400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.An isolator is meant for
- ABreaking abnormal current.
- BMaking under fault condition.
- CBreaking the circuit under no-load condition.
- DNone of the above.
2.Isolators used in transmission lines are capable of breaking :
- AFault current
- BNo current
- CCharging current
- DLoad current
3.The oil switches may be
- ARemote or manually controlled.
- BUsed for capacitor switching, street lighting control and automatic disconnect on power failure.
- CUsed for high voltage and large current circuits.
- DAll of the above.
4.Which of the following sequence of operation is correct for operation of circuit breaker, isolator and earthing switch while opening a circuit ?
- AOpen circuit breaker ? open isolator ? close earthing switch.
- BOpen isolator ? Open circuit breaker ? close earthing switch.
- COpen earthing switch ? open isolator ? then Open circuit breaker.
- DOpen circuit breaker ? close earthing switch ? open isolator.
5.Which of the following sequence of operation is correct for operation of circuit breaker, isolator and earthing switch while closing a circuit ?
- AEnsure circuit breaker is open ? close isolator ? open earthing switch ? close circuit breaker.
- BEnsure circuit breaker is open ? open earthing switch ? close isolator ? close circuit breaker.
- CClose circuit breaker ? open earthing switch ? close isolator.
- DOpen earthing switch ? Close circuit breaker ? close isolator.
6.Purpose of backup protection is
- ATo increase the speed
- BTo increase a reach
- CTo leave no blind spot
- DTo guard against failure of primary
7.Protective relays are the devices that detect abnormal conditions in electrical circuit by
- AMeasuring Voltage
- BMeasuring Current
- CMeasuring Constantly the electrical quantities which differ during normal and abnormal conditions.
- DNone of the above.
8.The actuating quantity for the relays may be
- AMagnitude
- BFrequency
- CPhase angle
- DAny of these
9.The protective relay is provided to
- AProvide additional safety to the circuit breaker in its operation.
- BClose the contacts when the actuating quantity attains a certain predetermined value.
- CLimit the arcing current during the circuit breaker operation.
- DEarth any stray voltage.
10.The operating speed of a relay depends upon the
- ARate of flux built up
- BArmature core air-gap
- CSpring tension
- DAll of these
11.Plug setting of an electromagnetic relay can be altered by varying
- ANumber of ampere turns.
- BAir gap of magnetic path.
- CAdjustable back stop.
- DNone of these.
12.The torque produced in shaded pole structure induction type relay is
- AProportional to the square of the current.
- BProportional to the current.
- CInversely Proportional to the current.
- DInversely Proportional to the square of the current.
13.The most efficient torque-producing actuating structure for induction-type relays is
- AShaded pole structure
- BWatt-hour meter structure
- CInduction-cup structure
- DSingle induction loop structure
14.A bimetal strip, in a thermal relay, consists of two metal strips of different
- ASpecific heat
- BThermal conductivity
- CCoefficients of expansion
- DAll of the above
15.Thermal relays are used for protection of motors against over-current owing to
- AShort circuits
- BHeavy loads
- CEarth fault
- DAll of these
16.Buchholz relay is
- ALocated in the conservator tank.
- BLocated in the transformer tank itself.
- CConnected in the pipe connecting main tank of transformer and conservator.
- DInstalled in the circuit breaker.
17.Buchholz relay are used on
- AAir cooled transformers
- BInstrument transformers
- CDistribution transformers
- DOil immersed power transformers of rating above 500 kVA
18.The Buchholz relay protects a transformer from
- ATypes of internal faults
- BA turn to turn fault
- CWinding to winding fault
- DNone of these
19.In an Overcurrent protection the setting of the earth fault relay is
- AMore than the phase fault relay
- BEqual to the phase fault relay
- CLess than the phase fault relay
- DThe two settings are unrelated to each other
20.Inverse time-current relays are used for the protection of
- AFeeders
- BTransformers
- CAlternators
- DBoth (a) and (b)