300 Important Alternator MCQ Question and Answer | PDF Free Download

Alternator  MCQ Question and Answer PDF Free Download

1.In a salient pole synchronous machine, the air gap is

  • Auniform under the whole pole shoe
  • Bleast under the middle of the pole she and increases outwards
  • Clargest under the middle of the pole shoe and decreases outwards
  • Dleast at one end of the pole shoe and increases to the maximum value at the other end.
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Correct Answer : (B)

least under the middle of the pole she and increases outwards

Explanation:

In a salient pole synchronous machine, the air gap is least under the middle of the pole she and increases outwards.

2.The number of poles on turbo alternator is usually

  • A2
  • B4
  • C6
  • D8
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Correct Answer : (A)

2

Explanation:

The number of poles on turbo alternator is usually 2.

3.To obtain sinusoidal flux distribution, chamfering of poles is done in

  • ASalient pole alternators only
  • BSmooth cylindrical pole alternators only
  • CBoth of the above
  • Dnone of the above
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Correct Answer : (A)

Salient pole alternators only

Explanation:

To obtain sinusoidal flux distribution, chamfering of poles is done in Salient pole alternators only.

4.The salient pole rotor is not suitable for high speed turbo generators due to

  • Aexcessive bearing friction
  • Bundesirable mechanical oscillations
  • Chigh centrifugal force and windage loss
  • Dlarge eddy current losses
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Correct Answer : (C)

high centrifugal force and windage loss

Explanation:

The salient pole rotor is not suitable for high speed turbo generators due to high centrifugal force and windage loss.

5.In turbo alternators, smooth cylindrical rotors have very long axial length because it

  • Areduces friction and windage loss
  • BReduces centrifugal force
  • CNumber of conductors being less they have to be necessarily long for generating the required voltage
  • DNone of the above
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Correct Answer : (C)

Number of conductors being less they have to be necessarily long for generating the required voltage

Explanation:

6.Cylindrical rotor alternators use ____ducts for efficient cooling

  • AOnly radial
  • BOnly axial
  • CBoth radial and axial
  • DNone of the above
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Correct Answer : (C)

Both radial and axial

Explanation:

7.In cylindrical rotor ____portion of rotor is wound

  • AOne ?third
  • BTwo third
  • COne half
  • DWhole
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Correct Answer : (B)

Two third

Explanation:

8.The maximum possible speed at which an alternator can be driven to generate 50 Hz and 4,000 V is

  • A4,000 rpm
  • B3,600 rpm
  • C3,000 rpm
  • D1,500 rpm
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Correct Answer : (C)

3,000 rpm

Explanation:

9.Two mechanically coupled alternators deliver power at 50Hz and 60 Hz respectively. The highest speed of the alternator is

  • A3,600 rpm
  • B3,000 rpm
  • C600 rpm
  • D500 rpm
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Correct Answer : (C)

600 rpm

Explanation:

10.The most appropriate operating speeds in rpm of generators used in Thermal, Nuclear and Hydropower plants would respectively be

  • A3000, 300 and 1500
  • B3000,3000 and 300
  • C1500,1500 and 3000
  • D1000,900 and 750
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Correct Answer : (B)

3000,3000 and 300

Explanation:

11.The aircraft alternators are designed to generate emf of high frequency of 400 Hz in order to

  • AReduce the bulk
  • BCompensate for high speeds
  • CMake the systems free from external disturbances
  • DAll of the above
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Correct Answer : (A)

Reduce the bulk

Explanation:

The aircraft alternators are designed to generate emf of high frequency of 400 Hz in order to Reduce the bulk.

12.Armature winding is one in which

  • AEmf is induced by the leakage flux
  • BEmf is induced by the main or working flux
  • CWorking or main flux is created by the filed current
  • DWorking or main flux is created by the armature current
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Correct Answer : (B)

Emf is induced by the main or working flux

Explanation:

Armature winding is one in which Emf is induced by the main or working flux.

13.Armature winding in ac machines

  • AIs always closed one
  • BIs always open one
  • CMay be either closed one giving delta connections of open one giving star connections
  • DNone of the above
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Correct Answer : (C)

May be either closed one giving delta connections of open one giving star connections

Explanation:

14.The stator of modern alternators are wound for _____phase groups

  • A180 degree
  • B120 degree
  • C60 degree
  • D240 degree
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Correct Answer : (C)

60 degree

Explanation:

15.Concentrated winding has

  • AOne coil per phase
  • BTwo coils per phase
  • COne coil per pair of poles per phase
  • DOne coil side per pole pair per phase
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Correct Answer : (C)

One coil per pair of poles per phase

Explanation:

Concentrated winding has One coil per pair of poles per phase.

16.For a two-layer winding the number of stator slots is equal to the number of

  • APoles
  • BConductors
  • CCoil sides
  • DCoils
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Correct Answer : (D)

Coils

Explanation:

For a two-layer winding the number of stator slots is equal to the number of Coils.

17.for a concentrated winding the polar group of each phase is ____electrical degrees part

  • A360
  • B180
  • C120
  • D60
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Correct Answer : (A)

360

Explanation:

for a concentrated winding the polar group of each phase is 360 electrical degrees part.

18.Distributed winding is preferred over concentrated winding as it

  • AReduces noise
  • BReduces the machine size
  • CReduces the amount of copper required
  • DImproves the generated emf waveform and adds rigidity and mechanical strength to the winding
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Correct Answer : (D)

Improves the generated emf waveform and adds rigidity and mechanical strength to the winding

Explanation:

Distributed winding is preferred over concentrated winding as it Improves the generated emf waveform and adds rigidity and mechanical strength to the winding.

19.In a synchronous alternator, which of the following coils will have emf closer to sine wave form?

  • AConcentrated winding in full pitch coils
  • BConcentrated winding in short pitch coils
  • CDistributed winding in full pitch coils
  • DDistributed winding in short pitch coils
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Correct Answer : (D)

Distributed winding in short pitch coils

Explanation:

20.If the space flux distribution is non sinusoidal , emf induced in the distributed winding will be

  • AMore sinusoidal in comparison to the flux distribution
  • BLess sinusoidal in comparison to the flux distribution
  • COf the same shape as that of flux distribution
  • DNone of the above
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Correct Answer : (A)

More sinusoidal in comparison to the flux distribution

Explanation:

If the space flux distribution is non sinusoidal , emf induced in the distributed winding will be More sinusoidal in comparison to the flux distribution.