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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When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
A. the motor stops
B. it runs as a reluctance motor at the same speed
C. it runs as a reluctance motor at a lower speed
D. none of the above
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The effect of increasing the load on a synchronous motor running with normal excitation is to
A. decrease both armature current and power factor
B. decrease armature current but increase power factor
C. increase armature current but decrease power factor
D. increase both its armature current and power factor
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Synchronous motor always runs at
A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above
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A synchronous motor can operate at
A. lagging power factor only
B. leading power factor only
C. unity power factor only
D. lagging, leading and unity power factors
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A pony motor is basically a
A. small induction motor
B. D.C. series motor
C. D.C. shunt motor
D. double winding A.C./D.C. motor
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The maximum power developed in a synchronous motor will depend on
A. the rotor excitation only
B. the supply voltage only
C. the rotor excitation and supply volt-age both
D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)
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Armature of a synchronous machine is
A. Of reducing number of slip rings on the rotor
B. Armature is associated with large power as compared to the field circuits
C. Of difficulty of providing high voltage insulation on rotor
D. All of the above reasons
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Synchronsizingpower 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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A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
A. remain same
B. go down
C. improve
D. none of the above
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Synchronous motors are
A. Not-self starting
B. Self-starting
C. Essentially self-starting
D. None of the above
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The standard full-load power factor ratings for synchronous motors are
A. zero or 0.8 leading
B. unity or 0.8 lagging
C. unity or 0.8 leading
D. unity or zero
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If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
A. the stator current will be zero
B. the stator current will be very small
C. the stator current will be very high
D. the back e.m.f. will be more than the supply voltage
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The speed regulation of a synchronous motor is always
A. 1%
B. 0.5%
C. positive
D. zero
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The construction of a synchronous motor resembles
A. a series motor
B. an induction motor
C. an alternator
D. a rotary converter
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A three-phase synchronous motor will have
A. no slip-rings
B. one slip-ring
C. two slip-rings
D. three slip-rings
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The operating speed of a synchronous motor can be changed to new fixed value by
A. changing the load
B. changing the supply voltage
C. changing frequency
D. using brakes
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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
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If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
A. it runs at a slower speed
B. the motor stops
C. it continues to run at the same speed
D. it runs at a very high speed
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A synchronous motor can be started by
A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above
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