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Switchgear and Protection MCQ Question and Answer

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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Correct Answer : (B)

Fire 

Explanation:

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

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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Correct Answer : (C)

All the three phases-to earth

Explanation:

The results in a symmetrical fault is All the three phases-to earth.

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

  • AAlternator
  • BTransformer 
  • COverhead lines
  • DUnderground cable
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Correct Answer : (C)

Overhead lines

Explanation:

Overhead lines of the transmission system is more prone to faults.

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

  • AAlternator
  • BSwitchgear
  • CTransformers
  • DOverhead lines
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Correct Answer : (A)

Alternator

Explanation:

Alternator of the power system is least prone to faults.

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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Correct Answer : (D)

Both (a) and (b)

Explanation:

The magnitude of fault current depends upon Total impedance up to fault and Voltage at the fault point.

6.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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Correct Answer : (A)

Single-phase-to ground

Explanation:

The most common type of fault is Single-phase-to ground.

7.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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Correct Answer : (A)

Three-phase bolted fault

Explanation:

The maximum short-circuit current occurs in the case of Three-phase bolted fault.

8.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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Correct Answer : (C)

Line-to-ground fault 

Explanation:

9.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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Correct Answer : (D)

Bring down the fault level within the capacity of the switchgear

Explanation:

Series reactors are used to Bring down the fault level within the capacity of the switchgear.

10.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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Correct Answer : (D)

Any of the above 

Explanation:

Current limiting reactors may be the following types 1. Air-cored air-cooled, 2. Oil immersed magnetically shielded, 3. Oil immersed non-magnetically shielded.

11.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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Correct Answer : (B)

Unbalanced 3-phae fault

Explanation:

Symmetrical components are used in power system for the analysis of Unbalanced 3-phae fault.

12.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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Correct Answer : (A)

Zero

Explanation:

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

13.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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Correct Answer : (B)

Positive-sequence currents only

Explanation:

A balanced 3-phase system consists of Positive-sequence currents only.

14.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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Correct Answer : (C)

Equal to Negative sequence current

Explanation:

The Positive sequence current of a transmission line is Equal to Negative sequence current.

15.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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Correct Answer : (B)

Positive and Negative sequence impedances are equal.

Explanation:

For a fully transposed transmission line Positive and Negative sequence impedances are equal.

16.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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Correct Answer : (D)

Only (a) and (b)

Explanation:

17.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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Correct Answer : (B)

The negative-and zero-sequence voltages are maximum.

Explanation:

18.In case of single line to ground fault 

  • AAll sequence networks are connected in parallel.
  • BAll sequence networks are connected in series.
  • CPositive and negative sequence networks are connected in parallel.
  • DZero and negative sequence networks are connected in series.
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Correct Answer : (B)

All sequence networks are connected in series.

Explanation:

19.When a line-to-ground fault occurs, the current, the current in the faulted phase is  100 A. the zero-sequence current in this case will be  :

  • AZero
  • B33.3 A
  • C66.6 A
  • D100 A
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Correct Answer : (B)

33.3 A

Explanation:

20.Zero sequence fault current is absent when fault is

  • ASingle-line-to ground fault.
  • BLine-to-line ground fault.
  • CLine-to-line
  • DDouble-line-to ground fault.
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Correct Answer : (D)

Double-line-to ground fault.

Explanation:

Zero sequence fault current is absent when fault is Double-line-to ground fault.