400 Important Switchgear and Protection MCQ Question and Answer | PDF Free Download
1.In a Circuit Breaker Contact wipe is necessary
- ATo decrease the speed of opening of the CB
- BTo increase the speed of opening and reduce the arcing of contacts
- CTo increase the dielectric strength across the CB contacts
- DNone of the above
2.The fluids used in circuit breakers should be of
- AHigh dielectric strength and thermal stability
- BNon-inflammability
- CArc extinguishing ability
- DAll of the above
3.Sparking between contacts can be reduced by inserting
- AA capacitor in parallel with the contacts
- BA capacitor in series with the contacts
- CA resistor in the line
- DA reactor in the line
4.For magnetic blow out of arc the magnetic field is produced
- AIn the load circuit
- BAt right angles to the axis of the arc
- CIn line with the axis of the arc
- DAny of the above
5.In a circuit breaker the contact space is ionized by
- AField emission from the contact surface
- BThermal emission from the contact surface
- CThermal ionization of gas
- DAny of the above
6.Ionization In a circuit breaker is facilitated by
- AIncrease in field strength
- BIncrease of mean free length
- CHigh temperature of surrounding medium
- DAll of the above
7.The stability of arc in vacuum depends on
- AThe contact material only
- BThe contact material and its vapour pressure
- CThe circuit parameters only
- DThe combination of (b) and (c)
8.The interrupting time of a circuit breaker is the period between the instant of
- AInitiation of short circuit and the arc extinction on an opening operation.
- BEnergizing of the trip circuit and the arc extinction on an opening operation.
- CInitiation of short circuit and the parting of primary arc contacts.
- DEnergizing of the trip circuit and the parting of primary arc contacts.
9. The total clearing time for a high speed circuit breaker is around
- AFew minutes
- BFew seconds
- C1 to 2 cycles
- D5 to 20 cycles
10.The resistance of an electric arc can be increased by
- AIncreasing the concentration of ionized particles.
- BReducing the arc length.
- CSplitting the arc.
- DIncreasing the arc x-section.
11.The arc voltage in a circuit breaker is
- AIn the phase with the arc current.
- BLagging the arc current by 90 degree
- CLeading the arc current by 90 degree
- DLagging the arc current by 180 degree
12.The active recovery voltage in a circuit breaker depends upon
- ACircuit conditions
- BPower factor
- CArmature reaction
- DAll of these
13.In a circuit breaker the current that exists at the instant of contact separation is called the ________ current.
- AThe Re-striking current
- BThe Breaking current
- CThe Arc current
- DThe Recovery current
14.The rate of rise of re-striking voltage (RRRV) is depends upon
- AResistance of the system only
- BInductance of the system only
- CCapacitance of the system only
- DInductance and capacitance of system
15.It is difficult to interrupt a capacitive circuit because
- AThe current has a leading power factor.
- BThe re-striking voltage can be high.
- CCurrent magnitude is very small.
- DStored energy in the capacitor is very high.
16.In circuit breakers, oil, as quenching medium, has the disadvantage(s) of
- ANeed of periodical reconditioning or replacement.
- BRisk of formation of explosive mixture with air.
- CPossibility of causing fire hazards.
- DAll of the above.
17.Main purpose of oil in OCB is to
- AProvide insulation
- BProvide cooling of contacts
- CQuenching arc
- DNone of above
18.The chances of arc interruption in subsequent current zeros
- AIncrease in case of ABCB but decrease in OCB.
- BDecrease in case of ABCB but increase in OCB.
- CDecrease in both cases.
- DIncrease in both cases.
19.In a minimum oil circuit breaker the oil is used
- ATo act as circuit breaking medium only
- BFor circuit breaking and providing insulation
- CFor providing insulation only
- DFor none of the above purposes
20.Air blast circuit breakers are suitable for
- Ashort duty
- Barc furnace duty
- Cnon-repeated duty
- Dair-cuts arc duty