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Switchgear and Protection MCQ Question and Answer

1.The most serious consequence of a major uncleared short-circuit fault could be

  • ABlowing of fuse 
  • BFire 
  • CHeavy voltage drop
  • DNone of these
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Answer:

Fire 

Explanation:

2.Which of the following results in a symmetrical fault?

  • ASingle-phase-to earth
  • BPhase-to-phase
  • CAll the three phases-to earth
  • DTwo phase-to earth
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Answer:

All the three phases-to earth

Explanation:

3.Which portion of the transmission system is more prone to faults?

  • AAlternator
  • BTransformer 
  • COverhead lines
  • DUnderground cable
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Answer:

Overhead lines

Explanation:

4.Which portion of the power system is least prone to faults?

  • AAlternator
  • BSwitchgear
  • CTransformers
  • DOverhead lines
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Answer:

Alternator

Explanation:

5.The magnitude of fault current depends upon

  • ATotal impedance up to fault
  • BVoltage at the fault point 
  • CLoad current being supplied before occurrence of fault 
  • DBoth (a) and (b)
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Answer:

Both (a) and (b)

Explanation:

6.Question

  • AA
  • BB
  • CC
  • DD
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Answer:

A

Explanation:

7.The most common type of fault is

  • ASingle-phase-to ground
  • BPhase-to-phase 
  • CTwo-phase-to ground
  • DThree -phase-to ground 
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Answer:

Single-phase-to ground

Explanation:

8.The maximum short-circuit current occurs in the case of  :

  • AThree-phase bolted fault
  • BDouble-line-to-ground fault
  • CLine-to-line fault
  • DSingle-line-to-ground fault
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Answer:

Three-phase bolted fault

Explanation:

9.For a fault at the terminals of synchronous generator, the fault current is maximum for a 

  • A3-phase fault
  • B3-phase to ground fault
  • CLine-to-ground fault 
  • DLine-to-line fault 
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Answer:

Line-to-ground fault 

Explanation:

10.Series reactors are used to

  • AImprove the transmission efficiency
  • BImprove the power factor of the power system
  • CImprove the voltage regulation
  • DBring down the fault level within the capacity of the switchgear
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Answer:

Bring down the fault level within the capacity of the switchgear

Explanation:

11.Current limiting reactors may be 

  • AAir-cored air-cooled
  • BOil immersed magnetically shielded
  • COil immersed non-magnetically shielded
  • DAny of the above 
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Answer:

Any of the above 

Explanation:

12.QUESTION

  • AA
  • BB
  • CC
  • DD
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Answer:

A

Explanation:

13.Symmetrical components are used in power system for the analysis of

  • ABalanced 3-phae fault 
  • BUnbalanced 3-phae fault
  • CNormal power system under steady conditions
  • DStability of system under disturbance 
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Answer:

Unbalanced 3-phae fault

Explanation:

14.In a star-connected system without neutral grounding, zero sequence currents are

  • AZero
  • BPhasor sum of phase currents
  • CSame as rms value of phase currents 
  • DSame as peak value of phase currents
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Answer:

Zero

Explanation:

15.A balanced 3-phase system consists of

  • AZero-sequence currents only
  • BPositive-sequence currents only
  • CNegative-and zero-sequence currents
  • DZero, Negative and Positive sequence currents
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Answer:

Positive-sequence currents only

Explanation:

16.The Positive sequence current of a transmission line is  :

  • AAlways zero
  • B1/3 of Negative sequence current
  • CEqual to Negative sequence current
  • D3 times Negative sequence current
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Answer:

Equal to Negative sequence current

Explanation:

17.For a fully transposed transmission line

  • APositive, Negative and zero sequence impedances are equal.
  • BPositive and Negative sequence impedances are equal.
  • CZero and Positive sequence impedances are equal.
  • DNegative and zero sequence impedances are equal.
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Answer:

Positive and Negative sequence impedances are equal.

Explanation:

18.QUESTION

  • AA
  • BB
  • CC
  • DD
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Answer:

A

Explanation:

19.In case of an unbalanced star-connected load supplied from an unbalanced 3-phase, 3-wire system, load currents will consist of 

  • APositive-sequence components.
  • BNegative-sequence components.
  • CZero-sequence components.
  • DOnly (a) and (b)
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Answer:

Only (a) and (b)

Explanation:

20.For an unbalanced fault, with paths for zero-sequence currents, at the point of fault

  • AThe negative-and zero-sequence voltages are minimum.
  • BThe negative-and zero-sequence voltages are maximum.
  • CThe negative-sequence voltages is minimum and zero-sequence voltages is maximum.
  • DThe negative-sequence voltages is maximum and zero-sequence voltages is minimum.
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Answer:

The negative-and zero-sequence voltages are maximum.

Explanation: