Induction Motor Objective Question Answer pdf - PSUs Interview Question

Induction Motor Objective Question Answer pdf - PSUs Interview Question


 Induction Motor is one of most important subject for electrical engg student. Most of question asked from this subject in every exam and in every interview. so here You will find previously asked Objective type questions and Answer, some important topic in full description, Interview question. MCQ type question of induction motor








Ques 1. The frame of an induction motor is usually made of
  1. Silicon steel
  2. Cast iron
  3. Aluminum
  4. Bronze
Answer 2. Cast Iron


Ques 2. In an induction motor, no-load the slip is generally
  1. Less than 1%
  2. 5%
  3. 2%
  4. 4%
Answer 1. Less than 1%

Ques 3. Slip ring of an induction motor is usually made up of
  1. Aluminium
  2. Copper
  3. Phosphorus Bronze
  4. Carbon
Answer 3. Phosphorus Bronze


Ques 4. The efficiency of an induction motor is about
  1. 100%
  2. 80-90%
  3. 50-60%
  4. Less than 50%
Answer 2. 80-90%

Ques 5. The good power factor of an induction motor can be achieved if the average flux density
in the air gap is
  1. Infinity
  2. Large
  3. Absent
  4. Small
Answer 4. Small

Ques 6. If any two phases for an induction motor are interchanged
  1. The motor will run in reverse direction
  2. The motor will continue to run in the same direction
  3. The motor will stop
  4. The motor will Burn
Answer 1. The motor will run in reverse direction

Ques 7. An induction Motor is
  1. Self-starting with high torque
  2. Self-starting with zero torque
  3. Self-starting with low torque
  4. Not self-starting
Answer 3. Self-starting with low torque


Ques 8. In a three-phase induction motor, the number of poles in the rotor winding is always
  1. Equal to number of poles in stator
  2. Zero
  3. More than the number of poles in stator
  4. Less than the number of poles in stator
Answer 2. Zero

Ques 9. At stand still condition the value of slip is
  1. 0
  2. Infinity
  3. One
  4. None of the above
Answer 3. One 

Ques 10. The condition for maximum starting torque is
  1. R= S* X/2
  2. R = X/2
  3. R =X*S
  4. R =X
Answer 4. R= X


Ques 11. Rotor resistance speed control method is not applicable in
  1. Slip Ring induction motor
  2. Squirrel cage induction motor
  3. Synchronous motor
  4. None of the above
Answer 2. Squirrel cage induction motor

Ques 12. If the terminal voltage of an induction motor is decreased then current
  1. Decreased
  2. Increased
  3. Remain same
  4. None of the above
Answer 1. Decreased

Ques 13. An induction motor is analogous to
  1. Auto-transformer
  2. Two windings transformer with secondary short circuited
  3. Two windings transformer with secondary open circuited
  4. Synchronous motor
Answer.2  Two windings transformer with secondary short-circuited



Ques 14.  No load test of 3-phase induction motor used to determine
  1. Variable loss
  2. Constant loss
  3. Eddy current loss only
  4. Hysteresis loss only
Answer 2. Constant loss

Ques 15. Which of the following losses are negligible in blocked rotor test?
  1. Mechanical losses
  2. Iron losses
  3. Both 1 & 2
  4. None of the above
Answer 3. Both 1 & 2.

Ques 16. In induction generator operation the slip is always
  1. Positive
  2. Negative
  3. Infinite
  4. Zero
Answer 2. Negative

Ques 17. In an induction motor if the air gap is increased than which of the following statement is correct
  1. Power factor will decrease
  2. Power factor will increase
  3. Speed will increase
  4. Speed will decrease
:Answer 1. Power factor will decrease

Ques 18.   what is the ratio of rotor input power to rotor copper loss in an induction motor?
  1. 1/(1 – S)
  2. 1 – S
  3. 1/S
  4. S
Answer 3. 1/S


 Ques 19.  Semi closed slots or totally closed slots are used in induction motors to improve
  1. Starting current
  2. Starting Torque
  3. Power Factor
  4. Pull-out Torque
Answer 3. Power Factor

Ques 20. The rotor slots are slightly skewed in squirrel cage induction motor in order to
  1. Increasing Rotor bar strength
  2. Prevent cogging effect
  3. Both 1 & 2
  4. None of the above
Answer 2. Prevent cogging effect

Ques 21. If an induction machine is run at above the synchronous speed it acts as
  1. Synchronous Motor
  2. Synchronous Generator
  3. Induction Generator
  4. None of the above
Answer 3. Induction Generator

Ques 22. The best method to increase the starting torque of a 3-phase slip ring induction motor is
  1. Rotor Resistance
  2. Supply voltage
  3. Supply Frequency
  4. None of the above
Answer 1. Rotor resistance

Ques 23. A small air gap in 3 phase induction motor helps to
  1. Reduce cogging effect
  2. Reduce Crawling effect
  3. Reduce Magnetizing effect
  4. All of the above
Answer 3. Reduce Magnetizing effect

Ques 24. In an induction motor, there is  decrease in maximum power factor when the dispersion coefficient is
  1. Remain Same
  2. Decreased
  3. Constant
  4. Increased
Answer 4. Increased
Ques 25. Induction motors have the advantage of
  1. Less Maintenace
  2. Less cost
  3. Simple in construction
  4. All of the above
Answer 4. All of the above

Induction Machine/Motor PSUs Interview Question and Answer 


1. Why do round rotor synchronous generators have small diameters and large axial length of core?
2. Why does open circuit synchronous machine have curved shape?
3. Do slot harmonics affect the torque-speed curve of a
three-phase induction motor?
4. Why are brushes of a d.c. machine made of carbon?
5. Why are interpoles used in a d.c. machines?
6. What is the all-day efficiency of a transformer?
7. Why are core-type transformer used in high-voltage
circuits?
8. How are iron losses in a transformer made very small?
9. Why is in a normal synchronous machine Xq smaller
than Xd?
10. Resistance of dampers for synchronous generators is
lower than that of dampers for synchronous motors. Why?
11. What is meant by an infinite bus?
12. Distribution transformers are designed for lower iron
losses. Why?
13. What are the functions of transformer oil?
14. Do we use laminations for all iron parts of an electrical
machine. If not, why?
15. Explain why in an induction motor a high value of rotor
resistance is preferred at starting?
16. Why is an ordinary induction motor not started at normal
voltage?
17. Why is the rotor core loss almost absent in normal
operating condition of an induction motor?
18. Why is star-delta starter not suitable for high voltage

induction motor?






Most Common Interview Question from Induction Motor 


1.Speed control of Induction motor ? 
2.Shell type construction,  if centre coil made primary than emf induced in other two coil,  If one of the outer coil is made as primary, then emf induced.    
3.Basic requirement for torque production ?
4.Concept of synchronous motor. 
5.Difference between rotor of IM and syn motor. 
6.Starting and damper winding concept. Torque  speed characteristic of sync motor.

7. What is Double cage Induction Motor and How double cage Induction Motor works ?

8. Induction Motor having 6 poles working at 4% slip. Calculate Speed?

9. What is Cogging and Crawling ?


10. What is Step & Touch potential?






What are the advantages of star-delta starter  with induction motor?
Answer:(1). The main advantage of using the star
delta starter is reduction of current during the
starting of the motor.Starting current is reduced to 3-4 times Of current of Direct online starting.(2).
Hence the starting current is reduced , the voltage
drops during the starting of motor in systems are
reduced.


What is meant by regenerative braking?
Answer:When the supply is cutt off for a running
motor, it still continue running due to inertia. In
order to stop it quickly we place a load(resitor)
across the armature winding and the motor should have maintained continuous field supply. so that back e.m.f voltage is made to applyacross the resistor and due to load the motor stops
quickly.This type of breaking is called as
"Regenerative Breaking".



Induction Motor Objective Question Answer pdf - PSUs Interview Question

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