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MCQ ON 3 - PHASE INDUCTION MOTOR PAGE - 1

1.

The speed of rotating magnetic flux of a 3-phase induction motor is given by the expression

Answer/ Hint      

Answer : C

Explanation :

2.

The synchronous speed of a 2,4 and 8 poles motor at 50 Hz can not be

Answer/ Hint      

Answer : B

Explanation :

3.

The no of poles of a 3-phase induction motor running at 500 RPM will be : (supply frequency =50 Hz)

Answer/ Hint      

Answer : A

Explanation :

4.

The relation of the torque developed in an induction motor and the supply voltage is given by the expression

Answer/ Hint      

Answer : C

Explanation :

5.

The starting torque of a 3 phase induction motor can be increased

Answer/ Hint      

Answer : A

Explanation :

6.

At the time of starting, the slip of an induction motor is equal to

Answer/ Hint      

Answer : B

Explanation :

7.

The reason of drawing high current at the time of starting by an induction motor is

Answer/ Hint      

Answer : C

Explanation :

8.

For the speed control purpose pole changing method can be adopted for

Answer/ Hint      

Answer : C

Explanation :

9.

The principle of operation of an induction motor is based on

Answer/ Hint      

Answer : B

Explanation :

10.

The speed of rotor of an induction motor is

Answer/ Hint      

Answer : C

Explanation :

11.

To reverse the direction of rotation of a 3 phases induction motor, it is necessary to

Answer/ Hint      

Answer : D

Explanation :

12.

Squirrel cage induction motor differs from a slip ring induction motor as if has no

Answer/ Hint      

Answer : A

Explanation :

13.

A squirrel-cage induction motor has

Answer/ Hint      

Answer : B

Explanation :

14.

The frequency of the rotor current (fr) in an induction motor is given by the expression

Answer/ Hint      

Answer : C

Explanation :

15.

The torque of a 3-phase induction motor

Answer/ Hint      

Answer : A

Explanation :

16.

The purpose of connecting  resistance in the rotor circuit of a slip ring induction motor is to

Answer/ Hint      

Answer : C

Explanation :

17.

If the induction motor of a pump is operated at 30% less supply voltage then what will happen?

Answer/ Hint      

Answer : C

Explanation :

18.

In an induction –motor, the fractional slip (s) is given by the expression

Answer/ Hint      

Answer : Select Correct Ans

Explanation :

19.

It is advisable to avoid the use of (d) O.L starter for starting an induction motor having 5 H.P capacity because

Answer/ Hint      

Answer : B

Explanation :

20.

A thermal overload relay is provided in a starter to protect the motor against

Answer/ Hint      

Answer : C

Explanation :

21.

In a 3 phase, induction motor stared by a (d)O.L starter, protection against short circuit is given by the

Answer/ Hint      

Answer : C

Explanation :

22.

When a squirrel cage induction motor is started directly by a (d) O.L starter, the starting current will be

Answer/ Hint      

Answer : D

Explanation :

23.

When we connect an induction  motor in star through a starter, the applied voltage across each winding becomes

Answer/ Hint      

Answer : C

Explanation :

24.

Total electrical degrees for a 4 pole (a) (c) machine is equal to

Answer/ Hint      

Answer : C

Explanation :

25.

A 3-phase, 400 V, 50 Hz induction motor has a rated speed of 715 r.p.m. How many poles are there in the machine?

Answer/ Hint      

Answer : B

Explanation :

26.

With a fractional slip of 0.07 , the rotor speed of a 4 pole squirrel cage induction motor fed from a 50 Hz supply is

Answer/ Hint      

Answer : C

Explanation :

27.

The starting torque of a squirrel cage induction motor is low because of

Answer/ Hint      

Answer : C

Explanation :

28.

If a 3-phase motor runs with two phases only it is called single phasing it will ultimately

Answer/ Hint      

Answer : B

Explanation :

29.

On switching ‘ON’ the starter, the magnetic contractor vibrates heavily. The possible cause is

Answer/ Hint      

Answer : D

Explanation :

30.

A squirrel-cage motor of above 3 H.P should not be started by a (d) O.L starter because

Answer/ Hint      

Answer : A

Explanation :

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