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.
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
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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
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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.
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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
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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.
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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
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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
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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
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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
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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
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44. To limit the operating temperature an electrical machine should have proper____________?
Voltage rating
Current rating
Power factor
Speed
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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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