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Electrical Engineering Objective Questions { Synchronous Motors }



57. Synchronous motor always runs at
A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above

58. An over-excited synchronous motor takes
A. leading current
B. lagging current
C. both (a) and (b)
D. none of the above

59. The minimum armature current of the synchronous motor corresponds to operation at
A. zero power factor leading
B. unity power factor
C. 0.707 power factor lagging
D. 0.707 power factor leading

60. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
A. d.c. excitation only
B. speed of the motor
C. load on the motor
D. both the speed and rotor flux

61. If load (or torque) angle of a 4-pole synchronous motor is 6? electrical, its value in mechanical degrees is
A.2
B.3
C.4
D.6

62. For V-curves for a synchronous motor the graph is drawn between
A. field current andarrnature current
B. terminal voltage and load factor
C. power factor and field current
D. armature current and power factor

63. The back e.m.f. of a synchronous motor depends on
A. speed
B. load
C. load angle
D. all of the above

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