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Electrical Engineering Objective Questions { Induction Motors }

22. In three-phase squirrel-cage induction motors
A. rotor conductor ends are shortcircuited through slip rings
B. rotor conductors are short-circuited through end rings
C. rotor conductors are kept open
D. rotor conductors are connectedto insulation
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23. In a three-phase induction motor, the number of poles in the rotor winding is always
A. zero
B. more than the number of poles in stator
C. less than number of poles in stator
D. equal to number of poles in stator
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24. DOL starting of induction motor is usually restricted to
A. low horsepower motors
B. variable speed motors
C. high horsepower motors
D. high speed motors
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25. The speed of a squirrel-cage induction motor can be controlled by all of the following except
A. changing supply frequency
B. changing number of poles
C. changing winding resistance
D. reducing supply voltage
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26. The 'crawling' in an induction motor is caused by
A. high loads
B. low voltage supply
C. improper design of machine
D. harmonics developed in the motor
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27. The power factor of an induction motor under no-load conditions will be closer to
A. 0.2 lagging
B. 0.2 leading
C. 0.5 leading
D. unity
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28. The `cogging' of an induction motor can be avoided by
A. proper ventilation
B. using DOL starter
C. auto-transformer starter
D. having number of rotor slots more or less than the number of stator slots (not equal)
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