In this article, we shared the switchgear & protection objective questions and answers for electrical engineers and technicians.
Switchgear & Protection Objective Questions
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 |
| E) | tapping |
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
| A) | voltage |
| B) | impedance |
| C) | all of these answers |
| D) | current |
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 |
| B) | porcelain |
| C) | copper tungsten alloy |
| D) | electrolytic copper |
10. The ground wire should not be smaller than no. ____ copper
| A) | 10 |
| B) | 2 |
| C) | 4 |
| D) | 6 |
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
| A) | SF6 |
| B) | air |
| C) | oil |
| 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 |
| B) | recovery |
| C) | arc |
| D) | surge |
| E) | operating |
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
| A) | power |
| B) | all of these answers |
| C) | voltage wave |
| D) | current |
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
| A) | silver |
| B) | carbon |
| C) | graphite |
| D) | tungsten |
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?
| A) | Copper |
| B) | Tin lead alloy |
| C) | Silver |
| 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 |
| B) | directional |
| C) | impedance |
| D) | non-directional |
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 |
| B) | long |
| C) | short |
| D) | medium |
38. The fuse blows off by
| A) | arcing |
| B) | none of these answers |
| C) | melting |
| D) | burning |
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 |
| B) | reactors |
| C) | earth wires |
| D) | isolators |
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.
| A) | supply |
| B) | recovery |
| C) | peak |
| D) | restriking |
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
| A) | feeder |
| B) | transmission line |
| C) | motor |
| D) | generator |
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
| A) | short-circuits |
| B) | overload |
| C) | reverse current |
| D) | open-circuits |
57. Discrimination between main and back up protection is provided by the use of relays which are
| A) | sensitive |
| B) | fact |
| C) | none of these answers |
| D) | slow |
58. Which of the following medium is employed for extinction of arc in air circuit breaker?
| A) | SF6 |
| B) | air |
| C) | oil |
| D) | water |
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?
| A) | Inductance |
| B) | Resistance |
| C) | Capacitance |
| D) | Reactance |
61. The fuse rating is expressed in terms of
| A) | kVA |
| B) | VAR |
| C) | current |
| D) | voltage |
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 |
| B) | relay |
| 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
| A) | grounds |
| B) | heavy loads |
| C) | short-circuits |
| 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 |
| B) | interception |
| 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 |
| C) | Conservator |
| D) | Operating mechanism |
74. In the event, of a fault on connected circuit, a circuit breaker will operate
| A) | manually through control switch |
| B) | manually |
| C) | depends on the design |
| D) | automatically |
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
| A) | infinity |
| B) | none of these answers |
| C) | unity |
| D) | zero |
80. To protect most of the electrical equipment handling low power, the types of relays used are
| A) | thermocouple |
| 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 |
| B) | fire |
| 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 |
| C) | temperature |
| 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
| A) | amperes |
| B) | MVA |
| C) | MW |
| D) | none of these answers |
| E) | volts |
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 |
| E) | Phase-to-phase |
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 |
| B) | transformers |
| C) | motors |
| D) | busbars |
| E) | generators |
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 |
| D) | motors |
113. Overload relays are of ____ type.
| A) | induction |
| B) | all of these answers |
| C) | solid state |
| D) | thermal |
114. ____ transmission line has reflection coefficient as one.
| A) | Long |
| B) | None of these answers |
| C) | Open circuit |
| D) | Short-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 |
| B) | alternators |
| 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 |
| B) | Relays |
| C) | Lightning arresters |
| D) | Switchgear |
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 |
| D) | Isolator |
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
| A) | overloads |
| B) | none of these answers |
| C) | short-circuits |
| 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
| A) | temperature |
| B) | short-circuit |
| C) | overload |
| D) | overvoltage |
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?
| A) | Transformers |
| B) | Transmission line |
| C) | Generators |
| D) | Motors |
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?
| A) | Unity |
| B) | None of these answers |
| C) | Infinity |
| D) | Zero |
135. ____ relay is preferred for phase fault on the short transmission lines.
| A) | Impedance |
| B) | None of these answers |
| C) | Reactance |
| 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 |
| B) | pyrometer |
| C) | thermometer |
| D) | thermocouple |
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 |
| C) | Switchgear |
| D) | Alternators |
143. The least number of faults are generally reported for
| A) | transmission lines |
| B) | transformers |
| C) | switchgears |
| D) | cables |
144. The over-voltage surges in power systems may be caused by
| A) | resonance |
| B) | switching |
| C) | any of these answers |
| D) | lightning |
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 |
| B) | reactors |
| C) | capacitors |
| D) | resistors |
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 |
| B) | Impedance |
| C) | Either Impedance or Reactance |
| D) | Reactance |
153. Fault diverters are basically
| A) | fuses |
| B) | circuit breakers |
| C) | relays |
| D) | fast switches |
154. In Railway applications ____ circuit breaker is used.
| A) | minimum oil |
| B) | SF6 |
| C) | bulk oil |
| D) | air break |
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