Electrical Engineering MCQs

Page No. 244

In a synchronous motor, damper windings are provided on____________?


a stator frame


brotor shaft


cpole faces


dnone of the above


View Answer pole faces

In a 3-phase synchronous motor, the negative phase sequence exists when the motor is_______________?


asupplied with unbalanced voltage


bunder-loaded


cover-loaded


dnone of the above



Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?


aHigh field current


bLow short circuit ratio


c High core losses


dLow field current


View Answer Low field current

A rotory converter can also be run as a___________?


ad.c. shunt motor


bd.c. series motor


cd.c. compound motor


dsynchronous motor


View Answer synchronous motor

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


aD.C. motor


bReluctance motor


cUniversal motor


dSynchronous motor


View Answer Synchronous motor

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


ait runs at a slower speed


bthe motor stops


c it continues to run at the same speed


dit runs at a very high speed


View Answer the motor stops

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


aspeed of the motor is reduced


bpower factor is decreased


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


d Er (net resultant voltage) in armature is increased



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


awill become more


b will become less


cwill remain unchanged


dnone of the above.


View Answer will become less

Stability of a synchronous machine:


adecreases with increase in its excitation


b increases with increase in its excitation


c remains unaffected with increase in excitation


dany of the above



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____________?


aincrease in both armature current and power factor angle


b increase in back e.m.f. but decrease in armature current


cincrease in both armature current and power factor which is lagging


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



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