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Electrical Engineering Objective Questions { Synchronous Motors }

92. The armature current of the synchronous motor has higher values for
A. high excitation only
B. low excitation only
C. both (a) and (b)
D. none of the above

93.  In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
A. one-third
B. twice
C. thrice
D. six times

94. The angle between the rotating stator flux and rotor poles is called angle.
A. torque
B. obtuse
C. synchronizing
D. power factor

95.  Which of the following methods is used to start a synchronous motor?
A. Damper winding
B. Star-delta starter
C. Damper winding in conjuction with star-delta starter
D. Resistance starter in the armature circuit

96. When the rotor speed, in a synchronous machine, become more than the synchronous speed during hunting, the damper bars develop
A. inductor motor torque
B. induction generator torque
C. synchronous motor torque
D. d.c. motor torque

97. As important advantage of a synchronous motor over wound round induction motor is that
A. its power factor may be varied at will
B. its speed in independent of supply frequency
C. its speed may be controlled more easily
D. none of the above

98. Power factor of a synchronous motor is unity when
A. the armature current is maximum
B. the armature current is minimum
C. the armature current is zero
D. none of the above

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