400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.The current of a single-phase load drawn from a 3-phase system has :
- AZero-sequence component of current as zero.
- BNegative-sequence component of current more than positive sequence component.
- CPositive, negative-and zero-sequence components equal.
- DNegative-sequence component of current less than positive sequence component.
2.Zero-sequence current can flow from a line to transformer bank if the windings are in
- AGrounded star/delta
- BDelta/star
- CStar/grounded star
- DDelta/delta
3.If the positive, negative ? and zero-sequence reactance of an element of a power system are 0.3, 0.3 and 0.8 pu respectively, then the element would be a
- ASynchronous generator
- BSynchronous motor
- CStatic load
- DTransmission line
4.If all the sequence voltages at the fault point in a power system are equal, then the fault is a
- AThree-phase fault
- BLine-to ground fault
- CLine-to-line fault
- DDouble-line-to ground fault
5.The three sequence voltages at the point of fault in a power system are found to be equal. The nature of the fault is
- AL - G
- BL - L - L
- CL - L
- DL - L - G
6.The zero-sequence current of a generator for line-to ground fault is j2.4 pu. Then the current through the neutral during the fault is
- AJ2.4 pu
- BJ0.8 pu
- CJ7.2 pu
- DJ0.24 pu
7.One current transformer (CT) is mounted over a 3-phase, 3-core cable with its sheath and armour removed from the portion covered by the CT. an ammeter placed in the CT secondary would measure
- AThe positive-sequence current
- BThe negative-sequence current
- CThe zero-sequence current
- DThree times the zero-sequence current
8.The positive sequence driving point reactance at the bus is
- A2.5 ohm
- B4.033 ohm
- C5.5 ohm
- D12.1 ohm
9.The zero sequence driving point reactance at the bus is
- A2.2 ohm
- B4.84 ohm
- C18.18 ohm
- D22.72 ohm
10.The primary function of a fuse is to
- AOpen the circuit
- BProtect the appliance
- CProtect the line
- DPrevent excessive currents from flow through the circuit
11.What is the advantage of HRC fuses over Rewirable fuses?
- AHigh speed operation
- BHigh rupturing capacity
- CNo ageing effect
- DAll of the above
12.In HRC fuse the time between cut-off and final current zero is called
- APre-arcing time
- BArcing time
- CTotal operating time
- DNone of these
13.If a combination of HRC fuse and a circuit breaker is employed, the circuit breaker operates for
- AShort-circuit current
- BLow overload currents
- CUnder all abnormal currents
- DThe combination is newer employed in practice
14.The least expensive protection for overcurrent in low-voltage system is
- ARewireable fuse
- BIsolator
- CCircuit breaker
- DAir-break switch
15.A Circuit breaker normally operates
- AWhen the power is to be supplied
- BWhen the line is to be tested
- CWhen the switch is to be put on
- DWhenever fault occurs in the line
16.When a fault occurs in a high voltage transmission line, first the
- ACircuit breaker operates then the relay
- BRelay operates then the Circuit breaker
- CRelay operates then successively the isolator and the Circuit breaker
- DIsolator operates, then successively the Relay and the Circuit breaker
17.The initiation of electric arc at the instant of contact separation is caused by
- AThermionic emission of electrons
- BField emission of electrons
- C(a) and (b) both
- DNone of the above
18.Arcing voltage will be the least in case of
- ACarbon
- BCopper
- CSilver
- DTungsten
19.The heat produced at the contact point owing to flow of electric current is least affected by
- ATemperature of the surrounding medium
- BContact resistance
- CMagnitude of electric current flowing
- DDuration of flow of current
20.Which of the following should have low value for the contacts and their material?
- AThermal capacity
- BContact resistance
- CThermal conductivity
- DNone of these