Synchronous Motor MCQ Or Quiz - CS Electrical & Electronics

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Quiz On Synchronous Motor

01. In a synchronous motor, self-starting can be made?

by providing the damper winding on rotor poles
by providing the damper winding on the stator
by providing the damper winding on the stator as well as rotor poles
none of the above

Ans: d

02. In the synchronous motor, the oscillations can be damped out by?

to maintain constant excitation
rotating the motor at leading power factors
In the rotor, pole faces by providing damper bars.
oscillations cannot be damped

Ans: c

03. In the synchronous motor, the shaft is made up of?

mild steel
chrome steel
alnico
stainless steel

Ans: a

04. In the synchronous motor, if the field is under-excited, the power factor will be

leading
lagging
unity
zero

Ans: b

05. In the synchronous motor, the speed regulation is always?

1%
0.5%
positive
zero

Ans: d

06. In the synchronous motor, the percentage slip is?

1%
100%
0.5%
zero

Ans: d

07. In the synchronous motor, the operating speed can be changed by?

changing the load
changing the supply voltage
changing frequency
using brakes

Ans: c

08. When synchronous motor will stop?

supply voltage fluctuates
load in motor varies
when the excitation winding gets disconnected
supply voltage frequency changes

Ans: c

09. In the synchronous motor, the rotor copper loss is met by

d.c. source
armature input
motor input
supply lines

Ans: a

10. In which motors the stator and rotor magnetic field rotates at equal speed?

Universal motor
Synchronous motor
Induction motor
Reluctance motor

Ans: b

11. Synchronous motors are

not-self starting
self-starting
essentially self-starting
none of the above

Ans: a

12. In the synchronous motors, the standard full-load power ratings are?

zero or 0.8 leading
unity or 0.8 lagging
unity or 0.8 leading
unity or zero

Ans: c

13. The synchronous motor running with normal excitation adjusts to load raises usually by an increase in?

back e.m.f.
armature current
power factor
torque angle

Ans: b

14. The synchronous motor has a better power factor then an induction motor. This is mainly because?

no-slip in the synchronous motor
the stator supply is not necessary to produce a magnetic field
the mechanical load remains constant on the rotor
the large air gap in the synchronous motor

Ans: b

15. The synchronous motor operating at a leading power factor is used as?

voltage booster
phase advancer
noise generator
mechanical synchronizer

Ans: b

16. The Slip rings in the motor are usually made of?

carbon or graphite
brass or steel
silver or gold
copper or aluminum

Ans: b

17. The over-excited synchronous motor can is used for?

fluctuating loads
variable speed loads
low torque loads
power factor corrections

Ans: d

18. In the synchronous motor, if the voltage applied is increased which of the following will reduce?

Stator flux
Pull-in torque
Both (a) and (b)
None of the above

Ans: d

19. The efficiency of the properly designed synchronous motor is usually?

60 to 70%
75 to 80%
85 to 95%
99 to 99.5%

Ans: c

20. To limit the operating temperature in the electrical machine, the machine should have proper?

voltage rating
current rating
power factor
speed

Ans: b

21. Why the synchronous motors are not self-starting, because?

(a) the rotation of direction is not fixed
(b) at the half cycle, the direction of instantaneous torque reverses
(c) on these machines, the starter can not be used
(d) on the machines, starting winding is not provided

Ans: b

22. In the three-phase synchronous if one phase of motor has short-circuited then the motor will?

(a) not start
(b) run at 2/3 of synchronous speed
(c) run with excessive vibrations
(d) take less than the rated load

Ans: a

23. 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

Ans: a

24. The synchronous torque can be developed in the synchronous motor?

(a) when under loaded
(b) while over-excited
(c) only at synchronous speed
(d) below or above synchronous speed

Ans: c

25. The synchronous motor can be started by?

(a) pony motor
(b) D.C. compound motor
(c) providing damper winding
(d) any of the above

Ans: d

26. How many slip-rings will have in the three-phase synchronous motor?

(a) no slip-rings
(b) one slip-ring
(c) two slip-rings
(d) three slip-rings

Ans: c

27. The hunting in the synchronous motor will occur due to?

(a) Periodic variation of load
(b) Over-excitation
(c) Over-loading for long periods
(d) Small and constant load

Ans: a

28. If the excitation of an unloaded salient pole synchronous motor will get suddenly disconnected, what happens?

(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

Ans: a

29. In the synchronous motor, the power developed will be maximum when the load angle is?

(a) zero
(b) 45°
(c) 90°
(d) 120°

Ans: c

30. The synchronous motor can be used as a synchronous condenser to improve the power factor when it is?

(a) under-loaded
(b) over-loaded
(c) under-excited
(d) over-excited

Ans: d

31. When the synchronous motor is running with normal excitation on load, now if the load on the motor is increased?

(a) The armature current and power factor will decrease
(b) The armature current and power factor will increase
(c) The armature current will decrease and power factor will increase
(d) The armature current will increase and power factor will decrease

Ans: d

32. Most of the synchronous motors are of?

(a) alternator type machines
(6) induction type machines
(c) salient pole type machines
(d) smooth cylindrical type machines

Ans: c

33. The synchronous motor always runs at?

(a) the synchronous speed
(b) less than synchronous speed
(c) more than synchronous speed
(d) none of the above

Ans: a

34. The over-excited synchronous motor will have?

(a) leading current
(b) lagging current
(c) both (a) and (b)
(d) none of the above

Ans: a

35. The working of a synchronous motor is similar to?

(a) gear train arrangement
(b) transmission of mechanical power by shaft
(c) distribution transformer
(d) turbine
(e) none of the above

Ans: b

36. In the synchronous motor, the minimum armature current corresponds to operation?

(a) zero power factor leading
(b) unity power factor
(c) 0.707 power factor lagging
(d) 0.707 power factor leading

Ans: b

37. The magnitude of stator back e.m.f. in synchronous motor depends on?

(a) d.c. excitation only
(b) speed of the motor
(c) load on the motor
(d) both the speed and rotor flux

Ans: a

38. If the load angle of a four-pole synchronous motor is 6-degree electrical, its value in the mechanical degrees is?

(a) 2
(b) 3
(c) 4
(d) 6

Ans: b

39. For the V-curves of the synchronous motor, the graph is drawn between

(a) field current and armature current
(b) terminal voltage and load factor
(c) power factor and field current
(d) armature current and power factor

Ans: a

40. In the synchronous motor, the back emf depends on?

(a) speed
(b) load
(c) load angle
(d) all of the above

Ans: c

41. The synchronous motor can operate at which power factor?

(a) lagging power factor only
(6) leading power factor only
(c) unity power factor only
(d) All

Ans: d

42. The loss varies with load in the synchronous motor is?

(a) Windage loss
(b) Bearing friction loss
(c) Copper loss
(d) Core loss

Ans: c

I hope this article may help you all a lot. Thank you for reading. If you have any doubts on synchronous motor mcq or quiz, then comment below.

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