polyphase induction motors MCQs – Page 2

Practise focused polyphase induction motors questions with marked answers for exam preparation and subject revision.

polyphase induction motors Mcqs

21. The crawling in the induction motor is caused by____________?
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A. high loads

B. improper design of the machine

C. none of the above

D. harmonics develped in the motor

E. low voltage supply

22. In induction motor, percentage slip depends on__________?
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A. supply frequency

B. supply voltage

C. none of the above

D. copper losses in motor

23. The number of slip rings on a squirrel cage induction motor is usually____________?
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A. four

B. three

C. two

D. none

24. Insertion of resistance in the stator of an induction motor___________?
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A. increases the starting torque

B. none of the above

C. increases the load torque

D. decreases the starting torque

25. The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type__________?
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A. A. and B. both

B. none of the above

C. delta connected only

D. star connected only

26. In the squirrel-cage induction motor the rotor slots are usually given slight skew__________?
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A. none of the above

B. to ensure easy fabrication

C. to reduce the magnetic hum and locking tendency of the rotor

D. to increase the tensile strength of the rotor bars

27. In case of the induction motors the torque is___________?
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A. inversely proportional to slip

B. directly proportional to slip

C. inversely proportional to (Vslip)

D. directly proportional to (slip)2

28. When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be considered__________?
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A. in parallel with stator

B. in series

C. in parallel

D. in series-parallel

29. The torque developed in the cage induction motor with autostarter is___________?
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A. K2 x torque with direct switching

B. k2/torque with direct switching

C. K x torque with direct switching

D. k/torque with direct switching

30. In an induction motor the relationship between stator slots and rotor slots is that_____________?
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A. none of the above

B. stator slots are not exact multiple of rotor slots

C. stator slots are exact multiple of rotor slots

D. stator slots are equal to rotor slots

31. Insertion of resistance in the rotor of an induction motor to develop a given torque?
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A. increases the rotor current

B. rotor current rernains same

C. rotor current becomes zero

D. decreases the rotor current

32. Reduced voltage starter can be used with_____________?
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A. squirrel cage as well as slip ring induction motor

B. squirrel cage induction motor only but not with slip ring motor

C. slip ring motor only but not with squirrel cage induction motor

D. none of the above

33. In a three-phase induction motor__________?
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A. power factor at starting in the same as that while running

B. power factor at starting is high as compared to that while running

C. power factor at starting is low as compared to that while running

34. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be__________?
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A. 0.03

B. 0.02

C. 0.01

D. 0.04

35. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor_______________?
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A. will stop and carry heavy current causing permanent damage to its winding

B. will continue running burning its one phase

C. will continue running without any harm to the winding

D. will continue running burning its two phases

36. In case of a double cage induction motor, the inner cage has__________?
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A. low inductance and low resistance

B. low inductance and high resistance

C. high inductance and high resistance

D. high inductance arid low resistance

37. Blocked rotor test on induction motors is used to find out?
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A. all of the above

B. power factor on short circuit

C. leakage reactance

D. short-circuit current under rated voltage

38. The rotor of an induction motor runs at__________?
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A. any of the above

B. above synchronous speed

C. synchronous speed

D. below synchronous speed

39. The vafcie of transformation ratio of an induction motor can be found by__________?
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A. short-circuit test only

B. none of the above

C. stator resistance test

D. open-circuit test only

40. Rotor rheostat control method of speed control is used for____________?
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A. squirrel-cage induction motors only

B. slip ring induction motors only

C. both A. and (b)

D. none of the above

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