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ELECTRICAL MACHINES II - Part Time Engineering - Question Bank

Anna University
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

QUESTION BANK
ELECTRICAL MACHINES II

BE-EEE-(PT)
Year : II year
Semester : III Semester

Note : This Question Bank is for Part Time B.E EEE Students.

UNIT - I
SYNCHRONOUS GENERATOR

PART - A

1. State the type of synchronous generator used in a hydro-electric power station.
2. What do you mean by single layer and double layer winding?
3. Define synchronous speed.
4. Name the two types of alternators depending on the rotor construction.
5. What are the various functions of damper winding provided with alternator?
6. Explain the meaning of synchronous reactance.
7. Define voltage regulation of an alternator.
9. State the condition required for paralleling two synchronous generators.
10. What is meant by synchronizing?

PART - B

1. Describe with neat sketch the constructional details of salient pole alternator.

2. A 3-phase star connected 1000 kVA, 11KV; alternator has a rated current of 52.5A. The ac resistance of winding per phase is 0.45 ohm. The test results are given below
OC test; field current = 12.5 A; Voltage between the lines 422V;
SC test; field current 12.5 A; line current 52.5 A
Determine the full load voltage regulation of the alternator by emf method at 0.8 power factor lagging and leading.

3. Explain dark lamp method of synchronizing an alternator with the bus bar.

4. Explain two reaction theory of salient pole synchronous alternator.

5. A 3 phase, 50HZ, 20poles salient pole alternator with star connected winding has 180 slots on the stator each slot consist of 8 conductors. The flux per pole is 0.025Wb and is sinusoidally distributed. The coils are full pitched .calculate speed and EPH.

UNIT-II
SYNCHRONOUS MOTOR

PART - A

1. What are the main parts of a synchronous motor?
2. List out the starting methods of synchronous motor.
3. Does the change in excitation affect the power factor of the synchronous motor?
4. What is a synchronous capacitor?
5. Explain what happens when the load on a synchronous motor is changed.
6. A synchronous motor always runs at synchronous speed, why?
7. What is meant by hunting?
8. What are uses of damper winding in synchronous motor?
9. What is V-curve?
10. Mention some specific application of synchronous motor

PART - B

1. Explain why a synchronous motor does not have starting torque.
2. Explain one method of staring a synchronous motor.
3. Why does the power factor of industrial installation tent to be low? How it can be improved
4. Mention the specific application of synchronous motor.
5. What is meant by hunting in a synchronous motor? What is done to minimize it?
6. Explain V-curves and inverted V –curves.

UNIT - III
THREE PHASE INDUCTION MACHINES

PART - A

1. What are the two types of 3-induction motor?
2. Why an induction motor is called asynchronous motor?
3. Explain why the no load current of an induction motor is much higher than that of an equivalent transformer.
4. .What is the advantages of the cage motor?
5. What is crawling of an induction motor?
6. What is cogging?
7. What is an induction generator?
8. What is synchronous induction motor?
9. What are the losses take place in induction motor?
10. Why the rotor slots of a three phase induction motor are skewed?

PART -B

1. Explain with neat sketch the principle of operation of a 3 –phase induction motor.
2. Draw and explain the torque slip characteristic of an induction motor. Mark the starting and maximum torque on the curve.
3. Discuss the effect of varying resistance of an induction motor on its speed –torque characteristics.
4. Describe with a neat diagram the principle of operation of induction generator.
5. Draw the circle diagram for a 20 hp ,50 Hz, 3 phase star connected induction motor the following data
No load test: 400 v, 9 amp and pf 0.2 lagging
Block rotor test: 200 v, 50 amp and pf 0.4 lagging
Determine the line current and efficiency at full load assumes stator and rotor copper losses on short circuit to be equal.

UNIT - IV
STARTING AND SPEED CONTROL OF THREE PHASE INDUCTION MOTOR
PART - A

1. State the effect of rotor resistance on starting torque
2. Explain why the power factor of an induction motor is very low at starting
3. Define starting current.
4. List the types of starters used in three phase induction motor.
5. List the types of speed control schemes used in three phase induction motor.
6. What is slip power recovery scheme
7. What are the advantages of star-delta starter?
8. Write the necessity of starter

PART -B

1. Explain any one method of speed control of 3-phase induction motor.
2. Enumerate the various methods of starting of induction motor.
3. Describe with a neat sketch, the principle and working of a star –delta starter for a 3-phase induction motor
4. Describe the operation of stator resistance and auto transformer starter.
5. Explain with neat diagram the working of rotor resistance starter.
6. Explain the following speed control schemes of three phase induction motor.
(i) Voltage control method
(ii) Change of number of poles
7. Draw and explain about slip power recovery scheme

UNIT - V
SINGLE PHASE INDUCTION MOTOR AND SPECIAL MACHINES

PART - A

1. What is the rating of single phase machine? state its application
2. How will you change the direction of rotation of split phase induction motor?
3. What type of motor is used for ceiling fan?
4. State application of shaded pole motor?
5. Can a shaded pole motor be reversed?
6. Why single phase motor has low power factor?
7. What is a universal motor?
8. How is the universal motor different from dc series motor?
9. State the application of universal motor
10. State the application of stepper motor.

PART - B

1. Explain double revolving theory applied to a single phase induction motor?
2. Explain with neat diagrams a following types of single phase induction motors
(a) Split phase
(b) Capacitor start induction runs motor
3. Discuss the principle operation of stepper motor?
4. Describe constructional features and principle operation of linear induction motor?
5. List the advantage of an ac series motor and application of linear induction motor
6. Explain operation of permanent magnet DC motors and its advantages.

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