1) WHEN A THREE PH ASE INDUCTION MOTOR IS ROTATING AT STEADY STATE. THEN IF THE LOAD IS INCREASED THEN THE SLIP WILL…….. AND THE EFFICIENCY WILL……………

- a. Decrease, decrease.
- b. Decrease, increase.
- c. Increase, increase.
**d. Increase, decrease.**

2) A 3-phase IM runs at a slip 5% at normal voltage. For the same load torque, if supply voltage reduced to 80% of normal voltage, the motor slip will be.......

- a. 1.5 %
- b. 6.2 %
- c. 3.9 %
__d. None of these answers__

3) frequency of rotor circuit of a standard 3-phase IM is……..at starting and……..at nominal operating speed.

- A. Maximum, maximum.
- B. Minimum, minimum.
**C. Maximum, minimum.**- D. Minimum, maximum.

4) For a three phase induction motor, the slip at maximum developed torque is

- A. Equal to that of max. rotor output power and less than that of max. airgap power
- B. Equal to that of max. rotor input power and greater than that of max. rotor output power
**C. Equal to that of max. rotor input power and less than that of max. developed power**- D. Equal to that of max. rotor output power and greater than that of max. rotor input power

5) A 6-pole, 3-phase IM develops the maximum torque at 1000 rpm when operated from a 60 Hz supply. Rotor resistance per phase is 1.2 ohm. Neglecting stator impedance, the speed at which it will develop the maximum torque when operate at 50 Hz is ----------

- a. 1000 rpm
**b. 833.33 rpm**- c. 800 rpm
- d. None of these answer

6) for standard 3-phase IM, the motor direction of motion is:

- A. Opposite to that of the rotating field.
**B. Same as that of the rotating field.**- C. Depends on supply voltage phase sequence.
- D. Depends on supply voltage phases.

7) In a 3-phase IM, maximum torque of 300 Nm occur at slip of 10%. The torque at slip of 5% would be…..

__a. 120 Nm__- b. 240 Nm
- c. 150 Nm
- d. 300Nm

8) In a 3-phase IM, maximum torque of 300 Nm occur at slip of 10%. The torque at slip of 5% would be…..

__a. 120 Nm__- b. 240 Nm.
- c. 150 Nm
- d. 300 Nm

9) A wound rotor induction motor can be distinguished from squirrel cage induction motor by--------------------

**a. presence of slip-rings**- b. shaft diameter
- c. frame’s structure
- d. all of the above

10) When a three phase induction motor is rotating at steady state. Then if the load is decreased then the efficiency will--------------and slip the will-------------

- a. Decrease, increase.
__b. Increase, decrease.__- c. Decrease, decrease.
- d. Increase, increase.

11) A 3-phase induction motor has a rotor resistance of 0.02 ohm and standstill reactance of 0.1 ohm per phase. The value of total resistance of a starter for the rotor circuit for maximum torque to be exerted at starting------------

- a. 0.02 Ω
- b. 0.06 Ω
- c. 0.04 Ω
__d. 0.08 Ω__

12) A 3-phase IM runs at slip of 5% at normal voltage. For the same load torque, if supply voltage reduces to 80% of nominal voltage, the motor slip will be--------------------

- a. 7.8 %
- b. 4%
- c. None of these answer
__d. 3.2%__

13) Torque developed by a 3-phase, 400 V, induction motor is 200 Nm. If the supply voltage is reduced to 200 V, the developed torque will be-------------------

- a. 75 Nm
- b. 100 Nm
__c. 50 Nm__- d. 200 Nm

14) Torque developed by a 3-phase, 400 V, induction motor is 100 Nm. If the supply voltage is reduced to 200 V, the developed torque will be

- a. 15 Nm
- b. 150 Nm
__c. 25 Nm__- d. 50 Nm

15) The rotor conductors of 3-phase squirrel cage induction motors are-----------

- a. short circuited through resistors.
- b. short-circuited through slip rings
- c. kept open
__d. short-circuited through end rings__

16) Under locked rotor condition, the rotor circuit frequency of a 3-phase induction motor connected to a 50 Hz supply will be------------

- a. 30 Hz
- b. 60 Hz
__c. 50 Hz__- d. 3 Hz

17) A 3-phase, 6-pole induction motor is supplied from a 3-phase, 400 V, 50 Hz supply. If it is operating at full-load with 0.04 slip,The speed of the revolving field relative to the stator structure is----------------------

- a. 40 rpm
- b. None of these answers
**c. 1000 rpm**- d. zero rpm

18) Assume that for an induction motor, all losses are taken in consideration. But stator copper losses is equal to rotor copper loss, then the efficiency is---------------------

- a. s
__b. 1-s__- c. None of these answer
- d. (1-s)/(1+s)

## More Three phase induction motor MCQ to practece

In a 3-phase slip ring induction motor, if some resistance is added in the rotor circuit.

- a. its both starting torque and maximum torque will increase
- b. its starting torque will decrease and maximum torque will increase
- c. its starting torque will increase but the maximum torque will remain the same
- d. its starting torque will remain the same but maximum torque will increase

For standard three phase induction motor, the speed of rotoating magnetic field in the rotor is---------

- a. Synchronous speed (Ns)
- b. None of these answers
- c. The motor speed (Nm)
- d. Relative speed (Ns-Nm)

The power input to a 400 V, 50 Hz, 4-pole, 3-phase induction motor running at 1440 rpm is 40 kW. The stator losses are 1 kW, the rotor copper loss will be------------------

- a. 1560
- b. 1600
- c. 1450
- d. 1500

If the electrical torque in IM equal 300 Nm and the slip decreased from 5% to 3% and rotor resistance decreased by the same ratio then the torque will be--------------

- a. 300 Nm
- b. 350 Nm
- c. 250Nm
- d. None of these answer

- a. Outer cage at starting and inner cage at normal speed
- b. At inner cage all the time
- c. None of these answer
- d. Outer cage at normal speed and inner cage at starting

in a 3 phase double cage induction motor , the rotor flows mainly through

- i. lower cage at starting and Upper cage at normal speed
- ii. Upper cage at starting and Upper cage at normal speed
- iii. Upper cage at starting and lower cage at normal speed
- iv. lower cage at starting and lower cage at normal speed

**Write your comment about each phrase**

- The double squirrel cage induction motor has an advantage over a single cage rotor.
- The starting torque for the squirrel induction motor is voltage is reduced to one-half per phase. when the applied rated
- The starting current of a 3-phase induction motor is supply voltage.
- The starting torque of an induction motor is the maximum when the ...
- The insertion of resistance in the rotor circuit during the starting of a slip ring induction motor with a rotor resistance starter results in:
- By use of double-cage and deep-bar rotors, squirrel-cage motors can be designed to have the good starting characteristics resulting from... .. rotor resistance.

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