Switchgear and Protection MCQs | Switchgear and Protection Multiple Choice Questions and Answers

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Questions
1 The main function of a fuse is to
A protect the line
B open the circuit
C protect the appliance
D prevent excessive currents

Answer: prevent excessive currents
2 SF6 gas
A is yellow in colour
B is lighter than air
C is nontoxic
D has pungent small

Answer: is nontoxic
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3 With which of the following, a circuit breaker must be equipped for remote operation ?
A Inverse time trip
B Time-delay trip
C Shunt trip
D None of the above

Answer: Shunt trip
4 Arc in a circuit behaves as
A a capackive reactance
B an inductive reactance
C a resistance increasing with voltage rise across the arc
D a resistance decreasing with voltage rise across the arc

Answer: a resistance decreasing with voltage rise across the arc
5 Relays can be designed to respond to changes in
A resistance, reactance or impedance
B voltage and current
C light intensity
D all above

Answer: all above
6 D.C. shunt relays are made of
A few turns of thin wire
B few turns of thick wire
C many turns of thin wire
D many turns of thick wire

Answer: many turns of thin wire
7 Circuit breakers usually operate under
A transient state of short-circuit current
B sub-transient state of short-circuit current
C steady state of short-circuit current
D after D.C. component has ceased

Answer: transient state of short-circuit current
8 The current zero interruption, in oil and air blast circuit breakers, is achieved by
A Lengthening Of The Gap
B Cooling And Blast Effect
C Both (A) And (B)
D Deionizing The Oil With Forced Air

Answer: Both (A) And (B)
9 Directional relays are based on flow of
A Power
B Current
C Voltage Wave
D All Of The Above

Answer: Power
10 A differential relay measures the vector difference between
A two currents
B two voltages
C two or more similar electrical quantities
D none of the above

Answer: two or more similar electrical quantities
11 When a transmission line is energized, the wave that propagates on it is
A current wave only
B voltage wave only
C both (a) and (b)
D power factor wave only

Answer: both (a) and (b)
12 Ionization in circuit breaker is facilitated by
A high temperature
B increase of mean free path
C increasing field strength
D all of the above

Answer: all of the above
13 Shunt capacitance is neglected while considering
A short transmission line
B medium transmission line
C long transmission line
D medium and long transmission lines

Answer: short transmission line
14 The time of closing the cycle, in modern circuit breakers is
A 0.003 sec
B 0.001 sec
C 0.01 sec
D 0.10 sec

Answer: 0.003 sec
15 Which of the following is the least expensive protection for overcurrent is low voltage system ?
A Rewireable fuse
B Isolator
C Oil circuit breaker
D Air break circuit breaker

Answer: Rewireable fuse
16 The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to
A lubricate the contacts
B insulate the contacts from switch body
C extinguish the arc
D all of the above

Answer: extinguish the arc
17 To protect most of the electrical equipment handling low power, the types of relays used are
A Thermocouple
B Electronic And Bimetallic
C Both (A) And (B)
D None Of The Above

Answer: Both (A) And (B)
18 The reflection co-efficient at the open circuited end of a transmission line.
A Zero
B Infinity
C Unity
D None Of The Above

Answer: Unity
19 When a wave propagates on a transmission line, it suffers reflection several times at
A Tapping
B Load End
C Sending End
D Sending And Other End

Answer: Sending And Other End
20 Discrimination between main and back up protection is provided by the use of relays which are
A Fact
B Sensitive
C Slow
D None Of The Above

Answer: Slow
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