ELECTRICAL MACHINES QUIZ

Which of the following is/are the advantages of carbon brush over the copper brush?

All of these

In case of any sparking they will be less damaged than copper brushes

They are not hard as copper brush

They are self lubricating in nature

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The application that need frequent starting and stopping is

paper mills.

lifts and hoists.

blowers.

jaw crushers.

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If the excitation is reduced, the power factor is

leading power factor

unity power factor

lagging power factor

None of these

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If the armature electric current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?

It will remain the same.

It will be halved.

It will becomes four times.

It will be doubled.

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The power factor of squirrel cage induction motor is

both A and B

low at rated load only

low at heavy loads only

low at light loads only

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Eddy current loss will depends on

Frequency

Thickness

All of these

Flux density

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A 220 V DC generator is run at full speed without any excitation. The open circuit voltage will be

about 2 V.

about 50 V.

zero.

220 V.

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In field flux method speed control of DC Motor is

constant power drive above base speed.

constant torque drive above the base speed.

constant torque drive below the base speed.

constant hp drive below the base speed.

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A delta/star transformer is connected in parallel to a star/delta transformer. The turn ratio former is x times latter, the x is

1/3

1/√3

√3

3

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YOUR ANSWER : ?

In induction motor when the length of the air gap is increased, the magnetizing current of the motor increases while the short circuit current __________________.

decreased.

increased.

kept constant to certain value.

remains unchanged.

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YOUR ANSWER : ?

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