Switchgear Protections

11. An efficient and a well designed protective relaying should have

1. good selectivity and reliability
2. economy and simplicity
3. high speed and selectivity
4. all of the above

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12. An isolator is installed

1. to operate the relay of circuit breaker
2. as a substitute for circuit breaker
3. always independent of the position of circuit breaker
4. generally on both sides of a circuit breaker

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13. Arc in a circuit behaves as

1. a capackive reactance
2. an inductive reactance
3. a resistance increasing with voltage rise across the arc
4. a resistance decreasing with voltage rise across the arc

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14. Arc in a circuit breaker is interrupted at

1. zero current
2. maximum current
3. minimum voltage
4. maximum voltage

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15. Burden of a protective relay is the power

1. required to operate the circuit breaker
2. absorbed by the circuit of relay
3. developed by the relay circuit
4. none of the above

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16. Bus coupler is very essential in arrangement

1. single bus
2. double bus, double breaker
3. main and transfer bus
4. all of the above

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17. Circuit breakers are essentially

1. current carrying contacts called electrodes
2. arc extinguishers
3. circuits to break the system
4. transformers to isolate the two systems
5. any of the above

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18. Circuit breakers usually operate under

1. transient state of short-circuit current
2. sub-transient state of short-circuit current
3. steady state of short-circuit current
4. after D.C. component has ceased

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19. D.C. shunt relays are made of

1. few turns of thin wire
2. few turns of thick wire
3. many turns of thin wire
4. many turns of thick wire

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20. Directional relays are based on flow of

1. power
2. current
3. voltage wave
4. all of the above

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