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synchronous motors MCQs

Practise focused synchronous motors questions with marked answers for exam preparation and subject revision.

synchronous motors Mcqs

1. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will__________?
0

A. stop

B. function as static condenser

C. run as induction motor

D. burn with dense smoke

2. The construction of a synchronous motor resembles____________?
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A. a series motor

B. an alternator

C. an induction motor

D. a rotary converter

3. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as___________?
0

A. pull-in torque

B. pull-out torque

C. none of the above

D. pull-up torque

4. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then_____________?
0

A. the stator current will be very small

B. the stator current will be very high

C. none of the above

D. the stator current will be zero

E. the back e.m.f. will be more than the supply voltage

5. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as__________?
0

A. reluctance torque

B. pull up torque

C. locked-rotor torque

D. synchronous torque

6. For power factor correction, synchronous motors operate at____________?
0

A. no-load and greatly over-excited fields

B. no-load and under-excited fields

C. normal load with minimum excitation

D. normal load with zero excitation

7. The coupling angle or load angle of synchronous motor is defined as the angle between the__________?
0

A. rotor and the stator poles of the same polarity

B. none of the above

C. rotor and the stator poles of opposite polarity

D. rotor and stator teeth

8. In a synchronous motor, the breakdown torque is__________?
0

A. inversely proportional to applied voltage

B. directly proportional to the square of the applied voltage

C. none of the above

D. directly proportional to applied voltage

9. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as_________?
0

A. condenser

B. static condenser

C. none of the above

D. synchronous condenser

10. A synchronous motor can develop synchronous torque:
0

A. below or above synchronous speed

B. only at synchronous speed

C. while over-excited

D. when under loaded

11. The maximum power developed in a synchronous motor will depend on__________?
0

A. the rotor excitation, supply voltage and maximum value of coupling angle (90)

B. the rotor excitation and supply volt-age both

C. the supply voltage only

D. the rotor excitation only

E. none of the above

12. A synchronous machine with low value of short-circuit ratio has___________?
0

A. good voltage regulation

B. none of the above

C. high stability limit

D. lower stability limit

E. good speed regulation

13. Exciters of synchronous machines are______________?
0

A. d.c. compound machines

B. any of the above

C. d.c. shunt machines

D. d.c. series machines

14. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________?
0

A. five degrees

B. two degrees

C. ten degrees

D. zero degree

15. In case one phase of a three-phase synchronous motor is short-circuited the motor will____________?
0

A. take less than the rated load

B. not start

C. run at 2/3 of synchronous speed

D. run with excessive vibrations

16. In a synchronous motor, the armature current has large values for____________?
0

A. high excitation only

B. low excitation only

C. both high and low excitation

D. none of the above

17. The armature current of the synchronous motor
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A. has large values for low excitation i niy

B. has large values for high excitation only

C. has large values for low and high excitation

D. any of the above

18. A pony motor is basically a_________?
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A. D.C. shunt motor

B. small induction motor

C. D.C. series motor

D. double winding A.C./D.C. motor

19. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor___________?
0

A. tends to becomes zero

B. remains same as the original value

C. decreases to half the original value

D. increases to two times the original value

20. The minimum armature current of the synchronous motor corresponds to operation at______________?
0

A. 0.707 power factor leading

B. unity power factor

C. zero power factor leading

D. 0.707 power factor lagging

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