Protection

OBJECTIVE ELECTRICAL ENGINEERING PROTECTION

1. When all the three phase are short circuited it gives rise to:

(a) Asymmetrical fault current(b) Symmetrical fault current(c) Zero current(d) None of the above

Ans b

2. The most common type of fault on the over head lines:

(a) Single line to ground fault(b) Double into ground fault(c) Three phase fault(d) Line to line fault

Ans a

3. Reactors are used in various point in the power system to

(a) Limit short circuit current(b) Short circuit (c) Avoid short circuit(d) None of the above

Ans a

4. The use of reactor permits installation of circuit breaker of the

(a) Lower rating(b) Higher rating(c) Same rating(d) None of the above

Ans a5. If a 5 amp. Fuse is blown frequently

house lightning circuit, it is required to

(a) Insert a fuse of higher current rating

(b) Insert a fuse of higher voltage rating

(c) Check the load(d) None of above

Ans c6. H.R.C fuse provide best protection

against(a) Open circuit(b) Short circuit

(c) Over load(d) Revers current

Ans b

7. The size of each wire is determined by

(a) The amp. Capacity of service wire

(b) Atmospheric condition(c) Voltage of the size service wire(d) None of the above

Ans a8. When a fault occure on the system a

circuit breaker(a) Open the automatically(b) Close automatically(c) Open the manually(d) None of the above

Ans a9. If the lenth of the arc of circuit

breaker increase, its will(a) Be extinguished(b) Decreases(c) Remain same(d) None of the above

Ans a10. Current chopping mainly

occure in(a) Oil circuit breaker(b) Air blast circuit breaker(c) Vaccume circuit breaker(d) SF6 gas circuit breaker

Ans b11. Capacitive current breaking

result in(a) Short circuit(b) Open circuit(c) Voltage surge(d) None of the above

Ans c12. The speed of circuit breaker

intruption in forced(air)blast circuit breaker

(a) Slow(b) Medium

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(c) Fast(d) None of the above

Ans c13. The normal practice to specify

the making current of(a) Circuit breaker in turn of(b) RMS value(c) Peak value(d) Everage value

Ans b14. Resistance switching is

normally resorted in case of(a) Air blast circuit breaker(b) Bulk oil circuit breaker(c) Minimum oil circuit breaker(d) All type circuit breaker

Ans a15. For remote operation circuit

breaker must be required with a(a) Time delay trip(b) Shunt trip(c) Inverse time trip(d) None of the above

Ans b16. Which of the following circuit

breaker is generally used in railway application

(a) Air break circuit breaker(b) Minimum oil circuit breaker(c) Bulk oil circuit breaker(d) SF6 circuit breaker

Ans a17. Which of the following circuit

breaker is used for E.H.T application(a) Air blast circuit breaker(b) Minimum oil circuit breaker(c) Bulk oil circuit breaker(d) SF6 circuit breaker

Ans d18. In circuit breaker the arcing

contents are made of (a) Porsline(b) Copper tungstone alloy(c) Aluminmum alloy(d) Electronic opper

Ans b19. Which statement is correct(a) SF6 gas is toxic(b) SF6 gas is lighter than air(c) SF6 gas is yellow in colour(d) SF6 gas has cumgent smell

Ans a20. A relay performs the function

of(a) Fault isolation(b) Fault detection(c) Fault prevention(d) All of the above

Ans b21. The relay operating coil is

supplied through(a) Fuse(b) Instrument T/F(c) Power T/F(d) None of the above

Ans c22. Most of the relay on service on

electric power system are(a) Electronic relay(b) Electro mechanical relay(c) Thermal relay(d) None of the above

Ans b

23. Back-up protection is generally imployed for protection against

(a) Short circuit fault only(b) Open circuit fault only(c) Both a and b(d) None of the above

Ans a24. MHO relay is a(a) Voltage restrand directional relay(b) Voltage controlled over current

relay(c) Directional restand over current

relay(d) Directional restand over voltage

relay

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Ans a25. Different relay are mused to

protect the equipment against(a) Internal faulty(b) Reverse current(c) Over current(d) None of the these

Ans a26. The least expensive protection

for over current in L.V system is(a) Isolated(b) Oil circuit breaker(c) Reverse able fuse(d) Air breaker circuit breaker

Ans c27. Impedance relay can be used

for(a) Earth fault(b) Phase fault(c) Both (a) and (b) (d) None of these

Ans c28. If the fault occurs near the

impedance relay the V/I ratio will be(a) Higher than the value if the fault

occur away from the realy(b) Lower than the value if the fault

occur away from the relay (c) Constant for all distance (d) None of these

Ans b29. Which of the following

material can not be used for contents of switching devices

(a) Copper(b) Aluminium (c) Copper alloy(d) Siver

Ans c

30. What is the most serious problem in vaccume circuit breaker

(a) Poor arc quenching(b) Low thermal stability(c) Current chopping(d) All of these

Ans c31. The positive sequence

reactance will be equal to negative sequence reactance in case of

(a) T/F(b) Generator(c) Transmission line(d) Motor

Ans a

32. Rated making capacity of circuit breaker is equal to

(a) /2 X rated symmetrical breaking capacity

(b) 2.55 X rated symmetrical breaking capacity

(c) 1 X rated symmetrical breaking capacity

(d) None of these Ans b

33. M.H.O realy is used to protect(a) Long transmission line(b) Medium lenth transmission line(c) Short lenth transmission line(d) All of these

Ans a34. Reactance relay is used to

protection against(a) Earth fault(b) Phase fault(c) Over voltage fault(d) None of these

Ans a35. The stability of arc in vaccume

circuit breaker is depends on(a) The control material(b) Its vaccume pressure(c) The circuit paraments(d) All of these

Ans d36. Why does minimum oil circuit

breaker has less volume of oil(a) There is insulation between

contents(b) The oil between breaker contacts

has greater streath

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(c) Solid insulation is provided for insulating the contents from earth

(d) None of these Ans c

37. Arcing on transmission line is prevented

(a) By circuit breaker(b) By protective relay(c) By inductor in the neutral(d) By capacitor in the neutral

Ans c38. The energy in a lightning

strock can be as high as (a) 10 units(b) 100 units(c) 250 units(d) 1000 units

Ans c39. In what shape of conductor

corona loss is less(a) Circular(b) Oval(c) Flat(d) Any of these

Ans a40. Merze price protection is used

to protect(a) Transmission line(b) T/F and generator(c) Motor(d) T/F

Ans c41. Switching and protection are

used under taken by(a) Switch gear(b) Fuse(c) Lightning arrestor(d) Relay

Ans a42. Distance relay operation is

depends on(a) Ratio of current to current(b) Ratio of voltage to current(c) Ratio of voltage to voltage(d) None of these

Ans b

43. Which relay is used to detect and protect internal fault of T/F

(a) Buchholze relay(b) Directional relay(c) Thermal relay(d) Distance relay

Ans a44. Surge protector provide(a) High impedance to normal

voltage(b) Low impedance to surge(c) Both a and b(d) None of these

Ans c45. An isolator operate under(a) No load condition (b) Full load condition(c) 50% of full load condition (d) At fault current

Ans a46. The lightning arrestor (L.A) is

connected(a) In series in the line(b) Between line and earth(c) To a pole near the line(d) None of these

Ans b47. Relay is using induction disc

principle operate(a) Only on D.C(b) Only on A.C(c) Either on D.C or A.C(d) None of these

Ans b48. Earthing is necessary to give

protection against (a) Voltage fluctuation(b) Over loading (c) Danger of electric shock(d) High temperature of conductor

Ans c49. The primary function of a fuse

is to(a) Protect the appliances

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(b) Open the circuit (c) Prevent excessive current(d) Protect the line

Ans c50. The accepted value of

dielectric strength of T/F oil is (a) 30 KV(b) 40 KV(c) 30 KV/minute (30 KV/2.5

mm/minute(d) None of these

Ans c51. As compare to air the relative

dielectric strength of SF6 gas is nearly (more)

(a) 1.5 times(b) 4 times(c) 2.5 times(d) 5 times

Ans b52. Which of the following gas has

been used as insulating medium in electrical appliances

(a) Nitrogen(b) Carbon dioxide (c) Sulphur haxa floride (SF6)(d) Freon

Ans c53. Liquids are generally used as

insulating material upto stress of about

(a) 100 M volt/cm(b) 50 mv/cm(c) 50 kv/cm(d) 500 kv/cm

Ans c54. Low voltage circuit breaker

has rated voltage less than(a) 66 KV(b) 33 KV(c) 11 KV(d) 1000 volt

Ans d55. When a H.V circuit breaker is

tested for inductance it is tested for at least

(a) 5000 open-closing operation(b) 3600 open-closing operation(c) 1000 open-closing operation(d) None

Ans c56. For H.V ac circuit breaker the

rated short circuit current is passed for

(a) 12 second(b) 3 second(c) 9 second(d) None

Ans c57. Air blast circuit breaker, the

pressure of air is of the order of(a) 40-50 kg/cm2

(b) 3-5 kg/cm2

(c) 1-3 kg/cm2

(d) 20-30 kg/cm2

Ans d58. The pressure of SF6 gas in

circuit is of the order of 1-14 kg/cm2 (a) 3-5 kg/cm2

(b) 20-30 kg/cm2

(c) 18-20 kg/cm2

(d) None Ans a

59. Air blast circuit breaker can be installed on

(a) 11 kv(b) 66 kv(c) 132 kv (d) 400 kv

Ans d60. Air blast circuit breaker for

400 kv power system are designed to operate in

(a) 50 milli second(b) 5 milli second(c) 100 milli second(d) None

Ans a61. Breaking capacity of a circuit

breaker is usually expressed in term of

(a) KVA

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(b) MVA(c) KVAR(d) MVAR

Ans c62. The capacitor switching is

easily done with(a) Air blast circuit breaker(b) Oil circuit breaker(c) Vaccume circuit breaker(d) Any of above

Ans c63. The most suitable circuit

breaker for short line fault without switching resistor is

(a) Air blast circuit breaker(b) SF6 gas circuit breaker (c) Minimum oil circuit (d) None

Ans b64. For rural electrification in a

country like india with complex network. It is preffer to use

(a) Oil circuit network(b) Minimum oil circuit breaker(c) Vaccume circuit breaker(d) Air breaker C.B

Ans c65. Where voltage are high and

current to be intrupted is low. The breaker preffered is

(a) Vaccume circuit breaker(b) Oil circuit breaker(c) Air blast circuit breaker(d) Any one of the above

Ans a66. To limit current chopping in

V.C.B the contect material used has (a) Low vapour pressure and high

conductivity properties(b) Low vapour pressure and low

conductivity properties(c) High vapour pressure and low

conductivity properties(d) None of these

Ans c

67. A 3Q circuit breaker is rated at 2000 MVA 33 KV,it making current will be

(a) 69 KA(b) 89 KA(c) 49 kilo ampere(d) None of these

Ans c68. While using air blast circuit

breaker, current chopping is a phenomenon often observed, when

(a) Long over head line switched off(b) A T/F on no load switched off(c) A bank of capacitors is switched

off(d) A heavy load switched off

Ans b69. In order to quench the arc

quickly and also optimize the dimentions, generally

(a) SF6 gas circuit breaker is prefferd(b) Air blast circuit breaker is

prefferd(c) Oil circuit breaker is prefferd(d) Minimum oil circuit breaker is

prefferd Ans b

70. A circuit breaker is a(a) P.F correcting device(b) Wave shape correcting device(c) Current intrupting device(d) A device to neutralize the effect

of transient Ans c

71. Circuit breaker usually operated under

(a) Steady state short circuit current(b) Sub-transient state of short

circuit current(c) Transient state of short circuit

current(d) None of the above

Ans c72. A circuit breaker normally

operater(a) When the line is to tested(b) When the switch is put on(c) When the power is to be supplied

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(d) When ever fault occur is the line Ans d

73. While selecting a gas for circuit breaker, the property of gas, that should be considered is

(a) Non- toxicity(b) Non-inflame ability(c) High dielectric strength(d) All of these

Ans d74. The fault clearly time of a

circuit breaker is usually of(a) Few cycle of supply voltage(b) Five second(c) Five minotue(d) One minotue

Ans a75. For high voltage A.C circuit

breaker the rated short circuit current is passed for

(a) 0.01 second(b) 3 second(c) 0.1 second(d) 30 second

Ans c76. Out of the following circuit

breaker which one has the lowest voltage range

(a) Air break circuit breaker(b) Air blast circuit breaker(c) Tank type oil circuit breaker (balk

oil)(d) Minimum oil circuit breaker

Ans a77. In minimum oil current

breaker, used oil for(a) Insulation only(b) Arc quenching only(c) Cooling only(d) Lubrication only

Ans c78. The medium used for arc

aretinction in the air circuit breaker is

(a) Oil(b) SF6 gas

(c) Air(d) Compressed air

Ans b79. Air used in air blast circuit

breaker must(a) Have least cor(b) Be-oinized (c) Have oil mixed(d) Be free from moisture

Ans d80. Under normal condition a

circuit breaker should be inspected(a) Every day(b) Once in six month or 12 month(c) Every week(d) Once in six years to 7 years

Ans c81. In a vaccume circuit breaker,

the vaccume in the order of(a) 1 torr(b) 10-12 torr(c) 10-6 torr(d) 10-16 torr

Ans b82. Plane break oil circuit breaker

can be used upto(a) 11 kv(b) 33 kv(c) 1.1 kv(d) 132 kv

Ans a83. For E.H.V line, which of the

following circuit breaker is preffered(a) Air breaker circuit breaker(b) Bulk oil circuit breaker minimum

oil circuit breaker(c) Minimum oil circuit breaker(d) Any of the above

Ans c84. Air blast circuit breaker for

400 KV power system are designed to operate in

(a) 5 milli second(b) 500 milli second(c) 50 milli second(d) None of the above

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Ans b85. For high speed circuit breaker

the total clearing time is nearly (a) 1-2 cycle(b) 50 cycle(c) 7-12 cycle(d) 60 cycle

Ans a86. If the least of the all of circuit

breaker is increased its resistance will

(a) Increase(b) Remain same(c) Decreases(d) None of these

Ans a87. If the dielectric strength of the

medium between contects build up more rapidly than the re-striking voltage, then the arc will

(a) Be extinguished(b) Not be extinguished(c) Increase(d) None of the above


breaker take minimum time for installation

(a) Air blast circuit breaker(b) Minimum oil circuit breaker(c) Bulk oil circuit breaker(d) SF6 gas circuit breaker

Ans c89. Bulk oil circuit breaker is

suitable for voltage upto (a) 6.6 kv(b) 11 kV(c) 36 KV(d) 132 KV

Ans c90. Which of the following circuit

breaker is most popular for out ultra H.V application

(a) Air blast circuit breaker(b) Minimum oil circuit breaker(c) Bulk oil circuit breaker (d) Vaccume circuit breaker

Ans a91. The voltage across the circuit

breaker pole, after final current zero is

(a) Recovery voltage(b) Re-striking voltage(c) Supply voltage(d) None of these


breaker does not use pneumatic operating mechanism

(a) Air blast circuit breaker(b) SF6 gas circuit breaker(c) Air blast circuit breaker(d) Bulk oil circuit breaker

Ans d93. Rutien tests are conductor on(a) Minimum oil circuit breaker(b) Air blast circuit breaker(c) Oil circuit breaker(d) All of the above

Ans d94. In modern E.H.V circuit

breaker the operating time between instant of receiving tripp single and final contect separation is of the order of

(a) .001 second(b) .015 second(c) .003 second(d) .03 second

Ans d95. The circuit breaker which have

high relabilty and negaligible maintenance

(a) Air blast circuit breaker(b) Minimum oil circuit breaker(c) SF6 gas circuit breaker(d) Bulk oil circuit breaker

Ans c96. For modern circuit breaker,

the time of closing the cycle is(a) .001 second(b) .1 second(c) .01 second(d) .003 second

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Ans c97. The arc voltage produced in

A.C circuit breaker is always(a) Leading the arc current by 900

(b) Lagging the arc current by 900

(c) In phase with the arc current(d) None of the above

Ans c98. The transient stability of

power system can be effectively improved by

(a) Excitation control (b) Phase shifting transformer(c) Single pole switching circuit

breaker(d) Increasing the turbine value

opening Ans c

99. Which of the circuit breaker is costly

(a) Air blast circuit breaker(b) SF6 gas circuit breaker(c) Minimum oil circuit breaker(d) None of these

Ans a100. The speed of circuit

instruption in forsed air blast circuit breaker is

(a) Slow(b) Fast(c) Medium(d) None of above

Ans c101. The fault current intrupted by

modern circuit breaker attain value as high as

(a) 10000 amp(b) 100000 amp(c) 60000 amp(d) None of above

Ans b102. In modern breaker at the time

fault current the temperature inside rise up to

(a) 30000 0C(b) 90000 0C(c) 60000 0C

(d) None Ans a

103. The circuit breaker of least design, are capable of intrupting current these condition with an arc duration of

(a) 5-20 mile second(b) 5-20 second(c) 5-20 minute(d) None of the above

Ans a104. A fuse blowns of by(a) Melting(b) Arcing(c) Burning(d) None of the above

Ans a105. A fuse operate on with effect

of electric current(a) Magnetic effect(b) Heating effect(c) Electrostatic effect(d) Photo electric effect

Ans c106. A delay fuse is generally used

for the protection of(a) 3 Q motor(b) Flourocent motor(c) G.l.S lamps(d) All the above

Ans a107. As compared to rewire able

fuse a H.R.C fuse has (a) High rupturing capacity(b) High speed of operation(c) No aging effect(d) All the above

Ans d108. A fuse wire made of which

material will have relatively sharp melting action

(a) Copper(b) Tin-lead-aloy(c) Silver(d) Aluminium

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Ans b109. A fuse should have(a) Low resistance and high melting

point(b) Low resistance and low melting

point(c) High resistance and high melting

point(d) High specific resistance and low

melting point Ans d

110. In H.R.C fuse major portion of heat generated is dissipated by

(a) Conduction(b) Radiation(c) Convention(d) None of above

Ans a111. Which fuse material is more

suspected to oxcidation as compare to the remaining

(a) Tin lead alloy(b) Copper(c) Silver(d) None

Ans b112. Protection by fuse is generally

not use beyond(a) 10 A(b) 25 A(c) 100 A(d) 250 A

Ans c113. Which of the following is used

in liquid fuse (a) Carbon tetra chloride(b) Sulphur hexa floride(c) Distilled water(d) Transformer oil

Ans a114. A fuse is never instated in (a) Phase lime(b) Positive of d.c circuit(c) Negative of d.c circuit (d) Neutral wire

Ans d

115. H.R.C fuse posses(a) Linear time current characteristic(b) Inverse time current

characteristic (c) Parabolic time current

characteristic(d) None of the above

Ans b116. H.R.C fuse can be used up to(a) 100 A(b) 33 KA(c) 1000 A(d) 330 KA

Ans c117. Under fault condition

information to the circuit breaker is provided by

(a) Rewire able fuse(b) Relay(c) H.R.C fuse(d) All the above

Ans c118. Out door type switch gear is

generally used for voltage beyond(a) 11 KV(b) 66 KV(c) 33 KV(d) 132 KV

Ans b119. A high speed circuit breaker

can compleat its operation time(a) 1 micro second(b) 1 mili second(c) 2-3 cycle of frequency (d) 4-8 cycle of frequency

Ans c120. The power factor of arc in a

circuit breaker is (a) 0 lagging(b) 0 leading(c) 0.8 lagging(d) Unity

Ans d121. The time instant from the

instant opening contact to the

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instant of extinction of arc is known as

(a) Arc clearance time(b) Break time(c) Arc duration time(d) None of the above

Ans a122. The time interval from the

instant of fault to the instant of energizing the trip coil is known as

(a) Arcing time(b) Breaking time(c) Operating(d) Protection time

Ans d123. The time interval from the

instant of energizing the trip coil to the instant of opening of the contacts is known as

(a) Arcing time(b) Operating time(c) Breaking time (d) Total clearing time

Ans b124. The time interval from the

instant of fault to the instant of extinction of arc is known as

(a) Clearing time(b) Making time(c) Break time(d) None of the above

Ans a125. The breaking capacity of 3 Q

circuit breaker is given by(a) Service voltage X rated

symmetrical current(b) 3 X service voltage X rated

symmetrical current(c) /3 X service voltage X rated

symmetrical current (d) None of these

Ans c126. Which of the following is not a

part of C.breaker(a) Explosion pot(b) Current T/F(c) Fixed and moving contacts(d) Operating machenism

Ans b127. Which of the following circuit

breaker the arc energy produced will be least

(a) Air blast circuit breaker(b) Minimum oil circuit breaker(c) Plane oil circuit breaker(d) Self generated pressure oil circuit

breaker Ans a

128. Air blast circuit breaker are used above

(a) 11 KV(b) 33 KV(c) 66 KV(d) 132 KV

Ans d128 A.In case of SF6 circuit

breaker the time of intruption is(a) 1 micro second(b) 3 mili second(c) 3 second(d) 3 cycle

Ans d129. Which of the following is not

true for SF6 gas (a) SF6 gas has insulation property(b) SF6 gas is not inflame able(c) SF6 gas is poisonous(d) SF6 gas is heavier than air

Ans c130. The dielectric strength of SF6

gas at atmospheric pressure is nearly

(a) Same as that of air(b) Less than that of air(c) 21/2 time that of air(d) 10 -15 time that of air

Ans c131. The circuit breaker for E.H.T

application is (a) Air blast circuit breaker(b) SF6 gas circuit breaker(c) Minimum oil circuit breaker(d) None of these

Ans b

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132. Relay can be design to change in

(a) Voltage (b) Lightning intensity(c) Current (d) Any of the above

Ans d133. The operating time for high

speed relay is usually (a) 1 second(b) 1 mili second(c) 1-2 cycle(d) 10-15 cycle

Ans c134. The operating of a distance

relay is based on the measurement of any of the following, expect

(a) Admittance(b) Impedance(c) Reactance(d) Frequency

Ans d135. The operating time of a relay

with inverse time characteristic could be

(a) 2-3 cycle(b) 5-10 mili second(c) 2-3 micro second(d) 5-10 second

Ans a136. A single phasing relay is used

on(a) Single phase motor(b) Universal motor(c) Three phase motor(d) Three phase motor

Ans c137. In distance relay the operating

depends upon(a) Voltage(b) Voltage to current ratio(c) Current(d) None of the above

Ans c

138. Which relay is used for protection protecting a T/F against frame leakage

(a) Directional relay(b) Intentanious earth fault relay(c) Intentanious over voltage relay(d) Intentanious over current relay

Ans b139. Translay relay is suitable for(a) Feeder(b) The welding T/F(c) Alternator(d) None of the above

Ans a140. Merg price protection relay is

used for(a) Air cooled T/F(b) Alternator(c) Short transmission line(d) Long transmission line

Ans b141. MHO relay is used for(a) Long transmission line(b) Feeder(c) Alternator(d) Transformer

Ans a142. The pilot relay is provided to

obtained(a) Pre-set tripping(b) Delayed tripping (c) High speed tripping(d) None of the above

Ans c143. For the protection of radial

feeder the relay used must have(a) Linear time characteristic(b) Inverse time characteristic(c) Extetion time characteristic (d) None of the above

Ans b144. Reactance relay are used for

phase fault in (a) Long transmission line(b) Medium transmission line (c) Short transmission line

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(d) All of the above Ans c

145. In induction type relay, torque is directly proportional to

(a) Current(b) /current(c) 1/current(d) Current2

Ans d146. The relay preffered for phase

fault along long transmission line is(a) Reactance relay(b) Impedance relay(c) MHO relay(d) Buchholze relay

Ans c147. Relay preffered for phase fault

along medium transmission line is(a) MHO relay(b) Buchholze relay(c) Impedance(d) Reactance relay

Ans c148. Relay generally used for

phase fault is(a) Distance relay(b) Induction relay(c) Over current relay(d) MHO relay

Ans a149. Which of the following is not a

distance relay (a) Reactance relay(b) Induction relay(c) Buchholze relay(d) MHO relay

Ans b150. Earth fault relay are,

invariable(a) Short operating time relay(b) Long operating time relay(c) Directional relay(d) Non-directional relay

Ans c

151. A thermal protection circuit provided protection against

(a) Over voltage(b) Short circuit(c) Over load(d) Temperature rise

Ans c152. A use of air core reactors is a

generally restricted up to(a) 1.1 KV(b) 3.3 KV(c) 11 KV(d) 132 KV

Ans c153. The used oil immersed

reactance is generally restricted up to

(a) 1.1 KV(b) 33 KV(c) 11 KV(d) There is no restricted of voltage

normally Ans d

154. The reactance for the protection of transmission line are connected in

(a) Series (b) Delta(c) Parallel(d) Star

Ans a155. Any voltage surge travlling on

the transmission line, will first enter in

(a) Switch gear(b) Current transformer(c) Circuit breaker(d) Lightning arrestor

Ans d156. A lightning arrestor is always

located(a) Before the isolator(b) Before the switch gear(c) Before the transformer (d) Before the current transformer

Ans c

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157. The main purpose of providing lightning arrestor in a sub-station is to protect

(a) Circuit breaker(b) Relay(c) Transformer(d) Civil-structure

Ans c158. Explution type lightning

arrestor are used with system having operating voltage up to

(a) 11 KV(b) 33 KV(c) 1.1 KV(d) None of the above

Ans c159. Which of the following needs

to protect a direct stock due to lightning

(a) Power station(b) Sub-station(c) Over head transmission line(d) All of the above

Ans d160. Which of the following system

suffer most from arcing ground(a) Solid ground neutral system(b) Insulated neutral system(c) Resistance ground neutral

system(d) Reactance ground neutral

system Ans b

161. Which section of power system generally suffer from more fault as compared to the remaining

(a) Generator (b) Transmission line(c) Transformer(d) Under ground cable

Ans c162. Least no. of fault reported for(a) Cable(b) Switch gear(c) Transformer(d) Transmission line

Ans a

163. Batteries are provided at sub-station mainly for

(a) Emergency lightning (b) Voltage regulation(c) Trip circuit(d) Meter movement

Ans c164. The gap lenth of rod type

surge divertor used for 132 KV line should be

(a) 10 cm(b) 50 cm(c) 15 cm(d) 65 cm

Ans d165. Wave trap is use to trap wave

of(a) Low frequency (b) Higher frequency (c) Power frequency (d) Micro wave frequency

Ans c166. When a transmission line is

energized the wave that propagates it is

(a) Current wave only(b) Voltage wave only(c) Current and voltage wave only(d) None of above

Ans c167. A circuit breaker is rated at

2000 amp 1500 MVA,33 KV 3 Q, OCB, then the making current is

(a) 1.2 KA(b) 67 KA(c) 26.25 KA(d) None of above

Ans c

Breaking capacity = 1500 MVA voltage = 33 KV breaking current = 1500 MVA/3X33 KV 103 = 26.25 KA Making current = 2.55 X breaking current

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= 2.55 X 26.25 =67 KA

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Protection

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open circuit b short

short circuit d

b open circuit fault

type circuit breaker

circuit paraments d

following circuit breaker

current d

speed of circuit breaker