ONLINE MCQ EE-Synchronous Motors 2
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(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.
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.
Answer: C
ONLINE MCQ EE-Synchronous Motors 2
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.
Answer: A
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.
Answer: B
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.
Answer: C
ONLINE MCQ EE-Synchronous Motors 2
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.
Answer: C
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.
Answer: C
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.
Answer: A
ONLINE MCQ EE-Synchronous Motors 2
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.
Answer: A
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.
Answer: B
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.
Answer: D
ONLINE MCQ EE-Synchronous Motors 2
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.
Answer: A
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.
Answer: B
ONLINE MCQ EE-Synchronous Motors 2
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.
Answer: C
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.
Answer: C
ONLINE MCQ EE-Synchronous Motors 2
