Induction Motor MCQ Questions

1. The poly-phase induction motors are, by a very considerable margin, the most widely used ac motors as

(a) these are cheaper in cost, simple and rugged in construction and require little maintenance.
(b) they are capable of operation under a wide range of power factors both leading and lagging.
(c) they have maximum efficiency and maximum starting torque.
(d) they have very good speed regulation.

2. Which of the following statements associated with polyphase induction motor is/are correct ?

(a) It can run in one direction only.
(b) It is simply a transformer whose magnetic circuit is separated by an air gap into two relatively movable portions, one carrying the primary and other the secondary winding.
(c) It needs more maintenance than that required by a dc shunt motor.
(d) It is more costly than a dc shunt motor of the same output rating.

3. The stator frame in an induction motor is used to

(a) hold the armature stampings in position.
(b) ventilate the armature.
(c) protect the whole machine.
(d) provide return path for the flux.

4. The frame of an induction motor is made of

(a) aluminum.
(b) silicon steel.
(c) closed grained cast iron.
(d) stainless steel.
(e) bronze.

5. The stator core of a 3-phase induction motor is laminated in order to reduce the

(a) eddy current loss.
(b) hysteresis loss.
(c) both eddy current and hysteresis loss.
(d) weight of the stator.
(e) windage and frictional losses.

6. Use of fractional pitch winding

(a) results in reduced leakage reactance.
(b) results in reduced axial length of the machine.
(c) makes it stiffer.
(d) all of the above.

7. If all the stator coils of an induction motor are connected for the same magnetic polarity, there will be formed an equal number of

(a) rotor poles with same polarity.
(b) rotor poles with opposite polarity.
(c) consequent poles with opposite polarity.
(d) consequent poles with same polarity.

8. The induction motor shaft should be

(a) hollow.
(b) stiff.
(c) flexible.
(d) any of these.

9. The induction motor shaft is made of

(a) mild steel.
(b) cast iron.
(c) high speed steel.
(d) stainless steel.
(e) aluminum.

10. Induction motors normally use die-cast aluminum rotor because aluminum is

(a) cheaper in cost.
(b) lighter in weight.
(c) easy to cast owing to its low melting point and is easily available.
(d) of low resistivity.

11. In a 3-phase squirrel cage induction motor

(a) rotor conductors are short circuited through end rings.
(b) rotor conductor ends are short circuited through slip rings.
(c) rotor conductors are kept open.
(d) none of the above.

12. The squirrel cage rotor of a 6-pole induction motor can be used for induction motor.

(a) only 6-pole
(b) 6 or 12 pole
(c) any number of poles in an
(d) none of the above

13. The squirrel cage induction motors are provided with blades in order to

(a) facilitate cooling of rotor.
(b) balance the rotor dynamically.
(c) eliminate noise.
(d) none of these.

14. The rotor winding for a 3-phase slip-ring induction motor having delta-connected stator must be connected in

(a) delta.
(b) star.
(c) delta or star according to need.
(d) none of the above.

15. In a 3-phase wound rotor induction motor the short-circuit gear is used to short circuit the

(a) stator phases of the motor.
(b) rotor at slip rings.
(c) starting resistances in the starter.
(d) none of the above.

16. Uneven gap in an induction motor is likely to cause

(a) heating of motor.
(b) unbalancing of motor shaft.
(c) both (a) and (b).
(d) none of these.

17. A smaller air gap in a poly-phase induction motor helps to

(a) reduce the chance of crawling.
(b) increase the starting torque.
(c) reduce the chance of cogging.
(d) reduce the magnetizing current.

18. In an induction motor, if the air gap is increased

(a) its speed will reduce.
(b) its efficiency will improve.
(c) its power factor will reduce.
(d) its breakdown torque will reduce. [I.E.S. E.E.-II, 2004]

19. Which of the following parameters in an induction motor influences the magnetizing reactance to the maximum extent?

(a) Axial length of the rotor stack.
(b) Axial length of the stator stack.
(c) Radial length of air gap.
(d) Number of slots on the stator. [I.E.S. 2006]

20. In an induction motor, the air gap flux density is usually kept low so as to

(a) improve efficiency.
(b) improve power factor.
(c) reduce machine cost.
(d) none of the above.

21. A 3-phase, 4-pole squirrel cage induction motor has 36 stator and 28 rotor slots. The number of phases in the rotor is

(a) 3
(b) 9
(c) 7
(d) 8 [GATE E.E. 2000]

22. The rotor slots are slightly skewed in squirrel-cage induction motor to

(a) increase the strength of rotor bars.
(b) reduce the magnetic hum and locking tendency of rotor.
(c) economize on the copper to be used.
(d) provide ease of fabrication. [I.E.S. E.E. II, 2003]

23. Skewing of the rotor in a three-phase squirrel-cage induction motor reduces

(a) noise, parasitic torque, starting torque and pull-out torque.
(b) noise and parasitic torque, but increases starting torque and pull-out torque.
(c) noise and pullout torque, but increases parasitic torque and starting torque.
(d) noise, parasitic torque and starting torque, but increase pull-out torque. [U.P.S.C. I.E.S. 2001]

24. Consider the following statements:

Skewing of rotor slots in a 3-phase induction motor (cage rotor) may

1. introduce additional leakage reactance.
2. eliminate slot harmonics.

Which of the statements given above is/are correct?
(a) 1 only.
(b) 2 only.
(c) Both 1 and 2.
(d) Neither 1 nor 2. [I.E.S. E.E.-II, 2005]

25. Which one of the following is the correct statement: In a 3-phase induction motor, the resultant flux is of a constant nature and is

(a) equal to ɸ_m, where ɸ_m is maximum flux due to any phase.
(b) 1.5 times maximum value of flux due to any phase.
(c) √3/2 times maximum value flux due to any phase.
(d) 3ɸ_m. [I.E.S. E.E.-II, 2007]

26. The principle of operation of a 3-phase induction motor is almost similar to that of

(a) synchronous motor.
(b) repulsion start induction motor.
(c) transformer with a shorted secondary.
(d) capacitor-start induction motor.

27. The rotor of a 3-phase induction motor rotates in the same direction as that of stator rotating field. This can be explained by

(a) Faraday’s laws of electromagnetic induction.
(b) Lenz’s law.
(c) Newton’s laws of motion.
(d) Fleming’s right hand rule.

28. The relative speed between stator and rotor fluxes is equal to

(a) synchronous speed, N_s.
(b) rotor speed, N.
(c) zero.
(d) N_s—N.

29. Stator flux induces emf in the rotor bars

(a) rotating at synchronous speed around stator.
(b) constant in magnitude.
(c) magnitude depending upon the load on the motor.
(d) none of the above.

30. The rotor circuit of an induction motor under operating condition is

(a) always closed.
(b) always open.
(c) may be open or closed depending upon the loading conditions.

31. The 3-phase induction motor with rotor circuit open will

(a) run normally.
(b) get overheated.
(c) not run.
(d) make noise.

32. If any two leads from slip rings are interchanged in a 3-phase induction motor, the motor will

(a) continue running in the same direction as before.
(b) run in a direction opposite to previous one.
(c) not run.
(d) get damaged.

33. Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance. When switched on to supply, the motor will

(a) rotate in the same direction as before maintenance.
(b) rotate in direction opposite to that before maintenance.
(c) not start at all.
(d) get heated and damaged.

34. The direction of rotation of a 3-phase induction motor can be reversed by

(a) transposing any two leads from supply.
(b) transposing any two leads from slip-rings.
(c) transposing all the three leads from the supply.
(d) disconnecting any one phase.

35. The rotor of an induction motor rotates in the direction of the rotation of stator field in order to

(a) reduce the relative speed between the rotating stator field and the stationary rotor conductors.
(b) oppose the rotor current.
(c) increase the relative speed between the rotating stator field and stationary rotor conductors.
(d) none of the above.

1. Polyphase Induction Motor MCQ
2. Induction Motor Questions
3. Induction Motor Question Bank
4. Induction Motor MCQ Questions
5. Induction Motor MCQ
6. Squirrel Cage Induction Motor MCQ
7. Induction Motor Objective Questions
8. Induction Motor Objective Type Questions
9. Speed Control of Induction Motor MCQ

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