400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.Which is the main relay for protecting up to 90% of the transmission line-length in the forward direction?
- ADirectional overcurrent relay.
- BMho relay.
- CCarrier-current protective relay.
- DImpedance relay.
2.For complete protection of a 3-phase transmission line, we require
- AThree-phase and three-earth fault relays.
- BThree-phase and two-earth fault relays.
- CTwo-phase and two-earth fault relays.
- DTwo-phase and one-earth fault relays.
3.How many relay are used to detect interphase fault of a three-line system?
- A1
- B2
- C3
- D6
4.The transmission line distance production relay having the property of being inherently directional is
- AImpedance relay
- BMHO relay
- COHM relay
- DReactance relay
5.Time graded protection of a radial feeder can be achieved by using
- ADefinite time relays
- BInverse time relays
- CBoth define and inverse time relays
- DNone of the above
6.The normal resistance of a pilot wire is
- AMore than 500 ohms
- BMore than 1500 ohms
- CLess than 500 ohms
- DLess than 1500 ohms
7.For protection of parallel feeders fed from one end, the relays required are
- ANon-directional relays at the source end and directional relays at the load end.
- BNon-directional relays at both ends.
- CDirectional relays at source end Non-directional relays at load end.
- DDirectional relays at both ends.
8.Pilot-wire protection scheme is most economical and provides high speed relaying for
- AShort length of lines up to 15 km.
- BMedium length of lines up to 60 km.
- CLong length of lines up to 200 km.
- DAll of the above.
9.Adjustable resistors are connected in the pilot wires in order to
- AChange the phase of the current flowing through the relay.
- BGet equipotential points on pilot wires.
- CReduce current flowing through the relay.
- DNone of the above.
10.Signal mixing transformers are used for
- AInduction disc type overcurrent relay.
- BDirection sensitive distance relay.
- CPilot-wire feeder protection.
- DPlain differential relay.
11.In a balanced voltage pilot-wire protection scheme, if the pilot-circuit gets short-circuited, the relay will
- AFail to trip on internal faults.
- BFail to trip on external faults.
- CTrip on full-load.
- DTrip instantaneously.
12.The frequency of carrier in the carrier current pilot scheme is in the range of
- A1 kHz to 10 kHz
- B10 kHz to 25 kHz
- C25 kHz to 50 kHz
- D50 kHz to 500 kHz
13.The frequency of carrier transmitted by microwave pilot is in the range of
- A1,000 kHz to 15,000 kHz
- B2,000 kHz to 5,000 kHz
- C900 MHz to 6,000 MHz
- D10,000 MHz to 15,000 MHz
14.The purpose of the wave-trap in carrier current protection is for
- ATrapping power frequency waves.
- BTrapping high frequency waves entering into generators/transformer unit.
- CBoth (a) and (b)
- DNone of the above
15.A line trap in carrier current relaying tuned to carrier frequency presents
- AHigh impedance to carrier frequency but low impedance to power frequency.
- BLow impedance to both carrier and power frequency.
- CHigh impedance to both carrier and power frequency.
- DLow impedance to carrier frequency but high impedance to power frequency.
16.A line trap in a long transmission line is used to
- AImprove the power factor.
- BDampen the overvoltage oscillations.
- CConfine the carrier signals in the line.
- DProduct the line against direct lightning stroke.
17.Distance protection scheme is preferred over graded time-lag over-current protection in HV and EHV lines because
- AIt is faster in operation.
- BIt is simple.
- CIt is cheaper in cost.
- DAll of the above.
18.Three step time-distance characteristic of distance relay can be had by
- AChanging taps on voltage transformer.
- BSeparate measuring elements for zones 2 and 3.
- CSwitching resistance in relay restraint circuit at pre-set time intervals by means of timer element.
- DAny of the above.
19.Lightning is a huge spark caused by electrical discharge taking place between
- AClouds
- BWithin the same cloud
- CCloud and earth
- DAny of the above
20.Switching over-voltages are more hazardous than lightning surges in case of
- ALow voltage system
- B33 kV system
- CEHV and UHV systems
- DAll of these