electrical

Synchronous Motor MCQ Questions and Answers Page - 2

1.

The phase of emf induced in the armature of a synchronous motor (Eb) depends upon

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2.

In a synchronous motor, the synchronizing power come into action when

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3.

Synchronizing power  of a synchronous motor varies

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4.

The coupling  angle or load angle of a synchronous motor is defiend as the space angle between the

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5.

The torque angle is defined as the space angle between

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6.

The value of load angle for a synchronous motor depends mainly upon its

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7.

Electromagnetic torque  is present in rotating machines when

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8.

In a synchronous motor electromagnetic power varies

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9.

The interaction  torque in a synchronous motor depends upon

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10.

The breakdown torque of a synchronous motor varies as

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11.

A 3-phse synchronous motor connected to an infinite bus bar with constant excitation is driving a certain load and operating is leading power factor. If the shaft load is reduced

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12.

A synchronous motor is supplying a load at unity pf . If the load on the motor is increased keeping its excitation and terminal voltage constant , the power factor

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13.

When does a synchronous  motor operate with leading power factor current

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14.

A synchronous generator connected to an infinite bus is over excited. Considering only he reactive power, from the point of view of the system  the machine acts as

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15.

A synchronous machine connected to a power system , grid bus-bar is operating as a generator . To make the machine operate as a motor the

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16.

A salient  pole synchronous motor  is running on no load. If its excitation is made off, it will

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17.

What is the effect of the field failure of salient pole synchronous motor connected with infinite bus

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18.

A salient pole synchronous motor continues running even if its excitation current is reduced to zero. This is due to

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19.

When the excitation of normally operaitn unloaded salient pole synchronous motor suddenly gets disconnected, it continues to run as a

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20.

A smooth cylindrical synchronous motor will always stop when

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21.

The speed of a synchronous motor can be varied by varying its

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Answer : C

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22.

For a 3-phase, 4-pole, 50 Hz synchronous motor the frequency, pole number and the load torque are all halved. The motor speed will be

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Answer : C

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23.

A synchronous motor with comparatively large air gap gives

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Answer : C

Explanation :

24.

In a 3-phase synchronous motor, the magnitude of back emf setup in the stator depends on

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Answer : A

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25.

The magnitude of counter or back emf in a s synchronous motor

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Answer : D

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26.

In a synchronous motor the excitation voltage on no load is approximately equal to the applied voltage. This will happen

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Answer : C

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27.

Which motor can conveniently operate at lagging as well as leading power factor?

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Answer : C

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28.

At constant load, the magnitude of armature current drawn by a synchronous motor is large for

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Answer : C

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29.

Variation in dc excitation of a synchronous motor causes variation in

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Answer : D

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30.

If the field of a synchronous motor is under excited, the power factor will be

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Answer : A

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31.

A synchronous motor is operating on no load at unity power factor. If the filed current is increased, the power factor will become

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Answer : D

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32.

The operating speed of a synchronous motor can be changed to new fixed value by

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Answer : C

Explanation :

33.

A synchronous motor will always stop when

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Answer : C

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34.

Hunting in a synchronous motor takes place

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Answer : B

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35.

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

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Answer : B

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36.

The rotor copper losses, in a synchronous motor are met by

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Answer : A

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37.

The maximum power developed in a synchronous motor occurs at a coupling angle of

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Answer : C

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38.

When the stator windings are connected in such a fashion that the number of poles are made half, the speed of a rotor of a synchronous motor

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Answer : D

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39.

In which of the following motors the stator and rotor magnetic field rotate at the same speed

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Answer : B

Explanation :

40.

Synchronizing power of a synchronous machine is

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Answer : B

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41.

Synchronous motors are

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Answer : A

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42.

The standard full-load power factor rating for synchronous motors are

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Answer : C

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43.

A synchronous motor running with normal excitation adjust to load increases essentially by increase in

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Answer : B

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44.

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because

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Answer : B

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45.

A synchronous motor working at leading power factor can be used as

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Answer : B

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46.

Slip rings are usually made of

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Answer : B

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47.

An over-excited synchronous motor is used for

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Answer : D

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48.

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

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Answer : C

Explanation :

49.

The speed of synchronous motor

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Answer : D

Explanation :

50.

Dust and dirt accumulation on motor winding will result in

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Answer : A

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51.

The efficiency of a properly designed synchronous motor will usually fall in range

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Answer : D

Explanation :

52.

To limit the operating temperature an electrical machine should have proper

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Answer : B

Explanation :

53.

Slip-ring in a synchronous motor carry

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Answer : A

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54.

A synchronous machine with large air gap has

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Answer : D

Explanation :

55.

The armature current of the synchronous motor has higher value for

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Answer : C

Explanation :

56.

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

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Answer : C

Explanation :

57.

The angle between the rotating stator flux and rotor poles and rotor is called …………. Angle

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Answer : A

Explanation :

58.

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

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Answer : C

Explanation :

59.

When the rotor speed, in a synchronous machine become more than the synchronous speed during hunting, the damper bar develops

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Answer : B

Explanation :

60.

An important advantage of synchronous motor over wound induction motor is that

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Answer : A

Explanation :

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