electrical

Three Phase Induction Motor MCQ Questions and Answers Page - 3

1.

A three phase 6 pole, 50 Hz, induction motor is running at 5% slip. What is the speed of the motor?

Answer/ Hint      

Answer : C

Explanation :

2.

At the instant of starting, the per unit slip of the 3-phase induction motor is

Answer/ Hint      

Answer : C

Explanation :

3.

The mmf produced by the current of a 3-phase induction motor

Answer/ Hint      

Answer : B

Explanation :

4.

The mmf produced by the rotor currents of a 3-phase induction motor

Answer/ Hint      

Answer : B

Explanation :

5.

A 3- phase induction motor is operating at slip s. If its two supply leads are interchanged then its slp at that instant will be

Answer/ Hint      

Answer : A

Explanation :

6.

The frequency of rotor currents at stand still is equal to

Answer/ Hint      

Answer : C

Explanation :

7.

In a slip ring induction motor, the frequency of rotor currents can be measured with a

Answer/ Hint      

Answer : C

Explanation :

8.

The direction of rotor current produced in an induction motor can be determined by

Answer/ Hint      

Answer : C

Explanation :

9.

In case of an induction motor the leakage, flux is more in comparison to that of a transformer. This is due to

Answer/ Hint      

Answer : B

Explanation :

10.

In an induction motor the phase reactance is _____in comparison to  phase resistance

Answer/ Hint      

Answer : A

Explanation :

11.

In a 3- phase induction motor reactance under running condition is less than as standstill value. This is due to reduction in

Answer/ Hint      

Answer : C

Explanation :

12.

In an induction motor under running condition, the rotor reactance per phase is _______its standstill phase reactance

Answer/ Hint      

Answer : A

Explanation :

13.

The torque developed by a 3-phase induction motor is approximately proportional to

Answer/ Hint      

Answer : C

Explanation :

14.

Insertion of resistance in the rotor circuit of an induction motor to develop a given torque causes ____its rotor current

Answer/ Hint      

Answer : A

Explanation :

15.

In an induction motor if the flux density is reduced to one half of its normal value then the torque will

Answer/ Hint      

Answer : A

Explanation :

16.

The torque developed in an induction motor is nearly proportional to

Answer/ Hint      

Answer : C

Explanation :

17.

The starting torque of a 3-phase induction motor varies as

Answer/ Hint      

Answer : A

Explanation :

18.

The starting torque of a squirrel cage induction motor is

Answer/ Hint      

Answer : C

Explanation :

19.

For achieving high starting torque and high operation efficiency an induction motor should have _____rotor circuit resistance at starting and ____circuit resistance under operating conditions

Answer/ Hint      

Answer : A

Explanation :

20.

In a 3-phase slip ring induction motor high stating torque is achieved by

Answer/ Hint      

Answer : D

Explanation :

21.

When the applied voltage per phase is reduced to one half, the starting torque of a three-phase squirrel cage induction motor becomes

Answer/ Hint      

Answer : B

Explanation :

22.

The torque developed by a 3-phase induction motor least depends on

Answer/ Hint      

Answer : D

Explanation :

23.

In an induction motor if air-gap is increased

Answer/ Hint      

Answer : A

Explanation :

24.

When R2 is the rotor resistance, X2 the rotor reactance at supply frequency and the slip, then the condition for maximum torque under running conditions will be

Answer/ Hint      

Answer : C

Explanation :

25.

In case of a double cage induction motor, the inner cage has

Answer/ Hint      

Answer : A

Explanation :

26.

The low power factor of induction motor is due to

Answer/ Hint      

Answer : D

Explanation :

27.

Insertion of reactance in the rotor circuit

Answer/ Hint      

Answer : A

Explanation :

28.

Insertion of resistance in the rotor of an induction motor to develop a given torque

Answer/ Hint      

Answer : D

Explanation :

29.

For driving high inertia loads best type of induction motor suggested is

Answer/ Hint      

Answer : A

Explanation :

30.

Temperature of the stator winding of a three-phase induction motor is obtained by

Answer/ Hint      

Answer : D

Explanation :

31.

The purpose of using short-circuit gear is

Answer/ Hint      

Answer : A

Explanation :

32.

In a squirrel cage motor, the induced e.m.f is

Answer/ Hint      

Answer : C

Explanation :

33.

Less maintenance troubles are experienced in case of

Answer/ Hint      

Answer : B

Explanation :

34.

A squirrel cage induction motor is not selected when

Answer/ Hint      

Answer : C

Explanation :

35.

Reduced voltage starter can be used with

Answer/ Hint      

Answer : C

Explanation :

36.

Slip ring motor is preferred over squirrel cage induction motor where

Answer/ Hint      

Answer : A

Explanation :

37.

In as tar-delta starter of an induction motor

Answer/ Hint      

Answer : D

Explanation :

38.

The torque of an induction motor is

Answer/ Hint      

Answer : A

Explanation :

39.

The rotor of an induction motor runs at

Answer/ Hint      

Answer : B

Explanation :

40.

The starting torque of a three-phase induction motor can be increased by

Answer/ Hint      

Answer : C

Explanation :

41.

Insertion of resistance in the stator of an induction motor

Answer/ Hint      

Answer : B

Explanation :

42.

An induction motor is identical to

Answer/ Hint      

Answer : D

Explanation :

43.

The starting torque of a 3-phase squirrel cage induction motor is

Answer/ Hint      

Answer : B

Explanation :

44.

In induction motor, percentage slip depends on

Answer/ Hint      

Answer : C

Explanation :

45.

The efficiency of an induction motor is ………… than that of a transformer

Answer/ Hint      

Answer : A

Explanation :

46.

If the rotor circuit of a squirrel cage induction motor is open, the rotor will

Answer/ Hint      

Answer : D

Explanation :

47.

The advantages of a slip-ring induction motor over a squirrel cage induction motor is that

Answer/ Hint      

Answer : C

Explanation :

48.

The magnetising current drawn by the induction motors and transformers is the cause of their ……. Power factor

Answer/ Hint      

Answer : B

Explanation :

49.

A 3-phase slip-ring induction motor is always started with

Answer/ Hint      

Answer : D

Explanation :

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