Synchronous Motors MCQ Questions & Answers

1

The percentage slip in case of a synchronous motor is

A) 1% B) 100% C) 0.5% D) zero

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Answer & Solution

Answer: Option D

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2

The maximum speed variation in a 3-phase synchronous motor is

A) 10 per cent B) 6 per cent C) 4 per cent D) 2. per cent E) zero

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Answer & Solution

Answer: Option E

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3

The ratio of starting torque to running torque in a synchronous motor is

A) zero B) one C) two D) infinity

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Answer & Solution

Answer: Option A

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4

When load on an over-excited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is

A) more B) less C) equal D) twice

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Answer & Solution

Answer: Option B

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5

A synchronous motor can be made self starting by providing

A) Damper winding on rotor poles B) Damper winding on stator C) Damper winding on stator as well as rotor poles D) None of the above

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Answer & Solution

Answer: Option A

Solution:

To make a synchronous motor self-starting, a damper winding on the rotor poles is provided.
The damper winding consists of bars embedded in the rotor poles and short-circuited at both ends. When the motor is started, the relative motion between the rotating magnetic field of the stator and the rotor induces currents in the damper winding. These currents produce a magnetic field that interacts with the stator's magnetic field, generating torque and assisting in the motor's starting process.
Hence, option A is the correct choice.

6

A synchronous machine with large air gap has

A) a higher value of stability limit B) a small value of inherent regulation C) a higher synchronizing power which makes the machine less sensitive to load variations D) all of the above

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Answer & Solution

Answer: Option D

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7

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

A) rotor excitation B) maximum value of coupling angle C) direction of rotation D) supply voltage

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Answer & Solution

Answer: Option C

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8

By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?

A) By changing the supply frequency B) By interchanging any two phases C) By changing the applied voltage D) By changing the load

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Answer & Solution

Answer: Option A

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9

Hunting in a synchronous motor cannot be due to

A) windage friction B) variable load C) variable frequency D) variable supply voltage

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Answer & Solution

Answer: Option A

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10

The duration of sudden short-circuit test on a synchronous motor is usually about

A) one hour B) one minute C) one second D) none of the above

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Answer & Solution

Answer: Option C

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Synchronous Motors MCQ Questions & Answers | Electrical Engineering