400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.Two-input phase comparator in a static relay is made up of a
- ATransformer amplifier.
- BTransistor logic circuit.
- CRectifier bridge.
- DThyristor bridge.
2.The phase comparators in case of static relay and electromechanical relay normally are
- ACosine and sine comparators respectively.
- BSine and cosine comparators respectively.
- CBoth are sine comparators.
- DBoth are cosine comparators.
3.Merz-Price protection is employed for protection of
- AAlternators
- BTransformers
- CTransmission lines.
- DBoth (a) and (b)
4.A negative-sequence voltage in the stator induces
- AHigh frequency currents in the rotor.
- BHigh frequency voltage in the rotor.
- CLow frequency currents in the rotor.
- DHigh frequency currents in the stator.
5.The short-circuit current of an alternator, in case of line to line fault, depends on its
- AShort-circuit resistance.
- BTransient reactance.
- CSynchronous reactance.
- DNone of the above.
6.We do not require any protection against prime mover failure in case of
- ATurbo-generator sets.
- BHydro-generator sets.
- CDiesel-engine driven alternators.
- DBack pressure turbo-generators.
7.For the protection of stator winding of an alternator against internal fault involving ground, the relay used is a
- ABiased differential relay.
- BDirectional overcurrent relay.
- CPlain impedance relay.
- DBuchholz relay.
8.The bias factor S in unit protection synchronous generator
- ALies between 0.05 and 0.1 pu.
- BIs less than 0.05 pu
- CLies between 0.1 to 0.25 pu.
- DIs greater than 0.025 pu.
9.Field failure in an alternator occurs due to
- AFailure of exciter
- BFaulty field circuit breaker.
- CInrush of large currents
- DBoth (a) and (b)
10.A soon as a fault develops in a generator stator, it is essential to suppress field excitation, otherwise
- ATerminal voltage will drop.
- BIt may lead to loss of synchronism.
- CIt will continue to supply power to the stator winding fault.
- DAll of the above.
11.If there is an open circuit in the field circuit of a generator
- AThe generator will continue to operate as an induction generator supplying load at a very low leading power factor.
- BThe supply voltage will drop, and the system stability will be affected.
- CThe circulating current at slip frequency may overhead the generator.
- DAll of the above.
12.The earth fault in stator causes
- AArcing to core.
- BSevere heating in conductors and thereby damaging the insulation.
- COpen-circuit in the stator
- DBoth (a) and (b)
13.Failure of insulation on stator winding of generator results in
- AShort circuit between turns.
- BShort circuit between one or more phases and earth.
- CShort circuit between phases.
- DAll of the above.
14.The magnitude of earth-fault current for a given fault position within a winding depends upon
- AThe winding connections.
- BThe method of neutral grounding.
- CUnmatched characteristics of CTs.
- DBoth (a) and (b)
15.For the protection of a large squirrel-cage induction motor against single phase normally
- AAn overcurrent relay is used.
- BA differential relay is used.
- CA directional relay is used.
- DNegative sequence current sensitive relay is used.
16.The main function of undervoltage protective device generally employed with a motor starter is to
- AOpen the supply circuit on failure of power supply.
- BControl the motor voltage.
- CPrevent the opening of supply circuit.
- DNone of the above.
17.While adding extra stop buttons to an existing control system they must be in
- AParallel to the load.
- BSeries with the contactor coil.
- CSeries with the motor.
- DParallel to the start button.
18.Negative-sequence currents flow in the stator windings of an ac motor due to
- AUnbalanced in the supply voltage
- BUnbalanced load
- CPhase reversal
- DWither (a) or (b)
19.A negative sequence relay is commonly used to protect
- AAn alternator
- BA transformer
- CA transmission line
- DA bus bar
20.Earth fault protection for an electric motor is provided by
- AInstantaneous overcurrent relay.
- BInstantaneous relay having a setting of approximately 30% of motor rated current in the residual circuits of two CTs.
- CGround wire
- DBoth (b) and (c)