Switchgear and Protection MCQ With Answers

81. Which of the following circuit breakers has the lowest operating voltage ?

(a) SF6 gas.
(b) Air-break.
(c) Air-blast.
(d) Minimum oil.

82. Which of the following circuit breakers produce the least arc energy?

(a) Plain oil.
(b) Minimum oil.
(c) Air-blast.
(d) Air break.

83. Which of the following circuit breakers has high reliability and negligible maintenance?

(a) Air-blast.
(b) SF6
(c) Oil.
(d) Vacuum.

84. Which of the following circuit breakers take minimum time in installation?

(a) Air-blast.
(b) Minimum oil.
(c) Bulk oil.
(d) SF6

85. Where voltages are high and current to be interrupted is low, the circuit breaker preferred is……..one.

(a) air-break
(b) vacuum
(c) oil
(d) air-blast

86. For rural electrification in a country like India with complex network, the circuit breaker preferred is………one.

(a) air-break
(b) oil
(c) vacuum
(d) minimum oil

87. The most suitable circuit breaker for short line fault without switching resistor is……..one.

(a) minimum oil
(b) air-blast
(c) SF6
(d) air-break

88. The rating of a circuit breaker is usually determined on the basis of……..fault.

(a) symmetrical
(b) line to line
(c) single line to ground
(d) double line to ground

89. The transient phenomenon lasts in a power system for a period ranging from

(a) few ms to 1 s.
(b) 1 s to 2 s.
(c) 2 s to 3 s.
(d) greater than 3 s.

90. Circuit breakers usually operate under

(a) steady short-circuit current.
(b) sub-transient state of short-circuit current.
(c) transient state of short-circuit current.
(d) none of these.

91. The restriking voltage is measured in

(a) RMS value.
(b) Peak value.
(c) Instantaneous value.
(d) Average value.

92. The making and breaking currents of 3-phase ac circuit breakers in power system are respectively in what form?

(a) rms value, rms value.
(b) instantaneous value, rms value.
(c) rms value.
(d) instantaneous value, instantaneous value.

93. The breaking capacity of a 3-phase circuit breaker is given as

(a) service line voltage in volts x rated symmetrical current in amperes x 10^-6 MVA.
(b) √3 service line voltage in volts x rated symmetrical current in amperes x 10^-6 MVA.
(c) 1.1 x service line voltage in volts x rated symmetrical current in amperes x 10^-6 MVA.
(d) √2 service line voltage in volts x rated symmetrical current in amperes x 10^-6 MVA.

94. Rated breaking capacity (MVA) of a circuit breaker is equal to

(a) the product of rated breaking current (kA) and rated voltage (kV).
(b) the product of rated symmetrical breaking current (kA) and rated voltage (kV).
(c) the product of breaking current (kA) and fault voltage (kV).
(d) twice the value of rated current (kA) and rated voltage (kV).

95. The making to breaking current ratio for an EHV circuit breaker is

(a) more than 1.
(b) equal to 1.
(c) less than 1.
(d) a negative number.

96. The making capacity of a circuit breaker is

(a) less than the asymmetrical breaking capacity of the breaker.
(b) greater than the asymmetrical breaking capacity of the breaker.
(c) equal to the symmetrical breaking capacity of the breaker.
(d) equal to the asymmetrical breaking capacity.

97. Which of the following statements is not correct?

(a) Arc chutes are used in air break circuit breakers.
(b) Air-blast circuit breakers are employed for high voltage traction system.
(c) Resistance switching is employed for overcoming current chopping.
(d) Linear resistors are used in resistance switching.

98. Capacitor switching in 33 kV power system is better done with……….circuit breakers.

(a) air-blast
(b) minimum oil
(c) vacuum

99. The probable cause(s) for fall in insulation resistance between phase terminal and earthed frame could be

(a) dirty insulation surface.
(b) ingress of moisture.
(c) sticking of carbon or copper particles to the internal surface.
(d) all of the above.

100. The probable cause(s) for failure of a circuit breaker on electrical compound could be

(a) trip circuit open.
(b) trip latch defective.
(c) spring defective.
(d) any of the above.

101. Routine tests are conducted on

(a) bulk oil circuit breakers.
(b) minimum oil circuit breakers.
(c) air-blast circuit breakers.
(d) all of the above.

102. An isolator is installed

(a) to isolate one portion of the circuit from another.
(b) usually on both sides of a circuit breaker.
(c) as a substitute for a circuit breaker.
(d) both (a) and (b).

103. Current rating is not necessary in case of

(a) isolators.
(b) circuit breakers.
(c) load break switches.
(d) circuit breakers and load break switches.

104. An isolator is meant for

(a) breaking abnormal current.
(b) making under fault condition.
(c) breaking the circuit under no-load condition.
(d) none of the above.

105. Isolators used in transmission lines are capable of breaking:

(a) fault current.
(b) no current.
(c) charging current.
(d) load current.

106. The oil switches may be

(a) remote or manually controlled.
(b) used for capacitor switching, street lighting control and automatic disconnect on power failure.
(c) used for high voltage and large current circuits.
(d) all of the above.

107. For a fault at the terminals of synchronous generator, the fault current is maximum for a

(a) 3-phase fault.
(b) 3-phase to ground fault.
(c) line-to-ground fault.
(d) line-to-line fault.

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