Switchgear & Protection Objective Questions and Answers

In this article, we shared the switchgear & protection objective questions and answers for electrical engineers and technicians.

Switchgear & Protection Objective Questions

Switchgear & Protection Objective Questions and Answers

The below list provides all the multiple-choice questions related to Switchgear & Protection.

Answers are available at the bottom of the article.

1. When a wave propagates on a transmission line it suffers reflection several times at

A)sending and other end
B)load end
C)all of these answers
D)sending end

2. The material used for bus bars should have

A)low cost
B)higher softening temperature
C)all of these answers
D)low resistivity

3. A differential relay measures the vector difference between

A)two currents
B)two voltages
C)two or more similar electrical quantities
D)none of these answers

4. Arc in a circuit behaves as

A)a resistance increasing with voltage rise across the arc
B)an inductive reactance
C)a capacitive reactance
D)a resistance decreasing with voltage rise across the arc

5. Induction cup relay is operated due to changes in

C)all of these answers

6. Series reactors should have

A)high impedance
B)low impedance
C)high resistance
D)low resistance

7. Insulation resistance of high voltage circuit breakers is more than

A)1 mega ohms
B)500 mega ohms
C)100 mega ohms
D)10 mega ohms

8. In circuit breakers, the advantage of using oil as a quenching medium is

A)absorption of arc energy
B)oil acts as insulator
C)oil has high dielectric strength
D)all of these answers

9. The arcing contacts in a circuit breaker are made of

A)aluminium alloy
C)copper tungsten alloy
D)electrolytic copper

10. The ground wire should not be smaller than no. ____ copper


11. A switchgear is device used for

A)switching an electrical circuit
B)circuit and equipment
C)switching, controlling and protecting the electrical
D)interrupting an electrical circuit
E)switching and controlling an electrical circuit

12. In a contactor, interrupting medium may be

D)​​all of the answers

13. The contact space in circuit breakers is ionized by

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

14. A lightning arrester provides

A)a high resistance path between line and ground, during operation
B)a low impedance path between line and ground, during operation
C)a low resistance path between line and ground, during operation
D)a high impedance path between line and ground, during operation

15. ​SF6 ​gas is transported in

A)solid form in boxes
B)none of these answers
C)gas cylinders
D)air cylinders
E)liquid form in cylinders

16. With which of the following a circuit breaker must be equipped for remote operation?

A)All of these answers
B)Inverse time trip
C)None of these answers
D)Shunt trip
E)Time-delay trip

17. Circuit breakers usually operate under

A)after D.C. component has ceased
B)steady state of short-circuit current
C)sub-transient state of short-circuit current
D)transient state of short-circuit current

18. When a transmission line is energized, the wave that propagates on it is

A)power factor wave only
B)current wave only
C)voltage wave only
D)current wave only and voltage wave only

19. If the fault occurs near the impedance relay, the V/I ratio will be

A)higher than that of if fault occurs away from the relay
B)lower than that of if a fault occurs away from the relay
C)none of these answers
D)constant for all distances

20. The voltage appearing across the contacts after opening of the circuit breaker is called ____ voltage.

A)none of these answers

21. Air blast circuit breakers for 400 kV power system are designed to operate in

A)0.1 sec
B)0.5 sec
C)50 milli-second
D)100 micro-second

22. Switching over voltages arc more hazardous than lightning surges in case of

A)low voltages
B)unbalanced systems
C)EHV and UHV systems
D)none of these answers
E)11 kV systems

23. The main function of a fuse is to

A)protect the line
B)prevent excessive currents
C)protect the appliance
D)open the circuit
E)none of these answers

24. Protective relays are devices that detect abnormal conditions in electrical circuits by measuring

A)current during abnormal condition
B)none of these answers
C)voltage during abnormal condition
D)constantly the electrical quantities which differ during normal and abnormal conditions

25. Which of the following is used in liquid fuses?

A)Transformer oil
B)Sulfur hexafluoride
C)Distilled water
D)Carbon tetrachloride

26. Directional relays are based on the flow of

B)all of these answers
C)voltage wave

27. The inductive interference between power and communication line can be minimized by

A)both transposition of the power line and transposition of the communication line
B)increasing the distance between the conductors
C)transposition of the communication line
D)transposition of the power line

28. Interruption of large currents by relay requires

A)all of these answers
B)high-speed opening of contacts
C)wide separation of the opened contacts
D)arc suppressing blow out coils

29. Minimum arcing voltage will be least in case of


30. In a circuit breaker the basic problem is to

A)maintain the arc
B)extinguish the arc
C)emit the ionizing electrons
D)transmit large power

31. Air blast circuit breaker is used for

A)short duty
B)intermittant duty
C)over currents
D)repeated duty

32. A.C. network analyzer is used to solve problems of

A)load flow and stability
B)load flow
C)none of these answers
D)load flow and short-circuit
E)load flow, short-circuit, and stability

33. Which fuse material is more susceptible to oxidation as compared to the remaining?

B)Tin lead alloy
D)all of these answers

34. Circuit breakers are essentially

A)current-carrying contacts called electrode
B)arc extinguishers
C)any of these answers
D)circuits to break the system
E)transformers to isolate the two systems

35. Admittance relay is ____ relay.

A)none of these answers

36. The rating of a circuit breaker is generally determined on the basis of

A)double line to ground fault current
B)symmetrical fault current
C)single line to ground fault current
D)line-to-line fault current

37. Reactance relays are used for phase fault in ____ line.

A)all of these answers

38. The fuse blows off by

B)none of these answers

39. The short circuit in any winding of the transformer is the result of

A)insulation failure
B)mechanical vibration
C)impulse voltage
D)loose connection

40. Thermal circuit breaker has

A)delayed trip action
B)instantaneous trip action
C)delayed trip action & instantaneous trip action
D)none of these answers

41. Burden of a protective relay is the power

A)absorbed by the circuit of relay
B)none of these answers
C)developed by the relay circuit
D)required to operate the circuit breaker

42. For which of the following ratings of the transformer differential protection is recommended?

A)equal to and above 25 MVA
B)none of these answers
C)equal to and above 5 MVA
D)above 30 kVA

43. To limit short-circuit current in a power system ____ is used.

A)H.R.C. fuses
C)earth wires

44. A fuse is never inserted in

A)negative of D.C. circuit
B)positive of D.C. circuit
C)phase line
D)neutral wire

45. Wave trap is used to trap waves of

A)higher frequencies entering generator or transformer units
B)none of these answers
C)power frequencies
D)either power frequencies or higher frequencies entering generator or transformer units

46. Ionization in circuit breaker is facilitated by

A)increase of mean free path
B)high temperature
C)increasing field strength
D)all of these answers

47. Bus coupler is very essential in ____ arrangement

A)double bus, double breaker
B)all of these answers
C)main and transfer bus
D)single bus

48. The transient voltage that appears across the contacts at the instant of arc extinction is called ____ voltage.


49. On which of the following routine tests are conducted?

A)All of these answers
B)Air blast circuit breakers
C)Minimum oil circuit breakers
D)Oil circuit breakers

50. The power loss is an important factor for the design of

B)transmission line

51. D.C. shunt relays are made of

A)few turns of thin wire
B)few turns of thick wire
C)many turns of thick wire
D)many turns of thin wire

52. Air used in air blast circuit breaker

A)must have oil mist
B)must have least​
C)must be ionized
D)must be free from moisture

53. The line insulation is ____ the insulation level of the station equipment.

A)not directly related with
B)less than
C)more than
D)proportional to
E)same as

54. The advantage of neutral earthing is

A)over voltages due to lightning can be discharged to the earth
B)all of these answers
C)simplified design earth fault protection
D)freedom from persistent arcing grounds

55. Resistance grounding is used for voltage between

A)none of these answers
B)33 kV to 66 kV
C)11 kV to 33 kV
D)3.3 kV and 11 kV

56. H.R.C. fuses provide the best protection against

C)reverse current

57. Discrimination between main and back up protection is provided by the use of relays which are

C)none of these answers

58. Which of the following medium is employed for extinction of arc in air circuit breaker?


59. On which of the following effects of electric current does a fuse operates?

A)Photoelectric effect
B)Electrostatic effect
C)Heating effect
D)Magnetic effect

60. Which of the following parameter can be neglected for a short line?


61. The fuse rating is expressed in terms of


62. Oil switches are employed for

A)all circuits
B)high voltages and large currents circuits
C)low currents circuits
D)low voltages circuits

63. The information to the circuit breaker under fault conditions is provided by

A)H.R.C. only
C)all of these answers
D)rewirable fuse

64. H.R.C. fuse, as compared to a rewirable fuse, has

A)high speed of operation
B)no ageing effect
C)high rupturing capacity
D)all of these answers

65. The single phasing relays are used for the protection of

A)three phase motors
B)two phase motors only
C)two single phase motors running in parallel
D)single phase motors only

66. Ungrounded neutral transmission system is not recommended because of system

A)all of these answers
B)being inadequately protected against ground fault
C)insulation overstress may lead to failure and subsequent phase to phase faults
D)insulation being overstressed clue to over voltages

67. The main factor in favour of the use of aluminium as bus-bar material is its

A)low melting point
B)low cost
C)high resistivity
D)low density

68. Thermal overload relays are used to protect the motor against over current due to

B)heavy loads
D)all of these answers

69. For the protection of power station buildings against direct strokes the requirements are

A)interception, conduction, dissipation and reflection
C)interception, conduction and dissipation
D)none of these answers
E)interception and conduction

70. A balanced 3-phase system consists of

A)zero, negative and positive sequence currents
B)positive sequence currents only
C)zero sequence currents only
D)negative and zero sequence currents

71. An arc in a circuit behaves like

A)an inductive reactance
B)a capacitive reactance
C)a resistance decreasing with voltage rise across the arc
D)infinite resistance

72. The positive sequence impedance of a transmission line is

A)none of these answers
B)one-third of negative sequence current
C)equal to negative sequence current
D)always zero
E)three times the negative sequence current

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

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

74. In the event, of a fault on connected circuit, a circuit breaker will operate

A)manually through control switch
C)depends on the design

75. A circuit breaker will normally operate

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

76. A fuse is connected

A)in parallel with circuit
B)none of these answers
C)either in series or in parallel with circuit
D)in series with circuit

77. Which of the following relays is used for protection of motors against overload?

A)Electromagnetic attraction type
B)Buchholz relay
C)Thermal relay
D)Impedance relay
E)None of these answers

78. Thermal relays are often employed in

A)none of these answers
B)motor starters
C)transformer protection
D)generator protection

79. The reflection coefficient at the open-circuited end of a transmission line

B)none of these answers

80. To protect most of the electrical equipment handling low power, the types of relays used are

B)electronic and bimetallic
C)thermocouple and electronic and bimetallic
D)none of these answers

81. Outdoor switchgear is generally used for voltage beyond

A)66 kV
B)33 kV
C)11 kV
D)132 kV

82. The torque produced in induction type relay (shaded pole structure) is

A)inversely proportional to the square of the current
B)inversely proportional to the current
C)proportional to the square of the current
D)proportional to the current

83. Distance relays are generally

A)impedance relays
B)split-phase relays
C)none of these answers
D)reactance relays

84. The arc voltage produced in A.C. circuit breaker is always

A)none of these answers
B)in phase with the arc current
C)leading the arc current by 90°
D)lagging the arc current by 90°

85. The most serious result of a major uncleared short-circuit fault could be

A)deterioration of insulation
C)heavy current in neutral
D)blowing off of fuse

86. Overheating of relay contacts or contact born out is due to

A)slow making and breaking of load circuit contacts
B)all of these answers
C)foreign matter on the contact surface
D)too low contact pressure

87. The relay with inverse time characteristics will operate within

A)1.5 sec
B)5 to 10 sec
C)5 to 20 sec
D)none of these answers
E)20 to 30 sec

88. In a single bus-bar system there will be complete shut down when

A)fault occurs with respect to earthing
B)fault occurs on the bus itself
C)fault occurs on neutral line
D)two or more faults occur simultaneously

89. 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)none of these answers
C)extinguish the arc
D)insulate the contacts from switch body
E)all of these answers

90. Which system will need the lightning arrester of least voltage rating?

A)Solid ground neutral system
B)Reactance grounded neutral system
C)Resistance grounded neutral system
D)Insulated neutral system

91. Relays can be designed to respond to changes in

A)voltage and current
B)resistance, reactance or impedance
D)light intensity
E)all of these answers

92. In a circuit breaker the time duration from the instant of the fault to the extinction of arc is known as

A)clearing time
B)lag time
C)lead time
D)operation time

93. A fuse wire possesses

A)inverse time characteristics
B)either direct time characteristics or inverse time characteristics
C)direct time characteristics
D)none of these answers

94. In order for that current should flow without causing excessive heating or voltage drop, the relay contacts should

A)be clean and smooth
B)be of sufficient size and proper shape
C)have low contact resistance
D)all of these answers

95. In a circuit breaker ionization is not facilitated by

A)material of contacts
B)increase of mean path
C)high temperature of surrounding medium
D)increase of field strength

96. Breaking capacity of a circuit breaker is usually expressed in terms of

D)none of these answers

97. A circuit breaker, under normal conditions, should be inspected

A)every month
B)every week
C)once in 6 months or 12 months
D)every day

98. ____ gives rise to a symmetrical fault?

A)Single phase to ground
B)Three-phase short-circuit
C)None of these answers
D)Double phase to ground

99. Arc in a circuit breaker is interrupted at

A)minimum voltage
B)maximum voltage
C)maximum current
D)zero current

100. Which of the following circuit breakers has high reliability and minimum maintenance?

A)Vacuum circuit breakers
B)Oil circuit breakers
C)Air blast circuit breakers
D)Circuit breaker with​ SF6 ​gas

101. Current limiting reactors maybe

A)oil immersed non-magnetically shielded
B)oil immersed magnetically shielded
C)any of these answers
D)air cooled air cored

102. The steady-state stability of the power system can be increased by

A)none of these answers
B)using machines of high impedance
C)connecting lines in parallel
D)reducing the excitation of machines
E)connecting lines in series

103. A differential relay responds to

A)algebraic difference between two electrical quantities
B)algebraic difference between two currents
C)vector difference between two electrical quantities
D)algebraic difference between two voltages

104. Series capacitors are used to

A)none of these answers
B)compensate for line inductive reactance
C)compensate for line capacitive reactance
D)improve line voltage

105. The material used for the fuse must have

A)low melting point and any specific resistance
B)low melting point and high specific resistance
C)low melting point and low specific resistance
D)high melting point and low specific resistance

106. The fuse wire, in D.C. circuits, is inserted in

A)either negative circuit only or positive circuit only
B)positive circuit only
C)negative circuit only
D)both negative circuit only and positive circuit only

107. The use of oil-immersed reactors is generally restricted up to

A)11 kV
B)5 kV
C)normally no restriction of voltage
D)22 kV
E)33 kV

108. Over fluxing protection is recommended for

A)station transformer of the power plant
B)distribution transformer
C)auto-transformer of the power plant
D)generator transformer of the power plant

109. The under voltage relay can be used for

A)all of these answer

110. The time of closing the cycle, in modern circuit breakers is

A)0.001 sec
B)0.003 sec
C)0.10 sec
D)0.01 sec

111. Shunt capacitance is neglected while considering

A)long transmission line
B)short transmission line
C)medium and long transmission lines
D)medium transmission line

112. The delay fuses are used for the protection of

A)light circuits
B)fluorescent lamps
C)power outlet circuits

113. Overload relays are of ____ type.

B)all of these answers
C)solid state

114. ____ transmission line has reflection coefficient as one.

B)None of these answers
C)Open circuit

115. Buchholz relay cannot be used on

A)1000 kV transformers
B)500 kV transformers
C)air-cooled transformers
D)three phase transformers

116. Which of the following statements is incorrect?

A)The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
B)The peak short current is (1.8 X √2) times the A.C. component
C)Lightning arrestors are used before the switchgear
D)Shunt reactors are used as compensation reactors

117. The inverse definite mean time relays are used for over current and earth fault protection of ​ transformer against

A)external short-circuits
B)all of these answers
C)heavy loads
D)internal short-circuits

118. Merz-Price protection is used for

A)short transmission lines
C)air cooled transformers
D)long transmission lines

119. Which of the following devices will receive voltage surge first traveling on the transmission line?

A)Step-down transformer
C)Lightning arresters

120. An isolator is installed

A)to operate the relay of circuit breaker
B)as a substitute for circuit breaker
C)always independent of the position of circuit breaker
D)generally on both sides of a circuit breaker

121. Short-circuit currents are due to

A)three phase faults
B)any of these answers
C)phase to phase faults
D)two phase to ground faults
E)single phase to ground faults

122. Which of the following is the least expensive protection for overcurrent is low voltage system?

A)Oil circuit breaker
B)Air break circuit breaker
C)Rewireable fuse

123. For cost and safety, the outdoor substations are installed for voltages above

A)60 kV
B)11 kV
C)33 kV
D)110 kV

124. Large internal faults are protected by

A)horn gaps and temperature relays
B)merz price percentage differential protection
C)earth fault and positive sequence relays
D)mho and ohm relays

125. H.R.C. fuses provide best protection in case of

B)none of these answers
D)open circuits

126. The relay operating speed depends upon

A)the spring tension
B)all of these answers
C)armature core air gap
D)the rate of flux built up

127. The pilot relay is provided to obtain

A)preset tripping
B)none of these answers
C)delayed tripping
D)high speed tripping

128. An efficient and a well designed protective relaying should have

A)economy and simplicity
B)high speed and selectivity
C)all of these answers
D)good selectivity and reliability

129. A thermal protection switch can protect against


130. Basically, a lightning arrester is a

A)surge absorber
B)surge diverter
C)surge alternator
D)surge reflector

131. For which of the following protection from negative sequence currents is provided?

B)Transmission line

132. Surge modifiers are used to

A)reduce the voltage of wave front
B)reduce the current of wave front
C)reduce the sleepness of wave front
D)modify the shape of wave front

133. The current zero interruption, in oil and air blast circuit breakers, is achieved by

A)both lengthening of the gap and cooling and blast effect
B)cooling and blast effect
C)lengthening of the gap
D)none of these answers
E)deionizing the oil with forced air

134. What will be the reflection coefficient of the wave of load connected to the transmission line if the surge impedance of the line is equal to the load?

B)None of these answers

135. ____ relay is preferred for phase fault on the short transmission lines.

B)None of these answers
D)Induction type

136. Which of the following statements is incorrect?

A)Station batteries are used to operate relay only
B)A high speed relay has an operation of 1 to 2 cycles
C)An impedance relay has maximum fault current when fault occurs near the relay
D)The lightning arresters are basically surge diverters

137. A ____ is used to measure the stator winding temperature of the generator.

A)resistance thermometer

138. The total time for high-speed breakers in nearly

A)five cycles
B)half cycle
C)one cycle
D)few cycles

139. A short-circuit is identified by

A)heavy current flow
B)voltage rise
C)voltage drop
D)no current flow

140. Which of the following protective devices can be used against lightning surges?

A)Any of these answers
B)Lightning arrestors
C)Surge diverters
D)Horn gap

141. ​SF6 ​gas

A)is lighter than air
B)none of these answers
C)is yellow in colour
D)is non-toxic
E)has pungent small

142. Which portion of the transmission system is least prone to faults?

A)Overhead lines
B)None of these answers

143. The least number of faults are generally reported for

A)transmission lines

144. The over-voltage surges in power systems may be caused by

C)any of these answers

145. The breaking capacity of a 3-phase circuit breaker is given by

A)3 x service voltage x rated symmetrical current
B)√3 x service voltage x rated symmetrical current
C)none of these answers
D)2 x service voltage x rated symmetrical current

146. An earth conductor provided on the top of the transmission line provides protection against

A)all of these answers
B)electrostatically induced voltage due to a charged cloud
C)travelling waves
D)direct lightning stroke

147. The interaction between a transmission line and communication line is minimized by

A)transposing transmission as well as communication lines
B)all of these answers
C)increasing the height of the transmission line tower
D)increasing the distance between the two lines

148. To reduce short circuit fault currents ____ are used

A)none of these answers

149. Magnetic circuit breaker has ____ trip action.

A)Electrical Welding
B)none of these answers
C)both Electrical Welding and Electrical Welding
D)Electrical Welding

150. Protection by fuses is generally not used beyond

A)50 A
B)20 A
C)100 A
D)200 A

151. A transmission line is protected by

A)time graded and current graded over current protection
B)none of these answers
C)both distance protection and time graded and current graded over current protection
D)inrush protection
E)distance protection

152. ___ relays are used for phase faults on long line.

A)None of these answers
C)Either Impedance or Reactance

153. Fault diverters are basically

B)circuit breakers
D)fast switches

154. In Railway applications ____ circuit breaker is used.

A)​minimum oil​
C)​​bulk oil
D)​​air break

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