Electrical Engineering MCQs

Page No. 245

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?


ainduction motor torque in field winding

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b induction motor torque in damper winding

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ceddy current and hysteresis torque in pole faces

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dall of the above methods

✓



A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?b


aremain same

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bgo down

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cimprove

✓


dnone of the above

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View Answer improve

Which of the following motors will be used in electric clocks?


aD.C. shunt motor

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bD.C. series motor

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cA.C. induction motor

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dA.C. synchronous motor

✓



Power factor of a synchronous motor is unity when_____________?


athe armature current is maximum

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bthe armature current is minimum

✓


cthe armature current is zero

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dnone of the above

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Which of the following methods is used to start a synchronous motor?


aDamper winding

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b Star-delta starter

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cDamper winding in conjunction with star-delta starter

✓


dResistance starter in the armature circuit

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In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately


aone-third

✖


btwice

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cthrice

✓


d six times

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View Answer thrice

A synchronous machine with large air gap has______________?


a higher value of stability limit

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ba small value of inherent regulation

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c a higher synchronizing power which makes the machine less sensitive to load variations

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dall of the above

✓


View Answer all of the above

To limit the operating temperature an electrical machine should have proper____________?


avoltage rating

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bcurrent rating

✓


cpower factor

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dspeed

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View Answer current rating

When the voltage applied to a synchronous motor is increased, which of the following will reduce?


aStator flux

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b Pull in torque

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c Both A. and (b)

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dNone of the above

✓


View Answer None of the above

An over excited synchronous motor is used for____________?


afluctuating loads

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bvariable speed loads

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clow torque loads

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d power factor corrections

✓



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