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Electrical Engineering Objective Questions { Synchronous Motors }

71. Hunting in a synchronous motor takes place
A. when supply voltage fluctuates
B. when load varies
C. when power factor is unity
D. motor is under loaded

72. When load on an over-excited or underexcited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is
A. more
B. less
C. equal
D. twice

73. The rotor copper losses, in a synchronous motor, are met by
A. d.c. source
B. armature input
C. motor input
D. supply lines

74. The maximum power developed in a synchronous motor occurs at a coupling angle of
A. 30?
B. 60?
C. 90?
D. 180?

75. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor
A. remains same as the original value
B. decreases to half the original value
C. tends to becomes zero
D. increases to two times the original value

76. In which of the following motors the stator and rotor magnetic field rotate at the same speed?
A. Universal motor
B. Synchronous motor
C. Induction motor
D. Reluctance motor

77. Synchronsizing power of a synchronous machine is
A. direcly proportional to the synchronous reactance
B. inversely proportional to the synchronous reactance
C. equal to the synchronous reactance
D. none of the above

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