Electrical Engineering MCQs

Page No. 249

In which of the following motors the stator and rotor magnetic field rotate at the same speed?


aUniversal motor


bSynchronous motor


cInduction motor


dReluctance motor


View Answer Synchronous motor

A synchronous motor running with normal excitation adjusts to load increases essentially by increase in______________?


aback e.m.f.


barmature current


cpower factor and field current


dtorque angle


View Answer armature current only

The efficiency of a properly designed synchronous motor will usually fall in range___________?


a 60 to 70%


b 75 to 80%


c 85 to 95%


d 99 to 99.5%


View Answer 85 to 95%

The armature current of the synchronous motor has higher values for_____________?


ahigh excitation only


blow excitation only


cboth A. and (b)


d none of the above


View Answer none of the above

When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop_________________?


a inductor motor torque


binduction generator torque


csynchronous motor torque


dd.c. motor toque



While starting a synchronous motor by induction motor action, field winding is usually_____________?


aconnected to D.C. supply


b short-circuited by low resistance


ckept open-circuited


dnone of the above



Armature of a synchronous machine is____________?


aof reducing number of slip rings on the rotor


barmature is associated with large power as compared to the field circuits


cof difficulty of providing high voltage insulation on rotor


dall of the above reasons



The power factor of a synchronous motor is better than that of induction motor because


astator supply is relieved of responsibility of producing magnetic field


b mechanical load on the motor can be adjusted


csynchronous motor runs at synchronous speed


dsynchronous motor has large air gap



If one-phase of a 3-phase synchronous motor is short-circuited, motor will ______________?


awill refuse to start


b will overheat in spots


cwill not come upto speed


dwill fail to pull into step


View Answer will refuse to start

The maximum speed variation in a 3-phase synchronous motor is____________?


a10 per cent


b6 per cent


c4 per cent


dzero


View Answer zero

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