Synchronous Motors Mcqs

This set of Electrical engineering Multiple Choice Questions & Answers (MCQs) focuses on study of “Synchronous Motors”. These questions are chosen from a collection of most authoritative and best reference books on Electrical engineering. Our aim is to prepare an individual for competitive exams like NTS, GAT, ECAT, University and College entrance exams, Jobs and interviews. One should practice our MCQS to assimilate Synchronous Motors Mcqs comprehensively.

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31.
In which of the following motors the stator and rotor fields rotate simultaneously?

D.C. motor

Reluctance motor

Universal motor

Synchronous motor

32.
If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then

It runs at a slower speed

The motor stops

It continues to run at the same speed

It runs at a very high speed

33.
A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

Speed of the motor is reduced

Power factor is decreased

Eb (back e.m.f.) becomes less than V (applied voltage)

Er (net resultant voltage) in armature is increased

34.
If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

Will become more

Will become less

Will remain unchanged

None of the above.

35.
Stability of a synchronous machine:

Decreases with increase in its excitation

Increases with increase in its excitation

Remains unaffected with increase in excitation

Any of the above

36.
If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to____________?

Increase in both armature current and power factor angle

Increase in back e.m.f. but decrease in armature current

Increase in both armature current and power factor which is lagging

Increase in torque angle but decrease in back e.m.f.

37.
While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?

Induction motor torque in field winding

Induction motor torque in damper winding

Eddy current and hysteresis torque in pole faces

ReHetance motor torque due to saliency of the rotor

All of the above methods

38.
A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?

Remain same

Go down

Improve

None of the above

39.
Which of the following motors will be used in electric clocks?

D.C. shunt motor

D.C. series motor

A.C. induction motor

A.C. synchronous motor

40.
Power factor of a synchronous motor is unity when_____________?

The armature current is maximum

The armature current is minimum

The armature current is zero

None of the above

41.
Which of the following methods is used to start a synchronous motor?

Damper winding

Star-delta starter

Damper winding in conjunction with star-delta starter

Resistance starter in the armature circuit

42.
In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately

One-third

Twice

Thrice

Six times

43.
A synchronous machine with large air gap has______________?

A higher value of stability limit

A small value of inherent regulation

A higher synchronizing power which makes the machine less sensitive to load variations

All of the above

44.
To limit the operating temperature an electrical machine should have proper____________?

Voltage rating

Current rating

Power factor

Speed

45.
When the voltage applied to a synchronous motor is increased, which of the following will reduce?

Stator flux

Pull in torque

Both A. and (b)

None of the above

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