Synchronous Motors PART 2
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Attempt Free Synchronous Motors PART 2 Here. Read The Important Electrical MCQ From Below.
16. 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 some speed
(C) it runs as a reluctance motor at a lower speed.
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17. The armature current of the synchronous motor has large values for
(A) low excitation only
(B) high excitation only
(C) both high and low excitation.
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18. What is the ratio of no load speed to full load speed of a 200 kVA, 12 pole, 2200 V, 3 phase, 60 Hz synchronous motor ?
(A) 1
(B) 1.1
(C) 1.21
(D) infinite.
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Synchronous Motors PART 2
19. If a synchronous motor drops too far behind, the power it takes from the supply also increases too much, and the armature tries to get accelerated, until it is in correct position. Sometimes, some motor overshoots the marks and then the process of acceleration-retardation continues. This phenomenon is known as
(A) synchronization
(B) hunting
(C) pulling out
(D) swinging.
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20. The maximum value of torque that a synchronous motor, can develop without losing its synchronism, is known
as
(A) breaking torque
(B) synchronizing torque
(C) pull out torque
(D) slip torque.
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21. In a synchronous motor if the back emf generated in the armature at no load is approximately equal to the applied voltage, then
(A) the torque generated is maximum
(B) the excitation is said to be zero percent
(C) the excitation is said to be 100%
(D) the motor is said to be fully loaded.
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22. A synchronous motor is connected
to supply voltage V
drawing current /. Resultant of v and back emf Eb is represented by E in the figure. From this diagram it can be concluded that
(A) power factor it lagging
(B) the resultant of V and Eb is consumed by synchronous impedance
(C) current I leads the applied voltage by I
(D) motor is running on full load.
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23. A 3 phase, 400 V, 50 Hz salient pole synchronous motor is fed from an infinite bus and is running at no load. Now if the field current of the motor is reduced to zero
(A) the motor will stop
(B) the motor will run
(C) the motor will run at synchronous speed
(D) the motor will run at less than synchronous speed.
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24. The purpose of embedding the damper winding in the pole face is to
(A) eliminate hunting and provide adequate starting torque
(B) reduce windage losses
(C) eliminate losses on account of air friction
(D) reduce bearing friction.
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Synchronous Motors PART 2
25. A synchronous motor is switched on to supply with its field windings shorted on themselves. It will
(A) not start
(B) start but continue to run as an induction motor
(C) start as an induction motor and then run as a synchronous motor.
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26. In case of a synchronous motor we have
I. Load
II. Speed
III. DC excitation. The magnitude of stator back emf depends on
(A) I only
(B) I and II only
(C) III only
(D) I, II and III.
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27. Which of the following motors is non-self starling ?
(A) squirrel cage induction motor
(B) wound rotor induction motor
(C) synchronous motor
(D) DC series motor.
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Synchronous Motors PART 2
28. The back emf in the stator of a synchronous motor depends on
(A) speed of rotor
(B) rotor excitation
(C) number of poles
(D) flux density.
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29. Which motor can conveniently operate on lagging as well as leading power factor ?
(A) squirrel cage induction motor
(B) wound rotor induction motor
(C) synchronous motor
(D) any of the above.
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Synchronous Motors PART 2
30. A synchronous motor working on leading power factor and not driving any mechanical, is known
(A) synchronous induction motor
(B) spinning motor
(C) synchronous condenser
(D) none of the above.
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