ONLINE Multiple Choice Questions EE-Synchronous Motors PART 2

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.

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.

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.

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.

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.

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.

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)
voltage by I
(D) motor is running on full load.

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.

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.

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.

26. In case of a synchronous motor we have
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.

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.

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.

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.