Electrical Engineering MCQs

Page No. 253

An over-excited synchronous motor takes__________?


aleading current


blagging current


cboth A. and (b)


dnone of the above


View Answer leading current

The synchronous motor is not inherently self-starting because_______________?


athe force required to accelerate the rotor to the synchronous speed in an instant is absent


b the starting device to accelerate the rotor to near synchronous speed is absent


ca rotating magnetic field does not have enough poles


dthe rotating magnetic field is produced by only 50 Hz frequency currents



When V is the applied voltage, then the breakdown torque of a synchronous motor varies as_________?


aV


bV312


cV2


d1/V


View Answer V

A three-phase synchronous motor will have_____________?


ano slip-rings


bone slip-ring


ctwo slip-rings


d three slip-rings


View Answer two slip-rings

In case one phase of a three-phase synchronous motor is short-circuited the motor will____________?


anot start


brun at 2/3 of synchronous speed


crun with excessive vibrations


dtake less than the rated load


View Answer not start

Synchronous motors are generally not self-starting because:


athe direction of rotation is not fixed


b the direction of instantaneous torque reverses after half cycle


cstartes cannot be used on these machines


dstarting winding is not provided on the machines



The capacitors used in single-phase capacitor motors have no__________?


avoltage rating


b dielectric medium


cpolarity marking


ddefinite value


View Answer polarity marking

If a D.C. series motor is operated on A.C. supply, it will____________?


aspark excessively


b have poor efficiency


chave poor power factor


dall of the above


View Answer all of the above

A universal motor is one which______________?


a can be operated either on D.C. or A.C. supply at approximately the same speed and output


bcan be marketed internationally


c runs at dangerously high speed on no-load


dNone of these



In a A.C. series motor armature coils are usually connected to commutator____________?


athrough resistance


bthrough reactances


cthrough capacitors


dsolidly


View Answer through resistance

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