Polyphase Induction Motors

21. For driving high inertia loods best type of induction motor suggested is

1. slip ring type
2. squirrel cage type
3. any of the above
4. none of the above

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22. For which motor the speed can be controlled from rotor side?

1. Squirrel-cage induction motor
2. Slip-ring induction motor
3. Both (a) and (b)
4. None of the above

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23. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move

1. in the opposite direction as the direction of the rotating field
2. in the same direction as the direction of the field
3. in any direction depending upon phase squence of supply
4. any of the above

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24. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as

1. humming
2. hunting
3. crawling
4. cogging

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25. If any two phases for an induction motor are interchanged

1. the motor will run in reverse direction
2. the motor will run at reduced speed
3. the motor will not run
4. the motor will burn

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26. In a squirrel cage motor the induced e.m.f. is

1. dependent on the shaft loading
2. dependent on the number of slots
3. slip times the stand still e.m.f. induced in the rotor
4. none of the above

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27. In a star-delta starter of an induction motor

1. resistance is inserted in the stator
2. reduced voltage is applied to the stator
3. resistance is inserted in the rotor
4. applied voltage perl stator phase is 57.7% of the line voltage

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28. In a three-phase induction motor

1. iron losses in stator will be negligible as compared to that in rotor
2. iron losses in motor will be neg¬ligible as compared to that in rotor
3. iron losses in stator will be less than that in rotor
4. iron losses in stator will be more than that in rotor

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29. In a three-phase induction motor, the number of poles in the rotor winding is always

1. zero
2. more than the number of poles in stator
3. less than number of poles in stator
4. equal to number of poles in stator

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30. In an induction motor if air-gap is increased

1. the power factor will be low
2. windage losses will be more
3. bearing friction will reduce
4. copper loss will reduce In an induction motor

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