Polyphase Induction Motors Objective type Questions and Answers pdf

61.    In a three-phase induction motor
(a)     iron losses in stator will be negligible as compared to that in rotor
(6)     iron losses in motor will be neg¬ligible as compared to that in rotor
(c)    iron losses in stator will be less than that in rotor
(d)    iron losses in stator will be more than that in rotor
Ans: d

62.    In case of 3-phase induction motors, plugging means
(a)     pulling the motor directly on line without a starter
(b)     locking of rotor due to harmonics
(c)    starting the motor on load which is more than the rated load
(d)    interchanging two supply phases for quick stopping
Ans: d

63.    Which is of the following data is required to draw the circle diagram for an induction motor ?
(a)     Block rotor test only
(b)     No load test only
(c)    Block rotor test and no-load test
(d)    Block rotor test, no-load test and stator resistance test
Ans: d

64.    In three-phase induction motors sometimes copper bars are placed deep in the rotor to
(a)     improve starting torque
(b)     reduce copper losses
(c)    improve efficiency
(d)    improve power factor
Ans: a

65.    In a three-phase induction motor
(a) power factor at starting is high as compared to that while running
(b) power factor at starting is low as compared to that while running
(c) power factor at starting in the same as that while running
Ans: b

66.    The vafcie of transformation ratio of an induction motor can be found by
(a)     open-circuit test only
(b)     short-circuit test only
(c)    stator resistance test
(d)    none of the above
Ans: b

67.    The power scale of circle diagram of an induction motor can be found from
(a)     stator resistance test
(6)     no-load test only
(c)    short-circuit test only
(d)    noue of the above
Ans: c

68.    The shape of the torque/slip curve of induction motor is
(a)     parabola
(b)     hyperbola
(c)    rectangular parabola
(d)    straigth line
Ans: c

69.    A change of 4% of supply voltage to an induction motor will produce a change of appromimately
(a)     4% in the rotor torque
(b)     8% in the rotor torque
(c)    12% in the rotor torque
(d)    16% in the rotor torque
Ans: d

70.    The stating torque of the slip ring induction motor can be increased by adding
(a)     external inductance to the rotor
(b)     external resistance to the rotor
(c)    external capacitance to the rotor
(d)    both resistance and inductance to rotor
Ans: b

Read More Questions:
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