Multiple Choice Question (MCQ) of Induction Motors page-2

11. Three-phase induction motor is mainly suitable for which of the following application

a) For running different machine tools where several speeds are required
b) For running paper machine requiring exact speed control
c) For running electric vehicles
d) For running rolling mills needing exact speed control

Ans: (a)

12. Wattmeter reading in no-load test of induction motor gives

a) Copper losses in the stator
b) Friction and winding losses
c) Sum of (a) and (b) above
d) Total losses in the rotor on no load

Ans: (d)

13. The slip frequency of an induction motor is

a) The frequency of rotor currents
b) The frequency of stator currents
c) Difference of the frequencies of the stator and rotor currents
d) Sum of the frequencies of the stator and rotor currents

Ans: (a)

14. The field winding of a three phase synchronous machine is excited by

a) Single-phase ac supply
b) Three- phase ac supply
c) Dc supply
d) Supply obtained from an inverter

Ans: (c)

15. With increase of load, the speed of induction motor operating in the stable region

a) Increases
b) Decreases
c) Remains constant
d) Increases and then becomes constant

Ans: (b)

16. When a polyphase induction motor is loaded

a) Increases and its frequency decreases
b) Increases and its frequency increases
c) Decreases and its frequency increases
d) Decreases and its frequency decreases

Ans: (a)

17. In the following motor, external resistance can be added to start the motor

a) Slip ring induction motor
b) Squirrel cage induction motor
c) Salient pole synchronous motor
d) Wound rotor synchronous motor

Ans: (a)

18. If in a 3-phase induction motor, two phases open accidently, the motor will

a) Run at dangerously high speed
b) Stop
c) Continue to run depending on load
d) None of these

Ans: (c)

19. An induction motor is running at its rated torque and rated applied voltage of 440 volts. The effect of reducing the applied voltage to say 350 volts is

a) That the motor stops
b) Current decreases slightly
c) Speed reduces slightly
d) Motor heats up with passage of time

Ans: (d)

20. A three-phase synchronous machine is a

a) Single excited machine
b) Double excited machine
c) Machine in which three-phase supply is fed to both stator and rotor winding
d) None of these

Ans: (c)

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