PROJECT TITLE

STUDY OF NEW AC DRIVE

SYSTEM AT PLTCM CRM

Under Guidance: - Mr. ARGHYA DEB

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ACKNOWLEDGEMENT

With a great pleasure we would like to express our deep sense of gratitude to Mr. Ajit Kar, Chief, and MEG; Mr.Arghay Deb, Head, MEG

And to our guide and training co-coordinator Mr. Nirbhay Kumar Gupta, Sr. Technologist, MEG, TATA Steel Limited, For their valuable instructions, guidance and illuminating criticism throughout our projectWithout their involvement and supervision we could not have been able to complete this project.

We would like to express our sincere thanks to Mr. K. Paswan, Sr. Manager, and PH-4;Mr. V.G. Rao, Consultant, MEG; Mr. O.P. Gupta, MEG and so many others countless people of TATA Steel Limited, Jamshedpur for helping us in our project during our entire internshipWe would also like to thank Dr. Mandal Training and Placement

Last but not the least we would like to thank all of our friends and the employees of Maintenance Expert Group for their sincere co-operation and help throughout our training. Thanks to everybody and to almighty for giving us this opportunity in our lifetime.

NAME: VIDYA KUMARI

UNIV.ROLL NO.: JSDPRFELTNKSOJUL1100776

REFE NO: VT20131799

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CERTIFICATEThis is to certify that the project report entitled

“STUDY OF NEW AC DRIVE SYSTEMS”, PLTCM CRM

Being submitted by Ms. VIDYA KUMARI, JAGDISH Institute of Industrial Technology, Bhubaneswar to TATA Steel, as a part of summer training course of DIPLOMA in Electronics curriculum is a bonafide record of work carried out by them under my supervision and guidance. The sincerity and sense of dedication shown by them during the project is commendable.

Mr. ARGHYA DEBHEADMaintenance Expert GroupTATA Steel LimitedJamshedpurDate:

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CONTENTS

COMPANY PROFILE PAGE NO.

Tata Steel 5-7

-MAINTENANCE EXPERT GROUP 10

ELECTRONICS DEVIVE 11-12

A.C. MOTOR 19

    Types 19

INDUCTION MOTOR  

     Construction 23

Working principle 24

Testing and Inspection parameter 24

OBSERVATION OF MOTORS 25

CONCLUSION 25

BIBLIOGRAPHY 31

THANKING YOU 35

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INTRODUCTION TO TATA STEEL

Tata Steel Limited

Type PublicTraded as NSE: TATASTEEL, BSE: 500470 (BSE SENSEX Constituent)Industry SteelFounded 1907Founder(s) Dorabji TataHeadquarters Mumbai, Maharashtra, India

Area served Worldwide

Key people CYRUS PALLONJI MISTRY (Chairman)HEMANT M. NERULKAR (Managing Director)

Products Steel, flat steel products, long steel products, wire products, plates

Tata Iron and Steel Company was established by Dorabji Tata on August 26, 1907, As part of his father Jamshedji's Tata Group. By 1939 it operated the largest steel plant in the British Empire.

The company launched a major modernization and expansion program in 1951. Later, the program was upgraded to 2 MTPA project. In 1990, it started expansion plan and established its subsidiary Tata Inc. in New York. The company changed its name from TISCO to TATA Steel in 2005.

Tata Iron and Steel Company was established by Dorabji Tata on August 26, 1907, As part of his father Jamshedji's Tata Group. By 1939 it operated the largest steel plant in the British Empire.

The company launched a major modernization and expansion program in 1951. Later, the program was upgraded to 2 MTPA project. In 1990, it started expansion plan and established its subsidiary Tata Inc. in New York. The company changed its name from TISCO to TATA Steel in2005.

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PLANS OF PROJECT

WEEK-1 Visit of electronics repair LAB, LDC Study of document.

WEEK-2 STUDY OF DOCUMENT AT AC DRIVE

WEEK-3 VISIT ON ELECTRICAL &AC REPAIR SHOP AND PROJECT WORK

WEEK-4 PROJECT WORK

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ELECTRONICS DEVICE

RESISTORA resister may be defining as an electronic component which is manufactured with a specified amount of resistance. Resistor is controls the flow of electric current.

RECTIFIERA rectifier is a circuit which is used to convert AC voltage in to the pulsating DC voltage .A rectifier circuit usage one or more diode.

DIODEIt has two terminal cathode (+) and anode (-).

TRANSISTORA semiconductor device consisting of a two p-n junction formed by sand witching either p-type or n-type semiconductor between a pair of opposites type is known as a Transistor.

THYRISTORTHYRISTOR is a generic term for a semiconductor device which has four semiconductor layers and operates as a switch, having stable ON and OFF.

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ELECTRICAL REPAIR SHOP

Defective electrical motors come here for repair and rectification and overhauling It is Asia second biggest electrical repair shop. ELECTRICAL REPAIR SHOP is one of the most important sections of the M.E.D. (Electrical) departments. The job of Electrical Repair Shop is to repair various kinds of electrical motors, main coolers changing sets and manufacturing panels for cranes .The ERS is divided into several sections for work efficiency

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ERS various sections are as follows:

1. Motor receiving section

2. Opening section

AC motor opening

DC motor opening

3. Motor washing area

4. Bearing section

5. Stripping section

6. Winding section

AC winding area

DC winding area

Heavy winding area

7. VPI (Vacuum Pressure impregnation) section

8. Assembly part

AC assembly area

DC assembly area

Heavy assembly area

9. Final testing Area

10. Final fitting Area

11. Motor Testing Area

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AC MOTOR

With the almost universal adoption of A.C. system of distribution of electrical energy for light

and power,

The field of application of A.C. motors has widened considerably during recent years.

TYPES OF AC MOTORS:

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INDUCTION MOTOR

Three phase induction motor is the most popular type of a.c. motor. It is very commonly used for

industrial drives since it is cheap, robust, efficient and reliable. It has good speed regulation and

high starting torque. It requires little maintenance. It has a reasonable overload capacity.

CONSTRUCTION:

A 3-Φ induction motor essentially consists of two parts: the stator and the rotor.

The stator is the stationary part of the motor’s electromagnetic circuit. The stator core is made up

of many thin metal sheets, called laminations. Laminations are

used to reduce energy loses that would result if a solid core were

used. Coils of insulated wire are inserted into slots of the stator

core. When stator windings supplied with 3-Φ currents, produce a

magnetic flux which revolves at constant speed & induces an

E.M.F. in the rotor by mutual induction.

Rotor is the rotating part and made up of thin laminations of the

same material as stator.

Squirrel-cage rotor: Motors employing this type of rotor are knows as squirrel-cage induction

motors. Almost 90 percent of induction motors are squirrel-cage

type. The rotor consists of a cylindrical laminated core with

parallel slots but little skewed for carrying the rotor conductor.

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Phase- wound or wound rotor: Motors employing this type of rotor are variously known as

phase wound motors or slip-ring motors. This type of rotor is provided with 3-Φ, double layer,

distributed winding consisting of coils as used in alternators.

Working principle of Induction

Motor

When three phase supply is given to three

phase stator winding, a rotating magnetic field

is produced.  Due to rotating magnetic field,

the flux passes through the air gap between

rotor and stator, sweeps past the rotor surface and so cuts the rotor conductor. Hence according

to Faraday’s law of electromagnetic induction, there would be a induced current circulating in

the closed rotor conductors. The amount of induced current is proportional to the rate of change

of flux linkage with respect to time. Again this rate of change of flux linkage is proportional to

the relative speed between rotor and rotating magnetic field. As per Lenz law the rotor will try to

reduce the every cause of producing current in it. Hence the rotor rotates and tries to achieve the

speed of rotating magnetic field to reduce the relative speed between rotor and rotating magnetic

field.

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TESTING & INSPECTION PARAMETER OF A.C. MOTOR

STATOR:

If the stator is ok in IR test then:

Step1: BTS: - In BTS (Balance test of stator) the stator is checked for

whether the three phases of the winding are drawing same amount or not.

Step2: Impregnation in Hot Box. Here the stator is inserted into hot box after

varnishing so that moisture and dust are removed.

Step3: storage

ROTOR:

If it is a squirrel cage rotor then it is send to Bearing Removing and checking and if it is a Slip

Ring Rotor first it undergoes IR Test then it is moved to Bearing Removing and checking

From there it is send for Washing .Then if machining is required then it is send to machining

section and then only Slip Ring is send for BTR.

If BTR result is ok

Step 1: Bearing fitting

Step 2: Storage ok Rotor

Assembly:-Both the Rotor and Stator are assembled for no load test in the Test

Bed.

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Test in Test Bed: -Here the motor is tested as per the SOP.

MEGGER TEST:Checking of insulation resistance of motor is done this method.

Check MEGGER test leads are proper insulated.

Use 1000V MEGGER for IR test.

Rotate the MEGGER handle slowly & increases the speed to the slip speed

and note IR.

Insulation resistance is to be measured between phases and also between

phases and ground of stator and rotor winding (in case slip-ring motor).

After meggering discharge the stator/rotor winding by reversing MEGGER

terminal.

Minimum acceptable IR value is as follows:

Voltage rating of M/C Minimum acceptable value

Up to 450V 5.0 MΏ

3KV-11KV 100 MΏ

BLOCKED ROTOR TEST:

Apply voltage slowly (by regulating the regulator) to the motor so as to

inject rated full load current.

During increasing the voltage watch the reaction of the person holding

the shaft .Whether the person facing any difficulties to hold or not .If

any reaction noticed –Immediately bring the regulator to zero position.

If full load current cannot be injected then inject half of full load current

and note the voltage applied.

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Acceptable limit of locked rotor test voltage at full load current is 1/8 to

1/4 of rated voltage of motor.

OPEN CIRCUIT TEST ( FOR SLIP-RING MOTOR ):

Apply full stator voltage slowly to the stator terminal and measure

the rotor voltage (phase to phase) at rotor terminal keeping rotor

winding open. Rotor voltage should be equal to rated voltage.

Note down stator magnetising current, rotor voltage and stator

voltage.

RUN (NO-LOAD) TEST:

The rated voltage at rated frequency is applied to stator slowly (by

regulating the regulator) to run the motor.

Run the motor for half an hour at rated voltage, rated frequency.

Note down current reading from ammeter.

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All 3 phase current should be balanced

Acceptable range of no load current as follows:

Type Allowable range General purpose motors 20% to 50% of rated current

High torque motors like Withdrawal & Mudgun motors

60% of rated current

In case of slip-ring motor after doing open circuit test short the rotor and

run the motor as squirrel cage motor as above.

Following reading are taken in run test:

No-load current

No-load speed

Vibration at bearing, body & foundation of body.

Temperature at bearing, shaft, body etc.

Bearing condition by SPM meter.

Sound using stethoscope.

Sparking in case of slip-ring motor

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TEMPERATURE MEASUREMENT:

Take temperature reading of bearing, shaft & body by temperature gun .

Maximum acceptable value of temperature after half an hour is as follows:

Location Maximum acceptable temperatureSurface temp. of bearing housing 75°C

Body temp. class B motor 55°C

Body temp. class F motor 70°C

Body temp. class H motor 90°C

VIBRATION TEST:

Put vibration probe gently on motor driving and no driving end bearing

housing.Body and foundation base in horizontal, vertical & axial direction

and take the reading.

Maximum acceptable value of vibration as follows:

SL. No

shaft height(mm) 56<H≤132 132<H≤225 225<H≤400 H>400

1 Range of speed 500 to 1500 >1500-3000 500 to 1500 >1500-3000 500 to 1500 >1500 - 3000 500-1500 >1500-3000

2 N(normal) 1.8 1.8 1.8 2.8 2.8 4.5 2.8 4.5

3 R(reduced) 0.71 0.71 0.71 1.12 1.8 2.8 - -

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4 S(special) 0.45 0.45 0.45 0.71 1.12 1.8 - -

SOUND CHECKING:

Put the probe of stethoscope on bearing housing and body and observe any

unsual sound(humming, metallic, etc.) is coming or not.

BEARING CONDITION:

Connect the SPM probe to the instrument(shock pulse tester) and enter the

bearing data in the instrument.

Put the SPM probe on the bearing housing at an angle 45° to the load zone.

SPEED CHECKING:

Hold the Tachometer correctly and measure the speed of the motor.

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AC DRIVES

AC drives provide a very efficient and direct method of controlling the speed of the most rugged and reliable of prime movers, the squirrel cage motor. AC drives provide many economic and performance advantages in a wide variety of adjustable speed drive applications.The following are some of the benefits provided:

1. High efficiency and low operating cost.2. Minimal motor maintenance.3. Controlled linear acceleration and deceleration provide soft.4. Starting and stopping and smooth speed changes.5. Multiple motor operations are easily accomplished.6. Current limit provides for quick and accurate torque control.7. Adjustable speed operation can be accomplished with existing AC motors.8. Improved speed regulation can be accomplished by slip compensation.9. AC motors are available in a wide variety of mechanical configurations.10. Flexibility of machine design due to the light weight and compact size of AC motors.11. IR compensation provides high starting torque easily and economically.12. AC motors are available in enclosures suitable for hazardous or corrosive environments.13. Fewer spare motors are required since the same motor can be used for both adjustable speed and constant speed operations.14. Cutler-Hammer rugged and reliable designs ensure minimum downtime expense.15. High speed operation can be economically accomplished using extended frequency operation.16. Reverse operation is accomplished electronically without the need for a reversing starter.

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ADJUSTABLE FREQUENCY AC DRIVE SYSTEM

INTRODUCTION

An adjustable frequency AC drive system consists of an ordinary three-phase induction motor, an adjustable frequency drive to control the speed of the motor and an operator's control station.

The most common motor used with an AF drive system is a standard NEMA design B squirrel cage induction motor, rated for 230 or 460 volt, 3-phase, 60 Hz operation. The adjustable frequency controller is a solid-state power conversion unit. It receives 240 or 480 volt, 3-phase,60 Hz power and converts it to a variable frequency supply which can be sleeplessly adjusted between 0 and 60 Hz. The controller also adjusts the output voltage in proportion to the frequency to provide a nominally constant ratio of voltage to frequency as required by the characteristics of the motor. The operator's station provides the operator with the necessary controls for starting and stopping the motor and varying the motor speed. These functions can also be performed by a wide variety of automatic control systems. There are several classifications of adjustable frequency AC drives. Some common types of drives are VariableVoltage Input (VVI) sometimes called Six Step drives, current source input (CSI), pulse width modulated (PWM) drives, Sensor less Vector drives, Field Oriented drives and Closed LoopVector drives.

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PRINCIPLES OF ADJUSTABLE FREQUENCY MOTOR OPERATION

The operating speed of an AC induction motor can be determined by the frequency of the applied power and the number of poles created by the stator windings. Synchronous speed is the speed of the magnetic field created in the stator windings. It is given by:

N = 120f /PWhere:n = speed in RPMf = operating frequencyP = number of polesWhen the frequency is changed, the voltage must also be changed, based on the formula for reactance and Ohm’s Law.XL = 2πfLWhere L = inductanceXL = reactanceV = voltageIm = magnetizing currentIm = V/XL

Combining the above equations yields:Im = (V/f). (1/2πfL)For steady-state operation, constant volts per hertz ratio must be maintained. This is equal to the motor rated voltage divided by the rated frequency.For the magnetizing current to remain constant, the V/f ratio, or the volts per hertz ratio, must remain constant. Therefore, the voltage must increase and decrease as the frequency increases and decreases.

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INDUCTION MOTOR SPEED CONTROL

Standard induction motors (NEMA design B) have approximately 3% slip at full load.If the drive only controls the output frequency, the motor speed will deviate from the set speed due to slip. For many fan and pump applications, precise speed control is not needed

CONCLUSION

Motors failure can lead to even higher cost in terms of lost production and efficiency. Industrial

companies need effective motor management strategies to minimize overall motor cost.

The maintenance practices that encompassed “excellent” reliability of motors are:

• Visual inspections

• Insulation resistance

• Cleaning

• Lubrication and/or filters

• Vibration analysis

• Bearing check/inspection

• Temperature checking

• Air gap checks

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• Alignment

• Check/change brushes, as applicable.

* The use of continuous-monitoring systems (i.e., temperature and vibration) and the

application of technologies and maintenance practices that will avoid or detect electrical

and mechanical faults

*The result is about a two-thirds reduction in failure rate and a significant decrease in

production downtime.

*Proper shaft alignment can prolong the life and improve the efficiency of motors and

other integral equipment. 

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