Objective Questions & Answers of Circuit Breaker page-9

81. For high-speed circuit breakers, the total clearing time is nearly

A) 1 to 2 cycles
B) 5 to 10 cycles
C) 10 to 15 cycles
D) Less than 50 cycles.

Ans : (A)

82. If the power factor is zero, the active recovery voltage will be

A) minimum
B) 0.5
C) 0.707
D) maximum.

Ans : (D)

83. Which of the following is not a part of the circuit breaker ?

A) Operating mechanism
B) Conservator
C) Fixed and moving contacts
D) Explosion pot.

Ans : (B)

84. The values of fault current depend on

A) voltage at the faulty point
B) total impedance up to the fault
C) both (A) and (B) above
D) none of the above.

Ans: (C)

85. The advantage of neutral earthing is

A) simplified design of earth fault protection
B) over-voltages due to lighting can be discharged to the earth
C) freedom from persistent arcing grounds
D) all of the above.

Ans : (D)

86. Which of the following circuit breaker will produce the least arc energy ?

A) Air blast circuit breaker
B) Minimum oil circuit breaker
C) Plain oil circuit breaker
D) All will produce same energy.

Ans : (A)

87. A circuit breaker will normally operate

A) When the power is to be supplied
B) Whenever fault in the line occurs
C) When the line is to be checked
D) When the switch is put on

Ans : (B)

88. The material used for bus bars should have

A) low resistivity
B) higher softening temperature
C) low cost
D) all of the above.

Ans : (D)

89. Which of the following are air-break switching devices ?

A) Isolator
B) Limit switch
C) Earthing switch
D) All of the above.

Ans : (D)

90. In circuit-breakers the contact space is ionized by

A) thermal ionization of gas
B) thermal emission from surface of contacts
C) field emission from the surface of contacts
D) any of the above.

Ans : (D)

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Objective Questions & Answers of Circuit Breaker page-9

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