Electrical Engineering MCQs

Page No. 243

The back e.m.f. in the stator of a synchronous motor depends on____________?


anumber of poles


b flux density


crotor speed


drotor excitation


View Answer rotor excitation

If the field of a synchronous motor is underexcited, the power factor will be_____________?


azero


bunity


clagging


d leading


View Answer lagging

In a synchronous motor, the damping winding is generally used to______________?


areduce noise level


breduce the eddy currents


cprovide starting torque only


dprevent hunting and provide the starting torque



In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then


athe motor is said to be fully loaded


bthe torque generated is maximum


cthe excitation is said to be zero per cent


dthe excitation is said to be hundred per cent



In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________?


a3000 r.p.m.


b1500 r.p.m.


c750 r.p.m.


d none of the above


View Answer 1500 r.p.m.

In a synchronous motor, V-curves represent relation between____________?


aarmature current and field current


bpower factor and speed


cfield current and speed


d field current and power factor



By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?


aBy changing the supply frequency


bBy interchanging any two phases


cBy changing the applied voltage


dBy changing the load



The torque angle, in a synchronous motor, is the angle between_______________?


a the supply voltage and the back e.m.f.


bmagnetising current and back e.m.f


cthe rotating stator flux and rotor poles


dnone of the above



A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed


athe motor will stop


b the motor continue to run in the same direction


cthe winding of the motor will burn


dthe motor will run in the reverse direction



The net armature voltage of a synchronous motor is equal to the_______________?


avector sum of Eb and V


barithmetic sum of Eb and V


carithmetic difference of Eb and V


dvector difference of Eh and V



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