Switchgear and Protection MCQ

101. Single bus-bar arrangement

(a) is cheapest in initial as well as maintenance cost.
(b) provides simple operation and relaying system.
(c) has the drawback that there will be complete shutdown when fault occurs on the bus itself.
(d) all of the above.

102. Double bus-bar arrangement makes use of two identical bus-bars and has the advantage(s) that

(a) it does not require any bus coupler and permits switchover from one bus to another whenever desired.
(b) it provides maximum flexibility and reliability.
(c) either bus-bar may be taken up for maintenance.
(d) the infeed and load circuits may be divided into two separate groups.
(e) all of the above.

102. A bus coupler circuit breaker is utilized in a substation for

(a) joining the transmission line with station bus-bar.
(b) joining main and transfer bus in a substation.
(c) joining the generator with transfer.
(d) joining the neutral of the generator with earth.

103. Zero-sequence impedance of the transmission line is

(a) equal to the positive-sequence impedance of the line.
(b) about 2.5-3 times the positive-sequence impedance of the line.
(c) less than positive-sequence impedance of the line.
( d) none of the above.

104. Which is the pilotless protection method for feeder line?

(a) Differential protection.
(b) Carrier current protection.
(c) Time graded protection.
(d) None of these.

105. The most commonly used method for the protection of 3-phase feeder is

(a) time graded protection.
(b) differential protection.
(c) reverse power protection.

106. A transmission line is protected by:

(a) inrush protection.
(b) distance protection.
(c) time graded and current graded over current protection
(d) both (b) and (c)

107. In the case of transmission line protection, overcurrent used is:

(a) only up to 110 kV.
(b) only upto 220 kV.
(c) only upto 50 kV.
(d) only upto 1,100 kV.

108. Which is the main relay for protecting up to 90% of the transmission line-length in the forward direction ?

(a) Directional overcurrent relay.
(b) Mho relay.
(c) Carrier-current protective relay.
(d) Impedance relay.

109. For complete protection of a 3-phase transmission line we require

(a) three-phase and three earth fault relays.
(b) three-phase and two earth fault relays.
(c) two-phase and two earth fault relays.
(d) two-phase and one earth fault relay.

110. How many relays are used to detect interphase fault of a three-line system ?

(a) One
(b) Two
(c) Three
(d) Six

111. The transmission line distance protection relay having the property of being inherently directional is

(a) impedance relay
(b) MHO relay
(c) OHM relay
(d) reactance relay

112. Time graded protection of a radial feeder can be achieved by using

(a) definite time relays.
(b) inverse time relays.
(c) both definite and inverse time relays.
(d) none of the above.

113. For protection of parallel feeders fed from one end, the relays required are

(a) Non-directional relays at the source end and directional relays at the load end.
(b) Non-directional relays at both ends.
(c) Directional relays at source end and non-directional relays at load end.
(d) Directional relays at both ends.

114. Pilot-wire protection scheme is most economical and provides high speed relaying for

(a) short length of lines up to 15 km.
(b) medium length of lines up to 60 km.
(c) long length of lines up to 200 km.
(d) all of the above.

115. Adjustable resistors are connected in the pilot wires in order to

(a) change the phase of the current flowing through the relay.
(b) get equipotential points on pilot wires.
(c) reduce current flowing through the relay.
(d) none of the above.

116. Signal mixing transformers are used for

(a) induction disc type overcurrent relay.
(b) direction sensitive distance relay.
(c) pilot-wire feeder protection.
(d) plain differential relay.

117. In a balanced voltage pilot-wire protection scheme if the pilot-circuit gets opened, the relay will

(a) fail to trip on internal faults.
(b) trip on full load.
(c) trip instantaneously on external faults.

118. In a balanced voltage pilot-wire protection scheme, if the pilot-circuit gets short-circuited, the relay will

(a) fail to trip on internal faults.
(b) fail to trip on external faults.
(c) trip on full-load.
(d) trip instantaneously.

• Switchgear and Protection MCQ Part – 1
• Switchgear and Protection MCQ Part – 2
• Switchgear and Protection MCQ Part – 3
• Switchgear and Protection MCQ Part – 4

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