400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.The short circuit in any winding of the transformer is the result
- ALoose connection
- BInsulation failure
- CImpulse voltage
- DMechanical vibrations
2.Which of the following relays has the capacity of anticipating the possible major fault in a transformer?
- AOvercurrent relay
- BDifferential relay
- CBuchholz relay
- DOver-fluxing relay
3.Which relay is used to detect and protect internal faults of a transformer?
- ABuchholz
- BDirectional relay
- CThermal relay
- DDistance relay
4.To prevent mal operation of differentially connected relay while energising a transformer, the relay restraining coil is biased with
- ASecond harmonic current
- BThird harmonic current
- CFifth harmonic current
- DSeventh harmonic current
5.The inrush current of a transformer at no load is maximum if the supply voltage is switched on
- AAt peak voltage value.
- BAt zero voltage value.
- CAt half voltage value.
- DAt 0.866 time voltage value.
6.Magnetizing inrush phenomena occur in
- ALarge transformer primary only, when the transformer is switched on.
- BLarge transformer primary when a 3-phase fault occurs in the secondary.
- CLarge transformer secondary only when the transformer is switched on in the primary.
- DNone of the above.
7.In case of power transformer :
- APositive, negative and zero-sequence impedances are all equal.
- BPositive and zero-sequence impedances are equal but less than negative-sequence impedance.
- CPositive sequence impedance is greater than both negative- and zero-sequence impedances.
- DPositive sequence impedance is less than negative - sequence impedance but equal to zero-sequence impedance.
8.For the protection of transformers, harmonic restraint is used to guard against
- AMagnetizing inrush current.
- BUnbalanced operation
- CLightning
- DSwitching overvoltage
9.The connection of CTs are opposite to that of transformer windings so that current in the pilot wires of two are/have
- ASame phase.
- BOpposite in phase.
- CA phase difference of 60 degree
- DA phase difference of 90 degree
10.For preventing the malfunction of Merz-Price protection scheme on inrush of magnetizing current
- AThe relay restraining coil is biased with second harmonic current.
- BTime lag is provided in the relay.
- CRelay sensitivity is reduced by employing a shunt.
- DAll of the above.
11.Problems associated with differential protection is/are
- AMagnetizing inrush current.
- BMismatching characteristics of CTs.
- CCharge of ratio as a result of tapping.
- DAll of the above.
12.Which of the following sections can be employed for bus-bars?
- ABars
- BRods
- CTubes
- DAny of the above
13.The material used for bus-bars should have
- ALow resistivity
- BLow cost
- CHigh softening temperature
- DAll of the above
14.A bus-bar is rated by
- ACurrent only
- BVoltage only
- CCurrent, voltage and frequency
- DCurrent, voltage, frequency and short-circuit current
15.Single bus-bar arrangement
- AIs cheapest in initial as well as maintenance cost.
- BProvides simple operation and relaying system
- CHas the drawback that there will be complete shutdown when fault occurs on the bus itself.
- DAll of the above
16.A bus coupler circuit breaker is utilized in a substation for
- AJoining the transmission line with station bus-bar.
- BJoining main and transfer bus in a substation.
- CJoining the generator with transfer.
- DJoining the neutral of the generator with earth.
17.Zero-sequence impedance of the transmission line is
- AEqual to the positive-sequence impedance of the line.
- BAbout 2.5-3 times the positive ? sequence impedance of the line.
- CLess than positive ? sequence impedance of the line.
- DNone of the above.
18.Which is the pilotless protection method for feeder line?
- ADifferential protection.
- BCarrier current protection.
- CTime graded protection.
- DNone of these.
19.A transmission line is protected by :
- ADistance protection.
- BCurrent graded overcurrent protection.
- CTime graded overcurrent protection.
- DInrush protection.
20.In the case of transmission line protection, overcurrent relay is used
- AOnly up to 110 kV
- BOnly up to 220 kV
- COnly up to 50 kV
- DOnly up to 1100 kV