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Electrical Engineering Objective Questions { Synchronous Motors }

85. When the voltage applied to a synchronous motor is increased, which of the following will reduce?
A. Stator flux
B. Pull in torque
C. Both (a) and (b)
D. None of the above
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86. The speed of the synchronous motor
A. increases with increase in load
B. decreases as load increases
C. varies with power factor
D. always remains constant
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87. Dust and dirt accumulation on motor winding will result in
A. rise in winding temperature
B. increased core losses
C. shorting of coils
D. eddy current flow
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88. The efficiency of a properly desiged synchronous motor will usually fall in range
A. 60 to 70%
B. 75 to 80%
C. 85 to 95%
D. 99 to 99.5%
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89. To limit the operating temperature an electrical machine should have proper
A. voltage rating
B. current rating
C. power factor
D. speed
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90.  Slip-rings in a synchronous motor carry
A. direct current
B. alternating current
C. no current
D. all of the above
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91. A synchronous machine with large air gap has
A. a higher value of stability limit
B. a small value of inherent regulation
C. a higher synchronizing power which makes the machine less sensitive to load variations
D. all of the above
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