 + PCS PCS PCS-1 . L E D indication Manual Manual Automatic Automatic Alarm chain pull indication With the above modification, flasher light will switch ON automatically during train parting both on passenger and freight trains. It is proposed to use above modification to give indication to driver and to stop the train during alarm chain pull on air brake trains. It is proposed to achieve above objective by increasing orifice size of alarm chain apparatus on coaches to 8mm from the existing 4mm size in second phase of modification after the completion of modification of locomotives as mentioned above. During this transition period, the existing PATB system (audio visual system connected with air flow measuring valve) should be retained on locomotives because with 4mm orifice size on coaches during alarm chain pulling, adequate brake pipe pressure drop will not be there on locomotive to activate audio visual indication provided by the modified system with Realase and Run position. Therefore the driver will get indication of alarm chain pulling from the existing PATB system.

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BRAKE SYSTEM VALVES

(28 L A V –1)

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A-9 AUTOMATIC BRAKE VALVE

1. Introduction The A-9 Automatic Brake Valve is a compact, self-lapping, pressure maintaining brake valve, which is capable of graduating the application or release of locomotive and train brakes. The A-9 Automatic Brake Valve has five positions: Release, Minimum Reduction, Full Service, Over-reduction, and Emergency. The full service application position is preceded by a zone in which brake pipe air is supplied or exhausted in proportion to brake valve handle movement through this zone, thus providing the graduation of an automatic application or release of the locomotive and train brakes. 2. Objective The A9 Automatic Brake Valve maintains 5kg/cm2-air pressure in Brake Pipe System against normal leakage at its release position. It also maintains air pressure drop in the system according to its handle position. 3. Construction The A-9 Automatic Brake valve consists of a self-lapping regulating portion, which supplies or exhausts the brake pipe pressure, and a vent valve which is actuated only when the brake valve handle is placed in Emergency position for the purpose of venting brake pipe pressure at an emergency rate. The self-lapping portion is actuated by regulating cam dog 3 on the brake valve handle shaft 32 which controls the supply or exhaust of brake pipe pressure. The vent valve 19 is actuated by special cam dog 23 attached to the brake valve handle which is operative only in Emergency position of the brake valve handle. The A-9 Automatic Brake Valve is provided an adjusting handle or set screw 15 which serves to permit the proper adjustment of the automatic brake valve to supply brake pipe air to the required operating pressure. There is a inlet valve assembly along with double ball check valve, which moves up and down, when handle moves. 4. Operation Charging The A9 automatic brake valve handle is kept at release position normally. The regulating cam dog 3 holds the inlet and exhaust unit at farthest down ward position. While the regulating valve spring 12 will cause the double ball check assembly 5 to be seated at the exhaust valve and unseated at the inlet valve (see diagrammatic). Main reservoir air is supplied at port No. 30 in the pipe bracket and passes through a strainer to the open inlet valve in to port No.5. This air in port 5 is also ported through a choke passage to the face of regulating valve diaphragm 9. When the pressure on the face of the regulating valve diaphragm 9 overcomes regulating valve spring 12 tension, the

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regulating valve diaphragm assembly moves down ward and allow the inlet valve spring to seat the double ball check assembly at the inlet valve seat. The A-9 Automatic Valve resumes a lap position. Application When the brake valve handle is moved into the minimum reduction, service application zone or full service position, the regulating cam dog 3 on the brake valve handle shaft 32 will permit the inlet valve assembly to move away from the exhaust port by the exhaust valve spring 7. The inlet valve assembly will carry the double ball check assembly with it. This movement will unseat the double ball check valve at exhaust valve seat, thus allowing brake pipe air to flow to exhaust. With the reduction of pressure on regulating valve diaphragm 9, the regulating valve spring 12 will cause a movement of the diaphragm assembly toward the inlet valve and the double ball check valve assembly will be seated at the exhaust valve seat again. The brake valve to assume a lap position. Pressure drop in Minimum reduction—.5/.7kg/cm2 Full service-------------1.7/2kg/cm2 Over-reduction--------2.5kg/cm2 Release after application Movement of the brake valve handle toward release position will cause regulating cam 3 to move the inlet valve assembly toward the regulating valve diaphragm assembly. This movement will cause the double ball check valve 5 to be unseated at the inlet valve. Main reservoir air will then flow through the inlet valve to port No. 5. The supply of main reservoir air to the face of regulating valve diaphragm 9 will increase and move down word, resulting in the compression of the regulating valve spring 12. When the force have equalized across the regulating valve diaphragm 9, the double ball check assembly 5 will again seat at the inlet valve due to the force of the inlet valve spring and the brake valve will assume a lap position. Thus it can be seen that the brakes can be graduated off in proportion to the brake valve handle movement from an application position toward release position. Emergency position When the brake valve handle is moved to emergency position, the brake valve will perform all the service operations. In the emergency position, the emergency cam dog 23 is actuated through special cam dog 23 to open vent valve 19 and allow brake pipe air to be vented at an emergency rate. Release after an emergency is the same as previously described under release after service.

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SA 9 INDEPENDENT BRAKE VALVE 1. Introduction The SA9 independent Brake Valve is a compact, self– lapping pressure maintaining independent brake valve, which performs the function of graduating the application or release of the locomotive air brakes independently of the automatic brake valve. The SA9 Independent Brake Valve is also capable of releasing an automatic brake application on the locomotive without affecting the application on the train brakes. The independent brake valve has three positions: Quick Release, Release, and Application. The quick release position is the farthest right-hand position of the brake valve and serves to release an automatic brake application on the locomotive. The application position consists of a zone in which regulated air pressure is supplied or exhausted in proportion to brake valve handle movement through this zone, thus piloting the graduating of brake cylinder pressure during an independent application or release. 2. Objective The SA9 Independent Brake Valve maintains 3.5kg/cm2-air pressure in the independent brake system against normal leakage through C2-Relay valve. It is suppose to maintain graduated application and release according to its handle position. 3. Construction The SA9 Independent Brake Valve consists of a self–lapping regulating portion, which supplies or exhausts air pressure for piloting the graduated application or release of brake cylinder pressure on the locomotive. This brake valve also includes a quick release valve. Both the self-lapping regulating portion and quick release valves of the SA9 Independent Brake valve is actuated by cams attached to the brake valve handle stem. It has regulating valve spring 12, which regulates supply pressure. Exhaust valve spring 7 regulates the movement of exhaust valve. Inlet valve spring keeps inlet ball valve at seat. Quick release valve 17 keeps port no.1&7 separate through its rubber ` o’ rings. 4. Operation Charging. In the release position of the brake valve handle, the inlet valve, due to the spring tension of exhaust valve Sparing 7, is positioned at its farthest travel from the regulating valve diaphragm assembly. Which will unseat the double ball check valve at the exhaust valve while being seated at the inlet valve by the inlet valve spring. With the exhaust valve open, there is no air pressure in the independent application port no. 20. Main reservoir air is supplied through port 30 in the pipe bracket and a strainer to the spring chamber of the inlet valve where it is blanked.

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Vacuum pressure in the vacuum brake pipe is supplied through port No. 1 in the pipe bracket to the spring chamber of the quick release valve where it is blanked. Vacuum reservoir pressure coming from the control valve is supplied through port No. 7 in the pipe bracket and is also blanked to the position of release valve 17. Application When the brake valve handle is moved in to the application zone, the regulating cam dog 3 on the brake valve handle shaft 24 forces the inlet valve assembly towards the regulating valve diaphragm assembly and causes the double ball check valve to seat at the exhaust port and open at the inlet valve, thus supplying main reservoir air through the open inlet valve in to the independent application and release pipe(Port 20) which will pilot the locomotive brake application. Main reservoir air is also ported through a choke passage to the face of the regulating valve diaphragm 9. When the pressure on the face of the regulating valve diaphragm 9 overcomes the force exerted by the regulating valve spring 12, the regulating valve diaphragm assembly will move down word. This will allow the inlet valve spring to move the double ball check assembly to the inlet valve seat, thus the brake valve will assume a lap position. Release after application When the independent brake valve handle is moved toward release position, the regulating cam dog 3 allows to move the inlet valve assembly up word, carrying the double ball check valve assembly with it, thus unseating the exhaust port while inlet valve remaining seated at the inlet valve seat. A graduated release of brake cylinder pressure will be there, in proportion to the movement of the brake valve handle. At the same time, pressure will be released from top of the diaphragm. When the forces across the regulating valve diaphragm 9 have equalized, the double ball check valve assembly will be seated at both the inlet and exhaust valve seats, and thus the independent brake valve will again assume a lap position. Quick release position The quick release position of the independent brake valve provides a means of releasing an automatic brake application on the locomotive without affecting the automatic brake application present on the train brakes. When the independent brake valve handle is placed in the quick release position, the release valve cam 19 positions the release spool valve 17 to connect vacuum control reservoir port 7 to vacuum brake pipe port 1. Since the automatic brake application is in effect on the train, the vacuum pressure in the vacuum control reservoir will be greater than that of vacuum brake pipe, thus the vacuum control reservoir will be permitted to equalize with the vacuum brake pipe. This will cause the proportionate brke valve to assume a release position and subsequently cause the release of the brake cylinder pressure on the locomotive. The equalizing of the vacuum control reservoir and vacuum brake pipe will have no effect on the VA1–B control valve, thus the vacuum train brakes will remain applied.

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24 – A DOUBLE CHECK VALVE 1. Introduction Double check valve is used to provide control of two sources without interaction between the two. 2. Objective The double check valve has two receiving ends, that is why this valve is used at several points in air brake system, wherever two air sources are possible. 2. Construction There is an internal floating check valve with "O" ring seal 7, automatically directs the flow of air from one or the other of the two controlling devices to a common discharge. At the same time, prevents this air from flowing to the inoperative controlling device. 3. Operation Referring to the assembly view, when a pressure differential exists between the two end ports, the higher air pressure forces the check valve 4 over to seal against its seat 3 on the flow pressure side. This closes the passage between the low-pressure port and the common port in the body 2. Air then flows from the high-pressure port through the common port to the control device.

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PROPORTIONATE BRAKE VALVE 1. Introduction The Proportionate Brake valve is a vacuum operated, automatic, self-lapping, pressure maintaining type valve designed to be controlled by vacuum pressure. It supplies and exhausts brake cylinder air pressure on locomotive. The movement of the automatic brake valve handle in application zone effects the brake cylinder air pressure. 2. Objective The Proportionate Brake Valve senses the vacuum drop in vacuum train pipe and applies proportionate brake on locomotive. 3. Construction The Proportionate brake valve consists of a pipe bracket and a valve portion. The valve portion contains two diaphragms large and small selected to provide for proper reference of vacuum train pipe and loco brake cylinder pressure. Movement of the spool valve controls the supply of air to pilot the brake cylinder pressure. During a brake application, the spool valve and large diaphragm assembly moves up to open the application check valve 3. The spool valve element also serves to exhaust at the bottom of the brake valve, the air pressure controlling the supply to the brake cylinders. Port I is connected to vacuum train pipe and the chamber A under the large diaphragm as w ell as to the top chamber through a ball valve. Top chamber is connected to port 7 and vacuum reservoir pipe. At release position ball valve is lifted connecting both the chambers to train pipe for creating same vacuum. Thus, initially, the pressure in the vacuum control reservoir and the vacuum train pipe is the same. 4. Operation MR air pressure is supplied to the top of the application check valve3 through port 30. When the A9 brake valve handle is moved to service position, brake pipe pressure is reduced. This pressure reduction affects the VA1-B control valve, which in turn, functions to admit atmospheric air in to the vacuum train pipe. Atmospheric air flows to port 1 of the proportionate brake valve where the vacuum in the chamber under the large diaphragm is destroyed. The increase of pressure in this chamber acts upon the diaphragm to move the spool valve stem up ward to open the application check valve 3. When the application check valve 3 is opened, the MR air through limiting valve flows to C2-Relay valve for piloting the loco brake cylinder pressure. Same air is ported through a choke to the spring chamber above the small diaphragm of Prop/valve. When the air pressure builds up and balances against force of the vacuum train pipe pressure on the large diaphragm. When this balance is reached, the spool valve moves down and closes the application check valve 3 at which time the spool valve will assume a lap position.

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As the brake valve handle is moved towards release position, the brake pipe pressure is increased, thus the VA1-B control valve functions to connect the vacuum train pipe to the exhauster. In the train pipe vacuum is created as well as in the bottom chamber of large diaphragm. The diaphragm follower will resume the previous position. The brake cylinder pilot pressure will be exhausted through the service valve stem at port 10. The exhaust of brake cylinder pressure will be proportional to the brake pipe pressure. With each movement of the brake valve handle towards release position, a proportionate amount of brake cylinder pressure will be exhausted. Thus, it can be seen that when the brake valve handle is moved from service position towards release position, a graduated release of locomotive brakes take place. The quick release of an automatic brake application on the locomotive is achieved through quick release position of SA9 valve. The vacuum control reservoir piped to port 7 is connected to the vacuum train pipe port 1. The equalization of pressures across the large diaphragm will permit the spool valve assembly downward. Thus causing the brake cylinder control air to flow through the spool valve and exhaust to atmosphere at port 10.

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C-2 RELAY VALVE

1. Introduction The C-2 Relay Valve is a diaphragm operated, self-lapping valve which functions to supply and exhaust brake cylinder air pressure during brake applications and release. 2. Objective The C2-Relay valve maintains 3.5kg/cm2-air pressure in locomotive brake system against normal leakage. 3. Operation Application While supply air pressure present in port 1 and no air pressure present on control diaphragm 36, both supply valve 6 and exhaust valve 23 will be seated by the respective springs. Assume that air pressure is admitted to the control port 2 of the valve. This pressure will be delivered to the upper side of diaphragm 36 causing it to move downward, carrying diaphragm stem 20 with it. During this movement, the diaphragm stem will contact the differential type supply valve 6 and unseat it by compressing supply valve spring 5. Supply air from port 1 will then flow past the unseated valve to the delivery port 3 where it is piped to the brake cylinders. Supply air also flows through a choke in the exhaust valve to the underside of the control diaphragm 36. When the pressure under the diaphragm is substantially equal to the control pressure on top of the diaphragm, the diaphragm assembly will move back toward its initial position, and supply valve 6 will seal, aided by spring 5 , thus cutting off further flow of supply air to the delivery port. The relay valve will maintain this delivery pressure against leakage. In the case of a reduction in delivery pressure, the high pressure on the upper side of diaphragm 36 will cause movement downward, repeating the application cycle and restoring the delivery pressure to the desired valve.

Release When the control pressure to the valve is reduced, the high pressure on the underside of diaphragm 36 will cause it to move upward, carrying stem 20 with it. During this movement, the shoulder on the diaphragm stem will contact differential type exhaust valve 23 and unseat it by compression of spring 27. Air from the delivery port will then flow past unseated exhaust valve 23 to atmosphere, reducing the pressure in the brake cylinders. When the pressure has been reduced to balance the pressure in the diaphragm, the diaphragm assembly will move back to its initial position and exhaust valve 23 will seal, aided by spring 27, thus cutting off the flow of brake cylinder air to exhaust. If the control pressure is completely removed from diaphragm 36, the valve will completely exhaust the delivery pressure to the brake cylinders.

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ADDITIONAL C2-RELAY VALVE The construction and internal function of Additional C2-Relay and C2-Relay valves are same and both are interchangeable. But in Add. C2-Relay pipe bracket ¾"dia.outlet port is provided for faster charging and C2-Relay has ½" dia. outlet port.

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MU – 2B VALVE 1. Introduction The MU- 2B valve is a two-position valve with a pipe bracket. It is used in multiple unit service. The MU-2B valve pilots the F-1 selector valve. It is a device that enables equipment of one locomotive to be controlled by equipment of another. It also controls the movement of the VA1 release valve. The two positions used in the MU- 2B valve is "LEAD" and "TRAIL or DEAD." 2. Objective This valve is provided to work in multiunit operation. In trail unit brake application valves are isolated through this valve. 3. Construction MU2B Valve has two positions, which works as a spool valve. It has number of port connections. 4. Operation In "LEAD" position, main reservoir air piped to port 63 is connected to port 53 and thus to the double check valve that leads to the piston of the VA–1 release valve. Independent brake control pressure is connected to port 2 &20 of the MU– 2B valve. Port 13 and port 3 are connected as a means of providing the passage to charge the brake pipe from the automatic brake valve. Port 30 connected to the F1 selector valve provides the connection for a supply of MR air that positions the F1 selector valve when the locomotive is used as a trailing unit. When the unit is used as a trail locomotive, the MU-2B valve is positioned in "TRAIL or DEAD" position. Ports 2, 3, and 20 are blanked at the MU-2B valve. Port 53 is connected to exhaust at the MU- 2B valve. Main reservoir piped to port 63 is connected to port 30, which in turn, positions the F-1 selector valve of trail position operation. At the F- 1 selector valve, brake cylinder equalizing pipe air, port 14, is connected to ports 16 and 20, both of which are connected through a double check valve and thus to the control port of the relay valve. This provides a passage for air emanating from the lead unit during a brake application.

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F1 SELECTOR VALVE

1. Introduction The F-1 Selector valve performs the function of arranging the brake equipment on the locomotive to lead or trail, other type of brake equipment. It performs the function of protecting a trailing locomotive brake equipment by automatically resetting the brake control to lead position in the event of a separation between locomotive units. 2. Objective To apply loco brake on trailing locomotives during parting of multi unit locos. It works as a safety valve. 3. Construction The selector valve consists of three sections and a pipe bracket. The pipe bracket has number of port connections. Port 15 controls the protection portion. The transfer sections are controlled by pressure in pipes Nos. 53 and 63. Connections are made as shown in the positioning chart for the positions "Lead", "Trail or Dead". There are three-spool valve no.6, 9 & 12. Which changes the port connections during trail and loco parting. 2. Operation Operation of the selector valve is under control of the MU2B valve. Lead position When the 28LAV-1 equipped locomotive is the lead unit, air pressure to ports 53 and 63 of the selector valve is vented and connections made as shown in lead position of the position diagrammatic. Control valve pressure flows from port 4 to 16 and from there through a double check valve to the C-2 Relay valve. Pressure from the brake cylinder line flows from port 30 to 14, hence to the brake cylinder-equalizing pipe of the lead locomotive. The brake cylinder-equalizing pipe is used to control brakes on trailing units. Trail position When the 28LAV-1 equipped locomotive is the trailing unit or the dead unit, operation of the selector valve is achieved by supplying MR pressure to port 53 of the selector valve, causing the selector valve to assume the position as shown in the position diagrammatic under "Trail or Dead". Under this condition, air pressure from the brake cylinder equalizing pipe enters port 14 and flows to ports 16 and 20 and thus to the C-2 Relay Valve of the trailing or dead locomotive. Thus, automatic and independent brake applications initiated at the lead -locomotive are transmitted to the trailing or dead 28LAV1quipped locomotive and result in the same brake cylinder pressures as on the lead locomotive.

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VA1B CONTROL VALVE 1. Introduction The VA1B Control valve controls the vacuum of train pipe. It connects the train pipe to atmosphere or exhauster as per variation in BP pressure. It is a very sensitive valve, which works on two deferent pressure 5kg/cm2 and 1.7 kg/cm2. It helps to operate the train vacuum brakes. This valve also acts as a pilot to operate the locomotive air brake through proportionate brake valve. 2. Objective VA1B control valve is deployed in vacuum brake system to apply and release the train brake. 3. Construction The control valve has three portions. Top cover, valve body and bottom cover with protection valve. The valve body contains sleeve, control valve 6, contacted on its upper side through its upper pusher pin 7 to small diaphragm 8 through diaphragm follower 9. It is also contacted on its bottom side through lower pusher pin 19 to large diaphragm 21 through diaphragm follower 22. The VA1B Control valve has six pipe connections (see piping diagram). 3 – Brake Pipe pressure 6 – Vacuum train pipe 2 --Vacuum train pipe 1 – Vacuum Control pipe 7 – Vacuum Reservoir Pipe to exhauster 8 – Atmosphere through GD-80 filter Top diaphragm makes two chambers, chamber A is connected to B P pressure 5kg/cm2 through port 3 and chamber B is connected to atmosphere through a breather port. Bottom diaphragm makes two chambers, chamber C is connected to vacuum train pipe through port2 and chamber D is connected to vacuum control pressure 1.7kg/cm2 through port1. 3. Operation The VA1B control valve is actuated through A9 valve. The deferent positions of A9 is described below.

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Release When 5kg/cm2 pressure is available in chamber A, 56cm vacuum in chamber C, and 1.7kg/cm2 pressure in chamber D, the valve remains in balanced or lapped position and all the ports are closed. Suppose there has been a brake application, in chamber A pressure will drop and in chamber C vacuum will drop. When the A9 valve handle is moved in release position the brake pipe pressure starts increasing, the pressure in chamber A also increases, the control valve moves down connecting port 7 to port 6. In this way the exhauster starts creating vacuum in the train pipe. As the vacuum is restored in the vacuum train pipe and in chamber C of the control valve, the 1.7kg/cm2 pressure supplied to chamber D moves the diaphragm 20 and valve 6 upward. When the vacuum in chamber C is increased to approximately 56cm the upward movement of the valve 6 will lap itself leaving only enough opening to permit the exhauster to maintain vacuum against leakage in the train pipe. Application When the vacuum is restored in the vacuum brake system and it is desired to apply the brakes, the brake valve handle is moved to application position, causing a reduction in brake pipe pressure. As chamber A of the VA1B Control Valve is connected to the brake pipe, a reduction in pressure in this chamber also takes place. The 1.7kg/cm2 pressure in chamber D then moves the diaphragm follower and control valve upward as the brake pipe pressure is reduced. The control valve connects pipe 6 and chamber C to atmospheric port 8. Thus, atmospheric air pressure enters the vacuum train pipe. Thereby the vacuum brakes are applied on train. The pipe connection no. 2 between chamber C and pipe 6 allows drop in vacuum in chamber C through a choke also and the valve comes to lap position. The constant braking force is maintained against normal leakage. It is understood that two pressure i.e. brake pipe and vacuum are varying and for different combination of these two forces the valve gets lapped position giving different braking forces. Emergency When it is desired to make the shortest possible stop, the brake valve handle is moved to Emergency position, causing an emergency rate of brake pipe reduction.

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HS-4 CONTROL AIR VALVE

1. Introduction The HS4 control air valve delivers a constant, uniform, predetermined air pressure. It serves to regulate the operation of another device in the system. In addition, the air delivered through the valve may be used to operate auxiliary devices. 2. Objective HS4 valve is provided to supply constant air pressure to bottom chamber of VA1B control valve. It is adjusted at 1.7kg/cm2. 3. Construction HS4 control air valve has inlet valve 5a, exhaust valve 5b, inlet valve spring seat 6a, exhaust valve spring seat 6b, inlet valve spring 7a, exhaust valve spring 7b, exhaust valve seat 10, valve spring 21, diaphragm 11, follower 12, diaphragm spring 17, and diaphragm spring seat 16. Turning adjusting handle 15 regulates the delivery pressure of the HS-4 valve. 4. Operation Air pressure enters the HS4 control air valve at the port marked "In" and flows through a strainer to the chamber above inlet valve 5a. In open position, diaphragm spring 17 acts through follower 12, exhaust valve seat 10 and exhaust valve 5b to raise and open inlet valve 5a. Exhaust valve 5b and exhaust valve seat 10 move upward together and the exhaust valve remains seated. Air from the supply port "in" flows by the unseated inlet valve 5a to the delivery port and through a choke to the chamber above diaphragm 11. When the delivered air pressure reaches the amount called for the setting of adjusting handle 15, it forces diaphragm 11 downward. Exhaust valve seat 10 moves with diaphragm 11 and inlet valve spring 7a seated the inlet valve 5a, cutting the connection between the "In" and "Out" passages. Spring 7a, acting through inlet valve 5a, also keeps exhaust valve 5b seated. The HS4 control air valve will remain in closed position until the air pressure in the delivery pipe and in the chamber above the diaphragm falls below the predetermined amount, allowing spring 17 to move diaphragm 11 upward. This movement, acting through exhaust valve seat 10 and exhaust valve 5b, lifts inlet valve 5a from its seat, again connecting the supply and delivery ports until the desired supply pressure is reached.

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The HS4 control air valve also contains provision for reducing any excess pressure in the delivery pipe, as when the pressure called for by the setting of adjusting handle 15 is lowered. Excess pressure in the chamber above diaphragm 11 moves the diaphragm and exhaust valve seat 10 downward away from exhaust valve 5b, The excess air pressure then flows past the unseated exhaust valve 5b, through the exhaust valve spring chamber and the diaphragm spring chamber and out to atmosphere through the opening in the bottom cover.

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VA1 RELEASE VALVE

1. Introduction The VA-1 Release valve without choke is used in some instances as a remote controlled cut out cock. It is installed in the vacuum brake pipeline between the VA1B control valve and the vacuum brake pipe. On a lead unit, the VA1 release valve is held open by supply MR air delivered from MU2B port no.53. On a trail unit, the VA1 release valve remains closed and is held open only during release of an automatic brake by the brake pipe pressure supplied from A1differential pilot air pressure valve. 2. Objective It functions during multi unit operation. The trail unit loco exhauster is cut off from train pipe during multi unit operation through this valve and connects at release position for few seconds. 3. Construction The release valve houses a piston type valve consisting of a valve stem 3, valve seat 4, follower 5 and valve stem spring 8. Three pipe connections are port 1 leads to vacuum train pipe, port 2 to VA1B control valve and port 3 to an auxiliary device that supplies air to unseat the valve stem. 4. Operation In normal operation, when the unit is in lead position, the VA1 release valve is unseated by the supply of air to pipe 3 connected to the bottom of the piston. Thus, as the exhauster is operating continuously, the vacuum in the vacuum train pipe may be created or destroyed by the movement of the VA1B control valve spool valve. The VA1 release valve on the trailing unit remains closed at all times. It is open only during release of an automatic brake, at which time air delivered to port 3 unseats the piston and thus permits the exhauster on the trailing unit to assist in evacuation of the vacuum brake pipe.

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A- 1DIFFERENTIAL PRESSURE VALVE

1. Introduction The A1 Differential pilot valve automatically operates the VA1 Release valve to restore the vacuum in the vacuum train pipe and release the trailing stock vacuum brakes, when the brake pipe is recharged. 2. Objective TheA1 Differential pilot valve opens the VA1 release valve to connect trail loco vacuum train pipe at release position after application. 3. Construction Referring to the diagrammatic, the differential pilot valve consists of the diaphragm 7, the diaphragm spring 18, the check valves 13 & 15 and the check valve spring 14. There are four ports in the valve 1 leads to the air brake pipe, 2 leads to the vacuum release valve, 3 leads to a volume reservoir and Exhaust choke is opening to atmosphere. 4. Operation The A1 Differential pilot valve is actuated through A9 valve position. Which described below.

Release When the handle of the automatic brake valve is in Running positions, air from the brake pipe enters the A-1 Differential pilot valve through port 1, charging chamber A above diaphragm 7. Chamber A is connected through choke 3 to chamber B below the diaphragm, but the charging of chamber B is restricted by choke 3 and the attached volume reservoir. Thus the faster build- up of pressure in Chamber A moves diaphragm 7 downward against the lower pressure in Chamber B, unseating check valve 15 to permit brake pipe air from Chamber A to flow to pipe 2 and the VA1 release valve. At the air brake pipe is charged, the air in chamber A continues to flow through choke 3 to chamber B, decreasing the differential pressure across diaphragm 7 until spring 18 moves the diaphragm upward. This movement seats check valve 15, cuttings off the flow of brake pipe air to pipe 2 and the vacuum release valve. The air trapped in pipe 2 exhausts through the choked opening Ex. to atmosphere, permitting the VA1 release valve to return to its normal position. Application

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When air brake pipe pressure is reduced, as occurs in service and emergency applications, a corresponding reduction takes place in chamber A of the differential pilot valve. As choke 3 limits the rate at which the air in chamber B can follow the reduction in chamber A, the resulting higher pressure in chamber B lifts check valve 13, connecting the two chambers. In this way chamber B air pressure closely follows the reduction in pressure in chamber A and the brake pipe. When the reduction is stopped, spring 14 seats check valve 13. The remaining slight differential in pressures between chambers A and B, due to spring 14, is equalized through choke 3. If the air brake pipe pressure is further reduced, check valve 13 again is unseated as explained above to allow the air pressure in chamber B to flow in to chamber A. When the brakes are released, the increase in air brake pipe pressure in chamber A unseats check valve 15, allowing air from the brake pipe to flow through pipe 2 to the VA1 release valve, as explained under "Release".

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COMBINED CUT-OUT COCK AND STRAINER

The combined cutout cock and strainer prevents the entrance of dirt and moisture in to the air brake devices. Thus device has the cut-out cock and strainer portion combined in to one casting and is readily accessible for cleaning or repairing of the cock key and removable curly haired strainer.

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N- 1 REDUCING VALVE 1. Introduction The N-1 Reducing valve reduces a supply of compressed air to a constant, predetermined pressure. Air supplied by the N-1 Reducing valve usually operates auxiliary devices. 2. Objective To supply constant pressure as per setting value continuously to any other device. 3. Construction See the diagrammatic view of the reducing valve. Compressed air enters at the port marked " Supply" and flows through passage `s’ to supply chamber C. As shown, the valve is in lap position with the inlet and exhaust valves seated, as when the system is charged to the setting of adjusting screw 45. 4. Operation When the air pressure in the delivery line and in chamber B and A has fallen to a predetermined level, spring 47 moves diaphragm follower 41, exhaust valve seat 39 and the exhaust & inlet valves upward. This movement unseats the inlet valve, and supply air from chamber C flows past inlet valve seat 31 in to chamber B and then through passage `r’ to the delivery port. The air also flows through choke D to chamber A above diaphragm 40. When the air pressure in passage `r’ and chamber A reaches the pressure for which adjusting screw 45 is set, the air pressure and exhaust valve spring 38 move diaphragm 40, follower 41 and exhaust valve seat 39 downward. Inlet valve spring 34 moves the inlet valve down on its seat 31, cutting- off further flow of air from chamber C to chamber B. If the delivery pipe and chambers B and A charged in excess of the setting of adjusting screw 45, the air pressure and exhaust valve spring 38 will move diaphragm 40 and exhaust valve seat 39 downward away from the exhaust valve. The overcharge of air from chambers B and A then flow past exhaust valve seat 39 in to spring housing 43 and out the exhaust opening to atmosphere. As the pressure in chamber A reaches the setting of screw 45, spring 47 moves diaphragm follower 41 and exhaust valve seat 39 upward to seat the exhaust valve, preventing further exhaust of air.

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D-1 EMERGENCY BRAKE VALVE 1. Introduction

The D-1 Emergency brake valve is connected to the vacuum train pipe and B P pipe, permits a vacuum brake or air brake application on train. It should be used only in case of actual danger and then should be left open until the train stops.

2. Objective D-1 Emergency brake valve is provided to stop the train at emergency position, when Driver wants to stop the train immediately. This valve stop the train at minimum possible distance.

3. Construction When installed the D-1 Emergency brake valve should be in a vertical position, so that the handle should be at vertical position and valve 13a rests closed on its valve seal 15b as shown in the assembly view. Handle pushes the discharge port of BP as well as provides sufficient opening of vacuum pipe to atmosphere.

4. Operation When the handle of the D-1 valve is pulled, the handle lever 4 lifts the valve 13a off its seat and permits atmospheric air to enter the vacuum train pipe at a fast rate due to the large opening. The other end of the handle pushes B P check valve to atmosphere through its large opening. This causes a fast vacuum brake or air brake application on train.

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D-24-B FEED VALVE 1. Introduction The D24B Feed valve supplies air pressure to feed pipe system. It is connected from MR-1. In single pipe operation D24B Feed valve is isolated through a cut out cock. 2. Objective The D-24-B Feed valve regulates the pressure in the Feed pipe. 3. Construction This feed valve is located in a branch pipe from the main reservoir (see-piping Diagram for location in this installation). The supply port is marked "7", the delivery port is marked "20" and the regulating port is marked "la", with external control, feed valve delivery pressure flows out port 20, through the brake valve and into the Feed pipe. Feed pipe air then flows back to regulate the feed valve through a branch pipe connected to port la. With internal control, the delivery port 20 is connected directly to the regulating port la through the feed valve pipe back. Body 2 encloses the parts of the regulating and supply portions of the feed valve. The regulating portion consists of pressure adjusting handle 26, for setting regulating spring 21 and bellows diaphragm 19 so that disc regulating valve 27 seats at the desired pressure thus controlling the air pressure delivered by the feed valve. Regulating valve 27, actuated by pusher pin 34 (located off center), permits a finer graduation by opening the valve with a tilting motion. Pusher pin 34 has a shield, which deflects any foreign matter in the air away from the guide portion. Regulating valve spring 32 keeps regulating valve 27 seated when the delivered air pressure is at the regulating valve spring setting. The supply portion consists of piston 7, which operates supply valve 11 to admit or cut-off, the delivered air as controlled by the regulating portion. Supply valve spring 9 keeps supply valve 11 closed when the delivered air pressure is at the regulating valve spring setting. 4. Operation Main reservoir air from passage 7 enters the feed valve at chamber A and flows through a strainer to chamber B, then through the choke in piston 7 to chamber C, passage 7a and chamber D. The regulating valve 27 is unseated so that the air from chamber D can flow to chamber E, passage 20a, chamber F, and discharge passage 20 to

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the brake valve. Due to the choke in piston 7, a pressure differential is created across the piston, so that the higher air pressure in chamber B moves piston 7 upward. This moves supply valve 11 off its seat 14 and compresses supply valve spring 9. Main reservoir air can then flow directly from chamber A past unseated supply valve 11 to chamber F and passage 20 to the Feed pipe thus charging the system. The delivered air pressure is reflected at the top of the bellows diaphragm through passage la, either from the brake pipe or directly through the pipe bracket. When the delivered air pressure and air in the chamber above the bellows diaphragm becomes greater than that of regulating spring 21, diaphragm 19 is moved downward, permitting regulating valve spring 32 to seat regulating valve27. Thus air from chambers C and D is cut off from chamber E. The air pressure in chamber C is the same as that in chamber B. Then supply valve spring 9 moves piston 7 downward seating supply valve 11 and cutting off the flow of main reservoir air to chamber F and delivery port 20. If there is leakage in the system the force of delivery air pressure on top of diaphragm 19 becomes less than that of regulating spring 21. The diaphragm 19 will then be moved upward, unseating the regulating valve and again connecting air from chambers C and D to chamber E. A pressure differential is thus created across piston 7, so that the piston is moved upward, unseating supply valve 11 from seat 14. Main reservoir air is permitted to flow from chamber A to chamber F and delivery passage 20, as previously described. The D-24-B Feed Valve is adjusted by turning adjusting handle 26. A clockwise movement increases the pressure setting and a counter clockwise movement lowers the pressure setting.

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AIR FLOW MEASURING VALVE 1. Introduction

The air flow measuring valve is suitable for use on locomotives that are equipped to operate trains fitted with 28LAV1 brake system and is designed for fitting in the main air supply pipe.

2. Objective This valve indicates the leakage of BP pipe through an indicator in term of wagon. Indicator is provided on driving control stand so that Driver can watch easily. 3. Construction

The AFM valve has two main connections, one is connected to main air supply and other to the Additional C2-Relay valve. Choke A is provided to supply MR air to top of disc valve. Disc valve has two small ports, one connects to MR air and other connects to Additional C2 Relay valve. Disc valve is pressed down through a follower & spring on its seat. Choke B is provided in between top chamber of main valve and MR supply line. Choke C is provided to supply `main diaphragm top chamber air’ to indicator, when diaphragm moves down word. Choke D is provided for calibrating the valve.

4. Operation

When the brake pipe is fully charged with air and the air brake is in the release

condition, the air flowing from the main air supply through the Air flow measuring valve and to the brake pipe is that necessary to overcome leakage. In this condition the check valve is closed as shown in diagram and air from the main supply passes through choke A in to the space under the check valve follower and out to the Additional C2-Relay valve. It also passes in to the chamber under the diaphragm via the space around the follower. At the same time, air from the main supply passes through a filter and choke B in to the chamber above the diaphragm.

So long as the pressures above and below the diaphragm are equal, the diaphragm

floats against the choke C. As brake pipe leakage occurs, the pressure at the outlet port and under the diaphragm falls and the diaphragm is moved down away from the choke C by the pressure above it. This permits air entering the chamber above the diaphragm via choke B, to flow through choke C to an indicator and through choke D to atmosphere.

Choke D is smaller than choke C and an intermediate pressure builds up in the

passage between them and registers on the indicator. This intermediate pressure is related to the flow of air through choke C that is controlled by the diaphragm reacting to the pressure under it. As the pressure under the diaphragm and at the outlet port relative

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to the main supply pressure, also determines the flow of air through choke A, it follows that the intermediate pressure is related to this flow of air as well. The indicator therefore provides a visual indication of the amount of air flowing to the brake pipe. During initial charging or release of brakes, when a large quantity of air passed to the brake pipe, the pressure at the out let port and in spring chamber reduces sufficiently. It allows the supply pressure to lift the disc valve off its seat and permit unrestricted flow of air to the brake pipe through Additional C2-Relay valve. Under these conditions a high intermediate pressure builds up in the passages between chokes C and D, and the indicator indicates a high rate of airflow. Choke D is variable to facilitate calibration and may be altered by means of an adjusting screw, turning the screw clockwise reduces the aperture and turning it anticlockwise enlarges it.

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AIR FLOW INDICATOR

1. Introduction It is an air pressure gauge with two pointers. Red pointer is called reference pointer, which is attached to a knurled knob and protrudes through the dial glass, so that it can be set manually in any desired position, where as the other pointer moves on the scale depending up on the air flow. The indicator is connected to the measuring valve through R-6 relay valve. The scale on the gauge is calibrated not in the units of airflow but in numbers which normally indicates the number of wagons. The 60 marks correspond to the maximum rate of airflow that can be accepted to overcome leakage on a 60 wagon train. 2. Objective It is a device through which BP (Air brake train ) leakage can be seen in the Driver’s cabin. 3. Operation When a train has been made up and the brake system is being charged with air before moving off, there is a high rate of flow of air to the brake pipe and the indicator pointer takes up a position in the uncalibrated sector of the scale. As the air pressure in the brake pipe rises and the rate of airflow consequently diminishes, the indicator pointer falls back. When the system is fully charged, it stabilises at a reading corresponding to the airflow, to overcome leakage. If the train comprises 60 wagons, for example, this reading is normally 60 or less, a higher reading indicates excessive leakage from the brake pipe. At this stage, before starting the train, the driver sets the reference pointer to coincide with the indicator pointer and thereby fixes a datum point on the scale. The indicator pointer should return whenever the brake is fully released during the ensuing journey, so long as the make- up of the train is not changed. Therefore, during the journey, the indicator pointer falls below the reference pointer or rises above it, indicates leakage decreased or increased respectively. During the release process, the indicator pointer falls back steadily towards the reference pointer and the deviation between the two pointers at any time indicates the state of release of the brake. When the system is fully recharged the two pointers approximately coincide again, if they do not coincide it is evident that the brake pipe leakage has changed and the amount of deviation between the two pointers gives the driver some idea of the magnitude of the change. An indicator pointer reading below the datum point shows that the leakage has been reduced, conversely a higher reading indicates an increase in the leakage. Some small variations are to be expected during a journey.

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If a guard emergency brake valve is opened or a brake pipe coupling is parted or broken, the indicator pointer rises rapidly to a corresponding high reading. Whenever the make–up of the train is changed, the reference pointer is reset manually to provide a new datum point. Calibration The Airflow measuring valve includes a calibration choke enclosed by a vent plug. This feature is provided to facilitate the calibration of the equipment on the vehicle. There is a test stand, where the needle valve setting is calibrated on 130 psi charging line. Where AFM valve indicator gauge reads 70 psi.

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R-6 Relay Valve 1. Introduction R-6 Relay valve is a simple relay valve which provides air pressure in 1:1 ratio and is mounted just near the AFM valve. It is required because of long piping from the AFM valve to the indicator. 2. Objective This is a simple relay valve, which provides air pressure in 1:1 ratio and mounted in between the indicator and the AFM valve. It is required because of long piping from the AFM valve to the indicator and unavoidable leakage at joints in both the cabs. 4. Construction R6-Relay valve consists of the cast aluminum cover, houses the spring loaded relay piston and tapped to receive an air pressure signal. The body also aluminum, contains the combined inlet and exhaust valve and is tapped to provide two supply and four delivery ports. A rubber disc protects the exhaust vent in the base. 5. Operation When air pressure signal from AFM valve, is received at port A of the R-6 Relay valve, air flows in chamber C between the cover1 and the top of the relay piston assembly 2. A relatively small-applied pressure reacts quickly over the larger area of the relay piston 2 and forces the piston down against the spring 7. This movement of the piston closes the exhaust passage 6 and the valve sheet 13 opens the inlet/exhaust valve11, which is also moved down against the return spring 10. Air then flows from main reservoir through port B to chamber D and from there it passes out of the delivery port E. This flow continues until the force of the applied air pressure above the piston balances the combined forces of the piston, valve return spring and the air pressure beneath the piston. After getting balanced the piston moves up closing the inlet/exhaust valve. The valve is now in the lapped condition with both the inlet and the exhaust closed. If the signal pressure from air flow measuring valve is reduced at the port A the force below the piston is now greater , and the piston rises until the valve seat 13 is lifted clear of the valve allowing air to atmosphere past the rubber flap at 6 through the hollow passage in the piston at 5. The exhaust of the air continues within the force below the piston is reduced to balance t hat above the piston and the exhaust of air closes again, bringing the valve in lap condition. This phenomenon is repeated wherever the applied pressure at port A is varied, either up or down as the valve is self-lapping.

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AIR DRYER 1. Introduction Air dryer is a complete air cleaning and drying unit, which is provided in between MR-1 and MR-2 of Diesel Locomotive. It helps to the Automatic Drain & Check valve also by purging the Dryer system. Purging is the removal of collected moisture from the desiccant beeds. Drying means the desiccant in the dryer is drying the compressed air by absorbing the water vapour from the air passing through that tower. It supplies dry and clean air to the locomotive brake system. 2. Objective The primary purpose of the dryer is to provide dry, oil free and clean compressed air to the locomotive brake system. 3. Construction The current design consists of a borosilicate coalescing filter known as pre coalescer and twin regenerative desiccant towers that operates simultaneously. These two towers are connected to pre coalescer to remove oil and water aerosols. Pre coalescer and dryer towers are connected by a common inlet and outlet manifold with solenoid assembly. All the electrical controls, which program the sequence of operation, are located in housing attached to the outlet manifold. The first component is a multi layered Pre coalescing element. Two other layers are constructed by small microscopic fibers, which are random in size to enhance the collection of oil and water aerosols. The unit is mounted with aluminum housing with a pneumatically operated double seated drain valve, attached to the sump. The second component is a pneumatically controlled inlet check valve located within the inlet manifold for each of the identically designed dryer tower. Each dryer tower consists of finned aluminum housing containing a desiccant canister. This canister includes a pneumatic compactor to hold the desiccant tightly within the canister to minimise attrition or dusting of the desiccant and a mesh filter that is attached to the bottom of the desiccant canister along with the pneumatically operated single seated purge. The third component is a spring-loaded outlet check valve mounted in the outlet manifold of the dryer towers adjacent to the humidity indicators.

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4. Function Air from no.1 MR flows into the Air dryer inlet manifold down to the cell of the pre coalescing element and exits through the pre coalescing element where oil and water aerosols are collected. Air then flows up around the out side of the element and through the interning manifold to both of the dryer towers. Contaminants such as oil and water aerosols are collected in the element, migrate to the sump. These contaminants are then discharged to the atmosphere through a double seated pneumatically operated drain valve attached to the bottom of the pre coalescing sump. This valve is activated momentarily each time of the dryer cycles. Filtered air leaving the pre coalescing element passes through the manifold with pneumatically operated inlet check valve and inters the top of each of the air dryer tower. The internal design of the housing slings the air down word around desiccant canister in a simplified path. This simplifical movement cools the air and separates moisture from the air, which settles in the sump at the bottom of each tower. The air then flows through a oval stainless steel mesh filter attached to the bottom of the desiccant canister. The secondary filter restricts and collects all droplets and contaminants not removed by the pre coalescing element. The filter is self cleaned each time the single seated pneumatically operated purge valve is operated at bottom. The actuation of the valve also expels to atmosphere any separated water, which is collected in the sump. The air passing through the secondary filter now passes upward through the desiccant bed where water vapour is absorbed by the desiccant beeds. The result is that the air existing top of the canister is very dry with an extremely low relative humidity. The dry airs now flows through the outlet manifold, which contains the humidity indicators and the outlet check valve prier to entering the locomotive air system. The identical airflow through both towers permits the maximum flow of air to charge the air system initially. When the locomotive air system pressure reaches a pre determined point normally 100 psi+/-5, a pressure switch within the dryer closes. This supplies power to the timing control circuit, which energises the solenoid on one tower and the tower start purging.

5. Drying and purging cycle There is an arrangement of drying and purging cycle, which is governed by timer circuit. One tower drying by collecting moisture from air while the other purging the collected moisture from the desiccant beeds. It continues for one minute. After one-minute timer circuit changes the position, the tower that was drying begins to purge and the tower that was purging begins to dry air. 6. Timer circuit The timer circuit is electronically timed to operate the tower. When air pressure reaches 100 psi, the pressure switch closes. The timing circuitry energises the solenoid on one tower, which provides pneumatic signal & closes the inlet check valve and at the same time opens the purge valve at the bottom of the housing. Simultaneously the spring loaded outlet check valve is closed and stops the flow of air to the tower. A

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small amount of dry filtered air from the top of the drying tower flows through an internal orifice and to the desiccant beeds removing collected moisture. At the same time the opposite tower collects moisture from the compressed air, which passing through the desiccant beeds. After one minute the electronic timer reverses the operation of the tower. The purging tower now becomes the drying tower. The solenoid is de-energised which causes the inlet and outlet check valves to open and the purge valve to close permitting full air flow through the desiccant beeds that absorb water vapour. Simultaneously the solenoid circuit on the opposite tower is energised.

7. Checking the proper function of the air dryer system This is accomplished by inspecting the humidity indicators, which indicates as follows. Blue indicator--- indicates dryer has been performing correctly. Lavender indicator--- dryer is suspect. White indicator--- possible damaged dryer. Check for water in final filters. Yellow or brown indicator--- damaged dryer.

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D1 PILOT AIR VALVE 1. Introduction D1pilot air valve is provided in synchronizing brake system and located between proportionate valve and C2-Relay valve. D1valve is kept open in normal operation. Proportionate valve supplies air to C2-Relay valve through this valve. 2. Objective This valve is provided to avoid the synchronizing brake / automatic brake application on the locomotive during dynamic brake application. 3. Construction D1valve has two ports, marked IN & OUT. These ports are positioned through a spool valve and spring. There is an air chamber against the spool valve spring force, which is connected to atmosphere through a vent hole in normal position. There is a magnet valve, which opens MR air to air chamber while magnet coil is energised. 4. Function The D1-Pilot air valve provides air path to C2-Relay valve in normal position. When dynamic brake is applied, magnet valve coil is energised and MR pressure port is opened. Then MR pressure reaches to D1 valve air chamber, which pushes the spool valve against spring force and disconnects the IN&OUT port. In this position the OUT port is connected to exhaust. Which ensures the loco brake is in release position. When dynamic brake is released, the D1 valve coil is de-energised, which closes the MR port and the existing air chamber pressure connects to the vent. In this way the spool valve regains the previous position.

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HB-5 RELAY AIR VALVE

1. Introduction The HB5-Relay air valve is provided in vacuum brake circuit. It is connected to protection valve, MR pressure pipeline and PCS. When train pipe vacuum drops below a pre determined value, it gets HS4 air pressure from VA1B protection valve. This valve works as a safety valve in vacuum brake circuit and relays vacuum drop in train pipe to Driver by power cut off and idling diesel engine speed. 2. Objective This valve is provided to power cut off and idling diesel engine during vacuum brake train parting and emergency brake application. 3. Construction This valve has a pipe bracket containing number of port connections and a valve body. The diaphragm makes two chambers, top is connected to VA1B protection valve and bottom (spring chamber) is connected to A1 Differential pressure valve through port 13. The passage below spring chamber is connected to exhaust and delivery port 11, which leads to PCS. There are two valves, valve 16 connects port 12 MR to port 11, which leads to PCS and valve 17 connects port 11 to port 9 exhaust. At bottom supply valve spring is there, which normally keeps the supply valve in close position. 4. Function Control pressure (HS4) enters through passage 10 to the chamber above diaphragm 10. See the line diagram of safety devices. When the pressure reaches above spring setting, the diaphragm and its follower 5 move down word, compressing spring 6 and seating valve 17 on the top of valve16. As the downward movement continues, valve 16 moves away from its seat, compressing the lower spring. Passage 9 is now closed by valve 17, while passage 12 MR is connected to passage 11, which leads to PCS. When control pressure above diaphragm 10 is vented, spring 6 returns diaphragm follower 5 and valve 17 to their upper position, unseating valve 17. The lower spring then seats valve16 and closes passage 12 MR, while passage 11 is connected to passage 9 exhaust through the unseated valve 17. In this way the air, which was supplied to PCS is exhausted. If the HS4 control pressure is not removed from top chamber due to stuck up of protection valve, the spring chamber gets BP pressure through port 13 from A1 Differential pressure valve. It will nullify the action of HS4 control pressure by returning the diaphragm follower 5 at its previous position. At the same time BP pressure will be supplied to spring chamber of protection valve to reset the protection valve.

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H5 RELAY AIR VALVE 1. Introduction The H5-Relay air valve is provided in BP System and works as a safety vale. It is connected to BP pipe, MR pressure line and PCS. It relays BP pressure drop to the Driver by power cut off and idling diesel engine speed. 2. Objective This valve is provided to operate power cut off switch (PCS) during train parting and emergency brake application. This also works, when BP pressure drops 2.5kg/cm2. 3. Construction This valve consists a pipe bracket and valve body, where diaphragm makes two chambers. Top chamber always gets 5kg/cm2 air pressure from BP pipe and bottom chamber (spring chamber) is connected to atmosphere through a breather port. Below the spring chamber passage is connected to supply port 9 MR, which is normally closed through valve 17. Valve 15 normally connects port 11(which leads to PCS) to exhaust. 4. Function BP pressure enters through passage 10 to the chamber above diaphragm. See the line diagram of safety devices. When the pressure reaches above spring setting, the diaphragm and its follower 5 move down word, compressing spring 6 and seating valve 17 on top of valve 15. As the downward movement continues, valve 15 moves away from its seat, compressing 19. Passage 9 is closed by valve 17, while passage 12 exhaust is connected to passage 11, which leads to PCS.

When BP pressure above diaphragm 10 is vented out, spring 6 returns diaphragm follower 5 and valve 17 to their upper position, unseating valve 17. Spring 19 then seats valve 15and closes passage 12 exhaust, while passage 11 is connected to passage 9 through the unseated valve 17. In this way the air, which was supplied to PCS is exhausted now.

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UNIT M 3- PLAIN BEARINGS OBJECTIVE The objective of this unit is to make you understand about the following: • Roll of Plain bearing in general and their application in diesel locomotive • Classification of bearings • To study desired properties of bearings in connection to material selection and

manufacturing. • Good workmanship practices • Failure mechanism and their remedies STRUCTURE 1. Introduction 2. Use of plain bearings in locomotives 3. Classification of plain bearings and their desired properties 4. Failure trend 5. Workmanship improvement 6. Failure mechanism and suggested remedies 7. Summary 8. Self assessment exercise

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1. INTRODUCTION Plain bearing plays a vital role in the Diesel Engine. This is being the weakest part of the diesel engine, for any abnormality in the operation of diesel engine and fitment lapses of bearings, they become the easiest prey. Hence knowledge on bearing is essential for the reliable and failurefree service of the Diesel Locomotive. The function of a bearing is to reduce friction and wear of the load-bearing shaft of a machine having rotational / sliding motion. But its function remains incomplete without the assistance of Lubrication. Optimum condition of bearing lubrication exists when the sliding surfaces are separated by a film of lubricant thick enough to prevent metal-to-metal contact of the shaft with the bearing, depending upon surface roughness and load characteristics. Favourable surface configuration, adequate oil viscosity and a high bearing characteristic number are essential to produce hydrodynamic film lubrication. A pure hydrodynamic Lubrication perfects the work of plain bearings, so they are also called hydrodynamic bearings. High loads, moderate speeds, extreme temperatures or insufficient lubricant promotes the most undesirable condition of lubrication. In limiting condition hydrodynamic Lubrication transforms to boundary layer lubrication and dry bearings and during this transition phase the bearing metallurgy meets the tribological requirement. Hence, selection of bearing material is very important to meet the boundary conditions specially during starting and stopping of engine while temporary loss of lubrication takes place. 2. USE OF PLAIN BEARINGS IN LOCOMOTIVES The important areas of Diesel Locomotive where plain bearings used are:- Main bearing (at crankshaft main journal), Con Rod bearings (Big and small end), TSC Bearings, Valve lever bushes, Cam bushes, T/Motor suspension bearings etc. In recent trend, Roller bearings are replacing the plain bearings in many areas, as in the case of suspension bearings of diesel locomotives. But there are some areas like crankshaft bearings and Con Rod bearings, plain bearings have no substitute because of their fitment constraint and superiority of performance at shock/impact loading. In Turbo supercharger also use of plain bearing is continued because of its superiority over roller bearing at higher speed range. 3. CLASSIFICATION OF PLAIN BEARINGS & THEIR DESIRED

PROPERTIES. Plain bearings are mainly designed to bear load in radial direction. They are either bush type or split type depending upon fitment requirement. Crankshaft bearings (Main bearings and con rod big end bearings) are split type and in other areas they are bush types. In 9th main bearing collared bearing is used to bear load both in radial and axial direction, they are called thrust bearings. Plain bearings are further classified as Bi-metal or Tri-metal bearings depending upon number of layer used to form bearing. In Bimetal bearing two layers are used having one babbit layer and the steel back. In Trimetal bearing two babbit layers are there with the steel back.

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The manufacturing process, material composition and thickness of the babbit layers are decided to meet the following desired properties of the bearing i.e. Load Capacity (Ability to withstand max pressure with low friction and moderate wear), Mechanical strength, Fatigue strength, Compatibility (Anti seizure & Anti scoring property), Bond strength, Conformability (Ability to compensate slight misalignment and variation in shape of shaft and bearing surface), embeddability and corrosion resistance. COMPATIBILITY: This is the measure of anti scoring & anti welding property of bearings, to meet boundary conditions during starting and stopping. CONFORMABILITY: Ability to compensate slight misalignment and to conform to variation in the shape of shaft and housing.(Materials with low Modulus of elasticity and good Plasticity have better conformability) EMBEDDABILITY: Ability to embed dirt and foreign particles. ( Embeddability and conformity are the parallel properties of metal) LOAD CAPACITY: Is the measure of Max Pressure that the bearing material can withstand with low friction and moderate wear. This depends upon Viscosity of Lubricant, Surface finish of Shaft, Operating temperature and composition of Bearing Materials. STRENGTH: Compressive and Shear Strength are important. Tensile and Yield Strength are the easy measure of Mechanical Strength.(In general low strength materials provides more deflection under load and better conformability.) A material with low Shear Strength can sustain shearing of small particles with little heat generation and welding FATIGUE STRENGTH: Ability to sustain load of reversible nature, such as in IC Engines. Sufficiently high Fatigue Strength is necessary to enable bearing to operate within Elastic limit without developing cracks and surface pits. A thin layer of soft materials with strong Steel backing gives the desirable combination of Fatigue Strength and Compressive Strength. CORROSION RESISTANCE: Acidic behaviour of lubricant (due to oxidation, mixing of exhaust gases etc) causes such corrosion. Pb is more prone to corrosion where as Sn and Al are not usually affected. HARDNESS: Softer the material, the better its antiscoring, conformability and embeddability properties. Higher hardness provides better load capacity and greater wear resistance.

Typical configurations of ALCO Bi-metal and Tri-metal bearings are sketched below for better understanding of the above aspects.

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Used in: Cam shaft bearing bushes, Con Rod little end bushes, Valve Lever bushes,

Push Rod lifter bushes etc. Configuration:

a) STEEL BACK: Remainder of thickness. Made of cold rolled steel, conforming to AISI C-1010 or C 1015 killed steel

b) BRONZE OVERLAY: 0.015” to 0.030” thickness, Cold Rolled.

Metallurgy: Cu: 77% (min). Pb: 8-11% , Sn: 8-11% , Zn: 0.75% (max), Sb: 0.50%

(max) Ni: 0.50%(max), Fe: 0.35% (max) and other elements 0.40% (max) It is essential that Pb globules are uniformly distributed without showing

of gravity segregation. The layer should show a uniform Eutectic structure.

Used in: Main Bearing Shells, Con Rod Big end Bearing Shells and Turbo Bearing Bushes. Configuration: a) STEEL BACK: Remainder of thickness. Made of cold rolled steel,

conforming to AISI C-1010 or C 1020 killed steel

b) INTERMEDIATE LAYER: Thickness: 0.015” to o.035” Cold rolled alongwith steel back

ALCO TRIMETAL BEARING

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Material Specification: Cu: 68-75%, Sn: 2-4%, Pb: 23-27%, Zn: 0.20%(max),Ag:0.20% (max),

Fe: 0.50%(max), Ni: 0.50%(max), Sb:0.25%(max), other elements 0.35%(max).

c) NICKEL DAM Thickness 0.000075” to 0.000100”, Centrifugally Cast. It prevents tin migration from overlay to intermediate layer.

d) OVERLAY Thickness 0.0015” to 0.002”, Centrifugally cast. Material specification: Cu: 2-3%, Sn: 8-12%, Pb: Remainder

A graphical analysis of Fatigue life in relation to babbit layer thickness and operating temperature is attached to understand the affect of babbit layer thickness and operating temperature on the fatigue life of bearings.

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BEARING TERMINOLOGIES (As per the sketch attached below, in fig 1 to 4) Knowledge on bearing terminology of split type bearings will help in understanding correct fitment technique of split bearings

Effect of babbit thickness and Temperature on Fatigue Life of Bearing

7

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FAILURE TREND The failure trend of bearing can be compared with the human mortality graph (A bath tub design). No of death (No of failures) Age Infant mortality Ageing death In case of bearings, infant mortality is caused either due to manufacturing and design defects or due to severe workmanship lapse (like blocked oil passages or dislocating of bearing with the oil passages) or due to severe abnormalities of the working behaviour of the engine. The failure due to ageing death of bearing can be arrested by correctly formulating and following the renewal schedule. In the region other than ageing death and infant mortality a proper investigation is required to diagnose the problem and to find solution accordingly. 4. WORKMANSHIP IMPROVEMENT Besides all other factors a good workmanship contributes a lot for saving failure. A few tips have been given below towards good maintenance practice: - I. Maintain clean & dirt free working environment. II. Do not rub or polish bearing surface. III. Clean the bearing and its housing using clean clothes only. IV. Ensure clean and free oil passage. V. Make the locating Dowel/Nick free from burrs, to ensure correct seat of

bearing at its housing. VI. Never apply oil at the backside of bearing and its housing. VII. Measure the bore dia & check the ovality and taperness of the housing and

also the eccentricity of the shaft & bore. VIII. Ensure positive Nip and Freespread. for correct fitting of bearings.

9

Nip:- Is the increased peripheral length of the bearing from its housing. It should be +ve to ensure interference fit.

Free spread:- In the free state the split end of the bearing is spread over than the actual dimension of its housing. This is called free spread. This is to ensure conformity of the bearing with its seat.

IX. Clearly mark on bearing its location with in the engine. X. Tighten bolts in correct sequence to the correct torque or stretch as defined in

the engine instruction manual. XI. Check that the shaft rotate freely inside the bearing after assembly. 5. FAILURE MECHANISM & SUGGESTED REMEDIES Besides badworkmanship many other reasons are there that led to premature failure of bearings. As such proper failure analysis is essential for their remedies. Some of the typical defects and their suggested remedies are listed below: - 1. Fatigue Failure: - Crack like appearance at initial stage. Starting from top

surface reaches bond layer and then propagates horizontally. Babbit layer gets peeled off and forms cavities, on severe attack. Probable reason:- (i) Mechanical: -

(a) Excessive dynamic loading (b) Higher cyclic variation of load, due to-

• Improper vibration damping. • Big range of variation of firing pressures in

different cylinders. • Excessive torquing.

(ii) Thermal: - Improper heat dissipation due to

a) Less clearance b) Improper Lubricant –Dirty, Less/More Viscous. Coolant character of lube oil lost due to depletion of

additives.

B

A

B + NIP B−A= FREE SPREAD

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c) Loss of heat conductivity between bearing and housing due to • Dirt/ Oil packing/air gap between bearing back and

housing. d) Oil temperature high due to dirty improper heat exchanger.

Remedial action can be taken accordingly.

2. Chemical Corrosion: - Can be viewed under microscope only. Black spots are noticed due to presence of PbSO4 in Pb matrix. Reason: - Acidified Lube oil (PH value of Lube oil should not go below 4.5). This is due to:

• Sulphur content of fuel oil high(should not be allowed more than 0.5%)

• Excessive blow by of exh gas through sump. • Periodicity of lube oil changing not followed.

Remedial measure can be taken accordingly.

3. Water Corrosion:- Whitish bordered localised shining surface at the loaded

zone and remaining portion looks dull. Reason:- Mixing of water with lube oil due to lube oil cooler tube burst or damaged Liner O ring etc.

Lube oil should be changed if water mixed with lube oil goes above 0.25% and proper rectification of the source of leakage should be done.

4. Cavitation erosion: - Erosion of babbit layer in hen track pattern appears

perpendicularly to the oil groove at the unloaded zone of the bearing. This is caused due to formation and collapsing of vapour bubbles in the oil film, under the state of rapid pressure variation during crank cycle.

Reason:-

(i) Lube oil improper due to the absence of proper antifoaming additives or antifoaming additive lost its character due mixing of water in lube oil.

(ii) Aeration in lube oil system. (iii) Excessive hunting (iv) Improper vibration damping (v) Under designed or partly choked oil holes.

5. Scoring/Mechanical wear: -Score and localised wear marks are noticed due to

• Bad filtration of lube oil.(Due to operating of by pass valve, clogged/damaged filter element).

• Bad filtration of charge air. • Distortion in housing. • Rough journal.

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• Deformed journal. • Foreign material between bearing back and housing. • Biased wear due to wrong fitment of bearing, misaligned bearing housing /

bend or twisted Con.Rod. 6. Wiping & Seizure: Starts with dislocation of the babbit layer and finally gets

welded with the shaft causing seizure.

It happens due to: - (a) Failure of lubrication due to leakage in 'S' pipe or

choked oil passage (b) Low lube oil pressure; insufficient to maintain required

oil film thickness for hydro dynamic lubrication. (c) Heavy Fuel/Water contamination.

5% Fuel Dilution leads to mechanical wear. 10% Fuel dilution may cause scizure. 20% variation in Lube oil viscosity causes wiping and

scizure. (Viscosity of oil goes high due to water contamination, oxidation of lube oil, heavy blow by through crankcase). (d) In compatible or adultered lubricant may lead to wiping

and seizure.

Zn additive in lube oil causes depletion of Ag lining from babbit layer. As such Zn additive should not be used where Ag is used as a constituent of babbit layer.

(e) Excessive Crank web deflection may lead to wiping and

seizure Crank web deflection should be restricted within ± .0008".

7. Split Line Fretting:- Relative motion between two halves at the split end develops fretting at the joint faces of split type bearings. Finally it leads to bond separation and seizure. This is due to:-

(a) Excessive torquing, beyond the capacity of the bolts to sustain both static and dynamic loading.

(b) Low capacity bolts (Suffered plastic deformation) Can’t sustain Nip stress and dynamic loading.

8. Creep/ back fretting:-This is developed due to relative motion of the bearing

with its housing. Fretting starts between bearing back and its housing and propagates upto the babbit layer. Thus it affects to heat dissipation and finally leads to seizure. This is due to: -

i) Negative or lesser Nip, causing inadequate interference.

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ii) In correct torquing (Both high or low torque) iii) Use of low capacity bolt.

9. Static Fretting: - Fretting developed at the loaded zone of bearing at static condition, due prolonged vibration sustained by the bearing originated from third source. This happens mainly, if the assembled component or engine is kept for a long time in such area where ground vibration is very high or, it may develop during transportation of machinery or component with improper mounting and clamping.

To arrest such failure due to static fretting it is always advisable to check bearings in assembled engines or its subassemblies before use, after keeping them for long days in reserve. Especially where ground vibration from 3rd sources is very high.

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6. SUMMARY

Plain bearing plays a vital role in diesel locomotive. Because of its sophisticated design and weaker structure knowledge of plain bearing about its design, working and maintenance aspects is very much essential for trouble free service of locomotive. Design, selection of material and manufacturing aspects of bearings are decided, based upon the desired properties of the bearings like load strength, fatigue life, embeddability, conformity, corrosion resistance etc. Plain bearings are either split or bush type depending upon their fitment requirement. Plain bearings are normally radially loaded, flanged bearings are also used to sustain both radial and axial loading. They are further classified to bi-metal or tri-metal bearings depending upon No of babbit layers used. Proper fitment technique in split bearings is very much important for the reliable service of bearings, as being discussed in this chapter. In addition to these, failure mechanism and their remedies as discussed in this unit will help in minimising the failure upto a great extent.

7. SELF ASSESSMENT EXERCISES

i) In what parameter performance of plain bearing supersedes roller

bearings? ii) What are Nip and free spread in a split bearing? What is their importance

for fitment of split bearings? iii) Discuss in brief about the following bearing failures:

a) Fatigue failure b) Chemical corrosion c) Split line and back fretting

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UNIT M 8- LOAD BOX TEST OBJECTIVE The objective of this unit is to make you understand about the following: • What is load box test? • Why, when and how it is conducted • What are the types of load boxes used in Indian Railways and their relative merits • What checks are conducted during load box test • How to diagnose problem from load box results STRUCTURE 1. Introduction

1.1 What is 1.2 Types of load box and their comparison 1.3 Why, when and where to conduct

2. Load box procedure 2.1 Preparation for starting Loco 2.2 Starting 2.3 Notch up 2.4 Preload testing

• Shut down condition • Running condition

2.5 Preparation for load box • Mechanical • Electrical

2.6 Break in test 3. Observation 4. Interpretation of load box observation 5. Summary 6. Self assessment Exercise

3

1.INTRODUCTION 1.1.WHAT IS? This is a test to check the capability and performance of the engine by simulating the actual working condition of the locomotive at rated output, in static condition. During load box test, the output of the engine is measured in terms of electrical parameter (volt and ampere).In this, the output of the generator is connected across a set of resistance (Load Resistance) instead of connecting it with the Traction Motors.The output of the engine is dissipated in terms of heat across the resistance during Load Box test. 1.2 TYPES OF LOAD BOX They are of two types, based on the type of load resistance connected: 1) Grid Resistance Load Box. 2) Water Resistance Load Box. COMPARISON WATER RESISTANCE GRID RESISTANCE

Merit De-Merit 1) Load resistance can be varied at infinite stages, hence a continuous HP curve can be plotted through this.

1) Load Resistance can be changed only at limited stages (3 to 6). Hence a complete graph can not be plotted to understand the complete behaviour of the output.

2) Load resistance can be changed during loaded condition.

2) To change the load resistance in grid type, the locomotive requires to be stepped down to lower notch as such load test gets interrupted as many times the resistance required to be changed.

3) Water load box can be conducted for a longer duration because of better heat dissipation facility

3) Grid resistance load box can not be conducted for longer duration, as it gets heated up quickly causing hazardous environment and gives erratic reading.

De-merit Merit

4) Requires permanent establishment to setup water load box, hence can not be shifted easily.

4) Comparatively handy and can be shifted with lesser effort

1.3 WHY, WHEN AND WHERE TO CONDUCT Why

1) To see whether the engine gives designed output or not. 2) Whether all systems are functioning properly or not. 3) Whether any problem is connected to any system or component.

4

When

1) After new manufacturing 2) Before and after major repairs 3) Before and after major schedule. 4) To diagnose any specific problem existing in the engine

Where It is conducted on the specified Load Box area in the shed or in the workshop. (In case of GM locomotive, the facility of Load Box Test exists within the loco itself) 2. PROCEDURE 2.1 PREPARATION FOR STARTING LOCO

1) Water filling 2) Fuel filling and bleeding test. 3) Supplement the engine with supplements e.g.T/G Gear Box oil, Gov. oil, Expressor Oil,

Intake filter oil, Right Angle gear box oil and also greasing Rod fan bearings, Horizontal shaft coupling, universal shaft coupling, cardium compound filling in Expressor Coupling etc.

4) Pre lubrication. Lube oil is not directly filled in the Engine sump. Instead , it is filled through an external pump by opening a dummy in the L/Oil main header (as shown in the figure below) so that the Lube oil can circulate through all the engine components and finally drops down to the sump.This is also termed as prelubrication. During prelubrication the following checks are necessary to carryout.

Main Dummy Header . L/Oil container

**During prelubrication Test filters are necessary to be fitted to arrest the worn out metal particles and the metal chips left out in the process of overhauling or manufacture. 9 Nos are fitted in place of S-Pipes and 2 Nos. in the secondary headers.

Check:during prelubrication The flow of lubricant during prelubrication will be as per the following pattern: Oozing : Con Rod bearings, M/Bearings, cam bush, valve lever bushes Spray like jets : Piston Pouring : F.P. Support, valve lever, Yoke Dripping : Liners

ENG

Pump

5

Trickling : Cam Gear. 2.2 STARTING 1)Engine is started immediately after prelubrication and allowed to run for a minute or two. During running unusual sound or leakage is observed, if any. 2) If O.K, run the engine for 5 minutes and stop. Check the following Check Main Bearing temperature, it should not vary more than 5°C from one bearing to another. Check and rectify if any leakage is there in L/oil system (specially S pipes ) or water system etc. Check the lube oil sump strainer for any foreign particle, metal dust etc.

3) Run for 30 minutes, observe unusual sound, leakage, smoke etc. if any. 4) Stop engine and check M/Brg temperature, internal leakage of water, L/ oil etc. if any. Exam crank case for any foreign material or worn out metals. 5) Continue run until temperature reaches 120°F and check between two stretch of runs. 6) Run the engine for 6 to 8 hours to complete idle run.

2.3 NOTCH UP 1) Engine is then notched up to 8 th notch with the continuation of 15 minutes run in each notch. 2) After notch up remove all the test filters and connect the original pipes before conducting load box.

Check all the test filters for any foreign materials or worn out metal particles, if any. Take remedial measures accordingly.

2.4 PRE LOAD TESTING • SHUT DOWN CONDITION 1) Electrical testing

a) Conduct insulation test (Meggar test ) between Power circuit to earth. Control circuit to earth. Power to Control and also in all cards.

Range: 1 to 5 Mega Ohms

b) Check all C- Brushes of rotating equipments. 2) Mechanical testing a)Exam crank case for the following:

i) Foreign material, split pin, loose nut etc. ii) Internal leakage, if any. • RUNNING CONDITION 1) Electrical testing

a) Notch wise voltage at No Load to be checked connecting voltmeter Across CK1&CK2 (fixed contact)

b) Check engine speed notch wise. c) Check reference volt across wire No 29 A&4 : 24.4 volt (E type )

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d) Check AC Volt across 31L-31M,31M-31N,31N-31L: 100 to 105 V on 8th notch. e) Check Battery Volt (across CK1&CK2 moving contact): 72 ± 2 volt. f) Check correct operation of LOPS, LWS, T1 T2 &ETS, PCS, GROUND

RELAY, WSR etc. 2) Mechanical testing

a) Check correct setting of OST.

b) Check Turbo Rundown Test : 90 to 180 secs 2.5 PREPARATION FOR LOAD TESTING. • Mechanical i) Fit adopter for KIENE gauge removing all decompression plugs. ii) Fit temperature gauge removing exhaust plugs. iii)Fit temp gauge before and after TSC.

iv)Connect temp gauge before and after After Cooler. v) Connect temp gauge before and after L/Oil Cooler. vi)Fit Pressure Gauge before and after L/Oil Filter tank. vii) Fit Pressure Gauge at Water Pump outlet and Water Headers. viii) fit Vacuum Gauge at Expressor Crank case. ix) Fit Water Manometer at crank case cover for measuring Crank case Vacuum.

(Specially fabricated for taking crankcase vacuum.) • Electrical

G F CK1 EXC. SYSTEM LOAD CK2 1. Disconnect 3 GA-2 cable from MG negative terminal. In their place connect 3, 2300/24 cables at the

negative side of water load box. 2. Disconnect 3 motor armature cable A1, A2, A3 and 3 GA 11 cables running each to P1, P21and P31

from negative side of ACCR. Connect three 2300/24 cables instead of six to the positive side of the water box.

3. Connect voltmeter, ammeter according to the figure, as above.

GEN

ACCR

V

A

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2.6 BREAK IN ON LOAD 25% of rated load 60 min / 30 min ( New / Overhauled Engine ) 50% of rated load 60 min / 30 min ( - do - ) 75% of rated load 120 min/ 60 min ( - do - ) 100% of rated load 120 min/ 60 min ( -do - ) 3. OBSERVATION Observation of load box test will be conducted as per the chart supplied.

LOAD TEST CHART Loco No. Engine No Trac Gen No Date Reason for load testing: Time started Time completed Name of supervisor Name of fitter (mech): Name of fitter (elec): Ambient Temp Altitude Fuel Temp Fuel density Readings to be taken on each notch (A) Notch Lube oil Pressure Fuel oil

Pressure Booster Air pressure

Engine Speed RPM

Rack Position in mm

LCP position

Excitation current Eng Com Exh

1 2 3 4 5 6 7 8 9 10 Idle 1st 2nd 3rd 4th 5th 6th 7th 8th

Notch Auxiliary

Voltage Reference Voltage

AC Voltage between 3ϕ

Load Current

Load Voltage

Horse Power

Corrected HP

Water Temp

11 12 13 14 15 16 17 18 19 20 Idle & 8th notch

8

Notch Colour of

smoke Current limit

Specific Fuel Consumption

Efficiency Crank case vacuum Remarks Engine Expr./

Comp 21 22 23 24 25 26 27 Idle & 8th notch

A) Readings to be taken on 8th notch Cyl. No Compression

Pressure Firing Pressure

Exhaust Gas Temp

Cyl. No Compression Pressure

Firing Pressure

Exhaust Gas Temp

1R 2R 3R 4R 5R 6R 7R 8R

1L 2L 3L 4L 5L 6L 7L 8L

Exhaust gas temperature Charge Air temperature Before Turbo: Before After Cooler: After Turbo: After After Cooler: Lubricating Oil temperature Lubricating Oil Pressure Before Lube Oil Cooler Before Filter Tank After Lube oil cooler After Filter Tank Cooling Water Pressure Water Temperature At the pump outlet Inlet to After Cooler At the header Rt. side Inlet to lube oil cooler Lt. side Efficiency After cooler Specific Fuel Consumption Lube Oil Cooler D.E. Thermal Efficiency Observation of the supervisors: Signature Remarks of Foreman: Signature Orders of the controlling officers:

Signature

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4. INTERPRETATION OF LOAD BOX OBSERVATION

SL NO

RPM RACK HP LCP TROUBLED AREA

REMARKS

1 OK OK OK I) Just active WW- 5:30 TO 3:00 GE -10:30 TO 9:00

II) More active

I) No trouble ii) Excitation

Control

More movement of LCP in active / Load control zone indicates more loading by MG. Because of defect/ wrong adjustment of card No 186, 292, 254, 293, & ACCR.

2 OK OK LESS Move towards load control

Diesel Engine and allied systems.

- Less TRD, low BAP indicate defective TSC/ After Cooler.

- Fall in fuel oil pressure indicates choked filters, leaky system or inefficient Fuel Booster Pump.

- Low compression and firing pressure indicate inefficient engine

- Neither of these defects indicate faulty calibration of FIP.

3 OK LESS LESS I) Active (Under load control) ii)Not in load control

i) Governor ii) Excitation control

i) LCP in load control zone with less rack and correct BAP indicates wrong adjustment of LCP in WW Gov LCPV should be adjusted both in 1st & 8th notch to get correct load control schedule. In GE Gov LCP brush arm must be set at 1:00(in dead condition) during o/hauling.

ii) Less rack & less HP

without load control indicate less loading by MG. The defect could be in 253,186,292,254,293 & ACCR.

Defective MG & exc. may also cause this problem in isolated cases.

4 As per notch

More in lower notches

i) Less or ok

ii) More

i) Diesel engine & allied systems

ii) Excitation

control

i) Incorrect FIP calibration ii) The MG is imposing

more load in lower notches. This may be due to defect/ wrong adjustment of 186,292,293 & ACCR

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SL NO

RPM RACK HP LCP TROUBLED AREA

REMARKS

5 Bogging down or excess hunting

More in lower notches or unstable

More in lower notches or unstable

Fluctuating Governor adjustment or LCP defective

Short-circuited commutator segments of LCP or loose contact between commutator & brush arm lead to sudden load variation

6 Drop in speed

Max i) Slightly less

ii) Less hp

GE: 7:00 WW: minimum

i)Excitation control

ii) DE & allied system

i) Probable defect cards - 253,186 & 254 ii) Less TRD, low BAP

indicate defective TSC/ after cooler

-Fall in fuel oil pressure indicates choked filters, leaky system or inefficient fuel booster pump

-Low compression and firing pressure indicate inefficient D/E -Neither of these defects indicate faulty calibration of FIP

5. SUMMARY Load Box test is conducted to check and verify the capability and performance of the diesel engine by simulating the actual working condition in static condition of the locomotive. This is also used as a diagnostic tool to identify problems related to any system or component. At every maintenance depot POH shop and manufacturing unit there is a specified area to conduct load box test. Based upon the type of resistances used, they are of two types, Water and Grid resistance type Load Box. During load box test, the output of the generator is connected across a set of resistance instead of connecting it with the Traction Motors. The output of engine is measured in terms of electrical parameters i.e. volt and ampere, across the resistances connected in load box. Several other mechanical and electrical parameters are also recorded to diagnose problems related to engine performance, based on the observations made during load box test. 6. SELF ASSESSMENT EXERCISES

1. What is Load Box test? Why, when and where they are conducted? 2. What are the types of Load Boxes used in Indian Railways? Compare their relative merits? 3. What is Prelubrication? What checks are to be conducted during Prelubrication? 4. What mechanical and electrical checks are conducted as pre load test during Load Box? 5. What is calculated HP? And how is it corrected?

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UNIT M 6-TRANSMISSION IN DIESEL LOCOMOTIVE OBJECTIVE

The objective of this unit is to make you understand about • the need for transmission in a diesel engine • the duties of an ideal transmission • the requirements of traction • the relation between HP and Tractive Effort • the factors related to transmission efficiency • various modes of transmission and their working principle • the application of hydraulic transmission in diesel locomotive STRUCTURE 1. Introduction 2. Duties of an ideal transmission 3. Engine HP and Locomotive Tractive Effort 4. Factors related to efficiency 5. Rail and wheel adhesion 6. Types of transmission system 7. Principles of Mechanical Transmission 8. Principles of Hydrodynamic Transmission 9. Application of Hydrodynamic Transmission ( Voith Transmission ) 10. Principles of Electrical Transmission 11. Summary 12. Self assessment

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1. INTRODUCTION A diesel locomotive must fulfill the following essential requirements-

1. It should be able to start a heavy load and hence should exert a very high starting torque at the axles. 2. It should be able to cover a very wide speed range. 3. It should be able to run in either direction with ease.

Further, the diesel engine has the following drawbacks: • It cannot start on its own.

• To start the engine, it has to be cranked at a particular speed, known as a starting speed.

• Once the engine is started, it cannot be kept running below a certain speed known as the lower critical speed (normally 35-40% of the rated speed). Low critical speed means that speed at which the engine can keep itself running along with its auxiliaries and accessories without smoke and vibrations.

• The engine cannot be allowed to run above a certain speed known as high critical speed. It is 112 to 115% of rated speed. The high critical speed is the speed at which the engine can keep itself running without damaging itself due to thermal loading, and centrifugal forces.

• It is a constant torque engine for a particular fuel setting irrespective of its speed. It can develop rated power at rated speed and fuel setting only.

• It is unidirectional.

• To de-clutch power, the engine has to be shut down, or a separate mechanism has to be introduced.

To satisfy the above operating requirements of the locomotive, it becomes necessary to introduce an intermediate device between the diesel engine and the locomotive wheels. This device, called transmission, should accept whatever the diesel engine gives, with all its limitations mentioned above and be able to feed the axles in such a way that the locomotive fulfills the essential requirements.

Any transmission should fulfil the following requirements. 1. It must transmit the power from the diesel engine to the wheels.

2 It must have a provision to connect and disconnect the engine from the axles for starting and stopping the locomotive.

3. It must incorporate a mechanism to reverse the direction of motion of the locomotive.

4 It must provide a permanent speed reduction, as the axle speeds are normally very low when compared with the speed of the crankshaft of the diesel engine.

5 It must provide a high torque multiplication at start, which should gradually fall as the vehicle picks up speed and vice-versa.

The requirements of traction are- 1. It requires high starting torque at zero speed so that the train can start without jerk. 2. Once the train is started, torque should reduce quickly, uniformly, and speed

should increase with high acceleration.

3

3. The sped and power characteristics should change automatically & uniformly depending on the road requirements so that the power transmission is jerk free.

4. The power transmission should be reversible with identical speed and torque characteristics with easy reversibility in both directions.

5. There should be a power de-clutching arrangement whenever required. 2. DUTIES OF AN IDEAL TRANSMISSION

1. It should be able to multiply the torque and reduce the speed to such a level that the train can be started without a jerk.

2. Once the train has started, it should decrease the torque and increase the speed as required, automatically.

3. The torque & speed characteristics should be varied uniformly throughout the traction depending upon the road requirements, so that the power transmission is jerk free.

4. It should be capable of reversing the power transmission easily, with identical torque & speed characteristics in both the directions.

5. It should be light, robust, and should occupy very little space. 6. It should be reliable and ask for minimum maintenance. 7. It should be approachable easily for maintenance and ask for low minimum nos. of

consumable. 8. It should not transmit road shocks and vibrations to the engine. 9. It should have good efficiency, good utilisation factor, and good degree of

transmission. 10. It should be capable of starting the engine, if required. 11. It should be able to apply brakes, if required.

3. ENGINE HP AND TRACTIVE EFFORT

The power produced by the diesel engine at its crankshaft is the horsepower, which is proportional to the multiplication of torque and the speed of the engine. In any diesel engine torque and speed are the two independent quantities- the torque produced by the engine is proportional to the load to overcome the resistance for its rotation, and the speed of the crankshaft depends on the HP produced by the engine. Tractive effort of a locomotive is the effort or force exerted by the driving wheels on the rails. The torque produced at the crankshaft of the diesel engine is multiplied by the transmission system, and is available at the axle as the axle torque. The wheel on the rail applies this torque, divided by the radius of the wheel gives the effort at the wheel-rims is called Tractive effort. As the horsepower of the diesel engine is constant for a fixed throttle setting and speed, the horsepower available at the axles will also be constant from zero to the maximum vehicle speed when using an ideal transmission system. Depending on the speed of the vehicle, the tractive effort is varied automatically (increased torque at decreased speed, and vice-versa). In other words, the tractive effort-speed curve of a diesel locomotive obtained by using an ideal transmission system would be a rectangular hyperbola. In this case the full installed horse-power at site is available at the rails from zero to the maximum track speed, but in actual practice, the tractive effort curve falls well below the theoretical curve mainly due to three reasons- 1. Power consumed by auxiliaries such as cooling fan, compressors, exhausters,

dynamo etc. 2. Power utilisation factor of the transmission. 3. Transmission efficiency at the rails.

4

4. FACTORS RELATED TO EFFICIENCY

Power Utilisation Factor The diesel engine when viewed as a constant torque engine is capable of developing its full rated horsepower only when running at its maximum speed and maximum fuel setting. Therefore to utilise its full power from zero to hundred percent of vehicle speed, the engine must run always at its maximum speed with full fuel setting. But this is not the case in actual practice. When the engine is coupled to the wheels through a transmission system such as a coupling or a multi-stage gearbox, the engine speed is directly governed by the inherent characteristics of transmission and hence its power varies proportionately. The ratio between the horsepower input to the transmission in peak notch operation at any instant of the vehicle speed and the maximum horsepower installed at the site conditions is known as power utilisation factor.

Transmission efficiency This is defined as the ratio between the rail horsepower and horsepower input to the transmission at any vehicle speed.

Degree of transmission This is a very important factor for selecting a transmission system for a diesel locomotive. This is defined as a product of power utilisation factor and the transmission efficiency. In other words, this is the ratio between the rail horsepower at any instant, and the installed horsepower at the site.

5. RAIL AND WHEEL ADHESION

The locomotive wheels run on a metal track. Any tangential force exerted at the wheel rims will cause a linear movement of the vehicle only if the driving wheels have a grip on the rails, as otherwise the wheels will slip and the vehicle will not advance. The maximum force that can be exerted by the driving wheels without causing a slip is called the adhesive limit of the locomotive. This depends primarily on the adhesive weight of the locomotive as well as friction between the contact surfaces of the rail and wheels. The coefficient of adhesion at start, between the rail and wheel rim, generally lies between 0.25 and 0.33, depending upon the type of transmission, axle configuration, bogie design etc. The selection of a transmission system for a locomotive should be in such a way that the tractive effort at start should always be well above adhesive limit of the locomotive, so that the starting load is limited by the adhesive factor and not by the engine power.

6. TYPES OF TRANSMISSION SYSTEM

Mechanical Transmission

• Gear

• Friction Clutch

• Belt and Pulley

• Chain and sprocket.

Hydrodynamic Transmission

5

• Fluid coupling

• Torque converter

Electrical Transmission

• DC electrical

• AC/DC electrical

• AC electrical

• Linear motor etc.

7. PRINCIPLES OF MECHANICAL TRANSMISSION In this system of transmission, a clutch and a multi ratio gearbox are employed.

The multi ratio gear box consists of several gear trains. The engine power is transmitted through one gear pair at a time. As the engine is rigidly connected to the wheels through a fixed gear ratio in each gear, the vehicle speed varies directly with the engine speed. As the power output of the engine is proportional to the engine speed, the power delivered by the vehicle also varies with the engine speed.

The transmission efficiency of the mechanical transmission is the highest, as there is no conversion of energy during the power transmission process. But the other parameters are inferior when compared with other types of transmission systems.

8. PRINCIPLES OF HYDRODYNAMIC TRANSMISSION In hydrodynamic mode of transmission the velocity / the momentum of the fluid is the contributing factor for transmission of power. The rate of change of momentum of the fluid from driving to the driven member decides the amount of torque being transmitted in this system. Hydrodynamic drives are of two types.

FLUID COUPLING

HYDRAULIC TORQUE CONVERTER.

Fluid coupling

It is a device employed in a power transmission system simply to transmit torque from one end to the other through a fluid medium. There are two principle members. Those are-

1 Impeller or pump, generally connected to the input side of the power transmission system.

2 Turbine or runner, connected to the output side. All the blades or wings in both the members are straight and radial. In most of

the cases, these two elements are produced by Aluminium castings. Working principle:

The power output of the engine is supplied to the impeller. The speed of every particle of the fluid that passes through the rotating impeller increases. In a turbine the reverse action takes place. The high speed fluid exerts a push on the turbine blades. This

6

causes the turbine to produce an output power. In this way, the coupling transmits power to the external load.

The two members of the coupling are identical with respect to the inside to their inside and outside diameters, design and positioning of blade diameters etc. Therefore, the kinetic energy or torque absorbed by the impeller is equal to that released in the turbine. Hence, there can be no torque conversion in a fluid coupling, and impeller torque is always equal to the turbine torque. Slip

This is the difference between impeller and turbine speeds. When there is no slip, there is no transfer of fluid from impeller to the turbine and hence no torque is transmitted. This is because the turbine sets up a head of fluid equal and opposite to the head of the fluid set up by the impeller. To transmit any torque, a fluid coupling must necessarily have some slip depending upon its size and speed. Torque can be transmitted either way depending upon the speeds of its two members. The higher speed member automatically becomes the torque receiving or input side. Hydraulic torque converter The principle components are three. Those are-

1. Impeller or pump, connected to the input side of the transmission system. 2. Turbine or runner, connected to the output side. 3. Reaction member or guide-wheel, which is placed in the fluid circuit to guide

the fluid coming from the turbine into the impeller, and is normally connected to the casing. This remains stationary.

The general working principle and the basic characteristics are very similar to those of fluid coupling, as described above, but for the following variations.

The principle members are not identical in construction and the wings or blades provided in them are shaped and positioned to form various angles with respect to the axis of rotation to obtain required performance. The torque condition of the impeller and turbine are not the same due to the existence of a reaction member in the fluid circuit. Therefore, the impeller torque undergoes a change in turbine, and is either increased or decreased according to the speeds of the two members. Some facts about torque converter

1. In transmitting power, a torque converter behaves like a gearbox having infinite gear ratios, and hence provides a stepless variation of torque at the turbine end for a constant input torque. This inherent characteristic suits very well with the output torque requirement of a locomotive.

2. Due to the conversion of energy from mechanical to hydraulic in the impeller, and hydraulic to mechanical in turbine, there is a loss of power in the transmission. Hence its transmission efficiency is poorer than a mechanical transmission. However, it compares well with the electrical transmission.

3. For a definite output speed, its transmission efficiency is superior, when working under part load. Hence, it is ideal for shunting locomotives.

4. It does not transmit shocks and vibration from either side due to the presence of a hydraulic medium.

5. It permits the selection of a high-speed diesel engine as its prime mover. Thus, it reduces its gross weight of the locomotive.

9. APPLICATION OF HYDRODYNAMIC TRANSMISSION REVERSIBLE HYDRAULIC TRANSMISSION (VOITH TRANSMISSION)

Advantages of reversible transmission

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1. Separate torque converters are provided for each direction of running of locomotive. A change in the direction of travel of locomotive is effected by filling /emptying the appropriate converter.

2. Mechanical components such as claw/clutches, external/internal splined components, shifting fork, slide blocks, pneumatic cylinders and linkage mechanism, tooth on tooth safety devices etc. are dispensed with.

3. While the vehicle is in motion, by engaging the converter intended for the opposite direction of the travel, hydrodynamic braking can be achieved till the vehicle comes to a standstill position. The retardation of the vehicle will be very smooth, and sharp without any wear and tear of brake blocks, brake-rigging components.

4. The controls and monitoring devices in the locomotive are much simplified when compared with the conventional type of mechanical reversible transmission.

5. The transmission can be instantaneously switched on to either direction of travel at any time, while the locomotive is stationary or is moving, unlike in mechanical reversible transmission where the shifting of the claw clutch is to be carried out only when both the primary and the secondary rotating components are absolutely standstill. MERITS OF HYDRODYNAMIC TRANSMISSION OVER CONVENTIONAL ELECTRIC TRANSMISSION Efficiency Transmission efficiency of any hydraulic transmission using torque converter is comparable to any electrical transmission. The efficiency of hydro-mechanical transmission is about 10 % higher. The comparative saving in fuel costs will be substantial especially in high horsepower super-fast train locomotive. Power to weight ratio The horsepower to weight ratio of a diesel hydraulic locomotive is comparatively higher due to the use of high-speed diesel engine and lower weight of transmission. For example, the power to weight ratio of the WDM2. (Electrical transmission) is 23 hp/tonne, as against 33 hp/tonne for the WDM3 (hydraulic transmission). One of the main reasons is that the hydraulic transmission permits use of high-speed (low weight) diesel engine, as power absorbing capacity of the torque converter is proportional to the cube of its impeller speed. In case of an electrical transmission, the peripheral speed of the generator -armature becomes a limitation for choosing the engine speed. Adhesion Coefficient of starting adhesion is comparatively higher owing to coupled axles of the diesel hydraulic locomotives as against the independently driven axle hung traction motors of the diesel electric locomotives. Part load efficiency The part load efficiency of the hydraulic transmission, whether using a converter, or using a coupling, is comparatively higher at lower vehicle speed than electric transmission, where generator and traction motor efficiency remain more or less constant, and independent of horse power transmitted. This advantage is predominant especially in shunting locomotives, where the diesel engine operates most of the time at part notches at low vehicle speeds.

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10. PRINCIPLES OF ELECTRIC TRANSMISSION

GENERAL Most of the Diesel Electric Locomotives serving in Indian Railways are single engined with one D.C. self ventilated, separately excited, single bearing main generator. This supplies power to six nose suspended, force ventilated, series wound D.C. motors connected in three series pairs. Power for electrically driven auxiliaries and control circuits is obtained from a self-excited, self ventilated auxiliary generator mounted on the end of main generator. This also supplies the battery charging current. Output of auxiliary generator is maintained constant at different speed by a voltage regulator. It also takes care about the limit of current going out to avoid damage to the generator. 8 lead acid batteries in series with four cells per battery, being provided for starting the engine by motoring the main generator, and to supply all the control circuits and the locomotive lighting. The locomotive is provided with electrical end jumper cables to enable it to work in multiple with a number of other locomotives.

POWER CIRCUITS The main generator is separately excited with or without a differential series field to give the required characteristic form. Each traction motor has separate reversing switch contacts for reversing the field current, and field diverting arrangements. Wheel slip sensing arrangement is provided between all three motor pairs using three relays. Ground fault sensing arrangement is provided in the generator circuit using a relay, to avoid damage to the electrical machines and circuits. FIELD WEAKENING AND TRANSITION As has already been mentioned the series type dc motors are used as traction motors. This type of motor draws a high current at low speed and a low current at high speed. If its load is heavy, it runs at low speed; if light, it runs at high speed. The generator delivers electrical power. When the load resistance is low, the amperes are high and when resistance is high, the amperes are low. To achieve maximum fuel efficiency, the engine should be loaded in such a way so that it gives constant horsepower for a particular speed setting, and accordingly the fuel for each throttle setting is scheduled. So to get most of the engine, one should stay on the constant horse power curve. As the traction motors are the load, and current changes with change in speed of the motor, the voltage also changes accordingly power being constant. When the train accelerates, i.e. the motor speed increases, the voltage output of main generator goes on increasing and at a particular train speed, generator voltage reaches its limit and horse power is reduced by the excitation system. With this situation more train speed can't be achieved. To get higher train speed, either the motor fields are weakened or the motors are rearranged in the circuit. This increases traction motor current. With higher current now the motor speed starts increasing. Normally the motor field is made weak, connecting resistor in parallel to the field, and rearrangement is done by changing the motors from series-parallel to parallel grouping. An automatic regulator, on getting signal about locomotive speed does the change in motor circuit.

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11. SUMMARY In a diesel engine an intermediate device is used to transmit the power of the engine upto wheels. This intermediate device is called transmission. It is essential to have a transmission in a diesel engine because of certain inherent limitations in it. An ideal transmission has to fulfil many a requirements: like, torque multiplication during starting, automatic picking up of speed with the submission of torque just after starting, modifying torque and speed characteristics automatically as per load and road condition and also to facilitate reversing facility to the train etc. There are various modes of transmission like mechanical, electrical, hydraulic etc. Amongst them suitability of transmission is based on the requirement of traction and their operating efficiency. Overall transmission efficiency, percentage utilisation of rail wheel adhesion and power to weight ratio should be given due consideration while selecting the type of transmission for a locomotive In consideration to the above facts, electrical transmission is widely used in the railways. But in shunting locomotives hydraulic transmission is also used, because of its relative merit over electric transmission on the areas like, - part load efficiency, coefficient of starting adhesion and power to weight ratio being high. Hydraulic transmission works on hydrodynamic principle. Previously, Suri transmissions were in use. It was a hydro- mechanical transmission, in which a reversing gearbox was in use to reverse the direction of movement of the locomotive. But in recent days, Voith transmission, the hydraulic transmission itself takes care of reversing facility. It is a superior version of hydraulic transmission over Suri Transmission. 12. SELF ASSESSMENT

1. Why transmission is necessary for a diesel engine? 2. What should be the duties of an ideal transmission? 3. What do you understand by Tractive Effort? What is its relation with rail wheel

adhesion? 4. Explain the working of fluid coupling and torque converter in hydrodynamic

transmission? 5. Based on what merits hydrodynamic transmission is applied in some shunting

locomotives? 6. Explain the principle of working of an electrical transmission?

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UNIT 2 D.C. MACHINES

DC machines have been widely used in Diesel Electric locomotives for their operating characteristics. These machines require frequent maintenance and attention to keep them in healthy state. It is important and necessary to be well informed about the construction, operating principle and probable areas of defects for a maintenance man so that they are confidant in maintaining these machines regularly. This block has been divided in five units to deal with the generator, motor, commutation, carbon brushes and flashover separately. The DC Generator has been discussed in Unit 2.1, DC Motor in Unit 2.2, commutation in Unit 2.3, carbon brush in Unit 2.4 and flashover in Unit2.5.

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UNIT 2 D.C. MACHINES

UNIT 2.1 DC Generator UNIT 2.2 DC Motor UNIT 2.3 Commutation UNIT 2.4 Carbon brushes UNIT 2.5 Flashover

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___________________________________________________________________________

UNIT 2.1 DC GENERATOR OBJECTIVES • After completing this unit, you will be able to: • understand the working principle of DC generator • appreciate the construction of DC generator • define the EMF equation of a generator • define and appreciate commutation of DC machine • identify types of DC generators and their characteristics STRUCTURE 1. Introduction 2. Constructional Details of DC generators

2.1 Yoke 2.2 Pole core or pole shoes 2.3 Field coils 2.4 Armature core 2.5 Armature winding 2.5.1 Lap winding 2.5.2 Wave winding 2.6 Commutator 2.7 Brushes and bearings

3. EMF equation 4. Principle of operation 5. Commutation 6. Types of DC generators 7. Generator characteristic

7,1 Open Circuit or no load Characteristic 7.2 External or load Characteristic 7.3 Internal or Total characteris tic 7.4 Critical Resistance

8. Summary 9. Self-assessment exercises

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1. INTRODUCTION A machine, which converts mechanical energy into electrical energy, is called a Generator. This energy conversion is based on the dynamically induced emf. According to the Faraday's law of electromagnetic Induction, an induced emf is produced in the conductor which cuts the magnetic flux. This emf causes a current to flow in the conductor if its circuit is closed. Hence the basic essentials for an electrical generator are: - (i) Magnetic field; (ii) Conductor or conductors and; (iii) Relative motion between magnetic field and conductors. 2. CONSTRUCTIONAL DETAILS OF A DC GENERATOR Here we are dealing with a DC generator. But there is a good similarity with a DC motor also as far as construction is concerned. The following are the main parts of a DC generator: • Yoke • Pole core or pole shoes • Field coils • Armature core • Armature winding • Commutator • Brushes and bearings 2.1 YOKE OR MAGNET FRAME This is the outer part of the DC generator. It provides the mechanical supports for the poles and acts as a protecting cover for the whole machine. It carries the magnetic flux produced by the poles. Yokes are made out of cast iron or cast steel. The modern process of forming the yoke consists of rolling a steel slab round a cylindrical mandrel and then welding it at the bottom. The feet and the terminal box etc. are welded to the frame afterwards. Such yokes possess sufficient mechanical strength and have high permeability. 2.2 POLE CORE OR POLE SHOES The field magnet consists of pole cores and pole shoes. The pole shoes serve two purposes. (i) They spread out the flux in the air gap and also being the larger cross section reduced the reluctance of the magnetic path. (ii) They support the exciting coils. 2.3 FIELD COILS The field coils or pole coils, which consist of copper wire, are former-wound for the current dimension. Then the former is removed and the wound coil is put into place over the core.

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2.4 THE ARMATURE CORE It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. Its most important function is to provide a path of very low reluctance to the flux through the armature from North Pole to South Pole. It is laminated to reduce the loss due to eddy currents. Thinner the lamination, greater will be resistance offered to the induced emf and hence smaller the current. And thus the loss is also small. 2.5 ARMATURE WINDINGS It is generally former wound. These are first wound in the form of flat rectangular coils and then are pulled into their proper shape in a coil puller. Two types of windings are mainly used - namely lap winding & Wave winding. 2.5.1 Lap winding In lap winding finish end of one coil is connected to a commutator segment and to the start end of the adjacent coil situated under the same pole and similarly all coils are connected. Since the successive coils overlap each other and hence the name (Ref. fig.1). 2.5.2 Wave winding It is also called as series winding. In this winding, the coil side is not connected back but progresses forward to another coil sides. In this way the winding progresses, passing successively every N pole and S pole till it returns to coil side from where it was started. As the winding shape is wavy, the winding is, therefore, called wave winding (Ref. fig.2). 2.6 COMMUTATOR The commutator, whose function is to facilitate the collection of current from the armature, is cylindrical in structure, built up of segments of high conductivity, hard drawn copper insulated from one another by mica sheets. It also converts alternating current into unidirectional current (DC). 2.7 BRUSHES&BEARINGS The function of brushes is to collect current from the commutator. These are rectangular in shape, made of carbon normally. These brushes are housed in brush holder usually of the box type variety. Generally ball bearings are employed due to their reliability but for heavy duty, roller bearings are also used. The balls and rollers are generally packed in hard oil for quieter operation. Sleeve bearings are also used where low wear is required. 3. E.M.F. EQUATION OF A GENERATOR Generated E.M.F, E = AZNP 60φ Volts Where, P = No. of poles. φ = Flux per pole in Wb (Weber) Z =Total nos. of conductors.

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N = r.p.m. A = nos. of parallel paths in Armature. (A = 2 for wave winding & A = P for lap winding) 4. PRINCIPLE OF OPERATION The principle of electro-magnetic induction, discovered by Faraday, states that when a conductor is moved across a magnetic field so as to cut the lines of force, electro-motive force or E.M.F. measured in volts, is generated across the conductor. Thus, if an open loop or wire is made to rotate between the poles of a permanent magnet, as shown in fig.3 and fig.4, there will be a tendency for electricity to flow through the wire. The magnitude of this EMF or voltage, depends on the speed of rotation, and on the strength of the magnet, i.e. "the magnetic flux". The direction of voltage generated in a conductor depends on the direction of the motion of the conductor across a magnetic field and the direction of the field itself. Since the magnet has two poles, two conductors can be connected together in series to form a loop and their voltages will be additive. Several loops can be joined together to form a coil having a number of turns, all the voltages being added together. For each half revolution, embracing one complete pole, the voltage will start from zero, rise to a maximum and fall to zero again. For the remaining half revolution a similar series of events will occur, but the direction of the voltage is reversed. This very simple form of alternating current (A.C.) generator is shown in fig.3. To change this primitive machine into a direct current (D.C. generator) fig.4, it is necessary to introduce a commutator. In order to attain constancy of direction, the ends of the loop, instead of being connected to slip rings, are connected to a split metal ring, the two halves being insulated from each other. By placing the collecting brushes (C & D) on the commutator in such a position that the voltage induced in the loop is zero when the brushes change from one segment to the other voltage at the brushes will be uniform in direction, although it will still be alternating, commutator simply alters the connection of the loop to the external circuit at the instant when the induced electromotive force changes in direction. If the loop of wire is closed by connecting the brushes (C&D) to an external resistance(R), which represents the 'load' imposed on the machine, electric current will flow through the loop and the resistance (R). In practice, the amount of current, which flows, is measured in amperes (amps). The magnitude of the current, which will flow through the circuit, depends on the voltage generated and on the value of the joint resistance of the loop of wire and the external resistance. Voltage, which the machine is capable of developing at the certain speed and with a magnet of the given strength, the current flow, measured in volts, divided by the total resistance of the circuit, measured in ohms. If the loop of wire be rotated in one direction, the current will flow in the wire under the south pole (S), in the direction of the arrow, that is, away from the brush (C), and then in the wire under the north pole (N) towards the brush (D). From the brush (D), it will go to the external circuit and then back to the brush (C); thus completing the electric circuit. After rotating such that the position of the segments is reversed, it will be noticed that the picture remains identical and therefore the current flow will be in the same direction.

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Although the primitive direct current generator, so far described, produces a uni-directional current flow, it is obvious that for each revolution of the coil the induced current will start from zero value, rise to a maximum value, fall to zero then rise to a maximum value again and finish at the zero point from which it started. However, by increasing the number of coils and spreading them out evenly, the flow of current can be made very nearly constant. This also means that there would be an increased number of segments in the commutator in proportion to the increased number of coils. In practice, a direct current generator has many coils consisting of insulated copper wire or strip, and in order to concentrate the magnetic flux where it is required, they are embedded in slots in a soft-iron laminated cylinder. This assembly is called the armature. The permanent magnet of the original example is replaced by an electro-magnet having many poles wound with insulated copper wire; these are field coils and are referred to as the field system. The field strength, or excitation, depends upon the number of turns of wire on each pole and on the magnitude of current flowing through the wire. From this it can be seen that there are two ready means of regulating the output of the generator; one by varying the speed of rotation of the armature and the other by altering the magnetic strength of the field system. The variation of speed of rotation is readily obtained by varying the governor setting on the diesel engine, which drives the armature, and by inserting variable resistance in the field system, the amount of current flowing through the coils of the Electro-magnets can be varied. In a diesel locomotive, the driver of the locomotive makes these adjustments, as required, by moving his control handle, thereby simultaneously affecting engine speed and generator excitation. The main generator frame is coupled directly to the diesel engine flywheel casing. The armature is of the single bearing type, that is to say, one end of the shaft is coupled to the engine flywheel, and the other end is supported in a roller bearing, housed in an end plate bolted to the generator frame. The main generator is self ventilated, having its own fan which draws air through the machine so as to cool the windings and maintain them at a safe working temperature. 5. COMMUTATION We have seen that current induced in the armature conductors of a DC generator is alternating and to make it unidirectional in the external circuit we use commutator. Also the flow of direction of current in the conductor envisages as the conductor's position changes from one pole to another i.e. as conductors pass out of the influence of a `N' pole and other that of a `S' pole the current in them is reversed. This reversal of current takes place along the Magnetic Neutral Axis (MNA). Thus, commutation is a group of phenomena related to current reversal in the conductors of an armature winding when they place through the M.N.A. where they are short-circuited by the brushes placed on the commutator. Commutation is said to be good if there is no sparking between the brushes and commutator when current reversal in the coil section takes place. Contrary to that, it is said to be poor if there is sparking at the brushes during current reversal in the coil section.

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6. TYPES OF GENERATORS In accordance with the method of excitation D.C. generators are divided into two categories - 1. Separately excited Generator 2. Self excited generators. Since the separately excited generators have limited application we look forward for self-excited generators. Generators with self-excitation can be divided according to the way of the field winding connection into following categories- 1. Shunt-excited generators 2. Series excited generators and, 3. Compound-wound generators 7. CHARACTERISTICS OF GENERATOR There are 3 important characteristics of a DC generator. 1. Open circuit characteristic (O.C.C.) 2. External characteristic or load characteristics 3. Internal characteristic or total characteristic

7.1. O.C.C. or NOLOAD CHARACTERISTIC It represents the relation between generated E.M.F. and field current. If it is practically the same for all types of generator whether they are self-excited or separately excited. 7.2. EXTERNAL OR LOAD CHARACTERISTIC It is a curve representing the relation between the terminal voltage V and the load current IL. 7.3. INTERNAL OR TOTAL CHARACTERISTIC It is a curve, which represents the relation between the generated EMF.(Eg.) and armature current Ia. 7.4. CRITICAL RESISTANCE The value of that resistance due to which field resistance line becomes tangent to the O.C.C. curve is called critical resistance.

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8. SUMMARY Necessary informations regarding operating principle, constructions, characteristic of DC generators have been given in this unit. These informations will help in maintaining the machines to ensure reliability and their trouble free functioning. Some informations have been given about commutation of DC machines, which would prove to be important to understand behavior of DC machines. Sketches and diagrams have been included in this unit to understand the block with more practical and systematic approach. 9. SELF-ASSESSMENT EXERCISES

1. Name different components of a dc generator and describe their functions. 2. State the EMF equation of a generator and mention detail names of different symbols. 3. Explain the commutation process of a dc machine with necessary diagrams.

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UNIT 2.2 DC MOTORS OBJECTIVES After completion of this unit, you should be able to: • understand the working principle of DC motor • appreciate the construction of DC motor • define the speed equation • understand characteristics of DC motors • appreciate brush grades and their selection criteria STRUCTURE 1. Introduction 2. DC motor and its principle of operation 3. Back emf. 4. Types of DC motors 5. Speed equation 6. Speed control 7. Characteristic of DC motors 8. Constructional details of DC motor 9. Heating and cooling 10. Rating of DC motor 11. Summary 12. Self-assessment exercises

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1. INTRODUCTION A motor is a mechanism by which electrical energy is converted into mechanical energy. Its operating principle is the reverse of a DC generator. When a coil, carrying current, is placed in a magnetic field, it experiences forces, which turn it about in a direction perpendicular to both the field and current. Thus the motor armature placed inside the magnetic field gets motion, converting electrical energy to mechanical. 2. DC MOTORS – Principle of operation A motor is a mechanism by which electrical energy is converted into mechanical energy. Both in principle and design, a DC motor is the reverse of a DC generator. A steady current is passed through the armature coil from the commutator and the brushes are so arranged as to reverse the current every half revolution. When a coil, carrying a current, is placed in a magnetic field, it experiences forces, which turn it about in a direction perpendicular to both the field and the current. Due to the rotating torque the motion of rotation will not be continuous, unless the direction of the current is reversed each half revolution with the help of a split ring commutator (in a 2-pole machine). The electric motor is fundamentally similar to the primitive form of D.C. generator described earlier and is based on the fact that, if a "loop of wire". If it is supplied, through its commutator, with electric current from a battery or any other source of direct current (D.C.) supply, the loop will rotate. If the brushes of the machine were connected to the terminals of a primary cell, instead of being connected to load R, the "loop of wire "would rotate. A greatly enhanced performance would be obtained by having an iron core on this loop, a further improvement would be to have many loops, another to have increased pole area, and a still further improvement would be obtained by having electromagnets instead of permanent magnets. When used for traction, the direct current electric motor is usually of the series wound type, that is, the current, which passes through the armature also, passes through the field coils. The reason for this is that a motor having this particular type of winding has characteristics eminently desirable for traction work, its torque being proportional to the current flow, multiplied by the magnetic strength of the field system. The series wound motor is capable; therefore, of producing a high torque when the vehicle is started, and also has the advantage that as the load increases its speed drops. The direct current traction motor can be considered as having the following major parts; 1. The electro-magnetic system consisting of the frame with pole pieces, the field windings

and brush gear. 2. The reduction gears between the armature shaft and the road wheels, together with the gear

case, which protects the gear wheels and holds the gear lubricant. 3. The axle bearing where the traction motor frame rests on the axle of the vehicle, this arrangement maintains a constant. 4. The nose suspension arrangement prevents the frame of the motor from rotating round the axle of the vehicle, The nose is spring borne on a bogie cross member.

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3. BACK EMF Due to the rotation of the armature coil (i.e. a conductor) in the magnetic field, the motor works as a DC generator and induced e.m.f acts in the circuit, which opposes the current. This induced e.m.f is called back e.m.f. 4. TYPES OF D.C.MOTORS Like DC generators, DC motors are also of 3 types- (i) Series wound motor, (ii) Shunt wound motor and (iii) Compound wound motor. 5. SPEED EQUATION We know that back e.m.f. is produced by the generator action of the motor

Hence back e.m.f. E = AZNP

60φ , where symbols have their usual meanings.

Let V be the applied voltage and Ia and Ra is the armature circuit current and resistance respectively. Then E = aa RIV −

aa RIVAZNP −=60φ

Or N = ZPARIV aa

φ60)( ×−

Or N φ)( aa RIV −∝ since P Z & A are constants. for a particular motor.

Or N φV∝ , Since Ia Ra drop is very small as compared to the applied voltage V.

Or N φ/1∝ , if applied voltage V is constant. Hence speed is inversely proportional to flux / per pole if the applied voltage is constant. 6. SPEED CONTROL OF DC MOTOR We know that, N = (V-Ia Ra) φ/ From this formula it follows that the speed of a D.C. motor can be regulated by: (i) varying the supply mains voltage V (ii) Varying the voltage drop in the armature circuit Ia Ra (iii) Varying the field flux Methods (ii) & (iii) are possible in any installation with constant supply voltage. But the first method is possible only in special installation; that permits the control of the supply voltage.

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7. CHARACTERISICS OF D.C.MOTORS There are three important characteristics of a D.C motor, which are given below: - (Ref. Attached figures) (i) Torque - Armature current characteristics This shows the relation between mechanical torque developed and armature current. (ii) Speed- Armature current characteristics As the name indicates, it relates speed with armature current. (iii) Speed - Torque characteristics The characteristics curve gives the relation between speed and torque of a DC motor. 8. CONSTRUCTIONAL DETAILS OF DC MOTOR 8.1 INTER POLES In addition to the main field coils of a motor being in series with the armature, there are also the coils of a smaller system of field magnets known as inter-poles. On generators with separately excited main fields, the inter-pole coils are in series with the armature. The inter-poles are smaller than the main poles of either a generator or motor, but are the same length and positioned alternatively with the main poles. In a generator the polarity of an inter-pole is the same as the main pole ahead of it according to the rotational direction of the armature. The polarity of an inter-pole in a motor is the same as the main pole proceeding it. An electrical machine with no inter-poles would have some magnetically neutral regions between its pole-pieces. When a coil of the armature reaches a position during its rotation in the neutral region, its connections are short-circuited with the connection of the armature coil in advance, because in this position the commutator brushes will be in contact with both of their corresponding commutator segments. The purpose of the inter-poles, being situated in the neutral regions, is to induce a current in the short-circuited armature windings, which flows in the same direction as the current, which will flow when it has left the neutral region. The use of inter-poles also serves to prevent the distortion of the main field of the generator by the reaction of the armature field, and thereby prevents the induction of Electro-motive forces into coil sides, which are being short- circuited by the brushes. In small machines the need for inter-poles is not important but on large generators and motors the net effect of the inter-poles is to improve the commutation. Ideally there should be no sparking of the brushes on the commutator surface, although this is often difficult to achieve in practice.

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9. HEATING AND COOLING Every electrical machine is a power (or energy) conversion device. During these power conversion some of the energy is wasted. In electrical machines the loss in energy occurs in electrical circuits and in portions of magnetic circuits also. There are also frictional losses in the dynamic parts of the machines. These losses are converted in the form of heat energy, which increases, or tends to increase the temperature of iron and copper above that of the ambient temperature, which in turn effects the winding insulation. In addition to the effect it has on the insulation, an excessive temperature rise may also adversely influence the mechanical operating conditions of a given machine part. Thus, for example the original dimension of the commutator may change. Solder between the commutator and windings may get washed out. So to avoid all these, it is very essential to provide a cooling system on machines. In most cases, the cooling is done by air currents. The cooling of machines by air streams is called ventilation. The ventilation employed depends on the environmental conditions of the place where the machine is to operate. According to the method of ventilation employed, the following types of machines are distinguished: - (i) Machines with natural ventilation. (ii) Machines with internal self-ventilation. (iii) Machines with external self-ventilation. (iv) Machines with independent ventilation. Enclosures have got the direct bearing with the ventilation. The following are the main types of enclosures: - (i) Open pedestal Rotor and stator windings are in free contact with the surroundings. (ii) Open end Bracket Rotors and stator windings are in contact with surrounding through openings. (iii) Protected (formerly called semi-enclosed) Openings in the frame are protected with wire, perforated covers etc. (iv) Drip proof Opening so constructed that no solid or liquid particles falling at an angle greater than 150 will enter the machine. (v) Splash proof Similar to drip proof but the angle of approach is 100O from vertical. (vi) Duct or pipe ventilated Air for ventilation enters and emerges through a pipe through the openings. (vii) Totally enclosed Exchange of air throughout side and inside of the machine is prohibited. (viii) Water proof The machine is totally enclosed so as to exclude water applied as a stream as specified. (ix) Flame proof It is designed normally for mines. (x) Resistant Machine is so constructed, that it will not be harmed easily by moisture fume, alkali etc.

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(XI) Submersible So constructed that it will work when submerged in water under specified condition of pressure and time. 10. RATINGS There are three types of ratings as specified. (i) Continuous Rating: This is an output, which a machine delivers continuously without exceeding the permissible temperature. It can deliver 25% overload for two hours. (ii)Continuous maximum Rating: This is similar to continuous rating but not allowing overload. (iii) Short time ratings: This is an output which a machine can deliver for a specified period (say 1 hr 1/2 hr, 1/4 hr etc) without exceeding the maximum temperature rise limit. 11. SUMMARY Informations regarding operating principle, construction, characteristic and selection of carbon brushes for DC motors have been given in this unit. These informations will help in maintaining the motors to ensure reliability and their trouble free functioning. Sketches and diagrams have been included in this unit to understand the unit with more practical and systematic approach. 13. SELF-ASSESSMENT EXERCISES

1. Describe and mention the speed equation of a dc motor. 2. What are the different types of cooling arrangements of DC motors? 3. What do you mean by rating of a motor? What are the types of ratings?

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UNIT 2.3 COMMUTATION OBJECTIVES After completion of this unit you will be able to understand: • cause of sparking in DC machines • reactance voltage • emf equation • contribution of commutating poles • reason for use of high resistance brushes STRUCTURE 1. Introduction 2. Cause of sparking 3. Reactance voltage 4. Emf commutation 5. Commutating poles 6. Use of high resistance brush 7. Summary 8. Self Assessment Exercise

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1. INTRODUCTION Owing to the thinness of the insulation between the commutator segments, it is obvious that a brush may be in contact with two or more segments at the same instant. Hence, if an armature coil has its ends connected to two of these segments, the coil will be short-circuited by the brush, and as the armature rotates, each coil will, of necessity, be short-circuited. This period of short-circuit is the period during which the current is being delivered from the commutator segments concerned, to the brush, and it is, therefore, called the period of commutation. By commutation we mean the changes that take place in an armature coil during the period that it is short-circuited by a brush. These changes are illustrated in figure 1, the winding being represented as a ring winding for simplicity. Currents of magnitude I amp are flowing to the brush through the armature from the right and left, the total current delivered by the brush, therefore, being 2I amps. In the first diagram the coil B is on the point of being short-circuited, and it is carrying, in a direction from left to right, half the current delivered by the armature to the brush. The second diagram shows the same coil in the middle of the short circuit period, from which it will be seen that it is possible for the current I flowing from right and left to reach the brush without passing through this coil. In the third diagram, the same coil B is shown immediately after short circuit, and in this position it is, or should be, carrying the full current in a direction from right to left. We thus see that during the short circuit period, the current in the short-circuited coil must be reversed and brought up to its full value in the reversed direction. 2. CAUSE OF SPARKING If the current in coil B has not attained its full value in the position shown in the third diagram, then since the coil C is carrying the full current, and this current must reach the brush, the difference between the currents carried by coil B & C has to jump from the commutator bar to the brush in the form of a spark. Thus suppose that the armature conductors are carrying a current of 50 amps, but the current in coil B has only reached 40 amps, then by the end of short-circuit, the difference of 10 amps will have to jump to the brush in the form of a spark. The energy in these sparks may be very high, the result being a very high temperature rise of the commutator, and pitting and roughening of the segments in a very short time. The cause of sparking at the commutator is, therefore, the failure of the current in the short-circuited coil to reach the full value in the reversed direction by the end of short-circuit. Suppose the current in each conductor is I amp, then what is required is that the current shall change from +I to -I during the time of short-circuit. This is represented in fig.2 in the form of a graph. "Curve I" shows what happened when the current does not reach the full value; "curve II" shows the ideal, a gradual change of current from +I to -I; "curve III" shows what may happen if one of the remedies for under commutation in overdone and the current in the reversed direction is forced up to a value greater than I. 3. REACTANCE VOLTAGE The difficulty experienced by the current in attaining the full value in the reversed direction by the end of short-circuit, is due to the fact that the current in the short-circuited coil is

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changing. When the coil is carrying a steady current, this current produces a magnetic field of constant strength, and the number of lines of force linking with, or threading, the coil is constant. Under these conditions there is no change in number of lines of force and consequently there is no e.m.f. induced in the coil other than that produced by the rotation of the coil in the main field. But when the current changes in magnitude, or direction, or both, then there is a change in the number of lines of force linking with the coil, and in consequence an e.m.f. is induced. The production of this e.m.f is thus exactly similar to the production of an e.m.f in a coil by thrusting a magnet in to it, the only difference being that the necessary change in the number of lines of force linking with the coil is produced, not by the introduction of a magnet, but by a change in the current carried by the coil. Like all induced e.m.f., this induced e.m.f. is a back e.m.f., it tries to stop the change of current. Now the direction of current is from left to right in the first diagram of fig.1, and right to left in the third, and so the induced voltage acts in the original direction of the current, thereby preventing it from attaining its full value in the reversed direction by the end of short-circuit. This induced voltage is called the reactance voltage. 4. E.M.F. COMMUTATION The cause of difficult commutation is the reactance voltage, and follows that if this voltage could be neutralized, spark-less commutation would be achieved. In order to neutralize the reactance voltage it is necessary to induce in the short-circuited coils another e.m.f which is opposite in direction to the reactance voltage, and, therefore, in same direction as the current when reversed. The old method of achieving this consisted in rocking the brushes forward until they were some way ahead of the magnetic neutral plane. The result of this was that the short-circuited coils were located ahead of the neutral plane, and were therefore, under the influence of the next pole further ahead. This pole induced an e.m.f in them in the required direction, because after commutation they would be entirely under its influence until they reached the next brush. There are two very serious objections to this method. The first is that with a changing load the position of the magnetic neutral plane is continually changing, thus necessitating the continual adjustment of the brush position. With modern dynamos it is invariably specified that they shall operate spark-less at any load between zero and full-load with a fixed brush position. The second objection is that the magnetic field which induces the commutating e.m.f. is the fringe of flux under the leading pole tip, and we have seen in a previous lesson that this flux is gradually wiped out as the load increases. With heavy leads it is, therefore, necessary to give the brushes a very large load, unless some other method of securing spark-less commutation is adopted. 5. COMMUTATING POLES In order that a commutating e.m.f may be induced in the short-circuited coils it is necessary that these coils shall be situated in a magnetic field, called the commutating field. Instead of making use of the fringe of flux under the leading tips of the main poles, the modern method is to employ separate poles called commutating poles, or interpoles. These are narrow poles placed mid-way between the main poles and excited, so that each one has the same polarity as the next main pole further ahead, thereby giving a commutating field of the right kind. This is illustrated in fig.4. By the use of these poles the necessity for rocking the brushes forward with increasing load is done away with and, as a result, the machine can be worked with a fixed brush position. Now the reactance voltage is proportional to the change of

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current, which takes place in the short-circuited coil, and this in turn is proportional to the current delivered by the armature. The commutating e.m.f and the commutation magnetic field produced by the interpoles must therefore be proportional to the armature current. For this reason, the exciting current through the interpole windings must not be kept constant but must vary with the load. This is achieved by series excitation of the interpoles; that is, their exciting coils are connected in series with the armature, thereby carrying a current equal to the armature current. For small machines the exciting coils consist of insulated cable capable of carrying the full armature current, but with very large machines delivering very large currents the exciting coils consist of very heavy copper strips wound on edge. An interpole of this type is shown in fig.3. In extreme cases the coil may consist of a heavy copper casting. The next illustration (fig.5) shows a complete stator with main and commutating poles. It will be readily understood that for a given armature current there is proper value of the commutating field, and that it is possible for this field to be too strong. In such a case the reversed current in the short-circuited coil is forced to too high a value by the end of short-circuit, and sparking at the commutator takes place in the reversed direction. This is called over-commutation and is represented graphically by "curve III" in fig.2. 6. USE OF HIGH RESISTANCE BRUSHES A second method of obtaining good commutation is to use brushes having a high contact resistance when pressing on the commutator segment, since brushes of this kind help to force the current coming up to the brush from the leading side of the armature, through the short-circuited armature coils. This can be understood from Fig.6 in which the winding is again represented as a ring winding for simplicity. The total current collected by the brush from the armature is represented as 2I, and one-half of this, namely I amp comes from the left and I amp from the right. The current I coming from the left reaches the brush via commutator segment a and it has to traverse the contact resistance r1 between this segment and the brush. It has also an alternative path to the brush via the short-circuited coil and across the segment b, the resistance in this path being the contact resistance r2 between segment b and the brush. At the commencement of short-circuit the brush will be mainly in contact with segment b and will only just touch segment a, with the result that the resistance r1 will be very high (because of the very small area of contact) while r2 will be low. A large portion of the current coming from the left will, therefore, at this instant, take the lower resistance path through the short-circuited coil. As the commutator moves past the brush, the area of contact with segment a gradually increases, while that with segment b decreases and therefore, contact resistance r1 gradually decreases while r2 increases. There is thus a gradual tendency for that portion of the current I coming from the left and flowing through the short-circuited coil, to leave the coil and take the direct path to the brush across the segment a. This is as it should be, because the current coming from the left is not in the reversed direction and it is necessary to eliminate it from the short-circuited coil as quickly as possible. Now consider the current I coming up to the brush from the right. There are also two parallel paths open to this current as soon as it reaches the commutator segment b. The first is straight across the segment b to the brush and the second is round the short-circuited coil and then across the segment a. With brushes having a low contact resistance with the commutator there is no inducement for the current to take this second path. With carbon brushes, which have a high contact resistance, more and more of the current flowing to the brush from the right hand will be shunted round the short-circuited coil as the segment b passes the brush, because, as we have seen, the contact resistance r2 is gradually increasing, where-as the resistance r1 is gradually

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decreasing. Finally when the period of short circuit is almost ended, the brush will only just be touching segment b and r2 will be very high, becoming infinitely great when the segment has left the brush. The whole of the current I from the right will then be flowing through the short-circuited coil. Furthermore, this current is in the necessary reversed direction. For the above reasons carbon brushes have almost entirely replaced the copper brushes which used to be used with older machines. The disadvantage of carbon brushes is that they can only be worked at a current density of about 40 to 50 amperes per sq. inch as compared with 150 to 200 for copper brushes. This necessitates a larger area of contact at the brush face and, therefore, a longer commutator. The properties of a few grades of brush are shown in the following table: - BRUSH TYPE MAX. CURRENT

DENSITY

(amp/in.2)

MAX.CONTACT RESISTANCE

(ohms/in.2)

PRESSURE ON COMMUTATOR

(lb/in2)

Copper Ordinary. 200 0.003 1.5

Carbon 40 0.04 2.0

Electro- graphite 60 0.02 2.0 For the same area of brush, (Contact resistance of carbon brush) / (Contact resistance of copper brush)= 003.0

04.0 =13

But for the same current collected, the contact area of the carbon brush must be 200/40 = 5 times the area of the copper brush, because of its smaller working current density. Hence, since the contact resistance is inversely proportional to the contact area, we have, for the same current collected, (Contact resistance of carbon brush)/ (Contact resistance of copper brush)=13/5=2.6 This is sufficient to give improved commutation. If a machine gives difficulty with commutation, it can often be cured by fitting new brushes having a higher contact resistance than the old ones. Brushes of high resistance often have a high coefficient of friction, and if such a change is made it is necessary to make sure that the armature temperature rise does not become too much high because of the increased brush friction. The specification for machines normally limits the temperature rise of the commutator to 45OC.

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7. SUMMARY Information has been given about commutation of DC machines, use of high contact resistance type carbon brushes, cause of sparking and how to avoid it, which would prove to be important to understand behavior of DC machines. The contribution of commutating poles to improve commutation has been described so that their importance is appreciated. 8. SELF-ASSESSMENT EXERCISES 1. Justify the use of high contact resistance type carbon brush in traction machines for

improving commutation. 2. What do you mean by emf commutation? How does it made proper by using

commutating poles? 3. Why an Electro-graphite carbon brush is used in traction machines? Justify.

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UNIT 2.4 CARBON BRUSHES OBJECTIVES On completion of this unit, you should be able to understand: • Brush material • Brush angles • Types of brushes • Electrical characteristics of brushes • Selection of brush grades • Service performance of brushes • Analysis of commutation problems • Technical data of brushes • Carbon brushes for BHEL machines STRUCTURE 1. Introduction 2. Brush material 3. Brush angles 4. Types of brushes 5. Electrical characteristics 6. Selection of brush grades 7. Service performance 8. Analysis of commutation problems 9. Technical data 10. Carbon brushes for BHEL machines

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1. INTRODUCTION Brushes provide connection between rotating armatures and external circuitry, and play a major role in satisfactory commutation of DC machines. During commutation, in the armature coil under short circuit by the brush, the current reverses from +I to -I. Since the change of current takes place in a very short period, an emf is induced in the armature coil undergoing commutation. Commutating poles are provided to nullify this emf by creating an equal and opposite voltage in the same coil. However due to design limitations/manufacturing tolerances, it is not possible to totally balance out the induced emf (known as reactance voltage), and therefore the residual voltage in the coil causes a circulation of current, which appears in the form of sparking under the brushes. As the process of commutation became more apparent, it was realised that a brush of comparatively higher resistance could materially assist the commutation. In the early experimentally period, before 1880, when DC motors were under development, copper brushes, in the form of brush and not as a solid block, were used. It was from the early period that the term brush emanated, and is still continuing. Copper brushes used to cause high commutator wear, heavy sparking, and even welding into the commutator surface. these problems and the fact that higher resistance of the brush assists commutation, led to the use of the carbon as a brush material. The other reason for using carbon for brushes on electrical machines is that the wear of the carbon brush and electrical erosion, considerably exceeds that of commutator resulting in higher commutator life. Charles Van Depoele, one of the early traction pioneers in America, was the first to try brushes made of carbon on traction motors after successful trials in 1884. 2. BRUSH MATERIALS Carbon is used for the brush in the following forms: 1. Natural Graphite 2. Hard Carbon 3. Electro-graphite Carbon 4. Metalized Carbons and Graphite These grades of carbon are obtained by varying the combination of raw materials, and the processes followed for mixing them. The following chart shows the cycle used for production of non-metallic carbon brush material. flow sheet for the production of non-metallic brush material A few examples of processes and material variants and their usual effect on the performance are given below: Raw materials Graphite - decrease friction Copper, Silver - decrease contact drop Pressing Pressing at higher pressures reduce the porosity, give greater strength, increased brush life

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and narrower blackened results. Graphitisation Reduces the hardness, friction and specific resistance. Impregnation • Oils and waxes generally improve friction, stability and increase contact drop slightly. • Resins strengthen brush material so that it becomes more resistant to breaking and

chipping. • PTFE reduces friction under humid conditions. • Barium floride reduces friction and wear at very low humidity. In view of the above an exceedingly complex multivariant relationship exists between the various aspects of performance requirements, specifications of raw materials and processing. Therefore, stability of a particular make and grade of brushes can only be established after extensive tests and trials. For traction machines, the Electro-graphite grades are most suitably used. Technical data on some of the most commonly used brush grades for traction machines is given in annexure. 3. BRUSH ANGLES Brushes are often defined by the methods of applying them to the commutator. They are three main classes: 1. Reaction 2. Trailing 3. Radial (No. 1 & 2 are used only on non-reversing machines.) Reaction Brushes The brushes are said to be `reaction' or `leading' when the commutator is rotated against the angle of tilt i.e. the brushes are inclined in a leading direction. The angle between the centre line of the brush and the normal lines between 30 to 40 degrees. Trailing Brushes The brushes are said to be `trailing' when the commutator is run in the same direction as the brushes are tilted. The tilt angle usually lies between 7 to 15 degrees. Radial Brushes Traction motors are invariably fitted with radial brushes i.e. their centre line is radial to the commutator, which permits operation under similar conditions for both direction of rotation. 4. BRUSH TYPES Split Brushes Commutator, howsoever well designed and manufactured, losses its truness in the long run of service and high/low spots are often formed on its surface. The unavoidable commutator eccentricity gives rise to radial forces, which tend to break commutator to brush contact. The split brush arrangements gives some freedom to each piece of carbon to move independently so that the commutator surface is closely followed and electrical contact is maintained. The biggest advantage is the resistance between leading and trailing edge of the split brush tends to reduce circulating currents.

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Rubber-Top Brushes Apart from damping the radial forces, the rubber-tops prevent passage of current through the brush holder springs. The springs thus do not get over heated and loose their tensions. 5. ELECTRICAL CHARACTERISTICS (BRUSH TO COMMUTATOR CONTACT) It is perhaps surprising that very little is known even today regarding brush to commutator phenomenon. Microscopic study has revealed that area of the contact initially is only of the order of 1/4000th of brush area. As the machine is started, due to very high current density at these contact points, the carbon gets heated up and a gaseous layer is formed between the brush and commutator, which helps in current conduction. The commutator losses its fresh copper colour, and initial high brush wear (due to initial high friction and high current density), gradually comes down. The colour of the film on commutator becomes stable after some hours, or in some cases after several days of running, depending on the operating conditions. If no mechanical/electrical or thermal disturbances occur, brush tracks present an uniform polished colour, varying from dark chocolet to mild black. During the course of service, the first indications of any commutation problem due to internal or external factors are often revealed from the condition of the commutator film. It is therefore extremely necessary to have adequate familiarity of the different types of the commutator films. This information is usually given in the brush literature. IEC specification No. 276 gives illustrations of some typical films. Part 4. of IS-3003, also includes some of such specifications. 6. SELECTION OF BRUSH GRADES Brush grade selection involves considerable tests both on the test bed and under actual service conditions. It is sometimes found that brushes which are considered satisfactory on the test bed do not operate satisfactorily in service. In view of this, the proper grade can only be selected after suitable service trials and evaluation. Indian Standard Specification IS-3003 covers dimensions, requirements and test procedures for carbon brushes. Divergence in the physical properties and dimensions of carbon brushes can cause considerable trouble in service. Verification of the properties involves exhaustive testing, and since the carbon brushes are required to be procured rather frequently, it is not practicable to carry out such a large amount of tests on each lot purchased. It is extremely important, therefore, to restrict the brush procurement from established and well proven sources only, even if the prices may be higher. Also, whenever a new supply source or a new brush grade is considered, detailed tests/service trials should be carriied out before approving the same for bulk use.

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Some of the defects usually noticed on the carbon brushes are: 1. Dimensions not confirming to the drawing 2. Bowed/Curved and chipped carbons 3. Poor quality of pig tails, which results in their getting frayed/broken in service

4. Bad joints between pigtail and carbons, resulting in high unequal voltage drops across the same

5. Hair line, invisible cracks at pigtail to carbon joints 6. Physical properties not conforming to the grade 7. SERVICE PERFORMANCE Howsoever good may be the design/manufacture of the machine, and the quality of the brushes, satisfactory performance cannot continue to be obtained without resorting to regular and proper maintenance of the brush-gear and commutator. The importance of early detection of commutation troubles cannot be over emphasized. As such it is imperative that from the time the machines are commissioned, suitable statistical information should be collected on the basis of regular observations. Analysis of the data thus collected will help to avoid the possibility of any particular commutation problem assuming epidemic proportions. Section II of BHEL's Workshop Manual covers the aspects which govern the satisfactory commutating performance of traction machines. In this section guidelines for operation, maintenance and trouble shooting are also covered. 8. ANALYSIS OF COMMUTATION PROBLEMS The commutation problems are caused by several factors, some of which are enumerated here:

8.1 Carbon brushes Poor quality of brushes, bad carbon to pigtail joints, wrong brush grades, mixing of grades on same machine, brushes too loose or tight in brush holders, improper bedding, brushes too thin or thick, brush angles not correct, etc.

8.2 Brush Gear Brushes in incorrect positions, low or high spring tensions, unequal current sharing by brushes of the same arm, incorrect brush stagger, spring carrying current, excessive vibrations due to poor/defective mounting of brush holders, high brush box to commutator clearance, unequal pressure on parts of split brush, brush holders prone to flashover damages, poor accessibility for maintenance, etc.

8.3 Commutator Eccentricity, ovality, high and low bars, flats on commutator, pround mica, oily or dirty surface, bridging of mica grooves, rough surface, high commutator temperatures, inadequate stability due to poor seasoning, etc.

8.4 Machine Faults Compole strength and gaps not correct, clogged ventilation ducts, poor ventilation, defective armature bearings, dynamic unbalance, wrong connections of compole or main field windings, armature or field winding faults, inadequate equalization, commutating zone too narrow or unsymmetrical, poor commutation performance in general, saturated compoles, low field/armature ampere turns ratio, etc.

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8.5 External Causes Excessive vibrations due to defects in machine mounting or defective bogie designs or poor rail track, leakage from ventilation ducts, collapsed bellows, prolonged light load running, rapidly fluctuating or excessive loads, faults in control circuitry, mal-operation of line contactors, unequal load sharing by machines, excessive wheel slips or wheel locking, humid or corrosive atmosphere, towing of motors without lifting the brushes, oil/water/brake-shoe-dust coming with cooling air, high voltage transients, high ripple contents, poor maintenance, inadequate facilities in maintenance depots, etc. Annexure-1 TECHNICAL DATA FOR CARBON BRUSHES ___________________________________________________________________________ EG0 EG236S EG14D EG225 EG59 EG259 EG7097 EG389 EG6754 (M) (M) (M) (M) (RE) (M) (LC) (LC) (LC) Normal current 10 11 9.5 11.0 11.5 8.5 10 10 10 density (Amp/cm2) Contact drop at 1.0 1.4 1.25 1.15 1.25 1.65 2.5 2.5 2.5 normal current (Volts) Specific resistance 1100 2200 4200 4100 5100 5800 4100 1700 4000 (ohm-cm) Apparent density 1.15 1.6 1.72 1.48 1.65 1.73 1.62 1.46 1.72 (gms/cm2) Coef. of friction 11 . 11 . 11 . 14 .15 . 05 .15 . 15 .15 % porosity (Apparent) 20 13.2 27.0 13 Shore hardness 36 65 77 34 65 65 70 30 86 (Scleroscope) Compr. strength (Kg/cm2)410 840 230 750 Transverse band 210 180 250 130 210 300 320 270 390 strength (Kg/cm2) Shear strength (Kg/cm2) 98 250 46 310 Normal max. 20 50 45 50 50 50 50 45 45 speed (M/sec) Note: Most carbon materials are of a brittle granular structure, thus the physical properties can not be held within close tolerances. The figures quoted above therefore are typical values but considerable variability is to be expected between individual measurements. Annexure-2

CARBON BRUSHES FOR BHEL TRACTION MACHINES Sl.No. Machine Type Brush Grade Size (TxWxL) Drg. No. Qty./Machine 1. 133AY / 133AX EG14D Morgan 2(9.5X63.5X57) D4775841 4 2. 253BW / 253AZ/ EG14D Morgan/ 2(12.7X44.45X60) D4775798 8 TM4601AZ/TM4603AZ EG7097 Le Carbone 3. TM4939AZ/165/165M 2(9.5X57.15X51) D4775839 12 EG14D Morgan/ EG6754 Le Carbone 4. AG15/AG2513 RE59 Ringsdroff 12.7X31.75X44.45 D4775293 8 5. MG51 (GENERATOR) RE59 Ringsdroff 12.5X31.75X43.2 D4775077 4 6. MG51 (MOTOR) EG225 Morgan 2(6.35X22.2X43.2) D4775076 2

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7. TG10931/TG10919 EG225 Morgan 2(11.1X31.75X64) D4775851 60 EG389 Le Carbone 8. EC9005/2 EGO Morgan 9.5X9.5X25 B4900350 4 9. TM2701AZ EG14D Morgan 16X64X65 D4775847 2 10. TM3603AZ EG14D Morgan 2(11X40X60) D4776200 8 9, SUMMARY In DC-DC and AC-DC diesel locomotives, a large number of DC machines have been used. Carbon brushes play an important role in these machines. Understanding the characteristics and its working helps the maintainers/users to run the machines trouble free. The brush material, brush rigging, types of brushes and electrical characteristics help the users in selecting proper grade for a particular application. The service performance is recorded and monitored in order to decide the proper selection of brush grade too. Commutation in DC machines is a critical phenomenon. Proper analysis of commutation problem helps in minimising the troubles. This unit also contains technical data of different carbon brushes, which are in use. A chart showing grades of brushes for specific application is given to help the reader . 11. SELF ASSESSMENT EXERCISE

1. Describe, How do you select a brush grade for an application. 2. Why is it necessary to monitor service performance of brush. 3. How do you analyse the commutation problem of a DC machine. 4. Why are the brushes placed at an angle in unidirectional machines. 5. Describe the process to obtain an Electro-graphite brush material.

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UNIT 2.5 FLASHOVER OBJECTIVES On completion of this unit, you should be able to: • Describe the cause of flashover. • Detect a machine running with the risk of flashover. • Suggest remedial actions. STRUCTURES 1. Introduction 2. The trouble

2.1 Dirt 2.2 Loss of contact 2.3 Sudden extreme load changing

3. The ultimate effect 4. Detection and remedy 5. Summary 6. Self-assessment exercises

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1. INTRODUCTION Flashovers are caused. They do not just happen. Something seems puzzling and mysterious only if it is not understood. With the gain of knowledge, the mystry disappears. If any one can find out what flashovers are and how are they caused, what to do to prevent them, that makes sense. A generator flashover, seen for the first time, is truly awesome. The blast of fire, the smoke and noise are enough to make one jump as if it was a stroke of lightening. The traction motor flashover is also caused in the same way. The commutator is the stage on which the flashover appears. Fig. 1 shows how the commutator is built up of copper segments separated from each other by thickness of mica. Each pair of segments has an armature coil connected between them. Electricity enters by way of one set of brushes, through the copper segments and into the winding. When it reaches the segment under the other set of brushes, it leaves. The mica insulation separates the copper segments and keeps the electricity flowing through the armature coil. If this insulation breaks down, electricity will short cut across the surface of the commutator. Almost instantly, the current jumps from one brush holder to other brush holder with explosive force forming an arc. This is known as flashover. 2. THE TROUBLE The voltage between the segments of a machine is quite low and the thicker mica has an insulation capacity many times greater for the purpose. What then causes such relatively wide spaces to breakdown and permit the machine to flashover ? (Fig. 2 indicates the distribution of voltage.) Across the top of the mica, there is an air space. If dirt does collect at these spaces and packs between the segments, the current begings to leak through it. The space is made wide so that it will take longer to fill with dirt and be harden to bridge. If the space is not cleaned in time, insulation breaks down and flash over may result. These insulating space may also be bridged by copper fins or copper dust left over from stonning and resurfacing the commutator. Dirt and foreign materials are not the only cause of flashover. Air, being a good insulator is broken down into conductive gas by the action of intense heat. The change of air to a conductive gas is known as ionisation. It can be caused by flame or spark, by high voltage or by certain kinds of radiation. Under certain operation conditions, motor or generator brushes will spark. The affect of this is not always serious. What happens depends upon how intense the sparking is and how long it lasts. Under some abnormal condition the spark at the brush may be so vicious and hot that it blasts a cloud of conductive gas and fiery particles across the commutator surface. These bridge the spaces between segments and electricity short cuts across the commutator surface. Every thing is then set for a flashover. The intense spark that sets off a flash over may occur when a brush bounches off the commutartor while the machine is carrying a load. It may also occur when there is a sudden extreme change in load, for greater than the machine can handle. The insulating spaces between the segments may be bridged by hot conducting gases generated by the intense heat resulting from :- i) Dirt between segments which burns when current flows through it. ii) Loss of contact of brushes from commutator which draws a hot spark.

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iii) Intense sparking at the brushes caused by sudden extreme load changing. 2.1 DIRT Dirt and foreign particles in the insulating space between commutator segments caused the majority of the flashovers. When enough dirts collects to bridge the space between segments, current begins to leak across (Fig. 5A) . The dirt heats and fuses into a better path. Current flow incfreases, specially as the oeprating voltage increases. The spot grows , and finally begins to glow (Fig.5B). As the commutartor turns, these glowing spot looks like a continuous ring of fire. Finally the spot gets white hot. Then it errupts conductive gases and incandescent particles (Fig.5C). As the commutator turns (Fig.6A), these form a fiery trail behind the spot. These breaks down the insulating air space between segments that may not be glowing and sets the stage for next act. The current short cuts (Fig.6B) from the hot spot, across the segments bridged by the firery gases, back to the brush holder in a sizzling vicious spark. The intense heat and energy in these spark blast conductive gases acrosss the commutator circuit (Fig.6C) with explosive violence. The gas cloud races ahead of the glowing spot and breaks down the air resistance across the rest of the commutator from brush to brush, then full power of the machine jumps across (Fig.6D) in the final flashover. 2.2 LOSS OF CONTACT Dirt may be the most frequent, but it is not the only cause of flashovers. Sometimes loss of brush contact will be to blame. These may be expected at high speed with a rough commutator surface or weak brush holder springs. It may also occur when brushes are jammed in the holders by muck or dirt so that they cannot follow the commutator surface quickly enough. Servere mechanical shock may jar the brush off the commutator. If brush breaks contact with the commutator, it draws an electric arc (Fig.7 ). If these are severe enough, it will spray conductive gases over the commutator. If the fiery gas bridges enough segments, the collective voltage will cause the current to arc back to the brush (Fig.6B). The blast of conductive gas from these arc back may reach across the surface of the commutator to the next brush (Fig.6C). The full power of the machine then flashes over these short cut path (Fig.6D). Again, instead of doing useful work, the energy will be expanded in the terrifically hot, destructive blast of flashover. 2.3 SUDDEEN EXTREME LOAD CHANGING (The surprise attack) Flashovers, that occur when the commutator is in perfect mechanical and electrical condition are most complexing. These are caused by sudden and extreme change in load, too great for machine to handle. Fig. 8A shows that, in a machine, current divides as it enters the winding. It remits and leaves through the out going brushes. Current flows in one direction when the coil is on one side of the brush and in the opposite direction when it gets to the other side. So the current must reverse in the split second it takes for the coil to pass under the brush, which is known as commutation. If the current does not reverse in time the coil will come out from under the brush with the current still flowing in old direction. The meeting point with the current in other part,

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which is known as neutral point will no longer will be in the brush. This shifting of neutral point corwds the current to one edge of the brush. Then it breaks out over the surface of the commutator in a spark to reach in a shifted point (Fig.8B). The greater the current, the harder it is to get it all completely reversed as the coil zips under the brush. Machines have interpoles or commutating poles , to speed up this current reversal and keeps the neutral point under the bursh. These are smaller poles located between the main poles in the machine frame. They help commutation only. The magentism of these poles builds up a voltage in the armature coil as they pass through the zone covered through the brush contact. This voltage speeds up the current reversal to get it done before the coil leaves the brush contact. These poles are designed to do a good commutating job up to, and even beyond full load. When , however, a very overpowering current flows through the winding, the magnmetism in the iron cannot build up quickly enough. This means there is not enough voltage to reverse the current in time and sparking results. Moreover, as after saturation of the pole pieces no more magnetism can be expected , hence, there is a limit to the help the pole can give in reversing the current in the coil. When the current gets so heavy that this help is not enough then this sparking is the ultimate result. When the machine is operating at full voltage, the jolt of sudden extreme overload causes vacious sparking at the brushes. Conductive gas bridges segments (Fig.8C). Current starts leak over the commutator surface (Fig,6B). The blast of fiery gas completes the short circuit between the brush holder (Fig.6 C&D). Every day motors and generators demonstrate their ability Still the flashover occur if anything goes wrong. For instance, a contactor fails to operate momentarily, short circuiting generator. A sudden surge of current occurs during high speed wheel slip. Taking a cross over at high speed may cause a brush of motor to bounce and flash a motor over. It is just like short circuiting of the generator because the current is no longer flowing through the motor winding, but short cutting across the commutator. So the current drawn from the generator reaches unreasonably high value. It knocks the generator off balance. The heavy sparking and flashover is the knock out blow. 3. THE ULTIMATE EFFECT The space surrounding the commutator is filled with flame and conductive gases. These reach between brush holder and also over the frame part of the machine. Current can now flow from the brush holder to the frame and through the frame back to opposite bursh holder. Flashover current can also strike from the commutator circuit through the fiery gases to the steel commutator cap. From here it finds its way to ground through shell, armature shaft and bearing. This is the cause of electric pitting of roller bearings and races. When the confined space around the commutator is filled with ionised air and flame, the current can strike in many directions with destructive force (Fig.9). String bands are burnt, brush holders are flashover, bearings are damaged and if grease and dirt are present they may

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be set on fire. However, the current strikes the ground and it is detected by the ground relay. 4. DETECTION AND REMEDY Detection of these types of defects can only be done visually. Insulation resistance between the segments cannot be taken with the help of a meter as they are connected to the windings. Megger readings and high pot tests are of no good because they check what is called resistance to ground. Inspecting the defects visually, they can be rectified by cleaning, undercutting mica so that they look white or grey, air curing the machine or by blowing the commutator surface with compressed air. In case of improper or inadequate brush pressure, the brush gear can also be attended. Polishing, grinding or machining may also be required if the commutator surface is rough, having the defects of high bar etc. In some of the cases short circuited or open circuited winding may also cause flash over and can be detected by bar to bar milli-volt drop test or taking the micro ohm readings. 5. SUMMARY Flashover of DC machines is a chronic disease. It is the prime cause of pre-mature failures of most of the DC machines. Moreover, it remains a mystery to the user that when the machine will fail and how an expert rectified the fault. This unit describes the causes of the flashover due to dirt deposition, loss of contact of carbon brushes and sudden extreme load changing, which are very common in case of traction machines. Stage wise development of defects and ultimate effect on the machine has been elaborately described to help the maintainer to understand these defects and take remedial measures. Checking to judge the healthiness of the machine has also been described. 6. SELF ASSESSMENT EXERCISES

1. Describe how does the dirt deposition on the commutator surface lead to flashover. 2. Describe the reason of flashover due to loss of contact between the carbon brush and

commutator. 3. Describe the process of detection and remedy of a machine suffered from flashover.

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UNIT 6 DYNAMIC BRAKING OBJECTIVES After completion of this unit, you should be able to: • Understand the principle of operation of Resistive Brake • Learn a motor can run as a generator • Appreciate the braking control • Understand the effectiveness of Dynamic Brake • Appreciate the characteristic of Dynamic Brake • Appreciate the requirement of auxiliary systems STRUCTURE 1. Introduction: Principle of operation 2. Motors as generators 3. Braking control 4. Re-calibration of system 5. Dynamic braking effectiveness 6. Protection against wheel sliding 7. Braking effort and its characteristics 8. Auxiliary systems: Resistor cooling and motor cooling 9. Train brake application with dynamic brake

1. INTRODUCTION PRINCIPLE OF OPERATION-RESISTIVE BRAKING

The installation of dynamic braking on diesel electric locomotives has become quite common. By taking advantage of the traction motors ability to act as a generator, the diesel electric locomotive offers a form of braking power which, without the use of air, can be used as a speed controlling brake on grades or a slowing brake on level track. Use of dynamic brake lessens brake shoe and wheel wear on both locomotive and train. On long down grades dynamic brake operation enables a train to be handled with fewer air applications. This results in safer train operation, due to the locomotive and car wheels running cooler. In Fig.1 the action of wheels with dynamic braking is shown. The momentum of the train turns the wheels. This drives traction motor as generator and forces current through the braking resistors as shown by the arrows and the resistors heat up. The traction motor, working as a generator, resists the turning of the wheels and tends to stop it, so the motor is used to do the same thing as the brake shoes. In this case the braking resistor and motor instead of the brake shoes and wheel get hot. Hence, the blowers must cool them. The wheels and brake shoes do not wear because there is no rubbing. To have dynamic braking the wheels must be turning. This is because generator generates only when it is turning. So the dynamic braking cannot be used to hold or stop train. For this purpose air brakes are to be used.

In Fig.2, how dynamic braking works on a four motor locomotive is shown. The

momentum of the train pushes the locomotive and turns the wheels, which drives the motors. The output of the motors is fed into the braking resistors. The driver controls the braking by moving the selector handle. A load-meter shows him how much braking current he is getting. 2. MOTORS AS GENERATORS

We know that DC machine can be used as either a motor or a generator. Fig.3 (a) shows the motoring connections. Current is being pumped through the motor armature and field by the generator. This causes the motors to turn and move the locomotive. In Fig.3 (b) switches have been shown to change the motor connections. Now the generator pumps current through the motor fields only. Two things have happened to the armature-

1. It was cut off from the generator, 2. It was connected across the braking resistor. Now we have separated the motor field from its armature and are pumping current

through the field only. If the locomotive is moving, the wheels are turning and driving the armature. It is connected across a resistor so that it has load. In electrical language we have a separately excited generator with a load resistance.

In Fig.3 (b) we see that the field current is flowing in the same direction as in

3(a). But the armature current is reversed in (b). If wee reverse the field current 39(c), the armature current will flow in the same direction as in motoring (a) i.e. if we change from

motoring to braking if the field current stays the same, the braking current will reverse. If the field current is reversed, the braking current will stay the same. There are some points about the Fig.3 circuit to be known for understanding dynamic braking: -

The more current we put through the motor field, (within certain limits) the more

braking current we will get. The lower the braking resistance, the higher the braking current (this resistance is

fixed when the locomotive is built). 3. The faster the armature turns, the higher is the braking current. 4. The higher the braking current, the more braking we get.

3. BRAKING CONTROL

The key to controlling the output of almost any generator is its field. In this case, it is the traction motor field. Ref. Fig.3, the main generator supplies the current to the traction motor field. In excitation system chapter we have seen how the main generator output is controlled in motoring. The same control is used for braking, but the generator is connected to the motor field only. By controlling this we control the dynamic braking current. The driver does this by moving the selector handle.

For example at high train speed we need a weak motor field to hold the braking

current to a reasonable value. This calls for a small main generator output. The driver achieves this by moving the selector handle. At low speed we need a strong motor field to get full braking current. He gets this by moving the selector handle further into the braking sector. The driver can get the amount of braking he wants for any speed by moving the selector handle.

The capacity of braking resistors is limited by the amount of heat it can withstand.

To prevent them from getting damaged blower fans are used. The power for driving these fans is used from the power generated during the application of dynamic brake. When there is no braking current, the fans do not run, but as the braking increases, with that the braking current and heat increases and also the fan speed increases hence giving more cooling. Braking resistors usually require little attention. Dirt and water are the biggest source of trouble.

4. RECALIBRATION OF SYSTEMS

Assume that a train is drifting downgrade, and that the engine-man is preparing to apply the dynamic brake moves the throttle to “IDLE” position. With the throttle in ‘idle’ all power contactors drop out and the motor-generator circuits become completely de-energized.

Now the engine-man moves the selector handle from whatever motoring position

it was in, to the ‘off’ and then to the ‘Big D’ position. Moving the SH to ‘Big D’ accomplishes the following:

i) Causes braking switch (BKT) to throw reconnecting the power circuits.

a) Connects all motor fields in series, b) Connects series motor fields across main generator, c) Connects motor armatures across braking grids.

ii) Energizes braking relay (BKR) which: a) Raises engine speed to 4th notch, b) Replaces engine speed signal with braking control signal at reference-

mixer circuit. c) Re-calibrates control circuits as required,

iii) Sets up braking potentiometer (BKCP):

Figure.5 shows a typical motor-generator circuit for a 4 motor locomotive. All power contactors are in their braking positions and the directions of current flow are shown.

Note that the starting field is in the circuit with the generator armature and motor

fields during braking. This is done to make the generator more stable at the very low range of voltages used in braking. Current in the starting field creates an opposite effect to that in the shunt field; consequently much more exciting terminal voltages than would otherwise be needed. This makes it possible to operate the exciter at output levels more nearly comparable to those in motoring.

5. DYNAMIC BRAKING EFFECTIVENES

Maximum braking excitation (selector handle all the way forward) will give maximum braking effort for any locomotive speed. If, for example, the engine-man imposes maximum excitation at a speed of say a few miles per hours; the braking effort will be relatively low because the armatures are turning slowly.

If, on the contrary, the train is moving faster, the higher rotational speed of the

armatures will tend to cause a higher current to flow through them, therefore, a greater braking effort will follows. In cases in which the tonnage is such that the train speed on a grade cannot be controlled fully with dynamic braking, and would tend to accelerate despite the use of dynamic braking, the engine-man can use the air brakes on the train to complement the action of dynamic braking.

6. PROTECTION AGAINST WHEEL SLIDING

It is desirable to provide protection against the possibility of wheel sliding. When two separately excited generators are connected in series with each other across a load and the speed of one is permitted to slow below the speed of the other, the faster generator feeds current through the armature of the slower generator. The latter generator thus has current flowing through its armature from a separate source (the faster generator) and excitation current in its field. This causes it to act as a motor with a torque applied to

it and it slows further. Eventually, it might possibly stop and skid the wheels or even reverse them. Even if wheel skidding does not occur, the fact that one motor and its connected wheels are rotating slower than the other wheels of the locomotive, will cause the slower wheels to be dragged along, thus causing what is best described a “rolling slide” 7. BRAKING EFFORT AND ITS CHARACTERISTICS

In dynamic braking, the system produces the traction motor characteristic shown in Figure 7. Variable limits are placed on both the traction motor field and armature current to provide smooth control and prevent damage to the motor or braking grids.

7.1 ARMATURE CURRENT LIMIT

In dynamic braking it is desirable to automatically limit the current which can be supplied by the motors, so as to protect the motors and the braking grids. This is done by measuring armature current in terms of traction motor voltage, using a voltage divider across a traction motor in braking.

8. AUXILIARY SYSTEMS

8.1 RESISTOR COOLING SYSTEM

The current which the traction motor armatures pumps through the braking resistors represents the power required to decelerate the train, which must be dissipated in the form of heat. To remove the heat from the resistance grids, motor driven fans blow air through them. The electrical energy to run the braking blower is taken from the energy supplied by the traction motors in braking.

The cooling system is self-controlled to provide the proper amount of cooling air for various degrees of braking power. As braking power and heat increase, the motor driven fans run faster to supply more cooling air.

8.2 TRACTION MOTOR COOLING SYSTEM

During normal motoring operation the traction motors are forced ventilated by mechanical blowers driven by the diesel engine. In dynamic braking, circuits are added to the engine speed control system to increase engine speed to approximately 4th. Notch in order to supply sufficient air for motor cooling during dynamic braking operation.

9. TRAIN BRAKING WITH DYNAMIC BRAKING

The brakes may be applied on the train while the dynamic brake is being used. The dynamic braking circuits include the dynamic brake interlock magnet valve coil. The magnet valve (BKIV) is a part of the locomotive’s air brake system. Its function is to prevent the locomotive’s air brakes from system. Its function is to prevent the locomotive’s air brakes from being automatically applied when dynamic braking is being used and a train line reduction is made.

10. SUMMARY

A diesel locomotive equipped with dynamic brake is very useful in controlling rate of acceleration in grades and speed in level track without using conventional air brake, which leads to excessive unwanted wear of brake blocks and wheels. Resistive brake with automatic limit is very common for diesel locomotives, which provides a facility of braking effort control through drivers' selector handle. The braking effort achieved with resistive brake has a typical characteristic of depending on train speed. The braking grids (resistors) have self-cooling arrangement, which does not involve separate energy source. To cool the traction motors during their operation as generators, the engine driven traction motor blowers are run as higher speed by increasing the engine RPM.

11.SELF-ASSESMENT EXERCISES

1. Explain the principle of resistive braking. 2. What do you mean by braking control and how it is achieved in diesel electric

locomotives? 3. Explain the effectiveness of resistive braking. 4. Explain the characteristic of resistive braking with necessary diagram. 5. What are the auxiliary systems involved in dynamic brake system?

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UNIT 7 SAFETY DEVICES OBJECTIVES After completion of this unit, you should be able to:

• Appreciate the functioning of low lube oil switch • Appreciate the functioning of hot engine alarm • Appreciate the function of low water level switch • Appreciate the ground fault detection devices • Appreciate wheel slip protection device • Appreciate function of pneumatic control switch STRUCTURE 1. Low lube oil switch 2. Hot engine alarm 3. Low water level safety 4. Ground in power circuit 5. Safety auxiliary relay 6. Wheel slip protection 7. MU stop button 8. Pneumatic control switch 9. Safety devices of YDM4/WDS6 10. Summary 11. Self-assessment exercises

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1. LOW LUBE OIL SWITCH

This safety device is provided to protect the engine against low lubricating oil pressure. When the lubricating oil pressure falls below 30 psi (2.1 kg/cm2) the oil pressure switch is repositioned. The Governor clutch coil is de-energised. The Governor arms A & B are separated by bias spring; also the Governor stabilising coil is energised. The Governor shuts down the engine. The engine start light comes on; low lubricating oil pressure indicating light (green) comes on.

2. HOT ENGINE ALARM (a) Variable speed drive for radiator fan

This device is used to keep the cooling water temperature within permissible limits. At predetermined temperature it starts first the radiator fan to run at medium speed, then at faster speeds, and finally brings the engine to idle if the radiator fan can not control the temperature.

(b) Hot engine safety circuit

Engine temperature sensitive switch, ETS, closes when the cooling water temperature rises above 84OC (1850F). The hot engine indication light (red) comes on. Signal relay SR is energised through ETS. Engine temperature relay ETR is also energised. The Governor speed coil is set for idle speed, also the alarm gong comes on.

3. LOW WATER LEVEL SAFETY (Fig.1&2)

This safety device is provided against low cooling water level. If the cooling water level drops to a predetermined level the alarm sounds and the engine shuts down. The LWS contact opens in clutch coil circuit. The Governor clutch coil is de-energised. The Engine is shut down through the governor circuit. LWS also energises wire 5B thereby the hot engine light comes on. The signal relay is energised (SR) and the alarm gong rings.

4. GROUND IN POWER CIRCUIT

The ground relay, GR, is energised whenever insulation resistance between main generator circuit and ground goes down. The reset knob of GR comes out. The ground relay contact GR opens and generator field contactor GF is de-energised. The Generator Field contact opens the generator field circuit, and power to motors is cut off. The Governor speed coil is set up for the idle speed when the GR contact closes in the Governor speed coil circuit. The ground relay light (white) comes on. The signal relay is energised, resulting in alarm gong sounding

5. SAFETY AUXILIARY RELAY

Whenever the governor speed coil starts getting the reference current, the safety auxiliary relay SAR operating coil is energised and its contact picks up. This safety device is provided to prevent the Diesel Engine from over speeding in case any open circuit takes place in the speed coil circuit. If this condition arises SAR operating coil will be de-energised, resulting in de-energisation of the clutch coil. The Governor arms A and B are separated by bias spring and the engine comes to stop.

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In addition to this a mechanical device is also provided to prevent the engine from over-speeding (over speed trip mechanism) when the Diesel engine speed goes to more than 1120 RPM this device trips the engine to shut mechanically by moving the fuel racks to no fuel position.

6. WHEEL SLIP PROTECTION

Whenever wheel slip relay WSR1 or WSR2 or WSR3 is energised wheels slip buzzer sounds by wire 10 through wire 13. Wheel slip light comes on. By closing WSR1 or WSR2 or WSR3 interlocks the PWM main turn off winding in the excitation system is connected across battery source and the generator power is reduced. 7. M.U.STOP BUTTON / SWITCH

When it is desired to stop all engines working in multiple unit operation, this emergency stop button is pushed. 8. PNEUMATIC CONTROL SWITCH

This switch (PCS) trips during emergency brake application, train partition, vigilance

control device being not minded by the driver at the specified time etc. When PCS trips, engine speed and power returns to notch one through the governor speed circuit.

9. SAFETY DEVICES - YDM4/WDS6

9.1 LOW LUBRICATING OIL PRESSURE

This safety device is provided to protect the engine against low lubricating oil pressure. As soon as the lubricating oil pressure falls below safe minimum the engine through the governor shuts down giving an alarm signal

9.2 HOT ENGINE ALARM

(a) Variable speed drive radiator fan

This device used to keep the cooling water temperature within permissible limits. Reaction is similar to that in the WDM2 locomotive.

(b) Hot engine safety circuit If engine water temperature exceeds the set value of temperature switch (ETS1) a contact

closes and energises signal relay (SR). The warning light comes on and alarm gong sounds. If the temperature continues to rise above the set value to temperature switch (ETS2) if used, a contact opens and de-energises the engine run relay (ERR) when ERR drops out the engine speed returns to idle.

9.3 LOW WATER LEVEL SAFETY (Fig.9)

This safety device is provided against low cooling water level. If cooling water level drops to predetermined level in the expansion tank the alarm sounds and the engine shuts down.

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9.4 GROUND RELAY

If a ground occurs in the power or control circuits, ground relay (GR) will operate. A normally closed contact drops out the generator field contactor (GF) thus the generator excitation is removed. GF interlock also opens in the separate excitation circuit to remove exciter excitation. Engine run relays are energized; all the governor speed solenoids drop out forcing the engine to return to idle speed.

9.5 WHEEL SLIP PROTECTION

Wheel Slip relays (WSR) are connected between points of equal potential in the traction motor circuits. If a motor slips during operation, a difference of potential will exist across the relay coil and the relay picks up. When the relay is energised, its contacts will light a lamp and sound the warning buzzer.

Also a contact on the wheel slip relay, in series with the governor over-ride solenoid will close. This action will reduce main generator output to the traction motors; automatically correcting wheel slip and then re-applying power when wheel slipping has stopped. The throttle handle does not have to be moved back unless slipping is corrected.

9,6 ENGINE OVERSPEED

If the engine exceeds a set value of engine speed, the over-speed mechanism operates the engine over speed switch (EOS de-energises ERR, and the engine shuts down. In this case alarm gong will not operate.

9.7 PNEUMATIC CONTROL SWITCH

This switch (PCS) trips during emergency brake application, train partition on vigilance control device operation (if used). When the PCS trips, the resulting circuit operation causes the engine speed and power return to notch 1.

9.8 ENGINE SHUT DOWN

Normal shutdown or stopping of the engine is accomplished by moving the engine control switch (ECS) to “SU STOP” position. If the locomotive is being operated in multiple, or if engine must be shut down in emergency, the ECS switch should be moved to “MU STOP” position.

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10. SUMMARY

Safety devices play a very important role in the diesel locomotive to avoid extensive damage of engine components as well as transmission components. Among the safety devices, some are to ensure safety of the engine components and the diesel engine and rests are for safety of the transmission. There are minor differences between the safety devices of WDM2 and YDM4 locomotives. The over speed safety of WDM2 is a mechanical device and that of YDM4 is electrical. The wheel slip protection system of WDM2 reduces excitation during the occurrence of wheel slip and over-ride solenoid comes in operation in YDM4 in order to have load control. 11. SELF-ASSESMENT EXERCISES 1. What does happen if the lube oil pressure of diesel engine falls below pre-set value? 2. Which device senses the cooling water level in expansion tank and what does it do in such

occurrence? 3. What does the ground relay do? 4. How do the wheel slip relays sense traction motor faults and what happens in such situation? 5. How does the over-speed safety device shuts down the engine in YDM4 loco?

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UNIT 4 TRANSITION OBJECTIVES

• After going through this unit, you should be able to: • Appreciate the need for transition in Diesel Electric Locomotives • Understand field weakening process • Understand Transition • Understand Wheel Speed Based transition and its regulation system • Appreciate Voltage-Ampere Based transition • Understand and identify the components involved in transition regulation STRUCTURE

1. Introduction: 1.1. Role of Traction motor 1.2. Traction Generator 1.3. Diesel Engine

2. Process of field weakening and paralleling: 2.1 Forward Transition 2.2 Backward Transition

3. Automatic transition regulation 4. Wheel speed based transition

4.1. System components 4.2. System operation

5. Generator Volts and Ampere based transition 6. Summary 7. Self Assessment Exercises

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1. INTRODUCTION The purpose of transition is to keep the diesel engine working on the full horse power part of the generator curve for the maximum possible period of locomotive operation- from its low speed to the maximum speed. In this we change the traction motor circuits, so that they draw value of current that falls on horsepower curve, as the locomotive speed changes. This change of motor circuits is called transition. For better understanding of the transition let us review our knowledge of traction motor, traction generator and diesel engine characteristics. 1.1 TRACTION MOTORS:- We use series type D.C. motors for traction purposes. This type of motor draws a high current at low speed and a low current at high speed. If its load is heavy, it runs at low speed if light it runs at high speed. The way such a motor acts is shown in Fig.E4.1. While doing Foot-plating, this can be noticed on the load meter. 1.2 TRACTION GENERATOR: - The traction generator is a d-c generator. It takes mechanical power from the diesel engine and converts it to electrical power for the traction motors. We have seen in the chapter on Excitation system how the generator is controlled so that it delivers power as shown Fig.E4.2. When the load resistance is low the amperes are high. When the load resistance is high the amperes are low. The generator characteristic can be obtained from the load test. 1.3 DIESEL ENGINE: - The diesel engine converts the energy of burning fuel into mechanical power. With the throttle at 8th: notch and full fuel the engine will run at its rated speed and produce its rated horsepower. If we try to get more power it will stall. If we try to get less power, the racks will back 'off' (the engine will take less fuel). To get the most out engine we must stay on the full horse power part of the generator curve Fig.E4.2. The purpose of transition is to obtain higher speed of the locomotive and still utilize the constant horsepower of the engine at a speed setting. The out put characteristic of the traction generator, as determined by the excitation system, is such that it holds the diesel engine at approximately constant horse power at a particular speed setting. When the locomotive is starting, and at low locomotive speeds, the main generator supplies a high current to the traction motors. As the traction motor armatures begin turning, they generate a voltage commonly called back EMF. This back EMF, as if increases the effective resistance to the current flow. Therefore, as the locomotive speed increases, the generator voltage must increase to maintain the traction motor current. The traction motor current will decrease however because of the constant power characteristic of the generator (Fig.E4.1). With further increase in locomotive speed, if the back EMF reaches the voltage limit of generator, the generator current starts falling and the horsepower reduces (Fig.E4. 2).

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However, by changing the generator motor connections, the back voltage is reduced and the generator can force more current to the motors to enable acceleration. To achieve higher starting torque, sometimes, two traction motors are connected in series during starting of the locomotive. In these locomotives, changing their connections from series to parallel can reduce the back emf. Weakening the motor fields can also reduce back emf. The change in the motor connections, or weakening of fields is known as an event of transition. The number of events is decided from the generator characteristic and the number of motors.

2. PROCESS OF FIELD WEAKENING AND PARALLELING

2.1 FORWARD TRANSITION

We want to keep the engine working on the constant horsepower part of the generator curve as much of the times as possible. To do this we use what is called transition. That is, as the locomotive speed changes, we change the traction motor circuits so that they will draw a value of current that falls on the horsepower curve. Let us see how transition is used to accelerate a train. At the start the traction motors are connected to the generator as shown Fig.E4.3 (This connection is called 2S-3PFF i.e. two traction motors in series and three parallel paths with full field). This means the generator supplies current through three paths to run six traction motors. So it has to supply only three times the signal motor current in starting. Even though the current drawn by each motor is very high, by using such a circuit the generator is kept to a reasonable size. In Fig.E4.3 we can see how the current drops off as the train moves out. This is shown by the arrows on the horsepower curve .At about 10 miles an hour we get on the full horse power portion of the curve. From this point it is necessary to stay on this part of the curve to get constant power from the engine. If we have a locomotive with 75 MPH gearing and 40 inch wheels, when we reach about 19.2 MPH (30.8 KMPH) point C in Fig.E4.3 is reached, the motor current will have dropped so much that continued acceleration would be at reduced horsepower along the field limit line. To prevent this, the motor fields are shunted as shown in Fig.E4.4 (this is called 2S-3P WF, i.e. two motors in series three parallel paths with weak field). Part of the motor current then flows around the field) through the shunting contractors (FS21, FS22 etc.), and the shunting resistors. This causes motors to draw more current from the generator, because of fall in counter emf. With this, operating point moves back down toward the bottom of horsepower curve as show n in Fig. E4.4. On some locomotives field shunting is done in two or more steps. This is done to keep the motor current to safe value. MATHEMATICALLY

N =KØ

RIV aa− By reducing K, speed N can be increased Also T = IØ ×

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When voltage is reduced, torque remaining the same, I has to increase so we slide down from point 3 to point 2 in Fig.E4.4. As the train continues to accelerate, the generator current, will again decrease as shown by the arrows in Fig. E4.4 (the generator current decreases as with the locomotive speed the back EMF of traction motors goes on increasing). At 30 M.P.H. (48 km/h), it will be back at the top of horsepower curve again. To prevent unloading, the motor current must be again increased by 2nd.transition. This time we do this differently. We change the motor connections from series parallel to parallel as shown in Fig.E4.5. Instead of three paths for the generator current there are now six. This causes generator current to increase. The operating point is now back at the bottom of the horsepower curve again as shown in Fig.E4.5 (We call this 6P-FF i.e. six traction motors in parallel with full field.). In making second transition the shunting contractors (FS21, 22 etc) Fig.E4.4 are first opened. This unshunts the motor fields. Then the series contactors S1, S2, S3 in Fig.E4.4 are opened and finally the parallel contactors, P1, P22, P31, P2, P22 and P32 in Fig.E4.5 pick up. This may happen in different sequence on various locomotives, but the end result is the same. Since the generator is at high voltage when this sequence begins its voltage must be reduced before switching of motors can be safely accomplished. This is done by opening the generator field contactor- G.F. This transition should take place at the right time. If it occurs too late, or at a too high a speed locomotive will loose power before transition. If it occurs too soon, there will be a loss of power after transition. In either case the operating point will not fall on the full horsepower curve. As the train continues to accelerate, the generator current again drops off. By the time speed reaches 50.8 M.P.H. (81.7 kmph), the generator will again be operating at the top of the horsepower curve, point C in Fig.E4.5. Now we go for parallel field shunting (transition 3). As in series field shunting, part of the motor current bypasses the motor field through the shunting resistor. The increased generator current moves the operating point down the horsepower curve as shown in Fig.E4.6, permitting further acceleration at full horsepower.

2.2 BACKWARD TRANSITION

If the train hits sufficiently steep grade, it will begin to slow down. As the speed drops, motor current increase as shown in Fig.E4.7. Suppose the train is travelling at 49 m.p.h. when it hits the grade. This point P is shown near the top of the curve. As the train slows down, generator current increases. At a speed of ground 30 m.p.h. the locomotive will be operating at the bottom of the full horsepower curve, point B. Something must be done or the operating point will go below B on locomotives without current limits this could mean overheating the generator. With current limit the locomotive will operate at reduced power, which reduces engine efficiency. The current that the generator must supply can be reduced by making a backward transition. This will transfer the operating point back to the top of the horsepower curve point as shown. If the speed continues to drop unshunting is done. There is one little difference in backward transition 3 to 2 from forward transition 2 to 3 on some locomotives, which at times is confusing. The generator field is left on in backward transition, but not in forward transition. There is a reason for it. If we look at the horsepower curve Fig.E4.8

5

we will see that backward transition takes place at point B where the generator current is high and the voltage is low. At this low voltage there is little chances of generator flashing ever when switching is done. Also during switching, this provides for the quickest rise to full voltage after the switching is completed so, we are still operating at full horsepower, but not at top of the horsepower curve. From the above, we can understand that transition takes place back and forth as train speed and load change. Its purpose is to hold operating point on the generator horsepower curve. This keeps the engine delivering full horsepower at all times. Let us now see how transition is done. 3. AUTOMATIC TRANSITION

We have seen that transition is made at a definite train speed and also at a definite point on the generator horsepower curve. This makes possible two methods of bringing about transition automatically, e.g. (i) Train speed based transition. (ii) Generator volts and amps based transition. 4. WHEEL SPEED BASED TRANSITION (Electronically controlled)

4.1 CONTROL SYSTEM COMPONENTS

The type E transition control is a fully automatic transistorised system for controlling traction motor field shunting and connections. It consists of an axle driven generator and a control panel. 4.1.1. CONTROL PANEL The panel is a steel fabricated housing contains semiconductor components mounted on plug-in-type cards with necessary adjusting facilities. 4.1.2 AXLE ALTERNATOR The alternator has 40 poles made up of permanent magnets imbedded in a plastic stator, and a rotor carried on a shaft driven by the locomotive axle. The rotor rotates within the stator. Voltages are induced in the stator coil by the action of alternator ‘L’ shaped and straight soft iron bars in the rotor. The ‘L’ shaped bars guide the flux in a path enclosing the coil while the straight bars short circuit the flux to avoid enclosing the coil. This voltage has a frequency proportional to the speed of the axle driving the rotor. Only a few volts are generated, even at high speed, at a frequency of 20 cycles per revolution.

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4.2. SYSTEM OF OPERATION 4.2.1 THEORY In order to properly control transition and since transition is based upon locomotive track speed, an accurate indication of that speed is required. The axle alternator in combination generates this speed sensitive signal with a saturating transformer. The saturable transformer requires the same amount of volt seconds to saturate it regardless of the speed at which saturation is achieved. The saturation characteristic at low speed and high speed of the axle alternator is shown in Fig.E4.9. The area of each pulse remains same regardless of speed. However, when rectified and filtered, the high-speed signal will result in a higher average voltage than the low speed signal since there are more pulses per unit time due to higher frequency. Since average voltage is directly related to frequency and frequency is directly related to speed, a straight-line characteristic of average volts versus speed can be obtained to give an accurate measure of speed. Fig.E4.9 shows a basic, linear speed measuring circuit in conjunction with a transistor switch. The speed varying voltage is sensed by a voltage divider connected to a NPN transistor and 5 volts zener diode. As the speed varying voltage increases, a point is reached where the sampling point on R1 is 5 volts which exactly equals the battery voltage of the reference diode. Any further increase in speed will raise the voltage of sampling point above the reference diode voltage and cause a current to flow from the base to the emitter of the transistor. This will turn "ON" the transistor and initiate the desired control function. A drop in speed will cause control functions to ease. Resistor R2 allows sufficient current to flow in the Zener diode to insure its operating beyond the knee of its characteristic and give sharp control. 4.2.2. ACTUAL CIRCUITS A typical automatic transition circuit is shown in Fig.E4.10. The 3-phase axle alternator feeds the circuit, with the leads connected to the automatic transition panel, providing an a-c. Voltage proportional to train speed. This a-c signal is rectified by a full wave bridge rectifier TRT consisting of potentiometers in series, the number of circuits being determined by the number of events to be controlled. Field shunting in series parallel is one event, requiring a potentiometer TP11, a transistor TT11 for actuating the sensitive relay TSSR1 controlling the event, and various resistors. The panel contains sensitive relays for controlling large control relays, a zener diode, various resistors and diode for protecting the transistors from negative voltage spikes and a capacitor for positive spike protection. Each of the circuits across the filtered output of the secondary winding of saturating transformer WET33 will have a voltage between the negative side of the D-C circuit and the brush arm of its potentiometer. This voltage is proportional to axle generator speed. The potentiometer is set so that the voltage of the zener diode TZD when the speed for the desired event is reached. As an example, considering the first event in a typical locomotive, potentiometer TP11 sees a portion of the d-c voltage resulting from a given train speed. Because field shunting in a series parallel is desired at a certain speed, the adjustment of TP11 is made so that the voltage of its brush arm

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will equal the breakdown voltage of TZD at that speed. This will feed current through TCR21 into the base of transistor TT11, through the emitter and resistor TCR4 and through the zener diode TZD back to the negative side of the circuit. This turn `ON' transistor TT11 and pick up relay TSSR1 and TSSR1 will then actuate the field shunting relay FSR, which is a heavy duty relay having contacts, which will set up the field shunting circuits. When the relay FSR picks up, it connects the brush arm of potentiometer TP21 through the new closed S21 finger to the positive side of the d-c circuit and this boosts the voltage at the brush arm of TP11. The actual point on the characteristics of the transistor TT11 and the relay TSSR1. Adjusting the TP21 potentiometer makes an adjustment of dropout speed. The voltage divider network made up of TCR2 provided approximately 25 volts across each of the transistors between the positive of the locomotive battery circuit and the common connection with the transistor emitters, to protect the transistors from operating at more than their normal working voltage. A small current fed from the locomotive battery negative to bias the Zener diode TZD to make control sharper and to get past the so-called knee of the Zener diode characteristic. This is done because the Zener diode will pass a very small current at a lower voltage than its normal breakdown value and then pass more current as this voltage is raised to the desired breakdown value. If control current is tending to turn ‘ON’ a transistor, it has to flow through the zener diode without the bias current flowing, sufficient current might flow at a voltage lower than the breakdown voltage to turn `ON' the transistor and actuate the system at a lower speed than intended. This speed would vary from day to day, depending on the characteristics of the various devices involved in the circuit. By biasing the diodes with current from another source which has no effect on the transistors, the transistor turn on current will flow only when the breakdown voltage is equalled or exceeded. 5. GENERATOR VOLTS AND AMPERES BASED TRANSITION

The second method of controlling automatic transition is based on generator volts and amperes. Relays that pick up on generator voltage at the top of the generator horsepower curve, point C in Fig.E4.2 bring about forward transition. Usually one relay is used for field shunting in series parallel and parallel. Another relay is used for series-parallel to parallel transition. One or more additional relays, that operate in generator current at the bottom of the horse power curve, point B in Fig.E4.2 are also required for backward transition. For satisfactory operation, these relays should be accurately calibrated on the bench.

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6. SUMMARY In DC-DC or AC-DC locomotives, where the traction motors are DC series motors, transition becomes unavoidable. Transitions from full field to weak field or series combination to parallel combination of traction motors help in achieving maximum speed of the locomotive by still using rated power of the engine in any of the notches. Automatic transition regulation is and important activity, which ensures the change at correct moment without which locomotive suffers from bad fuel efficiency and time loss in line. Wheel speed based transition is superior to voltage-ampere based transition as the latter has low response control components e.g. relays etc. The sensitivity and maintainability has improved substantially with use of electronic components in the system. The availability of components in the open electronics market is possible which reduces downtime of control panels and requirement of unit exchange spares. 8. SELF-ASSESMENT EXCERCISES 1. Explain the need for transition briefly. 2. How does the process of field weakening help in achieving higher loco speed? 3. What do you mean by forward and backward transitions? 4. Which system do you feel better (whether wheel speed based or voltage ampere based) and

why?

UNIT8 TROUBLE SHOOTING OBJECTIVES After going through this unit, you will be able to identify and understand: • The locomotive troubles • Troubles in dead and idling locomotives and the trouble shooting • Trouble shooting in running locomotives STRUCTURES 1. Introduction 2. Troubles 3. Troubles in dead and idling locomotives

3.1 Engine not taking start 3.2 Some of the auxiliary machines are not running

3.3.Loco can not move (Not getting Power) 3.4.Loco starting with heavy jerk 3.5.Loco is moving but load-meter is showing zero or negative 3.6.Low Hauling Power 4. Fault experienced when the loco was moving

4.1 Engine over-speeds 4.2 Engine not responding to throttle or speed is erratic 4.3 Engine hunting 4.4 Engine shuts down and crew unable to restart 4.5 Low HP 4.6 Engine bogs down under load 4.7 Operation of ground relay 4.8 Operation of wheel slip relay 4.9 GF not picking up 4.10 Operation of Power Contactors is erratic 4.11 Transition is picking up 4.12 Wheel slip indication in a particular transition 4.13 Hot engine indication 4.14 Battery charging stopped

5. Summary 6. Self-assessment Exercises

1. INTRODUCTION A considerable portion of road troubles are experienced due to some defects in electrical components and machines, which can be rectified with very little effort. In some of the cases they be temporarily attended to save the road failure of the locomotive. As the road troubles are faced by the supervisors/officers first on foot-plate, it would be very much helpful if they rectify the fault on road (temporarily or permanently) and avoid the stalling of rolling stock. Keeping in view all these situations, the Railway Officials are given brief knowledge of Diesel Electric Locomotives with circuit analysis, as the trouble shooting can not be really done without knowing their working etc. This chapter includes the defects and possibilities of the place of defects with their remedial actions, which can only be rectified en-route. One smart and intelligent official on foot-plate can also attend the troubles, which have not been covered in this, with the help of the schematic diagram attached to this chapter. 2. TROUBLES Road troubles may be classified in two categories : 1. Failure of component, which can not be rectified, but can be temporarily attended or by-passed to save or avoid a road failure. 2. Troubles due to accumulation of foreign particles like dirt, dust, etc, which leads to erratic or non-operation of the respective circuit and component. These faults can be rectified en-route, if they are pin-pointed. Road troubles are experienced in three stages : 1. When the engine is dead and one driver is taking over charge. 2. Engine is idling, when driver is taking charge. 3. Fault or trouble is experienced while loco was hauling the load. 3. TROUBLES IN DEAD AND IDLING LOCOS Normally when one driver takes charge of one locomotive at out-station, he gets the loco in engine idling condition, but sometimes locos are found in dead condition also. During checking of the locomotives, some troubles are faced. They are as under : 1. Engine can not be started 2. Some of the auxiliary machines are not running 3. Loco can not move (Not getting Power) 4. Loco starting with heavy jerk 5. Loco is moving but load-meter is showing zero or negative 6. Low Hauling Power

3.1. Engine not taking start Before going to start the diesel engine, the driver is supposed to put on some of the breakers just to run some of the auxiliary machines and energise some circuits to make the fuel available to the fuel pump etc. The switches and breakers to put on (STARTING SEQUENCE): a) Close the knife switch b) Put on the MB1 (Battery Breaker) c) Put on the MB2 (Control Breaker) d) Put on MCB1 & MCB2 (Master Control Breakers) fitted in the control stands - DMR

should pick up e) Put on MFPB1 & MFPB2 (Master fuel pump breakers) - FPC should pick up f) Put on FPB (Fuel Pump Breaker) g) Put on AFPB (Addl. Fuel pump bkr.) - Fuel Pump Motor should run and fuel pressure

should run and fuel oil pressure should develop g) Put on CEB (Crank case exhauster Breaker) - Crank case motor should run Now engine is ready to take start If any of the motors etc. are not functioning then the machines and respective wires etc. are to be checked according to starting circuit (Aux. Control Circuit) 3.1.1 Engine not cranking To start the engine ECS to be kept in idle and engine start button is to push - CK1 & CK2 should pick up and engine should crank - if not check the interlocks in series with opt. coil of CK1 & CK2 namely, ESR4-N.C. (71-50T), ECS-close (50T-50C), P22-NC(43-43A), S1-NC (43A-43B). If CK1 is picking up and CK2 is not then the interlock of CK1 (43B-43C) is to check for correct operation (it should make when CK1 is closed). 3.1.2 Engine cranking but shuts down with release of Start Button If this fault is experienced, then it is clear that the condition mentioned in 1.1 is fulfilled. The checking regarding this fault are : a) Whether the lube oil pressure is building up or not, operation of OPS (oil pressure switch) can be checked by tthe stop of glowing of engine start lamp provided near the start button.

b) Water level may be inadequate or LWS (low water level switch) is defective - if LWS is in operated condition, then the alarm gong will sound both in idle and run position of ECS. c) Tachometer generator may not be giving out put or taco-generator drive gear is worn out - Tacho-generator wires should be checked for proper connection etc. NOTE In some cases if incoming driver stops the engine at 800c of cooling water temperature, then it takes excessive time to cool down (specially in summer). In that case also fresh driver (out going) could not start the engine because the lube oil pressure does not build up as needed (2 to 2.2 kg/cm2) till engine cools down and viscosity of lube oil increases. 3.2. Not running of auxiliary machines and leads to non-starting of the engine as discussed

above in 1.1 3.3. Loco unable to move (Not getting power) This defect is related mainly with problems in propulsion control circuit, power circuit and excitation circuit. 3.3.1 Not getting power due to defects in propulsion circuit After putting on the GF switch and notching up the throttle to 1st. notch putting the Reverser handle either in forward or reverse, the GF cont. should close. With the closure of GF cont. the traction generator should produce voltage and the power is transmitted to the traction motors to move the wheels. Cause of not getting power to be checked according to the sequence as follows : 3.3.1.1 Check the GF Contactor's operation If not operating - Check BKT1-NC (6-6A) ECS RUN (6A-6B) close GR-NC (6C-6D) TR-NC (6D-6E) CK1-NC (6E-6F) CK2-NC (6F-6H) Maximum possibility of non-operation, however, may be due to welding of either CK1 or CK2 contactor. Sometimes TR interlock (6D-6E) also remains in open condition due to accumulation of dirt. 3.3.1.2 Check the operation of S1, S21 & S31 power contactors 3.3.1.2.1 S1 is not picking up - details of interlocks can be seen through diagrams. Maximum possibilities - (i) Contact of ECS (8D-18A) should remain closed (ii) TR-NC (8E-8F)

(iii) P1-NC (8F-8M) 3.3.1.2.2 S21 is not picking up - (S1 picking up) Maximum possibility - P21-NC (8M-8G) 3.3.1.2.3 S31 is not picking up - (S1 & S21 picking up) Maximum possibility - P31-NC (8M-8G) 3.3.1.3 Position of BKTs and REVs is also to be checked 3.3.2 Power is not getting due to defect in power circuit It is noticed very often that some of the power contactors through which electricity is fed to the traction motors do not operate due to defective magnet valves. Normally defective magnet valves can not be rectified en-route. However, bypassing one or more traction motors loco can be proceeded if possible. In such cases load meter may show or may not show. Power may also not be available due to wheel slip or power ground. Fault may be in the power circuit but the wheel sli[p and power ground will be described in separately. 3.3.3 Power not getting due to defects in Excitation Control Panel The panel is to control the excitation of main generator. Normally the failure of the panel components / cards can not be rectified until there are separate cards available. However, it sometimes happens that two locos are failing with different reasons in one station or place. And if one loco is failing with some trouble in excitation circuit / panel causing no power, can be rectified replacing the cards taking from other loco. a) It is advisable to replace all the excitation panel cards as a set to help the shed people in maintaining record. If any one becomes interested to identify the defective card, the cards are then to be replaced one by one and the result can be seen. Card 253 or 293 or 186 or 188 may be the defective one. Sometimes more than one card may also be found faulty. b) Wire at FCP (field control panel) may get disconnected or burnt. FCP tubes are always hot. They should be allowed to cool down first and then proceed for repair. If it is clear that from which point the wire got disconnected, then they can be connected. c) Sometimes BKR (braking relay) interlocks (22E-32D) and (32C-32D) do not make proper contact. They should be in closed condition during motoring. If there is any dirt accumulation, they can be cleaned. d) LCP (load control potentiometer) in governor may not be touching with commutator and reference voltage increases causing low or no power.. Normally it is due loose brush arm mounting screw. However, before tightening the screw the commutator surface and the brush-arm should be cleaned thoroughly.

e) NO contacts of WSRs (10H-10T) also create this problem being closed. They should be separated if the concerned WSR is not operated. f) If the exciter fails to generate voltage, Traction Generator does not produce output due to no excitation.

By checking the carbon brushes and connection on terminal board, its defect can be identified very often. 3.4. Heavy jerk experienced during starting the loco Jerk is caused due to excessive 1st. notch current to the traction motors. The reason may be the following :(Remedial actions are also indicated) 3.4.1 GF interlock (61E-61EE) may be wrongly adjusted.

It should close when GF contactor is in open condition. If the interlocks are not getting closed properly, they can be rectified bending the finger. Sometimes they remain electrically separated due to accumulation of dirt. This fault can be rectified cleaning the contacts. 3.4.2 Defect in 188 card : Due to sudden notching down, sometimes it happens that diode ERD20 & 21 get punctured (short circuited). It causes no current through suicide winding of PWM (pulse width modulator). By replacing this card with a healthy one the fault can be rectified. In this case availability of spare 188 card is the main factor. 3.4.3 Defect in other cards : Card No. 253, 186, 254 may also create the problem of jerk. In all these cases by replacing the cards the fault can be rectified. 3.4.4 Current flow through PWM suicide winding may also get disrupted if the ER15 resistor inside control compartment gets open circuited and leads to jerk in 1st. notch. In such condition nothing can really be done en-route. It requires replacement. 3.5. Loco is moving but load meter is showing zero or negative Load-meter indicates the current flow through traction motor no.1. S1 power contactor is related with this motor. If S1 does not operate or if there is an open circuit in the concerning circuits, then the load-meter may not show. But in that case full power (in fact the tractive effort) will also not be available.

In some of the cases due to ground fault in battery charging circuit or excitation circuit, polarity of main generator gets reversed and uncontrolled amount of current flows to traction motors in reverse direction. Normally jerk is also experienced during starting of train or locomotive. Engine also sounds unusually due to overloading. Load meter shows negative. To save the traction motors, loco should be stopped as quick as possible. However, the driver can proceed in lower notches with a close watch to the load meter and the shed people is informed for assistance. Fault in excitation circuit also creates this problem. 3.6. Low hauling power In maximum cases, such indication is due to inability of the engine. However, due to defect or mull-operation of the circuits, sometimes, may cause such problems. By checking the rack movement at 8th. notch on load, cause of low HP can be pin pointed. If the rack movement is not maximum as specified (29.5mm in WDM2), then electrical may be held responsible. Of course in case of PG Woodward governor the argument will not stand because insufficient booster pressure or even wrong adjustment inside the governor may also force the rack not to move full. If the rack movement is less than the limit in 8th. notch, then check the following :

3.6.1 In motoring condition, BKR contact 32D-22E should remain closed. Contact can be assured cleaning the contact tip.

3.6.2 Breakage of FCP wire may cause the same problem 3.6.3 Movement (unwanted) of LCP in PG Governor causes this problem. 3.6.4 If the LCP brush-arm of GE Gov. becomes loose, same problem occurs. The

mounting screw is to be tightened then. 3.6.5 Exciter should also be checked for proper brush fitting etc. In case, if the brush sets of brush gear is found defective, one set from another brush gear can be taken out and fitted in the defective gear. One set of brushes per brush gear is allowed in case of emergency. One set from auxiliary generator can also be taken out and fitted accordingly.

3.6.6 Operation of WSR also causes no or low power, which is dealt latter. 3.6.7 Defects in cards : Card 254, 293, 186, 188 may also cause this problem on certain defective conditions. 4. FAULT EXPERIENCED WHEN THE LOCO WAS MOVING In maximum cases locos do fail in this condition, and it has been seen that because of nervousness or inadequate knowledge of the crew, the fault could not be rectified though they should have been rectified en-route with minimum effort.

The failures of this condition can be classified in following categories :

4.8 Engine over-speeds 4.9 Engine not responding to throttle or speed is erratic 4.10Engine hunting 4.11Engine shuts down and crew unable to restart 4.12Low HP 4.13Engine bogs down under load 4.14Operation of ground relay 4.8 Operation of wheel slip relay 4.9 GF not picking up 4.10 Operation of Power Contactors is erratic 4.11 Transition is picking up 4.12 Wheel slip indication in a particular transition 4.13 Hot engine indication 4.14 Battery charging stopped

DEFECT CAUSE REMEDY 4.1 Engine Over-speeds No oil in Gov. Top up (In case of emergency only fuel oil can be used in PG Gov. and in GE Gov fuel oil and crank case oil with a ratio of 2:1 can be used)

Gov. Amphenol plug loose Tighten Tacho gen. wire broken Connect Wire form ECP broken Connect 4.2 Engine not Notch wise ESR oprations Check the broken contact responding to TH are not correct on ESR and connect (erratic speed) Open the back cover of control stand and clean the fingers (ESR operations - ESR1, ESR3, ESR1+3, ESR2+3+4, ESR1+2+3+4, ESR2+3, ESR1+2+3.)

DEFECT CAUSE REMEDY 4.3 Engine hunting Dirty Gov. oil - Change Foaming of Gov. oil Attend leakage Stab. Rheostat dirty or Clean & Tighten brush arm loose.

Wire on ECP or Gov. broken Connect Cam of ECS broken Separate 50L-50P ESR2interlock open (50L-50P) Clean the tips 4.4 Engine shuts down Fuel Booster Pump is not If the motor is working but and unable to restart working pump is not working then (pressure is not building up) coupler allen screw may be There may be two tightened. If the motor is not conditions, either it moving, check. carbon brushes, shuts down on load or comm.and connection to motor without load. If it shuts down on load, then can Breakage of wire in ECP & Gov. Connect be restarted

Breakage of wire in Tach. gen. Connect

Failure of inter locks as indicated Attend as stated in para 1(Engine not cranking) (Unable to start condition) . 4.5 Low HP Discussed in 6. 4.6 Bogs down on load - NC of BKR (32C-32D) Clean

DEFECT CAUSE REMEDY 4.7 GR Operation:- Explosive: Check the source The operation may if from main generator be during engine starting. Such (a) Dirty commutator Clean surface with 00 ground fault is . sand paper commonly known as starting ground (b) Brushes are sticky and is difficult inside pockets Polish the brushes to rectify without adequate facility (c) Pig tails worked Cut the pigtail en-route. The loco out of brush and and throw out may be allowed to touching ground run with this fault. But if it (d) Foreign particle Throw it out is a power ground on commutator The loco fails positively if not rectified. First check whether if from power contactor explosive or non-explosive (a) Metal deposition inside arc Replace with parallel cont. chute arc chute. .

*Loco should run at slow speed so that parallel contactors do not operate. (b) Sluggish operation Disconnecting the magnet valve

of Power Conts on or two motors may be by passed, if the load permits.

(c) Foreign particles Throw it out. If from Traction Motor(s) (a) Commutator dirty Clean (b) Broken or sticky carbon brush Attend as T/Gen (c) Foreign material - do -

If from FS Contactors To be attended as power contactors excepting magnet valve portion.

DEFECT CAUSE REMEDY Non-Explosive:- (A man with knowledge of power circuit can only rectify this type of ground fault with adequate facility eg. Megger, Avometer etc. However, some effort still can be made to find out the faulty member and rectify, if possible, as stated below). Foreign material inside Main Gen, Throw out the foreign material. Traction motor, BKTs, REVs, PCs,FS Conts, WSRR, WSRs,. FCP etc Any broken wire touching Isolate or cut out the piece ground if possible Traction motor cable(s) rubbing Separate them and tieing with with motor cap(s) and the rope so that rubbing avoided insulation is damaged (cut). 4.8 Wheel slip indication:- First locate, which relay is getting energised and at what speed to understand the motor combinations (transition). For 0 to 30KMPH One or some of the FS contactors Separate them manually. Also (1st. Transition) got welded. clean the tips. WSR1 Unequal current flow Check BKT1, REV1 and S1 in TM No. 1 & 4 for proper operation

. Try to make them OK manually if any fault is noticed

WSR2 Unequal current Check BKT2, REV1 and S31 in TM No. 2 & 5 for proper operation. Attend as above . WSR3 Unequal current Check BKT1, REV1 in TM No. 3 & 6 and S21 for correct operation. Attend as above . All the relays are WSRR open circuited Connect the broken wire if operating . possible.

NOTE In some of the cases due to brake binding, wrong adjustment of slack adjuster, inadequate brake cyl. travel, oil dropping on particular wheel etc., wheel slip is experienced. They are also to be checked. Also in case of pinion slip same wheel slip indication will be experienced and can be found out on checking only. DEFECT CAUSE REMEDY Wheel slip experienced One or some of the FS Check for Mechanical blocking. at speed range of contactors are not operating. Check broken wire of opt. coil. 30 KMPH to 47 KMPH or at 30 KMPH only. FS22,23,24 & 26 not operating Check FS21interlock operation

for closure during operation. Check broken wire from opt. coil & interlock. Wheel slip at a speed of 47 KMPH and above WSR1 operating Either P2 or P31 not operating Check leakage on magnet

valves WSR2 operating Either P22 or P32 not operating -do- WSR3 operating Either P1 or P21 not operating -do- Other than these, if any of the six motors got defective, two motors can be isolated and loco can be run with four motors. In that case, S1 or S21 or S31 can be dumied putting wedge inside concerned magnet valve. Following chart will help to locate the concerned contactor for any motor with different WSR operations. Combination Contactor Motors WSRs Series Parallel S1 1 & 4 1 S21 3 & 6 3 S31 2 & 5 2 Parallel P1 & P21 4 & 6 3 P31 &P2 5 & 1 1 P22 & P32 3 & 2 2

Finding out a faulty motor Say, in one locomotive, in series parallel circuit (0 to 47 Kmph) WSR1 is getting operated. S1 magnet valve is to be disconnected or wedged first. If load permits, train speed increase. Transitions will take normally. But when it will attain a speed of 47 Kmph. and second transition will pick up, wheel slip will again be experienced. Check the relay getting operated. If WSR1 is getting operated again, then TM1 is faulty. Disconnect or wedge P2 magnet valve. Above 47 Kmph, the locomotive will run with 5 Motors. If WSR3 operates during parallel transition (above 47 Kmph), isolate TM4 wedging or disconnecting P1 magnet valve. This type of isolation helps in Mail/Express services, where loco runs with lesser loads. DEFECT CAUSE REMEDY 4.9 GF not picking ECS cam broken, unable to put ECS Short circuit 6A-6B up in run (All RUN contacts should be shorted opening IDLE contacts)

GR 6B-6C open Make it close TR 6D-6E open Short the contact. CK1 or CK2 welded Get them separated Make sure that CK16E-6F

& CK2 6F-6H are closed. (Sometimes due to wrong fitting of CK1/CK2 arc chutes causes

this problem.) GF switch defective Both GF switches can't be defective at a time. Find out the defective and short circuit it. Both the switches shouldn't be shorted (GF contactor should not be closed with wedge, because it would give jerk in 1st. notch.) 4.10 Operation of PC are erratic: It is dependent on magnet valve operation. Find out the faulty contactor and operate manually by wedging respective magnet valve armature. If it operates, then check the circuit if given : DEFECT CAUSE REMEDY S1 not operating BKR 8C-8D (NC) open Make them close ECS 8D-18A (RUN) or or clean contact P1 8F-8M (NC) open

DEFECT CAUSE REMEDY S21 not operating P21 8M-8Z (NC) open -do- but S1 operating S31 not operating P31 8M-8G (NC) open -do- S1&S21 operating P1 P21 & P31 not S31 8L-8S (NC) open -do- operating P2 not operating S1 8K-8U (NC) open -do- P22&P32 operating P22 not operating S21 8K-8W (NC) open -do- P2&P32 operating P32 not operating S31 8K-8W (NC) open -do- P2&P22 operating P2, P22 & P32 GF 8L-8R (NC) open or excessive gap Adjust gap (not more than 1/8") not operating of P21 8E-8K (NO) and ensure proper operation . Sometimes Reverser magnet valves do not operate due to loss of contact in control stand. In that case, driver should work from other control stand. Driver should also try to operate from other control stand, in case of any trouble experienced in controlling engine speed. 4.11 Transition is not picking up DEFECT CAUSE REMEDY 1st. Transition not picking up Operation of six FS contactors is the indication of 1st transition. But to operate them, FSR must operate. FSR not operating Close P2 6T-6V (NC) Close S21 6V-6W (NO) Close TR 6W-6X (NC) (If still not working, operate FSR usually because fault is inside first 210 card)

DEFECT CAUSE REMEDY FSR picking up but FS Contactors are Clean FSR 6-19H (NO) (contact not picking up can also be changed with spare) FS21 & FS25 are operating rests FS21 13-19J (NO) is to be are not operating cleaned and broken wire etc. to be connected 2nd. Transition not picking up Operation of six parallel contactors is the indication of 2nd. transition. For their operation TR must operate. TR not picking up Fault inside 2nd. 210 card.

Operate TR manually. (If Manual switch is there, use it.) TR operating but PCs not operating Clean and make TR NO contact 8E-8L

Parallel PCs are operating but GF Make sure that P326C-6E (NO) not picking up is closing Adjust if required

3rd. Transition not picking up Operation of FS contactors is the indication of 3rd. transition. FSR not operating Clean and make TR6V-6X (NO) contact If still FSR not picking up, defect is in 3rd. 210 Card. 4.12 Wheel Slip Indication: - Covered in 3.8 in details. 4.13 Hot Engine indication: It is experienced in summer season to the maximum extent. Normally locos do not fail en-route due to hot engine. But if the locomotive is equipped with ETR, the diesel engine comes to IDLE after ETS operation. As the viscosity of lube oil goes down with increase in temperature, due to sudden fall in engine speed, the lube oil pressure drops below the drop out setting pressure of OPS. As a result engine shuts down and could not be restarted, till the temperature of the diesel engine comes down, and the viscosity of lube oil goes up. Normally most of the sheds bypassed the ETR so that after operation of ETS, engine speed does not drop to idle. Driver gets the audio-visual indication only. Getting this indication, driver should notch

down to 6th. notch or so and slowly pass the blocked section. The alarm gong will go on sounding. As soon as he reaches the next station, he should notch down to 3rd. notch and not to IDLE. GF switch should be put off on 3rd. notch itself, so that the lube oil pressure is maintained at its safe value. After putting off GF, he should start FAST PUMPING. In summer, if engine gets shut down causing low lube oil pressure, it normally takes 1 hour or more to cool in a state when radiator fan does not work, and leads to loco failure. 4.14 Battery is not taking charge: (B.A. showing discharge) It indicates failure of Battery Charging Circuit. Proceed to check the cause as follows : Check VRP fuse Renew with spare if doubtful. Check AGFB Reset if tripped. Check VRP base for loose or cut wire Tighten/connect. Check Aux. Gen. brush gear and brushes. Attend/replace as required. Check BX-BN Card for proper placement. Cards should be placed properly, after

putting off AGFB. 5. Summary

Troubles experienced by the driver or other inspectors travelling in the footplate both in dead and idling locomotives have been dealt in this unit. What could be the probable reasons of troubles and how the trouble shooting should be done have been described in the form of charts. It is expected that this unit would help the officials in footplate to rectify the fault without taking assistance of maintenance people.

The reasons of road failures e.g. engine not taking start, not getting power, low hauling power, load meter showing zero, transition trouble, jerk in first notch, etc. which contribute about 70% of the electrical failures, have been described in this unit. Identification of probable areas, which normally go wrong, would help the Railway in minimising detentions, if appropriate actions are timely taken by the officials on footplate. There are some defects, which, perhaps, are difficult to rectify en-route, without proper assistance and spares, have also been incorporated in this write-up.

6. Self-assessment Exercises

1. Write the probable causes of automatic shut down and suggest en-route trouble shooting for them.

2. What could be the probable reasons of jerk in first notch? What actions could be taken en-route to rectify the defects?

3. How to proceed to rectify a fault of wheel slip? 4. How to identify the cause of low hauling power and what actions should be taken for these

causes? 5. Writ down the steps of checking for battery not taking charge.