CIRCUIT BREAKER-1

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.
Answer
D

2.The function of protective relay in a circuit breaker is
(A) to each any stray voltages
(B) to close the contacts when the actuating quantity reaches a certain predetermined value
(C) to limit arcing current during the operation of circuit breaker
(D) to provide additional safety in the operation of circuit breaker.
Answer
B

3.Low voltage circuit breakers have rated voltage of less than
(A) 220 V
(B) 400V
(C) 1000 V
(D) 10,000 V.
Answer
C

4.The fault clearing time of a circuit breaker is usually
(A) few minutes
(B) few seconds
(C) one second
(D) few cycles of supply voltage.
Answer
D

5.The medium employed for extinction of arc in air circuit breaker is
(A) SF_6
(B) Oil
(C) Air
(D) Water.
Answer
C

6.Which of the following circuit breakers is preferred for EHT application
(A) Air blast circuit breakers
(B) Minimum oil circuit breakers
(C) Bulk oil circuit breakers
(D) SF_6 oil circuit breakers.
Answer
D

7.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.
Answer
C

8.Which of the following is not a type of the contactor for circuit breakers ?
(A) Electro-magnetic
(B) Electro-pneumatic
(C) Pneumatic
(D) Vacuum.
Answer
D

9.Interrupting medium in a contactor may be
(A) air
(B) oil
(C) SF_6 gas
(D) any of the above.
Answer
D

10.In air blast circuit breakers, the pressure of air is of the order of
(A) 100 mm Hg
(B) 1 kg/cm^2
(C) 20 to 30 kg/cm^2
(D) 200 to 300 kg/cm^2 .
Answer
C

11.SF6 gas is
(A) sulphur fluoride
(B) sulphur difluoride
(C) sulphur hexafluorine
(D) sulphur hexafluoride.
Answer
D

12.SF6 gas
(A) is yellow in color
(B) has pungent odor
(C) is highly toxic
(D) is non-inflammable.
Answer
D

13.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 limes as compared to that of air.
Answer
D

14.The pressure of SF_6 gas in circuit breakers is of the order of
(A) 100 mm Hg
(B) 1 kg/cm^2
(C) 3 to 5 kg/cm^2
(D) 30 to 50 kg/cm^2 .
Answer
C

15. 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.
Answer:D