electrical

Three Phase Induction Motor MCQ Questions and Answers Page - 7

1.

Induction motors, when directly switched on across their normal rated supply voltage, the torque developed at starting is about _____of their full load torque.

Answer/ Hint      

Answer : B

Explanation :

2.

_____starter is used for starting a 3-phase induction motor that needs frequent starting and operating in forward and reverse directions.

Answer/ Hint      

Answer : A

Explanation :

3.

With DOL start of an induction motor the heating during acceleration of inertia load is proportional to

Answer/ Hint      

Answer : D

Explanation :

4.

A 3- phases squirrel cage induction motor is started by means of a star/delta switch. What is the starting current of the motor?

Answer/ Hint      

Answer : B

Explanation :

5.

In auto transformer starting of 3- phase induction motor, if the tapping used is x then the starting line current and starting torque will be ___and ____times respectively with direct on line starting.

Answer/ Hint      

Answer : C

Explanation :

6.

for the purpose of starting an induction motor. Y/  switch is an equivalent to an auto transformer of ratio.

Answer/ Hint      

Answer : B

Explanation :

7.

The starting torque of a 3-phase slip ring induction motor can be increased by connecting an external resistance in the

Answer/ Hint      

Answer : A

Explanation :

8.

Which of the following starting methods cannot be used for starting a 3-phase squirrel cage induction motor?

Answer/ Hint      

Answer : C

Explanation :

9.

An induction motor can run at synchronous speed if it is operated

Answer/ Hint      

Answer : C

Explanation :

10.

The speed regulation of a 3-phase induction motor at full load is about

Answer/ Hint      

Answer : A

Explanation :

11.

The speed of an induction motor depends on

Answer/ Hint      

Answer : D

Explanation :

12.

Smooth speed control can be achieved by

Answer/ Hint      

Answer : D

Explanation :

13.

The speed of a slip ring three phase induction motor can be controlled from the rotor side by

Answer/ Hint      

Answer : C

Explanation :

14.

Synchronous speed of an induction motor can be increased by

Answer/ Hint      

Answer : D

Explanation :

15.

In ac motor control V/f is kept constant to

Answer/ Hint      

Answer : A

Explanation :

16.

In rotor resistance control method ____with the increase in speed

Answer/ Hint      

Answer : B

Explanation :

17.

In rotor resistance control of induction motor, the harness of speed torque characteristic

Answer/ Hint      

Answer : B

Explanation :

18.

In case of voltage injection method of speed control, the injected emf should be of

Answer/ Hint      

Answer : B

Explanation :

19.

Speeds higher than synchronous speed can be had by

Answer/ Hint      

Answer : B

Explanation :

20.

Slip changing method of speed control can be used in case of

Answer/ Hint      

Answer : A

Explanation :

21.

During plugging of an induction motor

Answer/ Hint      

Answer : A

Explanation :

22.

In dynamic braking of 3-phase induction motors

Answer/ Hint      

Answer : C

Explanation :

23.

In a 3-phase induction motor, the regenerative braking occurs when

Answer/ Hint      

Answer : A

Explanation :

24.

The stator of a 2/4 pole changing cage motor is initially wound for 2-poles. The reconnection of the stator winding to 4- poles through a changeover switch, while the motor is running would result in

Answer/ Hint      

Answer : D

Explanation :

25.

If a squirrel cage induction motor runs slow, the probable cause could be

Answer/ Hint      

Answer : D

Explanation :

26.

If a squirrel cage induction motor run hot, the probable cause could be

Answer/ Hint      

Answer : D

Explanation :

27.

If an induction motor hums during starting up, the possible cause could be

Answer/ Hint      

Answer : D

Explanation :

28.

Three phase induction motor should preferably be mounted on

Answer/ Hint      

Answer : D

Explanation :

29.

The large sized induction motors are protected against overload by

Answer/ Hint      

Answer : C

Explanation :

30.

The insulating materials employed for motor windings are classified according to

Answer/ Hint      

Answer : B

Explanation :

31.

The factor (s) to be considered in selection of motor is / are

Answer/ Hint      

Answer : D

Explanation :

32.

Armature short circuits can be detected and identified by ____tests(s)

Answer/ Hint      

Answer : D

Explanation :

33.

Induction generator deliver power at

Answer/ Hint      

Answer : A

Explanation :

34.

A 3- phase induction motor is fed from a balanced 3-phase supply on the rotor side short circuiting the stator terminals. The speed of the rotating magnetic field is

Answer/ Hint      

Answer : D

Explanation :

35.

A dual voltage single phase ac motor can be operated on either

Answer/ Hint      

Answer : C

Explanation :

36.

The rotor slots in an induction motor are, usually not kept parallel to the shaft as it

Answer/ Hint      

Answer : B

Explanation :

37.

If a single phasing occurs when the motor is running. It should not be loaded beyond

Answer/ Hint      

Answer : C

Explanation :

38.

The overheating of an induction motor may be due to

Answer/ Hint      

Answer : D

Explanation :

39.

Imbalance in shaft of the induction motor occurs due to

Answer/ Hint      

Answer : B

Explanation :

40.

The reversing of 3-phase A.C motor is achieved by

Answer/ Hint      

Answer : D

Explanation :

41.

Which of the following is not determined by circle diagram?

Answer/ Hint      

Answer : C

Explanation :

42.

What is the advantage of the slip ring induction motor over the squirrel cage induction motor?

Answer/ Hint      

Answer : D

Explanation :

43.

What is the advantage of starting a slip-ring induction motor with the help of rotor resistance as compared to other methods?

Answer/ Hint      

Answer : C

Explanation :

44.

What is the advantage of the double squirrel-cage rotor as compared to the round bar cage rotor?

Answer/ Hint      

Answer : C

Explanation :

45.

Synchronous speed is defined as

Answer/ Hint      

Answer : B

Explanation :

46.

The speed of a three-phase cage-rotor induction motor depends upon

Answer/ Hint      

Answer : D

Explanation :

47.

When a Scharge motor runs exactly at synchronous speed, then

Answer/ Hint      

Answer : D

Explanation :

48.

Under average service conditions, motor bearing may be safely operated at temperature upto

Answer/ Hint      

Answer : C

Explanation :

49.

Which of the following statements is correct regarding a 3-phase motor?

Answer/ Hint      

Answer : B

Explanation :

50.

The most important factor in motor maintenance is to keep

Answer/ Hint      

Answer : A

Explanation :

51.

The two important parts of a3-phase induction motor are

Answer/ Hint      

Answer : B

Explanation :

52.

In a wound 3-phase induction motor, brushes should be connected to

Answer/ Hint      

Answer : D

Explanation :

53.

Phase advancers are used with induction motors to

Answer/ Hint      

Answer : D

Explanation :

54.

In moist surroundings which frames of motor will preferred?

Answer/ Hint      

Answer : B

Explanation :

55.

The principle of operation of a three-phase induction motor closely resembles to that of which of the following?

Answer/ Hint      

Answer : C

Explanation :

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Three Phase Induction Motor MCQ Questions and Answers Page - 7