 Home » Electrical Engineering » Electrical Engineering MCQ » Switchgear and Protection ### 1.The most serious consequence of a major uncleared short-circuit fault could be

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

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

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
• DUnderground cable

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

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)

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

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

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

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

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

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

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

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

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

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.

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 current will consist of

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

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.

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.

All sequence networks are connected in series.

Explanation:

• AZero
• B33.3 A
• C66.6 A
• D100 A

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.