synchronous motors MCQs – Page 5

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

synchronous motors Mcqs
81. The back e.m.f. of a synchronous motor depends on______________?
comments icon0

A. all of the above

B. load

C. speed

D. load angle
82. A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
comments icon0
A. the motor continue to run in the same direction

B. the motor will run in the reverse direction

C. none of the above

D. the motor will stop

E. the winding of the motor will burn

83. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
comments icon0
A. By changing the supply frequency

B. By interchanging any two phases

C. By changing the applied voltage

D. By changing the load

84. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?
comments icon0

A. induction motor torque in field winding

B. induction motor torque in damper winding

C. eddy current and hysteresis torque in pole faces

D. reHetance motor torque due to saliency of the rotor

E. all of the above methods
85. Synchronous motors are_____________?
comments icon0

A. none of the above

B. essentially self-starting

C. self-starting

D. not-self starting
86. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop_________________?
comments icon0

A. inductor motor torque

B. induction generator torque

C. synchronous motor torque

D. d.c. motor toque

E. none of the above

87. In a synchronous motor, the maximum power developed depends on all of the following except:
comments icon0

A. supply voltage

B. maximum value of coupling angle

C. rotor excitation

D. direction of rotation
88. The power developed by a synchronous motor will be maximum when the load angle is____________?
comments icon0

A. 120

B. 90

C. zero

D. 45

89. Which of the following motors is non-self starting ?
comments icon0

A. D.C. series motor

B. Wound round induction motor

C. synchronous motor

D. Squirrel cage induction motor

90. To limit the operating temperature an electrical machine should have proper____________?
comments icon0
A. current rating

B. power factor

C. voltage rating

D. speed

91. . In a synchronous motor which loss varies with load ?
comments icon0
A. Copper loss

B. Bearing friction loss

C. Windage loss

D. Core loss

92. Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?
comments icon0

A. High field current

B. Low field current

C. High core losses

D. Low short circuit ratio

93. Which of the following losses is not dissipated by the stator core surface in a synchronous motor?
comments icon0

A. Iron losses in the stator

B. Windage losses

C. None of the above

D. Eddy current losses in the conductors

E. Copper losses in the slot portion of the conductors

94. If the field of a synchronous motor is underexcited, the power factor will be_____________?
comments icon0

A. zero

B. leading

C. lagging

D. unity

95. Which of the following losses, in a synchronous motor, does not vary with load?
comments icon0

A. None of the above

B. Any of the above

C. Windage loss

D. Copper losses

96. A synchronous motor will always stop when:______________?
comments icon0

A. load in motor varies

B. supply voltage frequency changes

C. excitation winding gets disconnected

D. supply voltage fluctuates

97. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
comments icon0
A. Er (net resultant voltage) in armature is increased

B. none of the above

C. power factor is decreased

D. Eb (back e.m.f.) becomes less than V (applied voltage)

E. speed of the motor is reduced

98. The torque angle, in a synchronous motor, is the angle between_______________?
comments icon0

A. magnetising current and back e.m.f.

B. the rotating stator flux and rotor poles

C. the supply voltage and the back e.m.f.

D. none of the above

99. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected______________?
comments icon0

A. it runs as a reluctance motor at the same speed

B. it runs as a reluctance motor at a lower speed

C. none of the above

D. the motor stops
100. When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is___________?
comments icon0

A. more

B. equal

C. twice

D. less