Q.31 In circuit breaker, if the dielectric strength of the medium between two contacts build up more rapidly than the restriking voltage___
A. the arc will continue and current cannot be interrupted
B. the arc will fail to restrike and current will be interrupted
C. the arc will continue and current will be interrupted
D. only current will be interrupted
Ans.: B
Q.32 The current interruption in the circuit breaker is depends upon the___
A. normal frequency voltage
B. recovery voltage
C. restriking voltage
D. none of the above
Ans.: C
Q.33 ____ is the normal frequency r.m.s voltage that appears across the contacts of circuit breaker after final arc extinction.
A. normal frequency voltage
B. recovery voltage
C. restriking voltage
D. transient voltage
Ans.: B
Q.34 The fault current is _____at the instant of current zero point.
A. leads the arc voltage by 90°
B. lags the arc voltage by 90°
C. lags the arc voltage by 45°
D. leads the arc voltage by 45°
Ans.: B
Q.35 In ac circuit the current drops to zero after _____
A. every one cycle
B. every two cycles
C. every half cycle
D. none of the above
Ans.: C
Q.36 Recovery voltage is also called as___
A. normal frequency voltage
B. transient frequency voltage
C. sub transient frequency voltage
D. peak voltage
Ans.: A
Q.37 Circuit breakers are classified on the basis of ___
A. arc quenching medium
B. voltage level
C. accommodation
D. all of the above
Ans.: D
Q.38 In oil circuit breaker ____ is used as an arc quenching medium.
A. food oil
B. transformer oil
C. crude oil
D. hydrogen gas in liquid form
Ans.: B
Q.39 What are the advantages of oil as an arc quenching medium in oil circuit breaker?
A. oil acts as an insulator which permits smaller clearance between live conductors and earthed parts
B. it absorb the arc energy
C. oil cools the arc
D. all of the above
Ans.: D
Q.40 During arcing in oil circuit breaker the oil is decomposed into
A. hydrogen gas
B. small percentage of methane,
C. small percentage of ethylene and acetylene
D. all of the above
Ans.: D
Q.41 Hydrogen gas has ____
A. high heat conductivity
B. excellent cooling properties
C. Both A and B
D. low heat conductivity and bad cooling properties
Ans.: C
Q.42 What are the disadvantages of oil as in arc quenching medium in oil circuit breaker?
A. form an explosive mixture with air
B. risk of fire because of oil is inflammable
C. quality of oil is deteriorates with successive operations
D. all of the above
Ans.: D
Q.43 The oil in oil circuit breakers
A. serve as arc quenching medium
B. it insulates the live conductors from earth and one another
C. Both A and B
D. it serves as insulators between live conductors only
Ans.: C
Q.44 Which of the following is the earliest type of circuit breaker from which all other circuit breakers are developed?
A. minimum oil circuit breaker
B. plain oil circuit breaker
C. bulk oil circuit breaker
D. arc control oil circuit breaker
Ans.: B
Q.45 In bulk oil circuit breaker the oil is used as__
A. arc quenching medium only
B. insulates the live parts from each other
C. insulates the live conductor from earth
D. all of the above
Ans.: D
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