1. A circuit breaker is

(A) power factor correcting device
(B) a device to neutralize the effect of transients
(C) a waveform correcting device
(D) a current interrupting device

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Answer. D

2. Low voltage circuit breakers have rated voltage of less than

(A) 220 V
(B) 400V
(C) 1000 V
(D) 10,000 V

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Answer. C

3. The medium employed for extinction of arc in air circuit breaker is

(A) SF6
(B) Oil
(C) Air
(D) Water

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Answer. C

4. For high voltage, ac circuit breakers, the rated short circuit current is passed for

(A) 0.01 sec
(B) 0.1 sec
(C) 3 seconds
(D) 30 seconds

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Answer. C

5. Interrupting medium in a contactor may be

(A) air
(B) oil
(C) SF6 gas
(D) any of the above

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Answer. D

6. SF6 gas is

(A) sulphur fluoride
(B) sulphur difluoride
(C) sulphur hexafluoride
(D) sulphur hexafluoride

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Answer. D

7. SF6 gas

(A) is lighter than hydrogen
(B) is lighter than air
(C) has density 2-times as compared to that of air
(D) has density 5-times as compared to that of air

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Answer. D

8. While selecting a gas for circuit breaker, the property of gas that should be considered is

(A) high dielectric strength
(B) non-inflammability
(C) non-toxicity
(D) all of the above

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Answer. D

9. Which of the following circuit breaker can be installed on 400 kV line

(A) Tank type oil circuit breaker
(B) Miniature circuit breaker
(C) Vacuum circuit breaker
(D) Air blast circuit breaker

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Answer. D

10. In modern EHV circuit breakers, the operating time between instant of receiving trip signal and final contact separation is, of the order of

(A) 0.001 sec
(B) 0.015 sec
(C) 0.003 sec
(D) 0.03 sec.

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Answer. D

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