switchgear and protection MCQs – Page 2

Practise focused switchgear and protection questions with marked answers for exam preparation and subject revision.

switchgear and protection Mcqs
51. Series reactors should have________________?
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A. high impedance

B. low resistance

C. low impedance

D. high resistance

52. The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to______________?
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A. none of the above

B. lubricate the contacts

C. extinguish the arc

D. insulate the contacts from switch body

E. all of the above

53. A fuse is connected_______________?
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A. in parallel with circuit

B. none of the above

C. either in series or in parallel with circuit

D. in series with circuit
54. A short-circuit is identified by_____________?
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A. heavy current flow

B. no current flow

C. voltage drop

D. voltage rise

55. Thermal circuit breaker has____________?
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A. delayed trip action

B. instantaneous trip action

C. both of the above

D. none of the above

56. H.R.C. fuses provide best protection against________________?
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A. overload

B. reverse current

C. short-circuits

D. open-circuits

57. Bus coupler is very essential in arrangement______________?
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A. main and transfer bus

B. all of the above

C. double bus, double breaker

D. single bus

58. Thermal overload relays are used to protect the motor against over current due to____________?
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A. grounds

B. heavy loads

C. all of the above

D. short-circuits

59. For cost and safety, the outdoor substations are installed for voltages above_________________?
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A. 33 kV

B. 110kV

C. 60kV

D. 11 kV

60. The steady state stability of the power system can be increased by_____________?
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A. none of the above

B. connecting lines in series

C. connecting lines in parallel

D. using machines of high impedance

E. reducing the excitation of machines

61. Oil switches are employed for_____________?
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A. low currents circuits

B. all circuits

C. low voltages circuits

D. high voltages and large currents circuits
62. Protection by fuses is generally not used beyond__________?
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A. 20 A

B. 100 A

C. 50 A

D. 200 A

63. The reflection co-efficient at the open circuited end of a transmission line___________?
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A. infinity

B. none of the above

C. zero

D. unity
64. Insulation resistance of high voltage circuit breakers is more than________________?
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A. 100 mega ohms

B. 500 mega ohms

C. 1 mega ohms

D. 10 mega ohms

65. Which of the following statements is incorrect ?
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A. Lightning arrestors are used before the switchgear

B. The peak short current is (1.8 xV2) times the A.C. component

C. Shunt reactors are used as compensation reactors

D. The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance

66. The short circuit in any winding of the transformer is the result of______________?
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A. mechanical vibration

B. loose connection

C. impulse voltage

D. insulation failure

67. The inductive interference between power and communication line can be minimized by__________?
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A. transposition of the power line

B. transposition of the communication line

C. both (A) and (B)

D. increasing the distance between the conductors

68. For which of the following ratings of the transformer differential protection is recommended ?
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A. none of the above

B. above 30 kVA.

C. equal to and above 5 MVA

D. equal to and above 25 MVA

69. Which of the following circuit breakers has high reliability and minimum maintenance ?
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A. Vacuum circuit breakers

B. Air blast circuit breakers

C. Circuit breaker with SF6 gas

D. Oil circuit breakers

70. A.C. network analyser is used to solve problems of_______________?
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A. load flow, short-circuit and stability

B. none of the above

C. load flow

D. load flow and short-circuit

E. load flow and stability

71. To reduce short circuit fault currents are used_____________?
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A. none of the above

B. capacitors

C. resistors

D. reactors
72. Which of the following devices will receive voltage surge first travelling on the transmission line ?
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A. Relays

B. Switchgear

C. Step-down transformer

D. Lightning arresters
73. Induction cup relay is operated due to changes in________________?
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A. impedance

B. voltage

C. current

D. all of the above
74. Distance relays are generally_____________?
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A. split-phase relays

B. none of the above

C. reactance relays

D. impedance relays

75. The short circuit in any winding of the transformer is the result of_______________?
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A. loose connection

B. mechanical vibration

C. insulation failure

D. impulse voltage
76. Arc in a circuit behaves as_______________?
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A. a resistance decreasing with voltage rise across the arc

B. a resistance increasing with voltage rise across the arc

C. an inductive reactance

D. a capackive reactance

77. On which of the following routine tests are conducted ?
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A. All of the above

B. Oil circuit breakers

C. Air blast circuit breakers

D. Minimum oil circuit breakers

78. Circuit breakers usually operate under______________?
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A. sub-transient state of short-circuit current

B. after D.C. component has ceased

C. steady state of short-circuit current

D. transient state of short-circuit current
79. Circuit breakers are essentially____________?
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A. circuits to break the system

B. current carrying contacts called electrodes

C. any of the above

D. transformers to isolate the two systems

E. arc extinguishers

80. Short-circuit currents are due to_______________?
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A. three phase faults

B. single phase to ground faults

C. two phase to ground faults

D. phase to phase faults

E. any of these
81. The information to the circuit breaker under fault conditions is provided by____________?
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A. all of the above

B. relay

C. rewirable fuse

D. H.R.C. only

82. The delay fuses are used for the protection of ___________?
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A. fluorescent lamps

B. motors

C. light circuits

D. power outlet circuits

83. A fuse in a motor circuit provides protection against__________?
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A. overload

B. open circuit, short-circuit and overload

C. none of the above

D. short-circuit and overload
84. Over voltage protection is recommended for______________?
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A. none of the above

B. all of the above

C. gas turbine generators

D. steam turbine generators

E. hydro-electric generators

85. Air blast circuit breaker is used for_____________?
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A. over currents

B. short duty

C. intermittant duty

D. repeated duty
86. The fuse rating is expressed in terms of_____________?
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A. voltage

B. kVA

C. VAR

D. current
87. relay is preferred for phase fault on short transmission line?
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A. Reactance

B. None of the above

C. Induction type

D. Impedance

88. relays are used for phase faults on long line?
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A. Reactance

B. Impedance

C. None of the above

D. Either of the above

89. A balanced 3-phase system consists of_______________?
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A. zero, negative and positive sequence currents

B. zero sequence currents only

C. positive sequence currents only

D. negative and zero sequence currents

90. Overfluxing protection is recommended for_____________?
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A. generator transformer of the power plant

B. station transformer of the power plant

C. distribution transformer

D. auto-transformer of the power plant

91. A fuse is never inserted in____________?
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A. phase dine

B. neutral wire

C. positive of D.C. circuit

D. negative of D.C. circuit

92. Interruption of large currents by relay requires______________?
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A. wide separation of the opened contacts

B. all of the above

C. high speed opening of contacts

D. arc suppressing blow out coils

93. The relay with inverse time characteristic will operate within____________?
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A. none of the above

B. 5 to 20 sec

C. 5 to 10 sec

D. 1.5 sec

E. 20 to 30 sec

94. transmission line has reflection coefficient as one?
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A. Open circuit

B. None of the above

C. Long

D. Short-circuit

95. Overheating of relay contacts or contact born out is due to_______________?
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A. all of the above

B. foreign matter on the contact surface

C. slow making and breaking of load circuit contacts

D. too low contact pressure

96. The voltage appearing across the contacts after opening of the circuit breaker is called__________voltage
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A. recovery

B. none of the above

C. surge

D. arc

E. operating

97. Magnetic circuit breaker has ___________ trip action
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A. delayed

B. instantaneous

C. both of the above

D. none of the above

98. The fuse wire, in D.C. circuits, is inserted in____________?
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A. negative circuit only

B. positive circuit only

C. both (A) and (B)

D. either (A) or (B)

99. Large internal faults are protected by_______________?
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A. earth fault and positive sequence relays

B. horn gaps and temperature relays

C. mho and ohm relays

D. merz price percentage differential protection
100. The material used for fuse must have_____________?
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A. low melting point and any specific resistance

B. low melting point and -low specific resistance

C. low melting point and high specific resistance

D. high melting point and low specific resistance