Electrical Engineering MCQs

Page No. 250

In a synchronous motor, the maximum power developed depends on all of the following except:


arotor excitation

✖


bmaximum value of coupling angle

✖


cdirection of rotation

✓


dsupply voltage

✖


View Answer direction of rotation

The effect of increasing the load on a synchronous motor running with normal excitation is to___________?


adecrease both armature current and power factor

✖


bdecrease armature current but increase power factor

✖


cincrease armature current but decrease power factor

✓


d increase both its armature current and power factor

✖



In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________?


aload on the motor

✖


bd.c. excitation only

✓


cboth the speed and rotor flux

✖


d none of the above

✖


View Answer d.c. excitation only

Hunting in a synchronous motor cannot be due to___________?


awindage friction

✓


bvariable load

✖


cvariable frequency

✖


dvariable supply voltage

✖


View Answer windage friction

A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?


ano change of power factor

✖


b lagging power factor with over-excitation

✖


c leading power factor with under-excitation

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dleading power factor with over-excitation

✓



A synchronous motor develops maximum power when load angle is____________?


a45°

✖


b 60°

✖


c90°

✓


d120°

✖


View Answer 90°

The armature current of the synchronous motor


a has large values for low excitation i niy

✖


b has large values for high excitation only

✖


chas large values for low and high excitation

✓


dany of the above

✖



Exciters of synchronous machines are______________?


ad.c. series machines

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bd.c. shunt machines

✓


cd.c. compound machines

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dany of the above

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View Answer d.c. shunt machines

The duration of sudden snort-circuit test on a synchronous motor is usually about_____________?


aone hour

✖


bone minute

✖


cone second

✓


d none of the above

✖


View Answer one second

The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as_____________?


aslip torque

✖


bpull-out torque

✖


cbreaking torque

✖


dsynchronising torque

✓


View Answer synchronising torque

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