electrical

Synchronous Motor MCQ Questions and Answers Page - 3

1.

A three-phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current

Answer/ Hint      

Answer : B

Explanation :

2.

A 3-phase synchronous motor is operating at a given load. If an increase in excitation reduces the armature current, it can be concluded that the motor is

Answer/ Hint      

Answer : A

Explanation :

3.

A synchronous motor installed at end of a transmission line is operating at lagging power factor. With the fall in supply voltage, the power factor of the synchronous motor will

Answer/ Hint      

Answer : B

Explanation :

4.

A synchronous motor operates at 0.8 pf lagging. If the filed current of the motor is continuously increased

Answer/ Hint      

Answer : D

Explanation :

5.

Stability of a synchronous motor_____ with the increase in excitation

Answer/ Hint      

Answer : A

Explanation :

6.

Armature reaction in a synchronous motor at rated voltage and zero power factor (lead) is

Answer/ Hint      

Answer : D

Explanation :

7.

The torque angle of a synchronous machine operating from a constant voltage bus, is usually defined as the space angle between

Answer/ Hint      

Answer : A

Explanation :

8.

A synchronous motor will deliver maximum power when

Answer/ Hint      

Answer : A

Explanation :

9.

A synchronous motor with negligible armature resistance runs at a load angle of 200 at the rated frequency. If supply frequency is increased by 10%, keeping other parameters constant, the new load angle will be

Answer/ Hint      

Answer : C

Explanation :

10.

The power developed by a synchronous motor for constant supply voltage and constant excitation will be maximum when load angle    is

Answer/ Hint      

Answer : C

Explanation :

11.

For a given developed power, a synchronous motor operating from a constant voltage and constant frequency supply, will draw the minimum and maximum armature currents. Imin and Imax respectively, corresponding to

Answer/ Hint      

Answer : A

Explanation :

12.

The V-Curve of synchronous motor shows the relation between which of the parameters?

Answer/ Hint      

Answer : A

Explanation :

13.

An inverted V-curve of synchronous motor shows the variation of

Answer/ Hint      

Answer : A

Explanation :

14.

Keeping the excitation voltage same, the load on the motor is increased such that the motor current increases by 20%. The operating power factor will become

Answer/ Hint      

Answer : D

Explanation :

15.

Synchronous capacitor is

Answer/ Hint      

Answer : C

Explanation :

16.

An induction motor and synchronous motor are connected to a common feeder line. To operate the feeder line at a unity pf, the synchronous motor should be

Answer/ Hint      

Answer : B

Explanation :

17.

Synchronous condensers, when operated at power factor ranging from lagging through unity to leading for voltage control, are called the

Answer/ Hint      

Answer : B

Explanation :

18.

The power factor of a synchronous motor

Answer/ Hint      

Answer : A

Explanation :

19.

A 3-phsae induction motor draws 1,000 kVA at a pf of 0.8 lag. A synchronous condenser is connected in parallel to draw an additional 750kVA at a power factor of 0.6 led. The pf of the total load supplied by the mains is

Answer/ Hint      

Answer : A

Explanation :

20.

synchronous condenser means

Answer/ Hint      

Answer : D

Explanation :

21.

Which of the following devices can be used as phase advancer?

Answer/ Hint      

Answer : C

Explanation :

22.

The phenomenon of oscillation in of the rotor of a synchronous motor about its equilibrium position corresponding to new load on sudden throwing off or increasing of load is called the

Answer/ Hint      

Answer : C

Explanation :

23.

A 3-phase synchronous motor hunts due to

Answer/ Hint      

Answer : D

Explanation :

24.

In a synchronous motor hunting can be reduced to minimum possible by

Answer/ Hint      

Answer : D

Explanation :

25.

The damper windings also called the squirrel cage windings or damper girds

Answer/ Hint      

Answer : D

Explanation :

26.

In a synchronous machine, damper windings are used to

Answer/ Hint      

Answer : C

Explanation :

27.

During hunting of synchronous motor

Answer/ Hint      

Answer : C

Explanation :

28.

When a synchronous motor is running at synchronous speed the damper winding produces

Answer/ Hint      

Answer : D

Explanation :

29.

In a synchronous motor when the rotor speed exceeds the synchronous speed during hunting

Answer/ Hint      

Answer : C

Explanation :

30.

The mechanical displacement of the rotor with respect to stator, in poly phase multipolar synchronous motor running at full load is of the order of

Answer/ Hint      

Answer : C

Explanation :

31.

Power factor of a synchronous motor is unity when

Answer/ Hint      

Answer : B

Explanation :

32.

Change of D.C excitation of a synchronous motor changes

Answer/ Hint      

Answer : C

Explanation :

33.

While starting a synchronous motor by induction motor action, field winding is usually

Answer/ Hint      

Answer : B

Explanation :

34.

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

Answer/ Hint      

Answer : D

Explanation :

35.

If in a synchronous motor, driving mechanical load and drawing current voltage supply, its field excitation is increased, then its power factor

Answer/ Hint      

Answer : B

Explanation :

36.

A synchronous motor installed at the receiving and substation operates with such an excitation that 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

Answer/ Hint      

Answer : C

Explanation :

37.

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

Answer/ Hint      

Answer : D

Explanation :

38.

Armature of a synchronous machine is kept fixed because

Answer/ Hint      

Answer : D

Explanation :

39.

If excitation of a synchronous motor running with a constant load is running with a constant, load is decreased from its normal value, ignoring effects of armature reaction, it leads to

Answer/ Hint      

Answer : A

Explanation :

40.

When a 3-phase synchronous generator is supplying a zero-power factor lagging loads, the armature field affects the main field in the following ways

Answer/ Hint      

Answer : B

Explanation :

41.

Stability of a synchronous machine

Answer/ Hint      

Answer : B

Explanation :

42.

The power factor of a synchronous motor is better than that of induction motor because

Answer/ Hint      

Answer : A

Explanation :

43.

If in a synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by its increase because

Answer/ Hint      

Answer : B

Explanation :

44.

A synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

Answer/ Hint      

Answer : D

Explanation :

45.

If one –phase of a 3-phase synchronous motor is short circuited, motor

Answer/ Hint      

Answer : A

Explanation :

46.

If the field current of an unloaded salient-pole synchronous motor gets suddenly open-circuited, then

Answer/ Hint      

Answer : B

Explanation :

47.

In which of the following motors the stator and rotor field rotates simultaneously?

Answer/ Hint      

Answer : C

Explanation :

48.

The speed of a synchronous motor

Answer/ Hint      

Answer : C

Explanation :

49.

A rotary converter can also be run as a

Answer/ Hint      

Answer : D

Explanation :

50.

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

Answer/ Hint      

Answer : D

Explanation :

51.

Which of the following resistance can be measured by conducting insulation resistance test on a synchronous motor?

Answer/ Hint      

Answer : D

Explanation :

52.

Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C field current?

Answer/ Hint      

Answer : D

Explanation :

53.

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

Answer/ Hint      

Answer : C

Explanation :

54.

In a 3-phase synchronous motor, the negative phase sequence exists when the motor is

Answer/ Hint      

Answer : A

Explanation :

55.

In asynchronous motor, damper windings are provided on

Answer/ Hint      

Answer : C

Explanation :

56.

The induced e.m.f in a synchronous motor working on leading power factor will be

Answer/ Hint      

Answer : A

Explanation :

57.

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

Answer/ Hint      

Answer : C

Explanation :

58.

The net armature voltage of a synchronous motor is equal to the

Answer/ Hint      

Answer : D

Explanation :

59.

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

Answer/ Hint      

Answer : A

Explanation :

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