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STUDY ABOUT HIGH VOLTAGE SUBSTATIONS.

1)GENERAL CONCEPT OF SUBUTATION:-

Electrical power station, substations and power lines are intended for generating, transmitting and distributing electrical energy among users. In present day electrical power system is A.C. i.e. electrical power is generated, transmitted and distributed in the form of alternating current. The electrical power is produced at the power stations which are located at favorable places. It is deliverable to the customer through a large network of transmission and distribution. This is accompanied by suitable apparatus called substation.

A distinguished characteristic of power generation, transmission, and distribution is continuity, which is due to the fact that electrical energy is consumed at the same time as produced and cannot be stored. Electrical power as the user needs at the moment (with allowance made for auxiliary power requirement and transmission losses).the demand for electric energy varies on both a daily and a yearly basis. Daily variation in power stations and line equipment should be rated for the peak load and ready to give continuous trouble free service during busy hours.

FIG. 1 – HIGH VOLTAGE SUBSTATION

Another distinguishing characteristic of power generation, transmission and distribution is that a electric power station and sub-station are for the most part interconnected by the power lines into an integrated system supplying power to the users throughout an economical region. Therefore any trouble or fault at a specific point or at any one of the substation will affect the performance of the entire

8TH Sem Electrical Engg.


system and may cause an interruption of power supply to the users. A power failure even a small one greatly impairs functioning of induction enterprises, electric transport and municipal utilities. The break down in the production process may result in damage to the products on line and to the production equipment.

Power users are sensitive not only to the power failures but also to variation from rated supply line voltage and frequency. A voltage drop slows down the electric motors abruptly, browns out electric device, radio and TV sets, etc. A decreases of output of the driven machinery and often involve a break down in production process and hence the manufacture of defective products. Therefore if a specific component of electric power plant is out of order, or its performance is erratic, it should be quickly disconnected from the supply lines in order to reduce the harmful consequences of the failures. The voltage of generator at the power plants is usually, 6.6, 13.2 or 15.7 KV to transmit the power over long distances the power and the distance in order to reduce transmission losses and to affect the economy also the customer do not use such high voltage and so they must be transferred to 11 KV by means of the transformer as s/s which is further stepped down at 230 V phase to neutral by means of pole mounted transformer. Thus s/s may be called as link between the generator and consumer.

1.1 substation :-

“The assembly of apparatus used to change some characteristic (e.g. voltage, current, frequency, p.f. etc.) of electric supply is called a Sub-station.”

It is an assembly of apparatus which transformer. The characteristics of electric energy of one form to another (say one voltage to another) i.e. link between the power house and ultimate consumers. A no. of transformers and switching is known as substation. Substations are important part of power system. The continuity of supply depends to a considerable extent upon the successful operation of substations. It is, therefore, essential to execiseut most care while designing and building a substation.



The following are the important points which must be kept in view while laying out a substation :-

1. It should be located at a proper site. As far as possible, it should be located at the center of gravity of load.

2. It should provide safe and reliable arrangement. For safety, consideration must be given to the maintenance of regulation clearances, facilities, for carrying out repairs and maintenance, abnormal occurrences of regulation such as possibility of explosion or fire etc.

3. It should be easily operated and maintained.

4. It should involve minimum capital cost.

1.2 classification of Substation:-

There are several ways of classifying substations. However, the two most important ways of classifying them are according to (1) service requirement, (2) constructional future.

1. According to service requirement: - A substation may be called upon to change voltage level or improve power factor or convert a.c. power into d.c. power etc. According to the service requirement, substation may be classified into:-



1.1 Transformer substations :- Those substations which change the voltage level of electric supply are called transformer substation. These substations receive power at some voltage and deliver it at some other voltage.

1.2 Switching substations:- These substations do not change the voltage level i.g. incoming and outgoing liens heave the same voltage. However they simply perform the switching operation of power lines.

1.3 Power factor correction substations:- Those substations which improve the power factor of the system are called power factor correction substations. Such substations are generally located at the receiving end of transmission Lines.

1.4 Frequency changer substations:- Those substations which change the supply frequency are known as frequency changer substations. Such a frequency change may be required for industrial utilization.

1.5 Converting substations:- Those substation which change a.c. power into d.c. power are called converting substations. These substations receive a.c. power and convert it into d.c. power with suitable apparatus to supply for such purpose as traction, electroplating, electric welding etc.

1.6 Industrial Substations:- Those substations which supply power to individual industrial concerns are known as industrial substations.

2. A ccording to constructional features:- A substation has many components (CB, switches, fuses, etc.) which must be housed properly to ensure continuous and reliable service.

2.1 Indoor substations:- For voltage up to 11 KV, the equipment of the substation is installed indoor because of economic considerations. However when the atmosphere is



contaminated whit impurities, these substation can be erected for voltage up to 66 KV.

2.2 o utdoor substations:- For voltage beyond 66 KV equipment is invariably installed outdoor.

2.3 Underground substations :- In thickly populated areas the space available for equipment and building is limited and the cost of land is high.

2.4 Pole mounted substations:- This is outdoor substation whit equipment installed overhead on H-pole or 4-pole structure. It is the cheapest form of substation for voltage not exceeding 11 KV.

3. CLASSIFICATION OF SUBSTATION ACCORDING TO KV RATING:-

400 KV Sub stations 220 KV Sub stations 132 KV Sub stations 66 KV Sub stations 11 KV sub stations

Location of substations:- Sub transmission circuit should reach as near the load possible and practicable in order to take advantage of sub transmission voltage before it is stepped down. It would, however, be a fallacy to extend these circuits to such a point that their additional cost would exceed the savings in distribution circuit. The balance is influenced greatly by the size and spacing of substations as well as the difference in voltage.

The following points should mainly be taken into consideration in choosing the location of substations:-1. It should be located at a proper site. It should be as close to the load center as

possible.2. It should be so located that all the prospective loads may be contently reached

without undue voltage regulation.3. The incoming transmission lines and outgoing distribution lines should be allowed

access.



4. It should allow for a reasonable amount of expansion of the substation.5. The site should be such that municipal restriction or property law would permit the

type of building necessary for the substation.6. The loads on the substations should be within such limit that an unduly large area or

number of consumers will not be affected in case the station is shut down.7. Cost of the land is less.8. It should provide safe and reliable arrangement.9. It should easily operate and maintained.

1.3 comparisons of outdoor and indoor substations:-

SR. NO

PARTICULER OUTDOOR S/S

INDOOR S/S

1. Space required More Less

2. Time required for erection

Less More

3. Future extension Easy Difficult

4. Fault location Easier Difficult

5. Capital cost Low High

6. Operation Difficult Easier

7. Possibility of fault escalation

Less More



2. GENERAL INTRODUCTION TO HIGH VOLTAGE 400 KV SUBSTATION:-

2.1 INTRODUCTION:-

There are nine substation of 400 KV in Gujarat electricity board FIRST at ASOJ which supplies power to north Gujarat 20 % of G.E.B power is supplies via SOJA substation. It covers 95 % of demand of north Gujarat. SECOND is SOJA substation, which supplies power to south Gujarat. THIRD is JETPUR which supplies power to saurashtra. FOURTH substation is KASOR in kheda. FIFTH is near CHORANIYA at limdi highway. SIXTH is VADAVI and SEVEN is HADALA. EIGHTH is at KANSARI and NINE is AMRELI. And one substation is under construction at KOSAMBA of SCADA base.

Fig-1 SOJA SUBSTATION

SOJA substation is located near the SOJA village. It is located 2 km from Dhendu char Rasta on way of KALOL. It is constructed in the year 1986.

SOJA substation has incoming lines from WANAKBORI, P.G.C.I.L. and GANDHINAGAR. Two 400 KV lines are incoming WANAKBORI and connected to 400 KV side yard which is stepped down by 220 KV yard power to 220 kv and connected to there are six transformer from two coming from WANAKBORI. One 400 KV kanshari line is outgoing. Most of this line is overloaded.

Two lines 220 kV is coming from GANDHINAGAR connected directly to 220 KV yard. The outgoing lines are all 220kv out of 10 outgoing lines four goes to MEHSANA. Two goes to VIJAPUR and two goes to SANRHAL and two circuits to JAMBLA S/S.



GETCO400 KV SOJA S/S

FAULT LEVEL400 KV 220 KV13156.27 MVA 12887.11

MVA18.99 A 33.82

KA

IN SOJA 400KV AND 220 KV SWITCH YARD AS SHOWN IN FIG.

FIG. 220 KV SWITCH YARD

FIG. 400 KV SWITCH YARD

So SOJA supplies power to four districts,

1. MEHSANS2. KUTCH3. BANASKANTHA



4. SABARKANTHA

In SOJA S/S control room is constructed between 220 KV yard and 400 KV yard. On the corner of 400KV yard there is 66 KV S/S which steps down to 400 V for S/S auxiliary’s compressor, battery charger, A.C. plant, switchyard lighting and quarter lighting.

2.2 layouts of substations:-

The layout of substation is done in such a way that the equipment flexible, no. of circuit is limited it the equipment of the load, and the no. Of circuit breakers is reduced. The double bus sections are provided where necessary and the correct size of equipment is chosen. The layout of the equipment in the substation should be such as to avoid consequential damage in case of faults and should have protection. The layout should provide case of inspection and maintenance of the equipment. Fire proof and explosion proof screens and brickwork walls for separation out parts of the equipment for safety should be provided.

In case of high voltage substation most of the equipment is located outdoor. The main control equipment or located in the control room. While laying out the equipment, the necessary clearance between the lines and earth or between lines and section should be maintained and provide safety. The layout is generally shown by a single line diagram.

Single line diagram gives specification of typical equipment used in the substations for illustration.



2 . 3 POWER LINES DIAGRAMS:-

A line diagram of 400/220 KV switch yard equipment with proper locations is shown in schematic diagrams, there is three bus system on both sides of the S/S two main buses and one transfer bus.



2.4 GENERAL INFORMATIONS REGARDING TO 400 KV SOJA SUBSTATIONS:-

Installed capacity = 2*500 MVA

SR. NO.

NAME OF FEEDER LENGTH IN km

DATE OF COMM.

MAX. LOAD IN MW

1. 400KV P.G.C.C. -1 107 28/01/87 596

2. 400 KV WANAKBORI-2 95.1 22/10/88 565

3. 400 KV KANSARI 135 08/02/2000 700

4. 220 K V GANDHINAGAR-1 16 26/11/86 205

5. 220 KV GANDHINAGAR-2 16 29/11/86 205

6. 220 KV MEHSANA-1 17 14/06/94 192

7. 220 KV MEHSANA-2 17 29/11/86 192

8. 220 KV VIJAPUR-1 15 21/03/87 128

9. 220 KV VIJAPUR-2 15 11/01/91 140

10. 220 KV MITHA 45 09/09/98 147

11. 220 KV ONGC 37 29/09/98 010

12. 220 KV JAMLA-1 03.5 14/08/98 180

13. 220 KV JAMLA-2 03.5 05/03/98 180

DATA OF COMMISSIONING:-

400/220/33 KV TRANSFORMER-1 16/01/1987

400/220/33 KV TRANSFORMRE-2 25/11/1988

26/11/1986



3. 400 KV SUB STATION SPECIAL FEATURES:-

400KV Substation is an important substation of G.E.B. looking to constructional details, this substation differs from other 220 KV and 132 KV substation of G.E.B important features by which it differs from others are as under.

3.1 THREE BUS SYSTEM:-

Generally there is one main bus and auxiliary bus in other substation whereas in 400 kv SOJA SUB STATION there are two main buses in 400 kv side as well as 220kv side. Load is being distributed on both buses. In addition to this there is one feeder of bus can be transferred in this bus to isolate the breaker of the feeder without giving interruption of power.

3.2 POWER TRANSFORMERS:-

There is a device which steps up or steps down the voltage depending upon purpose for which it is concentrated. In SOJA SUB STATION step down transformers 220kv are used capacities of power transformers installed at this substation is very large compared to other substation. Here two bank of 400^I3, 220/N 3 33kv, 500MVA power transformers are installed having 3 no. of single phase autotransformers having capacity of 167 MVA. Each phase units are connected from outside from delta connected on L.V. side for two lines there are 6 transformers and one transformer is an oil forced (OFAF). Force cooling exhausts fans and oil circulating pumps also in service at full load when temp. Rises 65oC. relay is provided starts fan for air and pump for oil circulation depending upon temp. Rise.



SPECIFICATIONS ARE GIVEN BELOW:-

MAKE : BHEL BHOPAL 1- PHASE, 50 HZ, 3*167, MVA

= 500 MVA

TYPE OF COOLING : OFAF

LOAD VOLTAGE .HV. : 400 /n 3 KV

LOAD VOLTAGE I.V. : 220/n 3 KV

LOAD VOLTAGE L.V. : 33 KV

LINE CURRENT H.V. : 361.57/723.13 AMP FOR 400KV

LINE CURRENT I.V. : 657.39 /314.78 AMP

LINE CURRENT L.V. : 843.44/1686.87 AMP FOR 220 KV

TEMP. RISE OF OIL : 50OC

WINDING : 55’’C

TOTAL WEIGHT : 162100 KGS.

► 400 / 220 KV power Transformer:-

MVA Capacity & KV

Changes voltage levels.



Step-up & Step-down transformers.

3.3 BATTERY AND PROTECTION SYSTEM:-

For production system 220 V d.c. battery exists in most of the S/S in the protection system work on 220 v D.C. Generally one set of battery charger where is in soja S/S there are two sets of battery is located equally. Each battery set is connected with battery charger heaving auto and manual control and controlling devices to give resultant are distributed on these two D.C. sources. Also two strips coils are provided in each breaker and connected with each D.C source.

3.4 CIRCUIT-BREAKERS:-

Most of the breakers installed at this S/S are ABCB. Working pressure for these is 27-31 kg/cm2. In other S/S the working pressure of breaker is 17-21 kg/cm2. When the air is fed in the CB. The center air resaved plant is providing the air to the CB. Compressors having capacity of 58 kg/cm2 also work simultaneously. In SOJA per compressors 5 kg/m2 capacity is for air resurved.

3.5 REACTORS:-

Shunt reactor is used for long E.H.V. transmission lines to control voltage during low load period and to compensate shunt capacitance of transmission line during low load periods. In soja S/S reactor is provided on 400 KV side to control voltage which is oil filled usually switched when it is necessary to control voltage it is switch on from remote.

3.6 BUS BAR PROTECTION SCHEME:-

Bus bar protection are commissioned in 400 KV as well as 220 KV systems at this SOJA S/S, now hear this scheme is commissioned in G.E.B.

3.7 EVENT LOGGER:-

Scheme of recoding the events occurred during in switchyard is introduced in this S/S. Equipment named event logger is provided along with display monitor and printer. All the scheduled events/status of equipment and fault alarming and without fault alarming events are being recorded in the equipment giving exact timing of events.

3.8 ADDITIONAL PROTECTIONS:-



In addition to general protection being adopted at other s/s 400 kv lines of this s/s are provided with following additional protection.

Micro mho:-

Distance protection in 220kv system are having MM3V type scheme as in 400kv lines micro mho scheme is there consisting of static type relays.

P- 40 :-

In additional to this other main protection scheme is provided for 400kv line which is called phase comparison scheme.

3.9 FAULT LOCATOR:-

Generally, zone of fault is decided form indication of zone under which lines have been tripped. However in addition to this for arriving at exact location of fault addition fault locator devices are provided on 400 KV lines of S/S.

3.10 DISTURBANCE RECODER:-

400 KV line and equipment of this S/S are also connected with one equipment called disturbance recorder. Parameters like current; voltage, etc. are being stored in the memory of this equipment is connected with printer. At the time of any disturbance is in normal conditions. The disturbance recorder the parameter disturbed and gets printed immediately on printer. This of fault condition and pre fault condition except 400KV S/S are now here such facilities are provided.

3.11 CONTROL ROOM:-

For healthy working of precession equipment installed at this S/S the entire control room in centrally air-conditioned. In control room various type of panel for each feeder which consists of various protective relays etc. Air conditioning plant of 55 tones is installed with 100 % stand by.

3.12 250 KVA D.G. SET:-

For reliability of auxiliary power supply a trolley mounted D.G. set of having capacity of 250 KVA is installed at this S/S. this D.G. ste run on auto mode also.

3.13 FIRE FIGHTING SCHEME:-



This scheme is also under progress for S/S which is as under:-

For example emulsifier scheme is adopted. For control room haling type fire fighting scheme is adopted. For yards equipment other than power transformer water scheme is provided.

3.14 CONDUCTOR:-

An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves. The term is also used more specifically to refer to insulating supports that attach electric power transmission wires to utility poles or pylons.

In SOJA ACSR conductor are used. In ACSR 54 Al. and 7 copper conductor are used.

FIG. Conducting copper wire insulated by an outer layer of polyethylene

Some materials such as glass, paper or Teflon are very good electrical insulators. A much larger class of materials, for example rubber-like polymers and most plastics are still "good enough" to insulate electrical wiring and cables even though they may have lower bulk resistivity. These materials can serve as practical and safe insulators for low to moderate voltages (hundreds, or even thousands, of volts).

3.14.1 Breakdown:-

Insulators suffer from the phenomenon of electrical breakdown. When the electric field applied across an insulating substance exceeds in any location the threshold breakdown field for that substance, which is proportional to the band gap energy, the insulator suddenly turns into a resistor, sometimes with catastrophic results. During electrical breakdown, any free charge carrier being accelerated by the strong e-field will have enough velocity to knock electrons from (ionize) any atom it strikes. These freed electrons and ions are in turn accelerated and strike other atoms, creating more charge carriers, in a chain reaction. Rapidly the insulator becomes filled with mobile carriers, and its resistance drops to a low level. In air, the outbreak


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of conductivity is called "corona discharge" or a "spark." Similar breakdown can occur within any insulator, even within the bulk solid of a material. Even a vacuum can suffer a sort of break down, but in this case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself.

3.14.2 Uses:-

Insulators are commonly used as a flexible coating on electric wire and cable. Since air is an insulator, no other substance is needed to "keep the electricity within the wires." However, wires which touch each other will produce cross connections, short circuits, and fire hazards. In coaxial cable the center conductor must be supported exactly in the middle of the hollow shield in order to prevent EM wave reflections. And any wires which present voltages higher than 60V can cause human shock and electrocution hazards. Insulating coatings prevent all of these problems.

In electronic systems, printed circuit boards are made from epoxy plastic and fiberglass. The nonconductive boards support layers of copper foil conductors. In electronic devices, the tiny and delicate active components are embedded within nonconductive epoxy or phenol plastics, or within baked glass or ceramic coatings.

In microelectronic components such as transistors and ICs, the silicon material is normally a conductor because of doping, but it can easily be selectively transformed into a good insulator by the application of heat and oxygen. Oxidized silicon is quartz, i.e. silicon dioxide.

In high voltage systems containing transformers and capacitors, liquid insulator oil is the typical method used for preventing sparks. The oil replaces the air in any spaces which must support significant voltage without electrical breakdown. Other methods of insulating high voltage systems are ceramic or glass wire holders and simply placing the wires with a large separation, using the air as insulation.

3.14.3 Power transmission insulators:-

Suspended wires for electric power transmission are bare, except when connecting to houses, and are insulated by the surrounding air. Insulators are required at the points at which they are supported by utility poles or pylons. Insulators are also required where the wire enters buildings or electrical devices, such as transformers or circuit breakers, to insulate the wire from the case. These hollow insulators with a conductor inside them are called bushings.



11 kV ceramic insulators, showing sheds

3.14.4 Material:-

Insulators used for high-voltage power transmission are made from glass, porcelain, or composite polymer materials. Porcelain insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed water. Insulators made from porcelain rich in alumina are used where high mechanical strength is a criterion. Porcelain has a dielectric strength of about 4–10 kV/mm. Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains. Some insulator manufacturers stopped making glass insulators in the late 1960s, switching to ceramic materials.

The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways:

• Puncture voltage is the voltage across the insulator (when installed in its normal manner) which causes a breakdown and conduction through the interior of the insulator. The heat resulting from the puncture arc usually damages the insulator irreparably.

• Flashover voltage is the voltage which causes the air around or along the surface of the insulator to break down and conduct, causing a 'flashover' arc along the outside of the insulator. They are usually designed to withstand this without damage.


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Most high voltage insulators are designed with a lower flashover voltage than puncture voltage, so they will flashover before they puncture, to avoid damage.

Dirt, pollution, salt, and particularly water on the surface of a high voltage insulator can create a conductive path across it, causing leakage currents and flashovers. The flashover voltage can be more than 50% lower when the insulator is wet. High voltage insulators for outdoor use are shaped to maximize the length of the leakage path along the surface from one end to the other, called the creep age length, to minimize these leakage currents. To accomplish this the surface is molded into a series of corrugations or concentric disk shapes. These usually include one or more sheds; downward facing cup-shaped surfaces that act as umbrellas to ensure that the part of the surface leakage path under the 'cup' stays dry in wet weather. Minimum creep age distances are 20–25 mm/kV, but must be increased in high pollution or airborne sea-salt areas.

3.14.5 Cap and pin insulators:-

FIG.Cap and pin insulator string (the vertical string of discs) on a 275 kV suspension pylon.

Higher voltage transmission lines use modular cap and pin insulator designs (see picture above). The wires are suspended from a 'string' of identical disk-shaped insulators which attach to each other with metal clevis pin or ball and socket links. The advantage of this design is that insulator strings with different breakdown voltages, for use with different line voltages, can be constructed by using different


http://en.wikipedia.org/wiki/File:Pylon.detail.arp.750pix.jpg


numbers of the basic units. Also, if one of the insulator units in the string breaks, it can be replaced without discarding the entire string. They are constructed of a ceramic or glass disk with a metal cap and pin cemented to opposite sides. In order to make defective units obvious, glass units are designed with Class B construction: an overvoltage causes a puncture arc through the glass. The glass is heat-treated so it will shatter, making the damaged unit visible. However the mechanical strength of the unit is unchanged, so the insulator string will stay together. Standard disk insulator units are 10 inches (25 cm) in diameter and 53⁄4 in (15 cm) long, can support a load of 80-120 kN (18-27 klbf), have a dry flashover voltage of about 72 kV, and are rated at an operating voltage of 10-12 kV.[5] However, the flashover voltage of a string is less than the sum of its component disks, because the electric field is not distributed evenly across the string but is strongest at the disk nearest to the conductor, which will flashover first. Metal grading rings are sometimes added around the lowest disk, to reduce the electric field across that disk and improve flashover voltage.

FIG. DISK TYPE INSULATOR


Line voltage(kV)

Disks

34.5 3

46 4

69 5

92 7

115 8

138 9

161 11

196 13

230 15

287 19

345 22

360 23


3.14.6 Insulation of antennas:-

FIG. Egg shaped strain insulator

Often a broadcasting radio antenna is built as a mast radiator, which means that the entire mast structure is energized with high voltage and must be insulated from the ground. Steatite mountings are used. They have to withstand not only the voltage of the mast radiator to ground, which can reach values up to 400 kV at some antennas, but also the weight of the mast construction and dynamic forces. Arcing horns and lightning arresters are necessary because lightning strikes to the mast are common.

Guy wires supporting antenna masts usually have strain insulators inserted in the cable run, to keep the high voltages on the antenna from short circuiting to ground or creating a shock hazard. Often guy cables have several insulators, placed to break up the cable into lengths that are not submultiples of the transmitting wavelength to avoid unwanted electrical resonances in the guy. These insulators are usually ceramic and cylindrical or egg-shaped (see picture). This construction has the advantage that the ceramic is under compression rather than tension, so it can withstand greater load, and that if the insulator breaks the cable ends will still be linked.

These insulators also have to be equipped with overvoltage protection equipment. For the dimensions of the guy insulation, static charges on guys have to be considered, at high masts these can be much higher than the voltage caused by the transmitter requiring guys divided by insulators in multiple sections on the highest masts. In this case, guys which are grounded at the anchor basements via a coil - or if possible, directly - are the better choice.

Feed lines attaching antennas to radio equipment, particularly twin lead type, often must be kept at a distance from metal structures. The insulated supports used for this purpose are called standoff insulators.


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3.15 SUBSTATION EQUIPMENT AND THEIR FUCTIONS:-

SR. NO.

EQUIPMENT FUNCTIONS

1. BUS-BAR Incoming and outgoing circuits connected to bus-bar.

2. CIRCUIT BREAKERS Automatic switching during normal or abnormal condition.

3. ISOLATORS Disconnectction under no-load condition for safety, isolation and maintenance.

4. EARTHING SWITCH To discharge the voltage on deadlines to earth.



5. POWER TRANSFORMER To step-up or step-down the voltage and transfer power from one a.c. voltage to anther a.c. voltage at the same frequency.

6. CURRENT TRANSFORMER To step-down current for measurement, control and protection.

7. VOLTAGE TRANSFORMER To step-down current for measurement, control and protection.

8. LIGHTNING ARRESTER To discharge lighting over voltage and switching over voltage to earth.

9. SHUNT REACTORS To provide reactive power compensation during low loads.

10. SERIES REACTORS To reduce the short circuit current or stating current.

11. NEUTRAL-GROUNDING RESISTOR

To limit the earth fault current.

12. COUPLING CAPACITORS To provide connection between high voltage line and power line carrier current equipment.

13. LINT TRAP To prevent high frequency signals from entering other zones.

14. SHUNT CAPACITORS To provide compensations to reactive loads of lagging power factors.

15. SERIES CAPACITORS Compensation of series reactance of long lines.

3.16 VARIOUS SUBSYSTEMS IN SUBSTATIONS AND THEIR FUNCTIONS:-

SR. NO.

SYSTEM FUNCTIONS

1. SUBSTATION EARTHING SYSTEM

- Earth mat- Earthing spikes- Earthing risers

To provide and earth mat for connecting neutral points, equipment body, support structures to earth. For safety of personnel and enabling earth fault protection.

2. OVERHEAD EARTH WIRE SHIELDING

To protect the outdoor substation equipment from lightning strokes.

3. ILLUMINATION SYSTEM To provide illumination for vigilance,



- For switchyards- Buildings- Roads. Etc.

operation and maintenance.

4. PROTECTION SYSTEM- Protection relay panels- Control cables- CB- CTs, VTs , etc.

To provide alarm or automatic tripping of faulty part from healthily part and also to minimize damage to faulty equipment and associated system.

5. CONTROL CABLING For protective circuit, control circuit, metering circuit is a underground power cables.

6. POWER CABLES To provide supply path to various auxiliary equipment and machines.

7. PLCC SYSTEM POWER LINE CARIER CURRENT SYSTEM

- Line trap- Coupling capacitor- PLCC panels

For communications, telemetry, power line carrier protection etc.

8. FIRE FIGHTING SYSTEM - Sensors, detection

system- Water tank and spray

system

To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to affected region to pin- point location of fire by indication in control room.

9. COOLING WATER SYSTEM - Coolers- Water tank

This system is required for cooling the valves in HVDC substation.

10. DC BATTERIES SETS AND BATTERYS CHARGERS

Auxiliary low voltage DC supply.

11. AUXILIARY STANDBY POWER SYSTEM

- Diesel generator sets- Switchgear- Distribution systems

For supplying starting power standby power for auxiliaries.

12. TELEPHONE, TELEX SYSTEM MICRIWAVE SYSTEM

For internal and external Communication.

3.17 MAIN DATA OF A TYPICAL 400/230 KV OUTDOOR AC SUBSTATION:-

OPERATING VOLTAGE 400 KV 230 KV

Rated current 2000A 2000A

Maximum short circuit current in bus bar 40 KA 40 KA



Minimum phase to phase clearance 5.75 m 2.5 m

Minimum phase to earth clearance 3.65 m 2.0 m

Number of horizontal bus bar of first level above ground

2 2

Height of tubular bus bar of first level above ground

7 m 6 m

Height of tubular bus bar of second level above ground

13 m 4 m

Tubular aluminum bus bar A1 ASTM B241 4”IPS 4”IPS

3.18 corona and corona loss:-

When the alternating potential between two parallel conductors’ increases beyond a certain limit, a point is reached when pale violet glow appears on the conductor surface, and accompanied by a hissing sound. This phenomenon is known as corona. The atmosphere contains some charged practical or ions and flow of current through a conductor causes such particles to move, which collide in their transit with the uncharged particles in air.

The phenomenon of corona is accompanied by a hissing sound, production of ozone, power loss and radio interference. The higher the voltage is raised, the larger and higher the luminous envelope becomes and greater are the sound, the power loss and the radio noise. If the applied voltage are increased to breakdown value, a flash over will occur between the conductors due to the breakdown of air insulation.

“The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as corona.”

Factor affecting corona:- The phenomenon of corona is affected by the physical state of the atmosphere as well as by the conditions of the line. The following are the factors upon which corona depends:-

1) Atmosphere:- as corona is formed due to ionization of air surrounding the conductors, there ions is more than normal and as such corona occurs at much less voltage as compared with fair weather.



2) Conductor size: - the corona effect depends upon the shape and condition of the conductors. The rough and irregular surface will give rise to more coronas because unevenness of the surface decreases the value of breakdown voltage.

3) Spacing between conductors:- if the spacing between the conductors are made very large as compared to their diameters, there may not be any corona effect.

4) Line voltage: - the line voltage greatly affects corona. If it is low, there is no change in the conductor of surrounding the conductor and hence no corona is formed.

Corona loss:- “The power is dissipated in the power system due to corona discharge is known as corona loss.”

When the surface voltage gradient at line conductor exceeds the critical breakdown stress, corona appears and energy is dissipated in form of light and heat. This called corona loss.

FACTOR AFFECTING CORONA LOSS:-

I. Effect of frequencyII. Effect of system voltage

III. Effect of conductivity of airIV. Effect of conductor diameterV. Effect of conductor’s surface

VI. Effect of atmospheric condition

Advantages and disadvantages of corona:-

Advantages:- 1. Due to corona formation, the surrounding the conductor becomes conducting and

hence virtual diameter of the conductor is increased.2. Corona reduced the effects of transients produced by surges.

Disadvantages:-1. Corona is accompanied by a loss of energy. This affected the transmission efficiency

of the line.2. Ozone is produced by corona and may cause corrosion of the conductor due to

chemical action.

In substation corona losses are less produced in round shape. So corona is reduces by using the corona ring.



Fig. corona ring Fig. corona ring used in connection

4. DETAIL OF SWITCHGEAR AT SUBSTATION:-

4.1 INTRODUCTION:-

In outdoor installations the various substation equipments are like CB, isolator, LA, relays etc installed under open sky. Necessary clearances are providing



between phases, phase, and ground. The equipment outdoor switchgear is manufactured separately and is erected at site as per the switchyard layout.

The fault is very essential in transmission, distribution i.e. short circulating and interrupting fault currents. In order to avoid damages equipment due to fault current every part of instruction to the associated CB to open. All equipment associated with the fault clearing processes are covered by the switchgear. Switchgears can also be fuses, CB, isolators, LA, CTs, PTs, relays, control panels etc.

Some of them are discussed:-

4.2 CIRCUIT BREAKER:-

INTRODUCTION:-

The CB plays an important role in the design and performance of power system during normal operating condition. A circuit breaker is a switching and current interrupting device in switchgear.

A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual appliance up to large switchgear designed to protect high voltage circuits feeding an entire system.

A circuit breaker is a piece of equipment which can,i) Make or break a circuit either manually or by remote control under normal

conditionsii) Break a circuit either normally under fault conditionsiii) Make a circuit either manually or by remote control under fault conditions



Operation:-

All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.

In low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source.

Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded case circuit breakers are usually discarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.

When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms.

Different techniques are used to extinguish the arc including:

• Lengthening of the arc

• Intensive cooling (in jet chambers)

• Division into partial arcs

• Zero point quenching [clarification needed]

• Connecting capacitors in parallel with contacts in DC circuits

Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.



Arc interruption:-

Miniature low-voltage circuit breakers use air alone to extinguish the arc. Larger ratings will have metal plates or non-metallic arc chutes to divide and cool the arc. Magnetic blowout coils deflect the arc into the arc chute. In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc. Gas (usually sulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc. Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (<2–3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts. Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc. Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished between 30 ms and 150 ms after the mechanism has been tripped, depending upon age and construction of the device.

Short circuit current:-

Circuit breakers are rated both by the normal current that are expected to carry, and the maximum short-circuit current that they can safely interrupt.

Under short-circuit conditions, a current many times greater than normal can exist (see maximum prospective short circuit current). When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc. In air-insulated and miniature breakers an arc chutes structure consisting (often) of metal plates or ceramic ridges cools the arc, and magnetic blowout coils deflect the arc into the arc chute. Larger circuit breakers such as those used in electrical power distribution may use vacuum, an inert gas such as sculpture hexafluoride or have contacts immersed in oil to suppress the arc. The maximum short-circuit current that a breaker can interrupt is determined by testing. Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset.

Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panel board; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers.



Classification of CB:- The type of CB is usually classified according to the medium of arc extinction and is as follow:-

1. Air break CB, miniature CB2. Air blast circuit CB (A.B.C.B.)3. Oil filled CB4. Minimum oil CB5. SF6 CB6. Vacuum CB

In substation most of A.B.C.B., SF6 CB, and vacuum CB are used.

4.2.1 AIR BLAST CIRCUIT BREAKERS (A.B.C.B.):-

At SOJA S/S both in 400 KV and 220 KV yard A.B.C.B. type are used. Air blast C.B. is used today 11 to 1100 KV for various applications. They offer several advantages such as faster operation suitability for repeat operations, auto closure unit type multi break construction. Simply assembly modest maintenance etc. a compressor plant is necessary to maintain high air pressure in the air receiver.

COSTRUCTION OF AN A.B.C.B.:-

In A.B.C.B high pressure air is forced on the arc through a nozzle at the instant of contact separation. The ionized medium between the contacts is blown away by the blast of the air. The ionized medium between the contacts is blown away by the blast of the air. After the arc extinction the chamber is filled with high pressure air which prevents restike. In some low capacity C.B. the isolator is an integrals part of the C.B. the C.B. opens and immediately after that the isolator opens.

COMPREEED AIR SYSTEM FOR A.B.C.B:-

The EHV- A.B.C.B. is outdoor equipment. The air pressure in the receivers of the C.B. is of the order of 20-30 kgf/cm2. The local receivers are of such a size that the air pressure is maintained for some 4 to 12 repeated operations. When the pressure in the receiver of the breaker recues below a certain limit {say 20 kgf/cm2} the pneumatic valves automatically open and air system of higher pressure {30 to 40 kgf/cm2} and pressure in the air receiver in maintained a desired value.



USE OF AIR DRIVERS:-

Remove the dust particle, gases, moister etc.



SEPCIFICATIONS AND RATING OF A.B.C.B :-

FOR 400 KV:-

MAKE : A.B.B.REATED VOLTAGE : 420 KVFREQUENCY : 50 HzNORMAL CURRENT : 2000 AMPBREAKING CURRENT : 37.5 KAOUT OF PHASE CURRENT : 7.78 KASHORT TIME CURRENT : 31.5 KA TO 35 KATRIP COLI VOLTAGE : 220 V D.C.CLOSE COIL VOLTAGE : 220 V D.C.RIL AT 50 Hz : 680 KVIMPULSE VOLTAGE : 1.2/50 MS, 1425 KV PEAKAWITCHING IMPULSE : 1050 KVMASS : 3120 kgSOPERATING PRESSURE : 27.21 Kg/Cm2

FOR 220 KV:-

MAKE : A.B.B.REATED VOLTAGE : 245 KVFREQUENCY : 50 HzNORMAL CURRENT : 2000 APMBREAKING CURRENT : 31.1 KAASYM : 35.4 KAMASS : 16.30 Kgs SHORT TIME CURRENT : 55 KATRIP COLI VOLTAGE : 220 V D.C. CLOSE COIL VOLTAGE : 220 V D.C.OPERATING PRESSUR : 27-31 KA/CM2

MARITS:- Air can be used at high pressure. Reliable operation due to external source of extinguishing energy. Free from decomposition. Clean, non inflammable. Freely available everywhere. Suitable pressure, the small contract travel is enough. High speed of operation.



Rapid auto recourse. Clean service no need of maintenance of oil. The risk of fore is eliminated.

Demerits:- The air has relatively inferior arc extinguishing properties. The air blast C.B. is very sensitive to the variation in the rate of rise of restricting

voltage. Considerable maintenance is required for the compressor plant which supplies the

air blast.

4.2.2 SULPHER HEXAFLURIDE (SF 6) C.B.:-

INTRODUCTION:-

SF6 is an inter gas having good dielectric and arc extinguishing properties. The dialectic strength of the gas increased with pressure and is more than that of dielectric of oil at a pressure of 3 kg/cm2. Several types of SF6 C.B. have been developed by various manufactures for rated voltage 3.6 KV to 760 KV.

C.B. have two types:-

1. Single pressure puffer type

2. Double pressure puffer type



At SOJA S/S in 220 KV yard single pressure type C.B. are used and in 400 kv yard double pressure type are used.

4.2.1 FUNCTION:-

In SF6 C.B. gas is used as an arc quenching medium dielectric strength of SF6 gas is more than that of air so the process of arc extinction is fast.In fig. shown single pressure puffer SF6 C.B. the two interrupters are mounted on hollow support insulator. The principal of are interruption is illustrated in fig. the operating mechanism installed at the base of the insulator is linked with the movable contact in the interrupter by means of insulating operating rod and a link mechanism. During the operating operation, the operating rod is pulled down motion in to horizontal motion. The link mechanism converts thee vertical. The contact and the movable cylinder in the interrupter are moved against the fixed position.



ADVANTAGES:- Due to superior arc quenching properly of SF6, such C.B. has very short arcing time. Since the dielectric strength of SF6 is 2 to 3 times, such C.B. can interrupt much

larger currents. The SF6 C.B>gives noiseless operation due to its closed gas circuit and no exhaust to

atmosphere unlike the air blast circuit breaker.



The closed gas enclosure keeps the interior dry so that there is no moisture problem.

There is no risk of fire. There are no carbon deposits. No frequent contact replacement. No over voltage problems.

DISADVANTAGES:- SF6 BREAKER is costly due to high cost of SF6. Since SF6 gas has to be reconditioned after every operation of the breaker,

additional equipment is required for this purpose. Double pressure sf6 C.B. is very costly.

SEPCIFICATION AND RATING OF SF 6 C.B.:-

FOR 400 KV:-

MAKE : A.B.B.

RATED VOLTAGE : 420 KV

Va : 220 V D.C.

FREQUENCY : 50 Hz

VW : 1425 KV

VS : 1050 KV

NORMAL CURRENT : 2000 AMP

SHORT CIRCUIT CURRENT : 40 KA

NORMAL PRESSURE : 7.0 BAR

OPERATING PRESSUER : 31.5 BAR

FOR 220 KV:-

MAKE : A.B.B.




RIL AT 50 Hz : 460 KV

NORMAL CURRENT : 2000 AMP

BREAKING SYM : 40 KA

SYSM : 48 KA

MASS : 2310 kg

SHORT TIME VOLTAGE : 40 KA 3-set

TRIP COIL VOLTAGE : 220 V D.C.

CLOSE COIL VOLTAGE : 220 V D.C.

IMPULSE VOLTAGE : 1.2/50 Hz, 1050 KV PEAK

OPERATING PRESSURE : 6 BAR

4.3 LIGHTING ARRESTORS:-

INTRODUCTION:-

Lighting is one of most serious cause of over voltage. If the power equipment specially at outdoor S/S which is not buzzing of insulation. Lighting is a Hugh spark caused by the electrical discharge taken place between the clouds, within the same clouds and between the clouds and the earth. The earthing screen and ground wires can well protect the electrical system direct lighting strokes but they fail provide protection against travelling wave which may reach the terminal apparatus. The lighting arrester or surge diverter provides protection against such surges. A lighting arrester or surge diverter is a protective device which conducts the high voltage surge on the power system to the ground.

As shown the basic form of a surge diverter. It consists of a spark gap in series with a non-liner resistor. One end of the diverter is connected to the terminal of equipment to be protected and the other end is effectively ground. The length of the gap is so set that normal line voltage is not enough to cause an arc across the gap



but a dangerously high voltage will break down the air insulation and form an arc. The property of the non-liner resistance is that its resistance decreases as the voltage increase and vice versa. LA should not carry any current during the normal operation. But during the over voltage surges are must provide and easy path to the earth. It means that power frequency is not function when abnormal frequency is applied. When the voltage is normal the resistance of L.A. is high and when the voltage is high the resistance of L.A. is low. The L.A. is worked on this function.

The following are the different types of L.A. which are commonly used.

1. Rod gape arrestor2. Sphere gap arrestor3. Horn gap L.A.4. Impulsive protective gap with electrolyte L.A.5. Expolsion type L.A.6. Electrolytic type L.A.7. Lead oxide peroxide type 8. Pellet type peroxide type9. Thyrite type10. Valve type

FIG. DIFFERENT TYPE OF L.A.



SELACTION OF L.A.:- It should take no current during normal power frequency condition. Transient over voltage of L.A. more than insulation withstand level should be

diverted to earth. The voltage across arrestor during discharge should not be too low or too high. Normal condition should be restored soon after the surge has been diverted.

When L.A. is connected between phase and earth the rated voltage of arrestor must be equal of more than the highest r.m.s .value of the power frequency voltage which can applied to it under normal condition.

SPECIFIATION OF 400KV L.A.:- Type : CPL surge arrestorVoltage max : 336 KVCurrent : 10 KANo. of units : 3Make : Elpro instrument Ltd.Station type : Zinc Oxide

4.4 ISOLATORS:-

INTRODUCTION:- Isolator are disconnecting switches which operates under no load condition isolator are designed to open and close under no load condition. Isolator does not have any specified current breaking or current making capacity.To prevent the mal-operation the isolator is provided with the interlocking.

1. Interlocking between the poles for simultaneous operation.2. Interlocking with C.B.

Isolator cannot open if C.B. is open and cannot be closed unless the C.B. is closed.



TYPES OF ISOLATORS:- Vertical break typeHorizontal break typeCenter breakDouble breakVertical pantograph type

At SOJA S/S in 400 KV yard pantograph isolator and center break are used. While in 220 KV yard center break isolator are used.

The operation mechanism for isolator is one of the following:-A. ManualB. Pneumatic mechanismC. Electrical motor mechanism

PENTOGRAPH ISOALTOR:-

It is shown fig. the construction of a typical pantograph isolator while closing the linkage of pantograph are brought nearer by rotating there insulator column. In closed position the upper two arms of the pantograph close on the overhead station bus bar given a grip. The current is carried by the upper bus bar to the lower bus bar through the conducting arms of the pantograph. While operating the rotating insulator column is rotated about its axis. There by the pantograph blades collapses isolator in vertical plane and vertical isolation is between the lines terminal and pictograph upper terminal isolator cover less floor area. At SOJA S/S pantograph isolator are operated manually and by electric motor mechanism both.

RATING AND SPECIFICATION:-

PENTOGRAPH ISOLATOR FOR 400 KV:-

OPERATING MECHANISM : Manual & electrical

VOLTAGE : 420 kV

RETED CURRENT : 2000 Amp.

SHORT TIME CKT DURATION : 40 KA/SEC

FREQUENCY : 50 Hz

WEIGHT OF ISOLATOR : 1200 Kegs.

MAKE : S & S Switchgear Ltd. Madras



CENTER BREAK (HORIZONTAL) ISOLATOR FOR 220 KV:-

MAKE : switchgear Mfg. Co. Pub. Ltd. , Hyderabad, India.


NORMAL CURRETN : 2000 KA

Ith : 40 KA

Vb : 1425 KV

Vs : 1050 KV

DRIVE : VS = 230 V D.C.

VM = 415 V D.C.

FREQUENCY : 50 Hz

CENTER BREAK ISOLATOR FOR 220 KV:-

MAKE : S & S Switchgear Ltd. Madras


NORMAL CURRETN : 1600 AMP

SHORT TIME AMP. : 40 KA/sec

IMPULSIVE VOLTAGE : 1050 KV

OPERATING MECHANISM : Manual

FREQUENCY : 50 Hz

4.5 EARTHING SWITCH:-

Earthing switch is connected between the line conductor and earth. Normally it is open when the line is disconnected, the earthing switch is closed so as the discharge the voltage trapped on the line. Through the line is disconnected, there is some voltage on the line to which the capacitance between line and earth is charged. This voltage is significant in high voltage system. Before proceeding with the maintenance work these voltage are discharged to earth by closing the earth switch.



Normally the earthing switches are mounted on the frame of the isolator.

SEQUENCY OF OPERATION WHILE OPNING AND CLOSING A CIRCUIT:-

WHILE OPENING:-

Open C.B. at both end S/S (first receiving end and then the at sending end) Open isolator -do- Close earthing switch -do-

WHILE CLOSING:-

Open Earthing switch at both end S/S Close Isolator -do- Close C.B. -do-

4.6 Transformer:-

Basic Concepts:-

A transformer is a static device which consists of two or more stationary electric circuit interlinked by a common magnetic circuit fir the purpose of transferring electrical energy between them. The transfers of energy form one circuit to another takes place without a change in frequency.

A transformer is a static piece of equipment used either for raising or lowering the voltage of an A.C supply with a corresponding decrease or increase the current. It mainly consists of two windings, the primary and the secondary, wound on a common laminated magnetic core. The winding connected to the A.C source is called primary winding and one connected to the load is called the secondary winding. The A.C voltage whose magnitude is changed is connected to the primary winding. Depending upon the numbers of turns of primary and secondary an alternating e.m.f is induce in secondary. This induce e.m.f in the secondary causes a secondary current. Consequently, terminal voltages appear across the load. If secondary voltage is greater than the primary voltage so it called as step up transformer, and if it less then so it called as step down transformer.



Working:-

When an alternating voltage is applied across the primary, due to that the current flows from the core. According to this an alternating flux is produce in the core. This flux links the both windings and induces e.m.f. according to the Faraday’s law of electromagnetic induction.

The following points may be noted carefully:-

1) The transformer action based on the law of electromagnetic induction.

2) There is no electrical connection between the primary and secondary. The A.C power is transferred from primary to secondary through magnetic flux.

3) There is no change in frequency.

4) The loses that occurs in the transformer are:

(i) Core losses- eddy current loss and hysteresis losses

(ii) Copper losses - in the resistance of the windings.

However in the practice, these losses are very small so that output power is nearly equal to the input primary power. So transformer has very high efficiency.



Types of Transformer:-

Depending upon the manner in which the primary and secondary are wound on the core, transformers are of following types:

1. Core type transformer, Shell type transformer2. Tap changing transformer3. Auto Transformer

Tap Changing Transformer:-

It is one of the most important transformers used to control the voltage. This method is commonly employed where main transformer is necessary. In this method a number of tapings are provided on the secondary of the transformer. The voltage drop in the line is supply by changing the secondary e.m.f. of the transformer through the adjustment of its number of turns.

There are mainly two types of tap changing transformer:

(i) Off load tap changing transformer

(ii) On load tap changing transformer

Off Load Tap Changing Transformer:-

In this transformer toppings are provided on the secondary side of transformer. As the position of tap is varied, the effective numbers of tapings are varied and hence the output voltage of the secondary can be changed. During the period of the light load the voltage across the primary is not much below the alternating voltage, so movable arm is on first stud. As the load increase, the voltage across the primary drops, but the secondary voltage can be kept at previous value by placing the movable arm on to a higher stud.


Transformer PartsMain Tank

HV & LV & NEUTRAL bushingsOLTCRadiatorBreatherMOGExplosion vent

Oil Circulating pumpBuchcholz relay .PRVOSROTI & ITS POCKET AT TOP PLATE.WTI * ITS POCKET AT TOP PLATE.Cooling fan


The main disadvantages of this type are that it can’t be used for tap changing at on load.

On Load Tap Changing Transformer:-

In supply system, tap-changing has normally to be performed on load so that there is no interruption in supply. In this the secondary consists of two equal-parallel windings which have similar tapings 1a…..5a and 1b….5b. In the normal working conditions, switches a, b and tapings with the same numbers are remain closed. Each secondary winding caries one-half of the total currents. Secondary voltage will be maximum where switches a, b and 5a, 5b are closed. However the secondary voltage. Voltage will be minimum when switches a, b and 1a, 1b are closed.

The main disadvantages of this method are as follows:

1. During switching, the impedance of transformer is increased and there will be a voltage surge.

There are twice as many tapings as the voltage steps.



CURRENT TRANSFORMER:-

INTERDUCTION:-

“A current transformer is defined as a transformer use with electrical measuring instruments and electrical protective device for the transformer of current and in which the current in the secondary winding in normal condition of use, is substantially proportional to the current in the primary winding and differing from it by an angle which is approximately zero for an appropriate direction of connections.

Current transformers are subdivided into two main categories from consideration of their duty requirement:-

1. Measuring current transformers:- Measuring C.T. is intended to supply to the indicating instruments, in degrading meter and similar apparatus. It has to be accurate within a specified working and integrating meters. Accuracy is not required on the high over current on fault indication.

2. Protection current transformer:- Protective C.T. is intended to supply current to protective devices. It is also generally required to have such accuracy class at normal current values but on the constant degree or accuracy on current in fault condition such as over current when actually the protective gear has to function. It is worthily or more that dual purpose C.T. are also in service for dual purpose i.e. both for measurement and protection. But care has to be taken in this case to see that the total connection burden or measuring and protective devices shall not exceed the lower or the C.T. viz one burned as measuring C.T. in other that accuracy as specified can be maintained.

CONSTRUCTION:- The C.T. has a two winding one is primary second is secondary winding. The primary conductor is at high voltage w.r.t. earth. Hence it is insulated by means of an insulator column filled with dielectric oil. The secondary winding conductor is then wound on the insulated core in the form of tutorial winding by hand winding or insulation resistance as two mega ohms. A polarity marking are properly done after a careful check. The connection of the various leads from the secondary winding should be marking. The normal rated secondary current is 5.0. Amp. Sometimes the current of 5.0 amps or 1.0 amp are also taken as second any current some also details is shown in figure.



FIG. C.T. FIG. LIVE TANKS OF CTs

C.Ts. Transforms current from say 1000 A to 1 A. Used as Metering and Protection Different range of C.T. ratio 1000/1 A, 600/1 A, 300/1 A, 150/1 A

SEPCIFICATION OF C.T. FOR 400 KV TYPE:-

MAKE : W.S. insulator Ltd.

B.I.L. : 420/630/1475 KV

FREQUENCY : 50 Hz

I(thermal) : 40 KA

TIME : 1 sec

I DYNAMIC : 100 KA (p)

RATIO : 2000/1000/500/1-1-1-1-1

TOTAL WEIGHT: 23650 Kg.

POTENTIAL TRANSFORMER:-

INTRODUCTION:-The function of the potential transformer is to transformer the higher voltage in an electrical system to lower values which are convenient for the operation of measuring instrument and protective device. They also serve to isolate these instruments of device from the high voltage power circuit.



FIG. Dead tank PTs

According to requirement P.T. are classified as:-

1) Measuring voltage transformer:- Measuring P.T. is intended to supply voltage to the indicating instrument integrating meters and similar apparatus. If has to be accurate within the specified working range of rated indicating and integrating meter.

2) Protective voltage transformer:-

Protective P.T. on the other hand is intended to supply voltage to the protective devices. They should have fairly request degree of accuracy on voltage in fault condition such as over etc. actually the protective gear has to function. The potential transformer may be either single phase or three phases. The primary potential transformer is connected directly to power circuit between and ground depending upon rated and application.

There are two types of construction:-1) Electromagnetic transformer2) The capacitor voltage transformer

1) ELECTROMAGNETIC TRANSFORMER:- Electromagnetic transformer is that which primary and secondary are wound on magnetic core like as usual as transformer. The construction is largely depending in the reacted primary voltage. In higher voltage the 66 KV electromagnetic PT’s are generally in cascade connections. They employ a no. of series connected primary coils as to keep the effective leakage at a value so an arrangement is in porcelain enclosure for high speed distance protection this type of PT are preferred.

2) CAPACITOR VOLTAGE TRANSFORMER (C.V.T.):-

The CVT is shown in fig. the CVT are used for line voltage meter, synch scopes, Protective relays and tariff meters. The performance of CVT is inferior to



that of electromagnetic voltage transformer. It performance is affected by supply frequency. Switching tangent magnitude of connected burden etc. the capacitors are connected in series as like a potential divider. To choose the value of capacitor for the intermediated side and transformer to connected a primary side and secondary are connected to a burden is adjusted to such a value that at supply frequency. It responds with the sum of two capacitors. The eliminated a ratio error. The constructions of CVT depend on the form of capacitor voltage divider.In SOJA CVT capacity= 50 to 500 KHz.


CVT

CC VT / PTOnly for PLCC.Allows to pass PLCC Signals through HF point.

Secondary voltage of PT is usedFor Line Voltage measurement,line protection relays ,Synch. etc.


CVT Construction Details:-

At SOJA S/S both P.T. are used for 400 KV and 220 KV. TYPE : CVBA 420/1425 INTERMEDIATED VOLTS : 223 KV TOTAL OUTPUT SIMULTANEOUS : 300 VA OUTPUT MAX. : 750 VA at fix AMB FREQUENCY : 50 Hz INSULATION CLASS : A



4.7 RELAYS:- A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contractor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device triggered by light to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays".

Basic design and operation:-


http://en.wikipedia.org/wiki/Contactor

http://en.wikipedia.org/wiki/Switch

http://en.wikipedia.org/wiki/File:Relay_Parts.jpg

http://en.wikipedia.org/wiki/File:Relay2.jpg


FIG. Simple electromechanical relay FIG. Small relay as used in electronics

A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was De-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include a diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle. By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a Thyristor or other solid-state switching device. To achieve electrical isolation an opt coupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.

In SOJA there are following relays used.

Tripping relay, directional over current relay, definite time relay, control relay, auxiliary relay, local breaker back up relay, trip CKT relay, numerical distance relay,


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carrier relay, lock out auxiliary relay, direction earth fault relay, bus-bar supervision relay, auto reclose relay, etc…

Types:-

1. Latching relay:-

Latching relay, dust cover removed, showing pawl and ratchet mechanism. The ratchet operates a cam, which raises and lowers the moving contact arm, seen edge-on just below it. The moving and fixed contacts are visible at the left side of the image.

A latching relay has two relaxed states (bitable). These are also called "impulse", "keep", or "stay" relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage. A remnant core latching relay requires a current pulse of opposite polarity to make it change state.

2. Reed relay:-

A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts against atmospheric corrosion. The contacts are closed by a magnetic field generated when current passes through a coil around the glass tube. Reed relays are capable of faster switching speeds than larger types of relays, but have low switch current and voltage ratings.


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Top, middle: reed switches, bottom: reed relay

3. Mercury-wetted relay:-

A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less) because of their low contact resistance, or for high-speed counting and timing applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are rarely specified for new equipment. See also mercury switch.

4. Polarized relay:-

A polarized relay placed the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay.

5. Machine tool relay:-

A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications.

6. Contactor relay:-

A contactor is a very heavy-duty relay used for switching electric motors and lighting loads. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor.[2] Such devices are often used for motor


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starters. A motor starter is a contactor with overload protection devices attached. The overload sensing devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for use where noise is a chief concern.

7. Solid-state relay:-

FIG. Solid relay, which has no moving, parts FIG. 25 A or 40 A solid state contactors

A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100 to 1,200 Amperes, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients.

8. Solid state contactor relay:-

A solid state contactor is a very heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

9. Buchholz relay:-

A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil.

10. Forced-guided contacts relay:-


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A forced-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forced-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".

11. Overload protection relay:-

Electric motors need over current protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. [3] One type of electric motor overload protection relay is operated by a heating element in series with the electric motor. The heat generated by the motor current heats a bimetallic strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

Applications:-

Relays are used to and for:

Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers,

Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,

Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays).

Relay application considerations :- A large relay with two coils and many sets of contacts, used in an old telephone switching system.


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Several 30-contact relays in "Connector" circuits in mid 20th century 1XB switch and 5XB switch telephone exchanges; cover removed on one

Selection of an appropriate relay for a particular application requires evaluation of many different factors:-

Number and type of contacts – normally open, normally closed, (double-throw) Contact sequence – "Make before Break" or "Break before Make". For example, the

old style telephone exchanges required Make-before-break so that the connection didn't get dropped while dialing the number.

Rating of contacts – small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current

Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15 000 V

Coil voltage – machine-tool relays usually 24 VAC, 120 or 250 VAC, relays for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few mill amperes.

Coil current. Package/enclosure – open, touch-safe, double-voltage for isolation between

circuits, explosion proof, outdoor, oil and splash resistant, washable for printed circuit board assembly

Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB post soldering cleaning, which is removed once assembly is complete.

Mounting – sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment

Switching time – where high speed is required "Dry" contacts – when switching very low level signals, special contact materials

may be needed such as gold-plated contacts Contact protection – suppress arcing in very inductive circuits Coil protection – suppress the surge voltage produced when switching the coil

current Isolation between coil circuit and contacts Aerospace or radiation-resistant testing, special quality assurance Expected mechanical loads due to acceleration – some relays used in aerospace

applications are designed to function in shock loads of 50 g or more Accessories such as timers, auxiliary contacts, pilot lamps, test buttons Regulatory approvals Stray magnetic linkage between coils of adjacent relays on a printed circuit board.


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Protective relay:-

A protective relay is a complex electromechanical apparatus, often with more than one coil, designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a fault is detected. Unlike switching type relays with fixed and usually ill-defined operating voltage thresholds and operating times, protective relays have well-established, selectable, time/current (or other operating parameter) curves. Such relays may be elaborate, using arrays of induction disks, shaded-pole magnets, operating and restraint coils, solenoid-type operators, telephone-relay style contacts, and phase-shifting networks. Protection relays respond to such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency, and even distance relays that would trip for faults up to a certain distance away from a substation but not beyond that point. An important transmission line or generator unit will have cubicles dedicated to protection, with a score of individual electromechanical devices. The various protective functions available on a given relay are denoted by standard ANSI Device Numbers. For example, a relay including function 51 would be a timed over current protective relay.

Design and theory of these protective devices is an important part of the education of an electrical engineer who specializes in power systems. Today these devices are nearly entirely replaced (in new designs) with microprocessor-based instruments (numerical relays) that emulate their electromechanical ancestors with great precision and convenience in application. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world.

Over current relay:-

An "over current relay" is a type of protective relay which operates when the load current exceeds a preset value. The ANSI device number is 50 for an instantaneous over current (IOC), 51 for a time over current (TOC). In a typical application the over current relay is connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize to trip (open) a circuit breaker.

Induction disc over current relay:-

These robust and reliable electromagnetic relays use the induction principle discovered by Ferraris in the late 19th century. The magnetic system in induction disc over current relays is designed to detect over currents in a power system and operate with a pre determined time delay when certain over current limits have been reached. In order to operate, the magnetic system in the relays produces rotational torque that acts on a metal disc to make contact.


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The relay's primary winding is supplied from the power systems current transformer via a plug bridge, which is also commonly known as the plug setting multiplier (psm). The variations in the current setting are usually seven equally spaced tapings or operating bands that determine the relays sensitivity. The primary winding is located on the upper electromagnet. The secondary winding has connections on the upper electromagnet that are energized from the primary winding and connected to the lower electromagnet. Once the upper and lower electromagnets are energized they produce eddy currents that are induced onto the metal disc and flow through the flux paths. This relationship of eddy currents and fluxes creates rotational torque proportional to the input current of the primary winding, due to the two flux paths been out of phase by 90º. Therefore in an over current condition a value of current will be reached that overcomes the control spring pressure on the spindle and the breaking magnet causing the metal disc to rotate moving towards the fixed contact. This initial movement of the disc is also held off to a critical positive value of current by small slots that are often cut into the side of the disc. The time taken for rotation to make the contacts is not only dependent on current but also the spindle backstop position, known as the time multiplier (tm). The time multiplier is divided into 10 linear divisions of the full rotation time.

Providing the relay is free from dirt, the metal disc and the spindle with its contact will reach the fixed contact, thus sending a signal to trip and isolate the circuit, within its designed time and current specifications. Drop off current of the relay is much lower than its operating value, and once reached the relay will be reset in a reverse motion by the pressure of the control spring governed by the braking magnet.

Distance relay:-

The most common form of protection on high voltage transmission systems is distance relay protection. Power lines have set impedance per kilometer and using this value and comparing voltage and current the distance to a fault can be determined. The ANSI standard device number for a distance relay is 21.

TYPES OF DISTANCE REALY:-

CLASSICAL TYPE:-

1. Impedance2. Reactance 3. Mho or admittance4. Ohm5. Offset Mho6. Modified impedance

NON-CLASSICAL TYPE:-



1. Complex characteristic’s type2. Electrical characteristic type3. Quadrilateral characteristics type

At SOJA S/S following types of relays are used made by English electrical:-

SR. NO.

TYPE NAME OF RELAY

1 VAJ Tripping relay

2 VAA Auxiliary relay

3 CDD Direction over current relay

4 SKD Check synchronizing relay

5 VAG Instantaneous under voltage relay



6 VARM Auto reclose relay

7 CTIG Local breaker back up relay

8 VAJC Control relay

9 YCG Mho measuring unit

10 VAT Zone time relay

11 VAPM Fuse failure relay

12 VTT Definite time delay relay

13 CAG Instantaneous differential relay

14 VTX Bus bar supervision relay

15 VDD Directional earth fault relay

16 VAX Trip circuit supervision relay

Winding temp relay

Buchholz relay

Oil temp relay

DLTC Buchholz relay

17 DTH-32 Transformer differential relay

18 CTL Thermal over load relay

19 GTT Natural displacement relay

20 VDG Phase comparison relay

21 P-40 Static distance protection relay

22 SHNB Static distance protection relay

5. DIFFERENT TYPE OF PROTECTION IN SUBSTATION:-

5.1 Why Protection is Necessary:-

In the design of a power system three aspects are generally considered viz,

1) Normal operation 2) Prevention of electrical failure3) Reduction of damaging caused by electric failure.

Normal operation involved major expanses for equipment and accessories but a system designed according it this aspect only does not meet the present day requirement. Additional provision must be made to minimize the damage to power



system equipment and interruption to services when failure occurs. The electrical failures that cause the greater concern are the fault or shout circuit condition.

Various methods adopted to prevent failure are: 1. Provision of adequate insulation 2. Use of overhead ground wire and low tower footing resistance. 3. Better mechanical design to minimize the like hood of failure caused by animal

birds etc.4. Strict adherence to proper operation and maintenance.5. Insulation co-ordination with the lighting arrestor.

Even with most care and also due to unforeseen circumstances it is not always possible to prevent the electric failure.

various features aimed at limiting the magnitudes of short circuit current are:

A. Avoidance of larger concentration of generating capacity.B. Use of current limiting reactors and ground fault neutralizers.C. Robust designing of power system equipment so as to withstand the stresses arcing

due to flow abnormally large fault current.

However, it is to be appreciated that whether may be the reasons of fault is should not be allowed to continue for a long time, not only because that it will damage the equipment but will also affect the stability of system and so the faulty equipment should be quickly disconnected from the rest of the system.

PRINCIPLE OF AUTOMATIC PROTECTION:-

The protective relay is mounted on protection panels housed in the control room. The protective relay includes over current and earth fault relay. Differential relay, impedance relay etc. the relay coil or measuring circuit are connected to the current transformer and voltage transformer in the main switch yard. The control cables are run between the control room to the switch yard. The abnormal condition such as short circuit in the protected zone results in increase in current above threshold from the D.C. battery system flows through the trip coli of the circuit breaker. The latch is pullers and the C.B. operated and performs the opening operation. The extent of damage by fault current several times the normal current minimized by rapid fault clearing.

5.2PROTECTIVE ZONE IN SUBSTATION:-

The protective zones in substation included the following: Bus bar protection zones: -each bus section is covered by a separate protective

zone.



Transformer protective zone: -each power transformer covered by a separate protective zone from each end.

LV side transmission line protective zones: -each illustrates these concepts of protective zones in a substation.

TRANSMISSION LINE PROTECTION:-

Transmission lines are a vital part of the electrical distribution system, as they provide the path to transfer power between generation and load. Transmission lines operate at voltage levels from 69kV to 765kV, and are ideally tightly interconnected for reliable operation.

Factors like de-regulated market environment, economics, right of-way clearance and environmental requirements have pushed limits. Any fault, if not detected and isolated quickly will cascade into a system wide disturbance causing widespread outages for a tightly interconnected system operating close to its limits. Transmission protection systems are designed to identify the location of faults and isolate only the faulted section. The key challenge to the transmission line protection lies in reliably detecting and isolating faults compromising the security of the system.

Factors Influencing line Protection:-The high level factors influencing line protection include the criticality of the line (in terms of load transfer and system stability), fault clearing time requirements for system stability, line length, the system feeding the line, the configuration of the line (the number of terminals, the physical construction of the line, the presence of parallel lines), the line loading, the types of communications available, and failure modes of various protection equipment.

The more detailed factors for transmission line protection directly address dependability and security for a specific application. The protection system selected should provide redundancy to limit the impact of device failure, and backup protection to ensure dependability. Reclosing may be applied to keep the line in service for temporary faults, such as lightning strikes. The maximum load current level will impact the sensitivity of protection functions, and may require adjustment to protection functions settings during certain operating circumstances. Single-pole tripping applications impact the performance requirements of distance elements, differential elements, and communications schemes. The physical construction of the transmission line is also a factor in protection system application. The type of conductor, the size of conductor, and spacing of conductors determines the impedance of the line, and the physical response to short circuit conditions, as well as line charging current. In addition, the number of line terminals determines load and fault current flow, which must be accounted for by the protection system. Parallel lines also impact relaying, as mutual coupling influences the ground current measured by protective relays. The presence of tapped transformers on a line, or reactive compensation devices such as series capacitor banks or shunt reactors, also influences the choice of protection system, and the actual protection device settings.



Particular at the SOJA substation there are three lines of 400 KV. Each line is provided with its main protection and back up protection.

There is several method of protection of transmission lines.

The first group is of non-unit type of protection which includes:-

Time graded over protection. Current graded over current protection. Distance protection.

Such non unit type of protection of lines is unit type of protection. The discrimination is obtained by conditioning the relay settings.The other group of protection of line is unit type of protection. Such as pilot wire is differential protection carrier protection etc.



OVER CURRENT PROTECTION:-

As the fault impedance is less than load impedance, the fault current is more than load current. If the S/C occurs, the circuit impedance is reduced to a low value and therefore a fault is accompanied by large current.Over current protection is the protection in which the relay picks up when the magnitude of current exceeds the pickup level.



The basic element in over current fault by means of:-

Instantaneous over current relay. Inverse over current relays. Direction over relay.

The choice of relay for over current protection depends upon the time current characteristics and other feature desired.The following relays are used:

For instantaneous over current protection, current type, moving type, moving iron type permanent magnet moving type.

For inverse time characteristics.

ELECTROMAGNETIC INDUCTION TYPE, PERMANENT MAGNET MOVING COIL TYPE, STATIC TYPE:-

Directional over current protection Double acting questing on relay with directional feature Static over current relay HRC fuses, drop out fuses etc. are used in low voltage, medium voltage and high

voltage distribution system generally up to 11 KV. The relay which are not instantaneous are called time delay relay.

In over current protection, the three current transformers and relay connected in star and the stare point is earthed. When short circuit is occurs in the protected zone the secondary current of CT’S increases. These current flows through relay coil and the relay pick up. The relay contacts close, there by the trip circuit is closed and the circuit breaker operates.

CRRIER CURRENT PROTECTION OF TRASMISSION LINE:- There are different methods of carrier current protection such as:-

Directional comparison method Phase comparison method

Phase comparison method compares the phase relation between current in the protected zone and current leaving the protected zone.At SOJA S/S, this type of protection made English electric know as P-40 scheme. In this method single are send from each end of line and received at other end. The single are relate to the current flow in mainline as they are derived from CT secondary current when there is no fault the single is send for alternate ½ cycle form one end remaining half from the other. The same condition holds good for external fault. As shown in fig. during internal fault the current in one of the lines reverses in phase or differs in phase and remains below the fault detector setting. So that carrier is sent only for half the time. The



relay is arranged to sense absence of single in the lines. Depending upon the setting the tripping occurs when the phase angle between two single reaches a certain value normally at 30.

5.2.2 BUS ZONE PROCTECTION:-

Cause of bus zone faults:-

Failures of support insulator resulting in earth faults. Flashover across support insulator during over voltage. Heavily polluted insulator during over voltage. Failure of connected equipment. Earthquake, mechanical damage etc.

NEED OF BUSBAR PROTECTION :-

BUSBAR PROCTEION NEEDS CAREFUL ATTENTION BECAUSE:-

Fault level at bus bar is very high. The stability of the system is affected by fault in bus zero. The fault on bus bar causes disconnection of power to a large portion of the system. A fault on bus bar should be interrupted in shortest possible time.

BUS BAR PROTECTION BY OVERCURRENT RELAY OF CONNECTED CIRCUITS:-

Such protection is providing as primary protection only when no other primary bus zone protection is applied. If other primary bus zone protection acts as back up protection to the bus bar. Fig. shown principal on which it is acts.The fault on bus can be sensed by over current of the incoming circuit and is disconnected by opening of incoming circuit. The over current is protection of incoming feeder gives protection to the bus.

DISADVANTAGES:-

Delayed action disconnection of more circuit in case there are two or more incoming lines.

Zone not clearly be used so exact discrimination is not possible.

BUS PROTION BY DISTANNCE PROTECTION OF INCOMING LINES AS A REMOTE BACK UP:-

Referring to fig. again the bus. A is covered in second step of distance relay at station B. thus foe a fault F on bus A the distance protection B will operate. The operating time of the second step can be order of 0.4 second. Distance protection is widely used in protection of transmission is widely used in protection of transmission lines; hence it is often economical to use same as for bus protection.



LIMITATIONS:-

Protection is slow. There can be unwanted disconnection of oil incoming paralleled circuits.

Due to the above limitation it is not desirable to use it as main protection for important buses.

5.2.3 TRANSFORMER PROTECTION:-

A Through fault is one which is beyond the protected zone of the transformer but fed through the transformer. The unit protection of transformer should not operate of through fault. The overload relaying may be provided to operate with a time lag to provide backup protection. Internal fault are those in the proceed zone of the transformer. These faults can be between phase to phase and phase to ground.

Transformers are a critical and expensive component of the power system. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. Some protection functions, such as over excitation protection and temperature-based protection may aid this goal by identifying operating conditions that may cause transformer failure. The comprehensive transformer protection provided by multiple function protective relays is appropriate for critical transformers of all applications.

Transformer Protection Overview:-

The type of protection for the transformers varies depending on the application and the importance of the transformer. Transformers are protected primarily against faults and Overloads. The type of protection used should minimize the time of disconnection for faults within the transformer and to reduce the risk of catastrophic failure to simplify eventual repair. Any extended operation of the



transformer under abnormal condition such as faults or overloads compromises the life of the transformer, which means adequate protection should be provided for quicker isolation of the transformer under such conditions.

Transformer Failures :-

Failures in transformers can be classified into,

• winding failures due to short circuits (turn-turn faults, Phase-phase faults, phase- ground, open winding)• Core faults (core insulation failure, shorted laminations)• Terminal failures (open leads, loose connections, short Circuits)• On-load tap changer failures (mechanical, electrical, short Circuit, overheating)• Abnormal operating conditions (over fluxing, overloading, overvoltage)• External faults

Over flux Protection:-

Transformer over fluxing can be a result of• Overvoltage• Low system frequency

A transformer is designed to operate at or below a maximum magnetic flux density in the transformer core. Above this design limit the eddy currents in the core and nearby conductive components cause overheating which within a very short time may cause severe damage. The magnetic flux in the core is proportional to the voltage applied to the winding divided by the impedance of the winding. The flux in the core increases with either increasing voltage or decreasing frequency. During startup or shutdown of generator-connected transformers, or following a load rejection, the transformer may experience an excessive ratio of volts to hertz, that is, become overexcited. When a transformer core is overexcited, the core is operating in a non-linear magnetic region, and creates harmonic components in the exciting current. A significant amount of current at the 5th harmonic is characteristic of over excitation.

Types of abnormal conditions:-

Incipient faults below oil level resulting in decomposition of oil. Faults between phase and between phases to ground.

Large internal faults phase to phase. Phase to ground below oil level. Faults in tap changer. Saturation of magnetic circuit. Earth faults. Over loads. High voltage surges due to lighting switching.

Incipient fault below tanks oil level :-

1. Buchholz relay ( gas actuated relay):-

Principle:-



The principle fault in transformer tank below oil level actuate Buchholz relay so as to give an alarm. The arc due to fault cause decomposition is being light, rises upwards and tries to go in conservator. Relay is fitted in between transformer tank and conservator so gases have to go through the relay operates and gives alarm. So operator know that there is some fault and the disconnect transformer as early as possible. Decomposition of oil starts at 350 oc.



LIMITATIONS:-

The relay is slow minimum operating time is 0.1 sec. average time 0.2 sec. It is not economical to provide relay below 500 KVA. This does not respond to a small arcing.

5.2.4 EARTH FAULT PROTECTION:-

When the current flows through earth return path fault is called earth fault. Since earth fault are relatively equine, earth fault portion is necessary in most cases. When separated earth fault protection is not economical the phase relays sense the earth fault currents. However such protection looks sensitivity. Hence separated earth fault protection is generally provided.

Earth fault protection senses earth current following are methods of earth fault protection:-

Rusticated earth fault portion on differential protection. Additional separate restricted earth fault protection. Leakage to frame protection. Neutral current relays.



6. BATTERY AND BATTERY CHARGER:-

6.1 INTRODUCTION:-

BATTERY 220 V D.C.:-

The storage batteries are installed in special room. The battery room should have adequate ventilation and lighting. The floor and walls should be acid resistance tiles. The battery cells are places on racks. The racks are placed on porcelain insulators. The D.C. bus bars are flat copper sections or tabular copper sections. The connections are made by soldering or brazing. The conductors are covered by grease or electrolyte resistant varnish. The positive leads are painted red and negative leads blue. Only acid-proof cables must be used upon D.C. switchboard.



Without battery the relay will not operate and also C.B. the D.C. supply is used for automatic control telemetering equipment, communication equipments, interlocking equipment and emergency lightening system.

6.2 TYPES OF BATTERIES:-

TWO TYPES OF BATTERIES AT SOJA are:-

P.L.C.C. STATION BATTERY

1. SUBSTATION BATTERY:-

MAKE: - Auto bat CAP.:- 250 A.H. VOLTAGE: - 220 V NO. OF CELL: - 108*2

2. P.L.C.C.:-

MAKE: - Standard CAP.:- 600A.H. VOLTAGE: - 220 V NO. OF CELL: - 25*2

Battery Set:-

► Battery is considered as the heart of sub-station.

► Sub-station battery sets:

220 V DC

► Single or double

110 V DC

► Single or double

48 V DC

Battery specifications:-

► Generally.. Telecom DC source.. 48 V dc.

► PLCC.. 1 extra cell to compensate cable drop.

► 50 V - 200 AH means Battery set is having 25 nos. of 2-Volts cells that can deliver…



► 10 Amps for 20 Hrs. 10 A×20 H = 200 AH OR,

► 20 Amps for 10 Hrs 20A×10 H= 200 AH considering 100 % efficiency.

Battery structure:-

► Hard rubber container

► Positive terminal post. Lead peroxide

► Negative terminal post. Sponge Lead

► Vent plug

► Float level indicator

► Inter-cell connector strips

► Electrolyte…H2SO4

Chemical Reaction:-

Pb + PbO2 + H2SO4

Discharge Charge

2 PbSO4 + H2O

Battery Charger:-

MAIN PARTS:-

1. FLOAT CHARGER

2. BOOTS CHARGER

Functions of Float charger:-

► Converts 3-Ph AC into 48 V DC. (Rectifier)

► Normally it delivers load & give trickle charging to Battery bank.

► Works on ‘Auto’ or ‘Manual’ mode.

► In ‘Auto’ mode, o/p DC voltage is controlled by ECU card to predefine value irrespective of amplitude of AC voltage.

► In ‘Manual’ mode, o/p DC voltage is to be controlled manually by external control.

Functions of Boost charger:-



► Converts 3-Ph AC into 48 V DC.(Rectifier)

► Normally, it is made OFF.

► Works on ‘CC’ or ‘CV’ mode.

► In ‘CC’ mode, battery can be charged at constant current.

► In ‘CV’ mode, battery can be charged at constant voltage.

Need for Boost charger:-

► Boost charging is required only if whole battery bank is drained considerably. At that time, Float charger will deliver the load.

► Boost charger is made on when Float charger is out of order. In this case, Boost section will charge battery bank and battery bank output from tap-cell will deliver load.

Battery capacity can be calculated from the following equations:-

1. Battery (kw) = Load KVA * Power-factor/Inverter Efficiency.2. Number of cells = Minimum allowable battery voltage/Final voltage per cell.3. Cells capacity (kw/cell) = Battery kw/Number of cells.

Unless the UPS has protection for excess discharge, 1.75V per cell should be selected to prevent battery damage. Battery discharge rates in kw at 250C are given in table.

Battery discharge rates in KW at 250C

Type 5 min 10 min

15 min 20 min 30 min 60 min

SB-45 0.201 0.155 0.128 0.108 0.086 0.530

SB-60 0.268 0.206 0.170 0.144 0.114 0.070

SB-75 0.365 0.258 0.213 0.180 0.143 0.088

SB-90 0.402 0.309 0.255 0.216 0.171 0.105

(A) Capacity of the Battery:-



The capacity of a battery is expressed in pampered hour(AH).This rating tells us about, how much amount of current that battery can supply 10 A of a current for 1 hour. Capacity of a battery depends on the following factors:

1. Rate of Discharge:-

AH rating decreases with increase in the rate of discharge. Due to rapid rate of discharge cell potential falls significantly, due to internal losses. Weakling of acid at higher discharge rate in porous plate is also greater at higher discharge rates. This also affects the capacity adversely. 2. Temperature:- Capacity of a battery is increase with increase in temperature.

3. Density of Electrolyte:-

As the density of electrolyte affects the internal resistance and the vigor of the chemical reaction, it has an important effect on the capacity. Capacity is increase with density.

(B)Efficiency of the Battery: - There are two different values of the battery efficiency:-

1. Ampere-hour efficiency 2. Watt-hour efficiency.

1. AH Efficiency:-

The ampere-hour efficiency is defined as the ratio of ampere hours taken from battery to the ampere hours supplied to it while charging.

AH efficiency = A-H during discharge/A-H input while charging

The typical value of A-H efficiency is 90 to 95%.5 to 10% reduction is due to the losses taking place in the battery. The ampere hour efficiency takes into account only the current and time but it does not consider the battery terminal voltage at all.

2. Watt-hour (WH) (Energy) Efficiency :-

The WH efficiency is defined as follows:-

WH-efficiency = AH-efficiency*Avg. cell voltage while discharging/

Avg. cell voltage while charging

= 70-80% usually.



If the changing volts increases or discharge volts decrease then WH-efficiency will also decrease. High charging and discharging rates will usually do this and hence are not recommended.

6.3 MAINTENANCE:-

Do not adjust factory preset potentiometers in the printed circuit board. Remove the dust collected inside the panel using blower or any other suitable

machine. Check for any white/black/red tap opening on the capacitor. Replace the blown

capacitor (once in six months). Check contactor power contact for wearing. Replace with spare kit (once in year). Maintain input AC voltage with it specified band. Normally it should be around 415

V AC +/- 10 % /230 V AC +/- 10 %.

6.4 DO’S:- Read “installation and operating manual” prior to installation of the batteries. Clean the batteries as and when dust accumulates. The batteries if places in cubical, provide sufficient ventilation. The terminal bolt connection to be torque in 10 Nm. Re-torque the connection once every six month. Keep the batteries away from heat source, sparks, etc. Charge the batteries once every six months, if stored for long periods. After a discharge recharge the batteries immediately. Note down module voltage readings once, every one mouth. Charge the batteries only at 13.5 v per module.

6.5 MAJOR ADVANTAGES:-

► No major topping up► No separate battery room required ► Spill and leak proof► No acid fumes► Ready to use► Low self discharge ► Savings: 50% in space,40% in voltage & 30% in weight

6.6 DONT’S:-

► Do not add water or acid► Do not attempt to dismantle the battery► Do not tamper with safety valves► Do not over tighten the terminal bolts



► Do not allow any metal object to rest on the battery or fall across the battery terminals

► Do not mix the batteries of different capacities of makes► Do not install physically damaged cell► Do not boots charge the batteries for more than 12 hours

6.7 OTHER ADVANTAGES:-

No stratification Explosion proof No post corrosion More power output Rugged construction

7. CONTROL PANELS AND CONTROL ROOM ARRGMENT IN SUBSTATION:-

In substation, the control and relaying equipment is installed in control rooms. The arrangement of control and relay equipment needs careful attention to suit the layout and operational requirement of the installation. The equipments are very widely with the type and size of the station.

(a)LARGE INSTALLATION:- when control of a number of circuit in desired, as in the case of generating station. The arrangement should be such that, the indicating should be clearly visible from the center place. The terminals should have good accessibility. To achieve trend is to provide separate panels for:-

(i) Control and indication equipment and(ii) Relay and indication equipment, voltage regular equipment.

The diagram of main connection are given on the front face of the panel, there diagrams indicate the positions of the circuit breakers and isolators. The control operator gets the ides as to which breaker open or closed. The controls of centrally is in front of main control board. Separate control desks are provided for prime movers and boilers.

(b)MEDIUM SIZE INSTALLATION:-



In medium size installation, panel width can be increased to accommodate relay and other equipment. In case of complex protective schemes, a separate relay panel is necessary.

CONSTRUCTION:-

The constructional features vary with the manufacturer and applications. However, a general pattern can be described. The control and relay board are built of self contained sheet steel cubicles. These cubicles are assembled on common channel iron base plates according to the needs.

The cubicles are fabricated as follows: the angle ions or channel irons are cut according to drawings. The pieces are welded to form the frame. Sheets are cut on shearing machine to required sizes. They are placed on the frame at appropriate position and are welded. The sheets of thickness 3 to 5 mm are used. The wiring is suitable for 250 V and is generally of grade 7/0.029 cable. The standard color code is generally used. Terminal blocks are used for connecting the wires.

SYNCHROINSING ARRANGEMENTS:-

The panel for synchronizing can be conveniently arranged on the upper portion of the cubicle. The indicating instrument are show “incoming volts”, and “slow or fast”.

CUBICLE ARRENGMENTS:-



The cubicles are arranged in a line, side by side. Sometimes, the relay cubicles are arranged back to back with their respective control cubicles, with a corridor on between. The corridor is roofed and troughs are provided for wiring which run between the control and relay panes. the operator’s control desk, personal computer and video display screen. Event recorders are usually located at the center of the control room. Mimic diagram boras is at the front.

PANEL TYPES:-

These are illustrated in figs. There are a variety of patterns. The dimensions of cubicles are standardized.

(A) Panel with mimic diagram(B) Instrument panel

Indicating ammeters, voltmeters, energy meters, their selector switches, recording instruments, if any, fitted on instrument panel.

(C) Synchronizing(D)Automatic voltage regulator panel(E) Process control panels(F) Event recorder

Every operation in the main control CKT is recorded on printout.(G) Fault recorder

The oscillographics record of variables is printed on graph sheet.

(H)SCADA

(I) Relay panel:-

As mentioned earlier, the relays are on a separate panel. Fig illustrates a typical panel. The type and no. of relays depends on requirements.



CONTROL ROOM LAYOUTS:-

The layout of control room depends on the size and type of installation. Fig. illustrates a typical layout. The types of panels installed in the room indicated in the fig.

Control Panel:-

► Semaphores

► Annunciation schemes

► TNC Switch

► Isolator TNC switches

► Indications for SF6 pr., ON/OFF breaker

► Meters for MW, Amp, KV…with phase selection switch ...etc

► DAS meter

► Annunciation Relay

Relay Panel:-

► Relays for:-

Distance relay for lines Main-1/Main-2...Micromho, numerical…etc.

Differential relay… Transformers

Auxiliary relays... Under frequency, under voltage, O/V, Master Trip …etc.

► Relays:-

Electromagnetic Attraction type

Induction type

Static type

Thermal type

Numerical type



Metering Panel:-

► ABT Metering of Inter-state and Intra-state lines.

► Data……weekly mail for billing

PLCC Panel:-

► PLCC connects---Co-axial cable--

► PLCC panel for:

PLCC Speech

Protection Coupler

RTU Panel

► RTU data flow to SLDC Gotri.

► Connection to PLCC panel

► DATA…. Parameters, position of barker, isolator…etc.



8. OPERATION AND MAINTENANCE OF SUBSTATION:-

8.1 INTRODUTIONS:-

These functions can only be performed provided all the equipment involved gives continuous all the equipment involved gives continuous troubles free services under specified operating condition to meet this requirements, the equipment has to be checked, attended to, trouble shooter, Operated under specified conditions etc.

By the operation and maintenance of station, substation and line equipment is meant all activity required to keep the entire system of power generation is meant all activity required to keep the entire system of power generation transmission and distribution in running order. The objective of operation and maintenance are to provide planned to output and supply at peak loads, to ensure continuity of power supply constant frequency and rated voltage and to keep power cost to min. yet the specific features peculiar to power generation place more stringent requirement on the operation and maintenance of



electrical power stations, substation and power lines. An important objective of operation and maintenance is to increase the cost of energy perdition the rate of power generation losses and by extending the equipment service life. Since electric power station perform with in a power system rather than individually. It is not only specific station transmission lines but primarily the entries system that must be operated economically. To achieve this goal, the load should be properly divided between electric power stations and generating sets, the required voltage level maintained at substation and line equipment repaired in accordance with the adopted schedule.

So the operation and maintenance of station, substation and line equipment should be organized within the power system as a whole with the aim:-

To realize the electric output target to supply power according to the preset load schedule. And to meet the peak the demand.

To ensure reliable performance of air equipment involved and uninterrupted power supply to the users.

To supply power at rated voltage and frequency. To keep the cost of the system operation as low as possible.

MANAGEMENT STRUCTRE:- The staff engaged in operating the substation and power network is divided into shift operators and maintenance men.

OPERATION:- The shift operators keep watch on and attend to the electrical equipment in operation, perform the switching operations, take out equipment for repair and put it back into service after repair , adjust and record thr operation condition, quickly find remind for any abnormal conditions, eliminate and emergency etc.

MAINTENANCE:- Maintenance may be defined as the up keeping of any equipment in healthy or working condition so as to get the following:

Reliable and effective operation Optimum utilization Availability Reduced down time Finding pre matured faults. Minimization of revenue loss



8.2 MANPOWER DETAILS FOR O & M SUSTATIONS IN POWERGRID:-

EXECUTIVE:-

Substation in charge – 1

Shift operation – 4

Maintenance – 2

Total – 7

JUNIOR ENGINEER:-

Maintenance – 2

Total – 2

WORKMEN:-

Operation – 4

Maintenance – 4

Total – 8

8.3 CLASSIFICATION OF MAINTENANCE ACTIVBITY:-

Breakdown maintenance Preventive maintenance Condition based maintenance Reliability centered maintenance

BREAKDOWN MAINTENANCE:- For low value and less important items only.

PREVENTIVE MAINTENANCE:- Planned in advance. Based on previous experience.



Based on guidance from equipment manufacturer. Development of equipment maintenance schedules. Preparation of annual maintenance plan.

CONDITION BASED MAINTENNACE:- Maintenance based on condition assessment tests of the equipment conducted

ON/OFF line. Planned in advance Ideal for prevention of equipment failure and other associated consequential

damages. Development of schedule for condition assessment checks or tests.

RELIBILTY CENTERED MAINTENANCE:- For gainful use of completed service life of equipment Part of equipment life extension technique Planned based on past maintenance data Not conducted at fixed interval Optimizes frequency and duration of equipment outage Reduces maintenance cots Economy without sacrificing reliability and availability

EQUIPMENT FAILUER ANALYSIS:- To prevent repeated failure of equipment To provide inputs for necessary change in - Design parameters- Equipment design- Quality plan- Erection and subsequent maintenance technique

OTHER TCECH NIQUE TO REDUCE DOWN TIME :- Hot line maintenance Maintenance of one line of a double circuit line with other circuit in the condition Deployment of emergency restoration system

MAINTENANCE SCHEDULES:- A large percentage of failures of electrical equipments are due to a deteriorated condition of the insulation, loose connection etc. many of these failures can be anticipated by regular application of simple tests and timely maintenance. If the failures are detected in the early stage it. The extent of damage can be reduced and the equipment can be reconditioned put back into service.



In general the electrical equipment is capacity to communicate with their ‘well –wishers’ through signals like heat, sound, vibration, etc. The detection of incipient faults in electrical equipment depends upon the possession of proper diagnostic tools, its effective use, correlation and proper interpretation of test results and observations based on experience, manufacturer’s recommendation etc.

Equipment wise maintenance schedule is prepared. The activities may be divided in the following manner:-

Daily checks Weekly checks Monthly checks Quarterly checks Half yearly checks Yearly checks Two Yearly Three Yearly Six Yearly As and when required

8.4 MAINTENANCE:-

DIFFERENT PERIODIC MAINTENANCE DONE AT SOJA SUBSTATON:-Following are the different types of maintenance taking place at the S/S. these maintenance can be classified according to the periods in which they are done

DAILY MAINTENANCE:-

The readings of the pilot cell are taken. The yard is observed daily if the inspector gets any abnormal smell then that

portion is attended. Tree cutting the portion of trees touching the lines of very near to line are cut so as

to prevent short circuit. The reading of certain meters which show critical factors such as transformers

temp. Are taken daily.

WEEKLY MAINTENANCE:-

The charger is switched off and voltage of each cell is measured. The temp. And gravity of each cell is also noted with the voltage. The solution in the cell has to be filled. This solution used is the distilled water.



The contacts and terminals are cleared and petroleum Jelly is applied on the contacts. This jelly helps in removing the products accumulated on contacts due to acid in solution. Maintenance of compressor used for maintain pressure in ABCB SF6 C.B. D.G. set is run every week for a check. The reading of the counter of lighting arrestor is taken.

MOTHLY MAINTENNANCE:-

The silica get used in breather of transformer is checked. The oil leveling of the transformer is checked. Oil sample is taken for the transformer and the PPM must be checked. The clamp connector D.C. gets neared up. The temp. Of it checked monthly. Carrier frequency is used for communication purpose in the S/S. the levels are

checked.

THREE MOTHLY MAINTENNANCE:-

Compressors are used to maintain pressure in ABCB & SF6 C.B. the oil used in compressor for its functioning is replaced every three mouths.

HALF YEARLY MAINTENANCE:-

Clearing of days are done twice a year, once pre monsoon and post monsoon. The IR drop of current transformer, potential transformer and transmission lines

are measured. The connection are tightened every six mouths. The insulations used for different equipment are cleaned twice a year.

YEARLY MAINTENCNANE:-

There are many type of relay used in substation. The proper working of each and every relay is checked once in year.

9. SUB-STATION EARTHING SYSTEM:-

9.1 INTRODUCTION:-

In substation earthing means connecting frame of electrical equipment or some electrical part of the system to earth i.e. soil. This connection to earth may be through a conductor or some other circuit element depending upon the situation. Regardless of the method of connection to earth or earthing offers two principal advantages. First it provides protection to the power system. And



second earthing of electrical equipment ensures the safety of the persons handling the equipment.

FIG. EARTHING SYSTEM

In Soja mesh earthing is used.

9.1.1 Concept of Earthing Systems:- All the people living or working in residential, commercial and industrial installations, particularly the operators and personnel who are in close operation and contact with Electrical systems and machineries, should essentially be protected against possible Electrification. To achieve this protection, earthing system of an installation is defined, Designed and installed according to the standard requirements. Also, earthing system in an Oil gas complex shall provide the best protection system against sparking, which could lead to disastrous explosions.

9.1.2. Under earthing system measures, the metal covering body and enclosure of all the equipments are connected to each other as a grid by means of appropriate conductors to establish an equal zero level potential among all the points which may come in contact with the operators. Zero potential, which is built-up and applied to the earthing conductor grid, is produced by special earth wells and their associated accessories.

9.1.3. Further to protection against the risks of electrification, earthing system is particularly installed in industrial areas where equipments are in possible exposure to Explosive material and gas such as oil and gas plants. Difference of electrical potential between the equipment and machinery is inevitably a source of spark, which definitely leads to an explosion in presence of explosive gases. Therefore a properly installed earthing system can provide an equal zero electrical potential throughout the plant Equipment, thus eliminating the risks of sparks and explosions.

9.1.4. Lightning, with its high electrical potential, is one of the most serious and Dangerous environmental threats, which could cause severe damages to both human Life and the installations. Lightning arresters, as part of the earthing system in an Installation, are the protective devices, which avert the risks of lightings.



EARTHING:- “The process of connecting the metallic frame of electrical equipment or some electrical parts of the system to earth is called Earthing.”

Earthing may be classified as:-

1. Equipment earthing2. System earthing

1. Equipment Earthing:- The process of connecting non-carrying metal parts of the electrical equipment to earth in such a way that in case of insulation failure, the enclosure effectively remains at earth potential is called equipment earthing.The equipment earthing also helps in the earth fault protection. The earth fault current from the equipment flows through the earthing system to the earth and is sensed by proteation system and CB are opened. The fault equipment is then repaied and recommission system earthed parts remain at approximatery earth potential even during flow of fault current. The equipment earth ing ensures safety to personnel.

2. System Earthing:- “The process of connectimg some electrical part of the power system to earth is called system Earthing.”

9.2.EARTHING SYSTEM COMPONENTS:-

Earthing system in an installation is normally comprised of these components:-

2.1. Earth wells and accessories2.2. Earthing grid conductors



2.3. Marshalling earth buses (earthing distribution buses)2.4. Earthing wires and cables.2.5. Lightning arresters and accessories

EARTHING SYSTEM COMPONENTS AND ACCESSORIES:-

a) Earthing system using ULG & ALG water pipesb) Earthing copper platec) Earthing copper rods and beamsd) Underground earthing copper grid.

9.3.EARTH WELLS AND ACCESSORIES:-

Earth wells for an specific building or installation are actually the location, where the pure zero potential is provided and practically act as drain pits for any rush current which accidentally appears in the earthing system grid in the event of an earth fault (connection of electrical live parts to the earthing system).

9.3.1. Earth Well Components:-Depending on the soil conductivity of the location in which the earth wells are installed and also depending on the required technical specifications of the earthing system, different types of components can be used to set up an earth well. Followings are the prime components and accessories of an earth well.1. Earth rod2. Earth plate3. Earthing clamp4. Earthing rod coupling5. Earthing rod tip6. Earthing rod driving head7. Carbon bedding mixed with salt8. Concrete earth pit9. Concrete slab cover

1. Earth Rods:-Depending on the design for an specific earth well, a number of rods are driven into the ground by means of hammering to form the main earthing electrode in the



earth well. In cases where two or more earth rods are to be driven, the individual rods are coupled to each other by means of “earth rod coupling”.

1. During the driving of rod into the ground, and to protect the earth rod againstImpact of hammering, a “driving head” is screwed onto the top of the rod.2. For easy and convenient driving of the earth rod into the ground an earth rod tipWith sharp point is screwed to the first rod.3. Earth rods are used in installation of plain earthing well where, based on designSpecification of the earthing system the carbon bedding is not necessary andApplicable.

2. Earthing Clamp:-

Earthing grid conductors are connected to the earth rods, already driven into the ground, by means of earthing clamps. Connection is essentially made by tightlyClamping of the grid conductor to the rod using the bolt and nut assembly of theearthing clamp. Earthing clamps and associated bolts nuts, washers, etc. are made of either brass or copper.

3. Earth Rod Material:-

Earthing rod and the associated accessories (coupling, tip and head) are made of both steel and copper. A steel core, coated with pure copper to the appropriate thickness, provides the sufficient rigidity for the earthing rod to help driving it straightly into the ground without any harm and bending. The copper coating of the earth rod provides the sufficient conductivity for the earthing system.

9.4 SUBSTATION EARTHING SYSTEM:-

Functions of substation earthing system:- 1. Safety of operation and maintenance personnel:-

The earthing system ensures safety against shocks tot operation and maintenance staff working in substation. The earthed part is safer then unearthed parts. Deaths by shocks can be avoided completely by proper equipment earthing. Before commissioning, the earthing system should be cheeked and certified. The earthed parts are held at near ground potential and safety is ensured.

2. Discharge of electrical charger to earth:- The earthing system provides return path for discharging fault current and discharge current/voltage from the earthed points of lighting masts, lighting conductors, earthing switch, surge arrester etc. these parts are connected to the undergrouned earthing system by solid or flexible earthing conductor of adequate short time current carrying capability and low resistance.

3. Earthing of overhead shielding wires:-



The overhead shilding wires and earthed flanges of insulation and bushing are held at earth potential by connection with the earthing system.

4. Electromagnetic interference:- The earthing system ensure freedom from electromagnetic interference in communication and data processing equipment in the substation .the control room are provided with earthed screen in the walls and window to ensure ferrdom from electromagnetic disturbances.

EARTH-RESISTANNCE OF EARTHING SYSTEM:- “Earthing resistance ER” is the resistance of the earthing electrode/earthing mat to the real earth and is expressed in ohms. ER is the ratio of V/ I where V is measured voltage between the electrode and the voltage spike and injected current during the earth resistance measurement through the electrode. The desirable values of earth resistance measurement are:-

EHV AC Installations <0.01 ohm

High voltage installation above 33 KV <0.5 ohm

Medium voltage installation 1 KV to 33 KV

<0.5 ohm

Low voltage installation up to 1 KV <1 ohm

Residential building <2 ohm

- For installation rated below 1000 V and earth fault current less than 500 A. the earth resistance shall be less than 125/Is.

- For installation rated less than 2000kVA and 1000V the earth resistance should not exceed 2 ohms.

Earth resistance value obtained would depend on:- 1. Whether the soil is dry or wet. During the rainy season lower values are obtained

and during summers, higher values are obtained. It is a good practice to irrigate the earth electrodes regularly during summers and winters.

2. The resistivity of soil varies widely between 1 ohm m to 10000 ohm m depending on the type of soil.

3. The design of substation earthing system.4. Method of measurement.



Soil Resistivity

TYPE OF SOIL RESISTIVITY ohm m

Marshy 1-5

Clay 3-150

Clay and gravel mixture 10-1250

Chalk 60-500

Sand 90-1000

Sand and gravel mixture 500-5000

Slate 100-500

Crystalline rock 500-10000

9.4 EARTH RESISTANCE MESUREMENT:- Measurement involves the electrode under test, a current spike and voltage spike. Current is injected into earth through the electrode under test and returned from the current spike. Voltage between the voltage spike and the electrode is measured.

ER= Vdc/Idc ohmsWhere,Vdc = voltage between voltage spike and earth electrode under test, voltsIdc = current injected through the earth electrode into earth returned through the current spikes, ohms.

9.5 EARTHING RESISTANCE:-

Under fault condition on an specific point in the overall earthing grid and earthing network, a relatively high amount of rush current flows into the earthing system to find its way to the earth wells. The closer an earth well to the fault point, the greater portion of the fault current is absorbed and drained by that well, and the remaining fault current is absorbed by the other nearby earth wells.

1. Based on the specification and location of the fault point, the fault current value can be calculated and therefore predicted. Four factors are influential with respect to the fault current value.2. The value of voltage applied to the fault point.3. The pure ohmic resistance of the fault point with respect to the ground, whichIncludes the ohmic resistance of each individual well, as well as the earthing gridConductors and earthing is wires and earthing cables.4. The number of rotating machineries (motors and generators) and their ratedpower at the time of fault.5. The distance between the fault point and the rotating machineries.



9.6. Earthing Resistance Measurement:-

Based on the overall electrical specification of an earthing system, established and erected in an installation, computerized measuring of the pure ohmic resistance for any specific point in the earthing network system is practically possible for electrical design engineers using the available software material and software packages. As an alternative to the above-mentioned method, the pure ohmic resistance of the earthing network at a specific point is also practicable by means of an “earth-resistance measuring equipment” or simply “earth tester”.

1. Earthing resistance for each individual earth well is measured by means of theearth tester once the earth rods are driven into the ground or once the earthingplates are positioned inside the carbon beddings.

2. The earthing resistance value measured for each earth well should not be lowerthan the prescribed value in the design specifications.

3. In the event of greater earthing resistance that that of deemed and prescribed inthe design specification, the number of earth rods should be inevitably increasedand more rods shall be driven into the ground.

4. To drive the additional earth rods into the ground, following alternative wayscould be implemented depending on the existing condition of the earthing welldue improved.

4.1. Coupling of additional earth rods to the existing rods already driven, anddriving the new arrangement into the ground by means of hammering.

4.2. In cases where coupling of additional rods to the existing (already driven)earth rods is not practically possible, the additional rods could be driven somewhere in the close vicinity of the existing earth well to form a separate but interconnected earth well. The overall earthing resistance is actually lower as a result of two earth wells now in parallel.

4.3. To achieve a low earthing resistance, the normal practice in design of theearthing system is to introduce three separate earth wells of similar specification inform of a triangle configuration. Actually the overall earth resistance (with theWells interconnected) shall be one third of the value for each individual well.

5. Earthing resistance for the lightning protection system shall not exceed 5 OHM.

6. Earthing resistance for the power system earthing in power station and powerPlants shall not exceed 5 OHM.

7. Earthing resistance for the electrical earthing (equipment earthing) shall notExceed 4 OHM.



8. Earthing resistance for the electronic devices and instrumentations shall notExceed 1 OHM.

9.7 EARTH RESISTANCE MEASUREMENT BY MAGGER:-

FIG. OF MAGGER

Examples of human electrocution:-

(a) : The neutral point of the transformer is connected to the Earth / Ground.(b) : Earth connection due to poor / broken-down insulation(c) : Line capacitance with respect to the ground(d) : Transformer’s neutral point connected to the earth / ground(e) : The floor of the area is wet and conductive(f) : The floor of the area is insulated, but the connection is made by other conductive material



EXTENSIBLE COPPER ROLLED EARTH ROD OR EXTENSIBLE COPPER BOND EARTH ROD:-



EXTENSIBLE COPPER EARTH ROD( BICC TYPE) EXTENSIBLE STAINLESS STEEL EARTH ROD:-



10. POWER LINE CARRIER COMMUNICATION:-

10.1 Introduction:-

PLCC is commonly used for voice communication, telemetry, telecontrolling purposes. Each end of the transmission line is provided with identical carrier current equipment with frequency range 30 to 500 ks/s. the high frequency signals are transmitted through the power lines.

It is most economical, since power line conductor doubles as the physical for carrying the carrier single. The carrier single is a signal of much higher frequency, compared to power frequency, which is coupled to the EHV line. Frequency band allocated to this service is 50-200 KHz. Thus the carrier single frequency is just above the audible frequency range and just below the medium wave radio broadcast band. Due to moderately low frequency of the carrier a small bandwidth is available. However protective relaying does not need a large bandwidth.

The communication flow of today is very high. Many applications are operating at high speed and a fixed connection is often preferred. If the power utilities could supply communication over the power-line to the costumers it could make a tremendous breakthrough in communications. Every household would be connected at any time and services being provided at real-time. Using the power-line as a communication medium Could also be a cost-effective way compared to other systems because it uses an existing infrastructure, wires exists to every household connected to the power-line network. The deregulated market has forced the power utilities to explore new markets to find new business opportunities, which have increased the research in power-line communications the last decade. The research has initially been focused on providing services related to power distribution such as load control, meter reading, tariff control, remote control and smart homes. These value-added services would open up new markets for the power utilities and hence increase the profit. The moderate demands of these applications make it easier to obtain reliable communication. Firstly, the information bit rate is low; secondly, they do not require real-time performance. During the last years the use of Internet has increased. If it would be possible to supply this kind of network communication over the power-line, the utilities could also become communication providers, a rapidly growing market. On the contrary to power related applications, network communications require very high bit rates and in some cases real time responses are needed (such as video and TV). This complicates the design of a communication system but has been the focus of many researchers during the last years. Systems under trial exist today that claim a bit rate of 1 Mb/s, but most commercially available systems use low bit rates, about 10-100 kb/s, and provides low-demanding services such as meter reading. The power-line was initially designed to distribute power in an efficient way, hence it is not adapted for communication and advanced communication methods are needed. Today’s research is mainly focused on increasing the bit rate to support high-speed network Applications.



The carried current equipment comprises are following:-

A. Coupling capacitorB. Line trap unitC. Tuning unitD. Transmitter receiver etc.

A. Coupling capacitor:- The carrier equipment is connected to the transmission line through coupling capacitor which is such a capacitance that it offers low reactance to the carrier frequency but high reactance power frequency. For example, 2000 pf capacitor offers 1.5 mega ohms to 50 Hz and 150 ohms to 500 KHz.

Thus coupling capacitors allows carrier frequency signals to enter the 50 HZ power frequency current to enter the crier equipment. To reduce impedance further a low inductance is connected in series with coupling capacitors to from a resonance at crier frequency.

B. LINE TRAP:- Line trap unit is inserted between bus bar and connection of coupling capacitor to the line. It is parallel turned circuit comprising L and C. it has low impedance to 50 HZ and high impedance to carrier frequencies.

C. RUNING UNIT:-

The tuning unit is mounted inside the main coil on the tension rod. The tuning unit is designed for one of the following:-

Single wave Wide band Double wave Adjustable tuning



High frequency singles are transmitted through the transmission line conductor for the purpose of communication, protection, signaling and monitoring. Carrier current equipments are installed at the sending end and receiving end of transmission line sections.

The power line carrier equipment can be used for the following:-

To send tripping signals to the other end of transmission line so as to open the circuit breaker at that end (inter tripping).

To send single to the remote end so as to accelerate the relays at the other end of the transmission line (carrier acceleration).

To send blocking single to the other end of transmission line so as to prevent tripping of circuit breaker at that end (carrier blocking).

Carrier current protection of transmission line based on differential principle.



10.2 INTRODUCTION OF WAVE TRAP:-

“Line trap also is known as Wave trap.” What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleportation panel in the substation control room (through coupling capacitor and LMU).

This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleportation signals and in addition, voice and data communication signals. Line trap also is known as Wave trap. What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleportation panel in the substation control room (through coupling capacitor and LMU).

Wave trap is a parallel tuned inductor - capacitor 'tank' circuit made to be resonant at the desired communication frequency. It is the effort to utilize the same transmission line between two substations for the purpose of communications. At this communication frequency the tank ckt provides high impedance and does not allow passing through them & onto the substation bus & into transformers.

A wave trap is a special case of a band stop filter. It notches out one frequency, and passes all others. Series tuned wave traps are placed across the transmission line, so that its low impedance at the resonant frequency short-circuits the undesired frequencies, while passing all others. The parallel resonant variety is placed in series with the transmission line, and uses its high impedance at resonance to block further transmission of the undesired signal.



Some wave trap circuits use both series and parallel forms. If the two wave traps are tuned to the same frequency, then the attenuation at that frequency is increased. If the two wave traps are tuned to two different frequencies, then the two traps will work independently of each other with minimum mutual interference. The wave trap has the same advantages as other filters. It also has the added advantage of taking out a single strong signal that is causing most of the problem. For example, if you live close to an AM or FM broadcast station, or a commercial land mobile radio station, then you might experience various forms of interference due solely to that signal. A wave trap to notch out the offending signal will work wonders for your reception on other frequencies.



The wave trap also has most of the disadvantages of the other forms of filter. In addition, they must be tuned to the frequency of the undesired signal.

Recommendations :- Use a wave trap when there is only oneor two strong local signals that need to be reduced.

[Note: Half wavelength shorted transmission line stubs are often used as wave traps.]

Important points for wave trap:- Line traps are either suspended from gantry or placed on pedestal insulators. For 400 KV, 220 KV, 132 KV & 66 KV. Allows passing 50 Hz power frequency signal in to the switch-yard. Low impedance

to LF. Blocks HF (50 kHz – 500 kHz) signals to enter into S/Y. High impedance to HF. Normal blocking band is 150 – 500 kHz.



11 TEMPRECURE MEASUREMENT OF SUBSTATION:-

11.1 PORTABLE INFRARED CAMERAS FOR PLANT CONDITION MONITORING:-

INTRODUCTION :- The use of Infrared Thermograph to evaluate the operating condition of electrical, mechanical and process equipment for early warning signs of impending failure has increased dramatically over the past few years. The industry is forecast to continue growing at unprecedented rates, driven by the following catalysts:-

Market Awareness and Acceptance – More information and articles are being printed worldwide on this technology than ever before.

Application Diversity – No other technology has the diversity of infrared Thermograph. It is used to inspect electrical and mechanical equipment, to detect leaks in underground pipes, subsurface metal corrosion, insulation deficiencies, building energy loss and roof moisture intrusion. It is also used in medicine and for process monitoring and control of a wide range of processes. New applications are continually being found.

Equipment – The equipment is more compact, it is easier to use, it provides better imagery, faster analysis and uses software that allows reports to be written easily. Prices are also continually dropping.

Standards – Standards for thermograph are beginning to come out (ASNT, ASTM, ISO) which means that it is gaining recognition and credibility. For example, in Canada, USA and Norway most companies are requesting that thermographers have a Level I status to perform infrared thermograph inspections.

Training – Training, educational programs and seminars are now available atLocations throughout the world.

11.2 INFRARED THERMOGRAPHY:-



Temperature is one of the first observable physical parameters that will indicate the operating condition of a component or equipment, and is by far the most measured Quantity in an industrial environment. For this reason, monitoring the thermal operating Condition of electrical, mechanical or process equipment is considered to be the key to any condition monitoring program. Infrared thermograph is a condition monitoring technique used to remotely gather thermal information from any object or area, converting it to a visual image. Infrared cameras provide the means for which trained and qualified technicians can examine the temperature distribution of plant equipment. Once a problem is identified a decision is made based on the operating condition of equipment, to either resolve the problem immediately, or continue to monitor the condition The latter may involve using another monitoring technique to provide additional information. Infrared condition monitoring techniques offer an objective way of assessing the condition of plant equipment in order to predict the need for maintenance.

BENEFITS OF THERMOGRAPHY:-

This technology is used independently or in conjunction with other condition monitoring techniques and test equipment. Benefits include reduced down time, lower maintenance costs, higher equipment and process availability and increased performance. A key benefit of the technology is the speed at which existing, new or recently repaired equipment can be inspected and problems diagnosed. This in turn maximizes availability. It can be applied to high risk equipment or processes, allowing them to be evaluated from a safe distance. Thermograph also has the ability to generate information that can be used to improve equipment and enhance operational and process modifications.

BRIGHT FUTURE FOR THERMOGRAPHY:-

Whether you are considering becoming involved in thermograph simply to help the company you work for, or are looking to set up an infrared service organization, there has never been a better time than the present. Market evaluation companies such as Frost & Sullivan, ManTech International and Thomas Marketing Information Centre have all prepared market studies and surveys that look at infrared thermograph. The results are similar and show that infrared thermograph is an emerging technology that is coming into its own. “The total market is projected to experience a compound annual growth rate of 31% from 1996 to 2003.”

APPLICATIONS:-

Total maintenance costs range from 15 – 40 percent of the total cost of goods produced and is the single largest contributor to controllable cost in most



manufacturing and process facilities. Infrared thermograph has been identified as the most diversified condition monitoring technique available today and has the potential to be the greatest contributor to the reduction of maintenance and process related costs. No other technique offers the variety and quantity of applications, from the inspection of electrical components, bearings, fluid levels, and insulation deficiencies to metal thinning and corrosion.

Areas where thermograph has proven to be very useful are:-

Electrical equipment – including switches, fuses, transformers, motors, motor control centers, ballasts, overhead lines, bushings, and electronic boards.

Mechanical applications – overheating bearings, couplings, pillow blocks, gears, belts, compressors, hydraulic systems, internal combustion engines, turbines, generators, valves, brakes, conveyors, and hvac systems.

Process equipment – steam systems, heat exchangers, storage vessels, boiler casing leakage, vacuum leaks, tank levels and sludge build-up, piping insulation and leaks, leaks in buried lines, product control and furnaces (both interior and exterior), furnace tubes and refractory.

Buildings – insulation, moisture, air leakage, flat roof leaks, concrete, hvac, refrigeration systems.

Firefighting, search and rescue, security, safety. Environmental applications – oil/gas leaks, oil spills on land and water,

finding buried storage tanks, thermal/chemical pollution into waterways. Other applications - include locating leaks and problems in steam systems,

piping and steam traps, UPS systems for dead battery cells, poor connections and diesel generator problems, metal applications such as thinning subsurface corrosion, weld integrity and robot welding equipment evaluation.

SIGNIFICANT ADVANCES:-

Infrared camera technology has advanced significantly since the early 1960’s when Swedish company, AGA introduced the first commercially available infrared imaging instrument. Early instruments were heavy and bulky, they required liquid nitrogen to operate, they provided black and white fuzzy images and offered only relative temperature measurement that required the use of long and complex formulae. Infrared imagers fall into three categories. Electromechanically Scanned Instruments collect and direct the incoming infrared radiation onto a single detector element, or linear array, by means of rotating or oscillating prisms or mirrors. They Piezoelectric Videocon Imager, the second type, uses a piezoelectric surface detector, which after being aimed at the target, develops a charge distribution that is proportional to the target’s radiant energy. The infrared focal plane array (IRFPA) camera, the third design, makes use of a high density mosaic of small detector elements, which are aimed at the target. Each element “sees” a single infrared pixel of the target, and no mechanically scanned



optics are required. The size of the array ranges from a matrix of 128 horizontal elements by 128 vertical elements to one that contains 512 x 512 elements. These instruments are classified as “staring” systems in contrast to opto-mechanical “scanning” infrared devices.

The greatest single benefit of an FPA is its ability to generate high quality images (Figure 1). In mechanically scanned single-element detectors, 14,000 to 26,000 picture elements make up the field-of-view. An FPA covering the same field-of-view will comprise 65,000 to 262,000 pixels. This means the FPA will have 3 – 10 times more image detail. An image with higher resolution allows problems to be identified without the camera operator having to change lenses, it enhances analysis procedures and it provides an image that is easier to read and understand. The FPA detector may be a significant breakthrough in technology but without advancements in the optics, electronics and microprocessor technology it would not have been the possible to develop these cameras. The interaction between these components is important and it determines the diversity and quality of the instruments available today.

FUTURE DEVELOPMENTS:-

Clearly, uncooked infrared FPA’s is representing a revolution in infrared instrumentation. The uncoiled micro bolometer technology has dramatically changed the industry and has helped create a number of opportunities for thermal imaging. It is expected that the technology will continue to develop particularly in the area of improved detector performance and reduced Noise Equivalent Temperature Difference (NETD) and electronics. As costs continue to decrease and production volumes rise, the price of solid state uncoiled, lightweight systems should drop significantly. Expect to see larger arrays (640x 480) and smaller, lightweight instruments using less power. There is a movement now into a new semiconductor based IRFPA detector technology, Quantum Well Infrared Photo detector (QWIP).

The interest in this technology is that it promises major advances for infrared focal plane arrays:-

Excellent pixel uniformity, imaging and sensitivity performance.

Large pixel format capability, up to 640 x 480.

QWIPs are tunable and can be made responsive from about 3 to 25 microns, can be made for broad band and dual band applications.

Can be produced at relatively low cost and in large quantities.



The simplicity, flexibility, high performance and low cost will guarantee the development of this technology.Initially, this technology will be used for military, surveillance and process monitoring and control, but, watch this technology as it is going to be a very interesting one. The interaction between these components is important and it determines the diversity and quality of the instruments available today.

Figure 1 - The image resolution of the two FPA images (right) are clearly superior to the single element detector image (left), making identification and analysis easier.

INFRARED PROGRAM:-

In order to profit from the benefits of infrared thermography, regardless of the technology chosen, much consideration should be given to establishing an infrared inspection program. One that is properly initiated is guaranteed to provide users with a quick return on investment. Typically this will



occur within 3 months of purchasing and using the equipment, but many companies claim receiving a payback the very first day on which they performed an infrared inspection.

The first of several steps in setting up a successful thermograph program is:-

Education:- The very first step is to find out some more about the products and technology that are available and how they can be used.

Go to introductory seminars and conferences Request product data sheets and application literature from equipment vendors. Browse the internet. This is a little time consuming, but there is a wealth of

Information on the web. Contract in an independent consultant to assist in the assessment and education

Process. Hire an experienced infrared service company and learn from their employees

while they are performing an inspection in the field. Take a training course before you purchase your instrument. This will provide you

with an understanding of the IR industry and technology, equipment and application knowledge, and allow you to gain valuable experience from the instructors and other students. You will also then be prepared to deal with and negotiate efficiently with the instrument sales reps. Make sure you go to independent training companies for this training, the vendors will be very biased in their course towards their products.

CONCLUSION:-

Although the methodology used to implement and purchase equipment, and program requirements vary from plant to plant or from person to person, the following key observations set out here should be helpful. Select an instrument that will make inspections successful, now and in the future. An IR camera is a diverse tool and, when deciding on a particular type, also takes into account as much as possible, your future requirements. Plan the implementation phase carefully. Decisions on how to collect and manage data should be made at the outset, and should focus on the desired output of the program. This planning will both simplify implementation and maximize the value of the program.



11. APPENDIX AND INDEX:-

EQUIPMENT SPECIFICATION :-

400 KV SIDE YARDAS :-

1. CIRCUIT BREAKER:-

No of C.B : 8 Make : ABB Capacity : 2000A

2. ISOLATOR:-

A. CENTER BREAK:-

No. of Isolator : 6 Make : S & S Rating : 2000A Type : RC 500 HGB

B. PENTOGRAPH:-

No. of Isolator : 60 Make : S & S Rating : 2000A Type : RP 700 GM-2

3. EARTH SWITCH:-

No. of Switch : 6 Make : S & S Rating : 2000A



Type : VLC

4. CURRENT TRANSFORMER:-

Total : 16 No. of units : 16*3= 48 (3-phase) Make : W.S.I CTR : 2000-100-500A

5. CAPACITOR VOLTAGE TRANSFORE:-

Total : 4 Make : WSI (2) CTR Connected : 400 W/ 110V/3 Type : CVBA

6. LIGHTENING ARRESTOR:-

Total : 6 No. of units : 16 Make : ELPRO (3) WSI (3) Type : CPL QL 11 ZMO 90

7. BUS REACTOR:-

No. of Reactor : 3 Make : Crompton Greaves Capacity : 16.67 MVAR Rated Voltage : 420/3 KV Date of Commissioning: 26-11-1991

200 KV SIDE YARD :-

1. CIRCUIT BREAKER:-

No of C.B : 30 { 220 KV - 16 , 11 KV – 1} Make : ABB, Crompton Greaves, Siemens Capacity : 2000A



2. ISOLATOR:-

No. of Isolator : 6 Make : Wigman, S & S Rating : 1600A Type : RC 500 HGB, RP 500

3. CURRENT TRANSFORMER:-

Total : 16 No. of units : 16*3= 48 (3-phase) Make : W.S.I., ABB, AE CTR : 1500-750-375/1 A, 1200-600-300-150/1 A

4. CVT AND CC:-

Total : 10 Make : WSI, ABB, Crompton Greaves CTR Connected : 245 KV/ 220 0KV/110 KV/3

5. LIGHTING ARRESTOR:-

Total : 14 No. of units : 14*3=42 Make : ELPRO, WSI Capacity : 198 KV

6. POTENTIAL TRANSFORMER:-

FOR 220 KV:-

Total : 2 No. of Units : 2*3=6 PT Ratio : 245 KV/110 KV/3 Make : BHEl

FOR 66 KV:-

Total : 2 No. of Units : 2*3=6 PT Ratio : 66 KV/110KV/3 Make : Hivlotran Elect.

400/220/33 KV INTERCONNECTED TRANSFORMER:-



Total : 7: 2 for R-Phase : 2 for Y-Phase : 2 for B-Phase : 1 SP. X’mer Make : BHEL Capacity : 167 MVA % Impedance : 12.58 OLTC : BHAL

66/11 KV AND 11/4.2 KV POWER TRANSFORMER:-

Total : 6 Make : Johnson Elect. Company, NEL, Apex, Ashok Capacity :5 MVA %Impedance : 5.93/5.6, 5/4.59

7. D.G. SET:-

Total :1 Make :Jyoti Kirlosker Capacity : 275 KVA Type : NTA 855 G2

8. COPRESSOR:-

FOR 400 & 220 KV YARD:-

AIR BLAST CB:-

Total : 4 Make : Ingersoll Capacity : 60 kg/cm2

Type : 30/15-t-2

SF 6 CB:-

Total : 5



Make : EIGI Capacity : 20-5 kg/cm2

Type : 234s000

13. SAFETY PRECAUTIONS FOR SUBSTATION:-

13.1 There were many safely recommendations made, which were strictly followed at the substation site:-

1. The electric shocks are usually received and taken while working with the electricity.

2. A great care should be taken against electric shock while working on the line whether its conductor is insulated or bared.

3. Never work with bare feet. It is better to were rubber shoes while working.4. Use safely belt before stating the work on an electric pole.5. Phase or positive wire should always be connected through the switch.6. Before the replacing the blown fuse, always switch off main switch.7. Do not touch electric installation without any purpose.8. Before stating the work, ensure that you are authorized to do the work.9. Safety depends upon good earthing, always keep earth connected in the good

condition.10. The battery charging room should be lighted and airy.11. Do not charge the battery in a dark room.12. In case of fire, do not throw water on a live and equipment, it is dangerous.13. No cable was taken out of the switchyard fence for any electfication purpose.14. For the purpose of watering the electrode, there was a piling network laid in the

substation.15. Piping network used for watering the earth electrode was not taken outside the

switch yard fence area.



16. Opening of the switching gate was don’t towards the switchyard end to avoid any transfer of potential outside the switchyard earth mat area.

Emulsifier, Hydrant and Helon Fire protection system:-



14. BIBLIOGRAPHY:-

1) ELECTRICAL POWER BY

S.L. UPPAL –KHANNA PUBLISHERS

2) SWITCHGERE PROCTECTIO AND POWER SYSTEM BY

S.S.RAO –KHANNA PUBLISHERS

3) ELECRICAL POWER SYSTEM DESIGN BY



M.V.DESHPANDE – TATA MCGRAWHILL

4) BROCHURE

400 KV SOJA SUBSTATIONS

5) PRINCIPLES OF POWER SYSTEM

V.K. MEHTA

ROHIT MEHTA

6) FUNDAMETALS OF POWER SYSTEM PROTECTION

Y.G. PARTHANKER

S.R. BHIDE

7) WEBSITES:-

1. www.electronicsforyou.com

2. www.Getco.com

3. www.allcircuitabout.com

4. www.efu.com

5. www.en.wikipedia.org

6. www.1000electricalproject.com

8) SOURCES OF COMPUTER:-

1. CIRCUIT MAKER.

2. PAINT


http://www.en.wikipedia.org/

http://www.efu.com/

http://www.allcircuitabout.com/

http://www.Getco.com/

http://www.electronicsforyou.com/

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