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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