Alternator MCQ Question and Answer

Alternator  MCQ Question and Answer

1.Alternator operates on the principles of

  • AElectromagnetic induction
  • BSelf-induction
  • CMutual induction
  • DSelf or mutual induction
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Correct Answer : (A)

Electromagnetic induction

Explanation:

Alternator operates on the principles of Electromagnetic induction.

2.In a synchronous machine, if the field flux axis is ahead of the armature field axis in the direction of rotation, the machine operating is

  • ASynchronous motor
  • BSynchronous generator
  • CAsynchronous motor
  • DAsynchronous generator
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Correct Answer : (B)

Synchronous generator

Explanation:

3.The armature of an alternator

  • Ais a stationary member
  • Bis a revolving member
  • Cis the frame
  • DConsists of the winding into which current is induced
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Correct Answer : (D)

Consists of the winding into which current is induced

Explanation:

The armature of an alternator Consists of the winding into which current is induced.

4.In modern alternators, the rotating part is

  • AField system
  • BArmature
  • CArmature as well as field system
  • DNone of the above
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Correct Answer : (A)

Field system

Explanation:

In modern alternators, the rotating part is Field system.

5.The current from the stator of an alternator is taken output the external load circuit through

  • ASlip rings
  • BCommutator segments
  • CSolid connections
  • DCarbon brushes
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Correct Answer : (C)

Solid connections

Explanation:

The current from the stator of an alternator is taken output the external load circuit through Solid connections.

6.What is the primary reason for placing field on rotor in an alternator?

  • ASmall power in the filed circuit
  • BInsulation of high voltage is made easy on stator than on rotor
  • CLarge power in stator
  • DLarge current in stator
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Correct Answer : (B)

Insulation of high voltage is made easy on stator than on rotor

Explanation:

The primary reason for placing field on rotor in an alternator is Insulation of high voltage is made easy on stator than on rotor.

7.Which type of alternator is used in hydroelectric power stations?

  • ANon salient pole alternator
  • BTurbo generator
  • CSalient pole alternator
  • DSteam turbine alternator
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Correct Answer : (C)

Salient pole alternator

Explanation:

Salient pole  type alternator is used in hydroelectric power stations.

8.In a synchronous machine, the stator frame serves the purpose of 

  • AHolding the armature stampings in position and also in some cases for circulating cold water for cooling
  • BInsulating the armature windings
  • CProviding path to the magnetic flux
  • DProtecting the whole machine
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Correct Answer : (A)

Holding the armature stampings in position and also in some cases for circulating cold water for cooling

Explanation:

In a synchronous machine, the stator frame serves the purpose of Holding the armature stampings in position and also in some cases for circulating cold water for cooling.

9.In a synchronous machine, the stator frame is made of 

  • AStainless steel
  • BCRGOS
  • CCast iron or welded steel plates
  • DLaminated silicon steel
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Correct Answer : (C)

Cast iron or welded steel plates

Explanation:

In a synchronous machine, the stator frame is made of  Cast iron or welded steel plates.

10.The stator core of a synchronous machine is built up of ___laminations.

  • AStainless steel
  • BSilicon steel
  • CCast iron
  • DCast steel
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Correct Answer : (B)

Silicon steel

Explanation:

The main function of the stator core is to carry the alternating flux. In order to reduce the hysteresis loss and eddy current loss, the stator core of silicon steel is laminated.

11.The stator core stampings also have opening which make____ ventilating ducts to provide efficient cooling.

  • AAxial
  • BRadial
  • Cradial as well as radial
  • DNone of the above
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Correct Answer : (C)

radial as well as radial

Explanation:

12.The open slots are commonly used in the stator of a synchronous machine as

  • AThe inductance of the winding is less
  • BThey permit the placement of form wound and insulated coils giving least expensive and more satisfactory
  • CBoth (a) and (b)
  • DNone of these
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Correct Answer : (C)

Both (a) and (b)

Explanation:

The open slots are commonly used in the stator of a synchronous machine as the inductance of the winding is less and they permit the placement of form wound and insulated coils giving least expensive and more satisfactory.

13.The field system of an alternator is usually excited at

  • A250/ 250 V DC
  • B110 / 220 V AC
  • C3-phase, 50 Hz 400 V
  • D230V AC
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Correct Answer : (A)

250/ 250 V DC

Explanation:

The field system of an alternator is usually excited at 250/ 250 V DC.

14.The slip rings employed in a 3 phase synchronous machines are insulated for

  • AOutput rated voltage
  • BLow voltage
  • CVery low voltage
  • DVery high voltage
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Correct Answer : (B)

Low voltage

Explanation:

The slip rings employed in a 3 phase synchronous machines are insulated for Low voltage.

15.Squirrel cage bars placed in the rotor pole faces of an alternator help reducing hunting

  • AAbove synchronous speed only
  • BBelow synchronous speed only
  • CAbove and below synchronous speeds both
  • DNone of the above
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Correct Answer : (C)

Above and below synchronous speeds both

Explanation:

16.Hydro-generators are generally employed to run at ___rpm

  • A500
  • B1000
  • C1500
  • D3000
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Correct Answer : (A)

500

Explanation:

Hydro-generators are generally employed to run at 500 rpm.

17.In case of turbo alternator, rotor is made of

  • AForged steel
  • BCast iron
  • CStainless steel
  • DLaminated silicon steel
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Correct Answer : (A)

Forged steel

Explanation:

18.The salient pole rotors have

  • AA large number of projecting poles carrying the filed coils
  • BThick steel laminations riveted together and fixed to the rotor by a dove tail joint
  • CPole faces usually provided with slots for damper windings
  • DAll of the above
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Correct Answer : (D)

All of the above

Explanation:

19.In salient pole field structure, the pole shoes cover about ___of pole pitch.

  • AOne third
  • BOne half
  • CTwo third
  • DWhole
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Correct Answer : (C)

Two third

Explanation:

20.Larger diameter salient pole rotors have shorter axial length because

  • Ait occupies much less space
  • Bif saves lot of copper in stator winding
  • Cit reduces weight of the rotor
  • Dnumber of conductors held in large circumference of rotor is very large and so they need not long
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Correct Answer : (D)

number of conductors held in large circumference of rotor is very large and so they need not long

Explanation: