Realtime Polyphase Induction Motors Multiple choice Questions and Answers pdf

21.    An induction motor is identical to
(a)    D.C. compound motor
(b)    D.C. series motor
(c)    synchronous motor
(d)    asynchronous motor
Ans: d

22.    The injected e.m.f. in the rotor of induction motor must have
(a)    zero frequency
(b)    the same frequency as the slip fre-quency
(c)    the same phase as the rotor e.m.f.
(d)    high value for the satisfactory speed control
Ans: b

23.    Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ?
(a)     By changing the number of stator poles
(b)     Rotor rheostat control
(c)    By operating two motors in cascade
(d)    By injecting e.m.f. in the rotor circuit
Ans: a

24.    The crawling in the induction motor is caused by
(a)     low voltage supply
(b)     high loads
(c)    harmonics develped in the motor
(d)    improper design of the machine
(e)    none of the above
Ans: c

25.    The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
(a)    star connected only
(b)    delta connected only
(c)    (a) and (b) both
(d)    none of the above
Ans: c

26.    The  torque  developed  in  the  cage induction motor with autostarter is
(a)     k/torque with direct switching
(6)     K x torque with direct switching
(c)    K2 x torque with direct switching
(d)    k2/torque with direct switching
Ans: c

27.    When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be considered
(a)     in series
(b)     in parallel
(c)    in series-parallel
(d)    in parallel with stator
Ans: b

28.    It is advisable to avoid line-starting of induction motor and use starter because
(a)    motor takes five to seven times its full load current
(b)    it will pick-up very high speed and may go out of step
(c)    it will run in reverse direction
(d)    starting torque is very high
Ans: a

29.    Stepless speed control of induction motor is possible by which of the following methods ?
(a)     e.m.f. injection in rotor eueuit
(b)     Changing the number of poles
(c)    Cascade operation
(d)    None of the above
Ans: b

30.    Rotor rheostat control method of speed control is used for
(a)     squirrel-cage induction motors only
(b)     slip ring induction motors only
(c)    both (a) and (b)
(d)    none of the above
Ans: b

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