EE 8 - Circuit Breaker, Generation of Electric Power

The function of protective relay in a circuit breaker is

A. to earth any stray voltages

B. to close the contacts when the actuating quantity reaches a certain predetermined value

C. to limit arcing current during the operation of circuit breaker

D. to provide additional safety in the operation of circuit breaker

B. to close the contacts when the actuating quantity reaches a certain predetermined value

Low voltage circuit breakers have rated voltages of less than

A. 220 V

B. 400 V

C. 1000 V

D. 10,000 V

C. 1000 V

A relay in which the measurement is performed by a stationary circuit and which has no moving parts

is known as

A. Static relay

B. Differential relay

C. Instantaneous relay

D. Time relay

A. Static relay

When a H.V. ac circuit breaker is tested for endurance, it is tested for at least

A. 1000 opening-closing operations

B. 100 opening-closing operations

C. 10 opening-closing operations

D. 5 opening-closing operations

A. 1000 opening-closing operations

For high voltage ac circuit breakers, the rated short circuit current is passed for

A. 0.01 sec

B. 0.1 sec

C. 3 sec

D. 30 sec

C. 3 sec

Which of the following is not a type of contactor for circuit breakers?

A. electromagnetic

B. electro-pneumatic

C. pneumatic

D. vacuum

D. vacuum

Interrupting medium in a contactor may be

A. air

B. oil

C. SF6 gas

D. any of the above

D. any of the above

In air blast circuit breakers, the pressure of air is of the order of

A. 100 mg Hg

B. 1 kg/cm2

C. 20 to 30 kg/cm2

D. 200 to 300 kg/cm2

C. 20 to 30 kg/cm2

SF6 gas

A. is lighter than hydrogen

B. is lighter than air

C. has density 2 times as compared to that of air

D. has density 5 times as compared to that of air

D. has density 5 times as compared to that of air

The pressure of SF6 gas in circuit breakers is of the order of

A. 100 mg Hg

B. 1 kg/cm2

C. 3 to 5 kg/cm2

D. 30 to 50 kg/cm2

C. 3 to 5 kg/cm2

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

A. high dielectric strength

B. non-inflammability

C. non-toxicity

D. none of the above

D. none of the above

Out of the following circuit breakers, which one has the lowest voltage range?

A. air-break circuit breaker

B. tank type oil circuit breaker

C. Air-blast circuit breaker

D. SF6 circuit breaker

A. air-break circuit breaker

Which of the following circuit breaker can be installed on 400 kV line

A. Tank type coil circuit breaker

B. Miniature circuit breaker

C. Vacuum circuit breaker

D. Air blast circuit breaker

D. Air blast circuit breaker

In a HRC fuse the time between cut-off and final current zero, is known as

A. total operating time

B. arcing time

C. pre-arcing time

D. any of the above

B. arcing time

The insulation resistance of high voltage electric circuit breaker is

A. 1 k Ω

B. 10 k Ω

C. 20 Mega ohms

D. 2000 Mega ohms

D. 2000 Mega ohms

15. Fusing factor for HRC fuse is

A. Minimum Fusing current / current rating

B. Minimum Fusing current / Minimum rupturing time

C. Maximum fusing current / Minimum rupturing time

D. Prospective current of a circuit / Minimum fusing current

A. Minimum Fusing current / current rating

There is definite objection to use of which of the following medium for extinguishing the arc in case

of a circuit breaker?

A. Air

B. SF6 gas

C. Vacuum

D. Water

D. Water

In a circuit breaker if the insulation resistance between phase terminal earthed frame is less than the specified limit, the probable cause could be

A. moisture

B. dirty insulation surface

C. carbon or copper particle sticking to the internal surface

D. any of the above

D. any of the above

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

A. recovery voltage

B. restriking voltage

C. supply voltage

D. peak voltage

B. restriking voltage

In a circuit breaker the active recovery voltage depends upon

A. power factor

B. armature reaction

C. circuit conditions

D. all of the above

D. all of the above

Best protection is provided by HRC fuse in case of

A. Open circuits

B. Short circuits

C. Over loads

D. None of the above

B. Short circuits

A fuse wire possesses

A. inverse time characteristics

B. direct time characteristics

C. neither of the above

A. inverse time characteristics

A relay used for protection of motors against overload is

A. impedance relay

B. Electromagnetic attraction type

C. Thermal relay

D. Buchholz’s relay

C. Thermal relay

Fuse protection is used for current ratings up to

A. 10 A

B. 20 A

C. 50 A

D. 100 A

D. 100 A

The fuse current in ampere is related with fuse wire diameter D as

A. 1 α 1/D

B. . 1 α D

C. 1 α D^3/2

^D. 1 α D²

C. 1 α D^3/2

A fuse wire should have

A. low specific resistance and high melting point

B. low specific resistance and low melting point

C. high specific resistance and high melting point

D. high specific resistance and low melting point

D. high specific resistance and low melting point

Fuse wire protection system is usually used beyond

A. 10 A

B. 25 A

C. 50 A

D. 100 A

D. 100 A

For extra high voltage lines which circuit breaker is preferred

A. Bulk oil circuit breaker

B. Vacuum circuit breaker

C. SF6 gas circuit breaker

D. Minimum oil circuit breaker

D. Minimum oil circuit breaker

The number of cycles in which a high speed circuit breaker can complete its operation is

A. 3 to 8

B. 10 to 18

C. 20 to 30

D. 40 to 50

A. 3 to 8

A material best suited for manufacturing of fuse wire is

A. Aluminum

B. Silver

C. Lead

D. Copper

B. Silver

In a circuit breaker, the current which exists at the instant of contact separation is known as

A. restriking current

B. surge current

C. breaking current

D. recovery current

C. breaking current

A Merz-Price protection is suitable for

A. transformers

B. alternators

C. feeders

D. transmission lines

B. alternators

‘Kick fuse’ has

A. square law characteristics

B. linear characteristics

C. inverse characteristics

D. direct characteristics

C. inverse characteristics

Air-blast breakers for 400 kV power systems are designed to operate in

A. 50 microseconds

B. 50 milliseconds

C. 500 milliseconds

D. 50 seconds

B. 50 milliseconds

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

A. amperes

B. volts

C. MW

D. MVA

D. MVA

Which of the following equations correctly represents the relation between contact resistance r and the applied force F?

A. F = k.r

B. F = k / r

C. r = k/Fⁿ

^D. r = kFⁿ

C. r = k/Fⁿ

As the force on contact is increased, the contact resistance will

A. increase linearly

B. increase exponentially

C. remain altered

D. decrease

D. decrease

The heat produced at the contact point, due to passage of current, will least depend on

A. contact resistance

B. time during which the current flows

C. current flowing

D. temperature of the surrounding medium

D. temperature of the surrounding medium

39. Minimum arcing voltage for platinum is 16 V. It can be therefore concluded that when the voltage is

below 16V

A. it will not possible to interrupt the circuit

B. it will possible to pass the current

C. it will be possible to interrupt any value of current without arcing

D. it will be possible to interrupt any value of current without bringing contact closer to another

C. it will be possible to interrupt any value of current without arcing

Which of the following is not the method of arc dispersion?

A. oil immersion contacts

B. magnetic blow out of arc

C. use of rectifiers

D. deionization of arc path

C. use of rectifiers

Which of the following contact point metals has the highest melting point?

A. Silver

B. Tungsten

C. Gold

D. Copper

C. Gold

The arc voltage produced in the circuit breaker is always

A. in phase with arc current

B. leading the arc current by 90 degrees

C. lagging the arc current by 90 degrees

D. leading the arc current by 45 degrees

A. in phase with arc current

Sparking between contacts can be reduced by

A. inserting resistance line

B inserting a capacitor in series with the contacts

C. inserting a capacitor in parallel with the contacts

D. inserting an inductor in series with the contacts

C. inserting a capacitor in parallel with the contacts

44. For magnetic blow out of arc the magnetic field is produced

A. in the load circuit

B. parallel to the axis of the arc

C. at right angle to the axis of the arc

D. at 45 degrees with respect to the axis of the arc

C

Sparking occurs when a load is switched off because the circuit has

A. high inductance

B. high capacitance

C. high resistance

D. low resistance

A. high inductance

For the same current, which of the following fuse wires will have the least fusing time?

A. 18 SWG TIN – 12.5 A

B. 20 SWG TIN – 10 A

C. 22 SWG TIN – 7.5 A

D. 24 SWG TIN – 5 A

D. 24 SWG TIN – 5 A

An automatic device that operates at present value is known as

A. mercury switch

B. relay

C. fuse

D. contactor

B. relay

The basic function of a circuit breaker is to

A. produce arc

B. ionize the surrounding air

C. transmit voltage by arcing

D. extinguish the arc

D. extinguish the arc

The power factor of arc in the circuit breaker is

A. always zero

B. always unity

C. always lagging

D. always leading

B. always unity

Flame proof switch gears are usually preferred

A. on transmission lines of low voltage

B. substations

C. in mines

D. in high MVA capacity circuits

C. in mines

Air is used in air-blast circuit breaker

A. must have least carbon dioxide

B. must be ionized

C. must be free from moisture

D. none of these

D. none of these

In a circuit breaker the time duration from the instant of fault to the instant of energizing of the trip coil is known as

A. lag time

B. lead time

C. protection time

D. operation time

C. protection time

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

A. operation time

B. total clearing time

C. lag time

D. lead time

B. total clearing time

In a circuit breaker the time duration from the instant of fault to the instant of closing of contact is known as

A. recycle time

B. total time

C. gross time

D. reclosing time

D. reclosing time

For high speed circuit breaker the total clearing time is nearly

A. 1 to 2 cycles

B. 5 to 10 cycles

C. 10 to 15 cycles

D. less than 50 cycles

A. 1 to 2 cycles

If the power is zero, the active recovery voltage will be

A. minimum

B. 0.5

C. 0.707

D. maximum

D. maximum

A circuit breaker will normally operate

A. when the switch is put on

B. when the line is to be checked

C. when the power is to be supplied

D. whenever fault in the line occurs

D. whenever fault in the line occurs

58. Which of the following circuit breaker will produce the least arc energy?

A. minimum oil circuit breaker

B. air blast circuit breaker

C. plain oil circuit breaker

D. all will produce the same energy

B. air blast circuit breaker

The breaking capacity of a circuit breaker in MVA ( 3 phase ) is given by

A. rated service voltage x rated symmetrical current

B. 1.1 x rated service voltage x rated symmetrical current

C. √2 x rated service voltage x rated symmetrical current

D.√3 x rated service voltage x rated symmetrical current

D.√3 x rated service voltage x rated symmetrical current

Which relay is used for feeders?

A. MHO relay

B. Translay relay

C. Merz-Price protection

D. Buchholz relay

B. Translay relay

Which of the following relays is used in transformers?

A. Buchholz relay

B. MHO relay

C. Merz-Price relay

D. None of the above

A. Buchholz relay

MHO relay is used for

A. rectifier

B. circuit breaker

C. transmission lines

D. Feeders

C. transmission lines

63. Merz-Price protection is used on

A. substations

B. capacitor banks

C. induction motors

D. generators

A. substations

64. The value of the fault current depend on

A. voltage at the faulty point

B. total impedance up to the fault

C. both A and B

D. none of the above

C. both A and B

65. The advantage of the neutral earthing is

A. simplified design of earth fault protection

B. over-voltages due to the lightening can be discharges to the earth

C. freedom from persistent arcing grounds

D. all of the above

D. all of the above

The over voltage surges in power system may be caused by

A. lightening

B. switching

C. resonance

D. any of the above

D. any of the above

The protection against the over-voltage due to the lightning is provided by

A. use of surge diverters

B. low tower footing resistance

C. use of overhead ground wires

D. any of the above

D. any of the above

68. Which of the following is a conducting medium for electric current?

A. Low temperature gas

B. High temperature gas

C. Dissociated gas

D. Plasma

D. Plasma

In circuit breakers the contact space is ionized by

A. thermal ionization of gas

B. thermal emission from surface contacts

C. field emission from the surface contacts

D. any of the above

D. any of the above

70. Which of the following are air-break switching devices?

A. Isolator

B. Limit switch

C. Earthing switch

D. All of the above

D. All of the above

71. Which of the following is the deremit of SF6 circuit breakers?

A. Sealing problem of gas

B. In flux of moisture in the gas system is dangerous

C. Deterioration of quality of circuit breaker affects reliability of circuit breakers

D. All of the above

D. All of the above

72. A fuse is normally a

A. current limiting device

B. voltage limiting device

C. power limiting device

D. power factor limiting device

A. current limiting device

73. Normally the fuse elements are in parts which are connected in the middle by tin bridge. The melting point of tin bridge is

A. 35 degrees celsius

B. 88 degrees celsius

C. 230 degrees celsius

D. 540 degrees celsius

C. 230 degrees celsius

The material used for bus bars should have

A. low resistivity

B. higher softening temperature

C. low cost

D. all of the above

D. all of the above

75. Which of the following is not valid in case of aluminum as compared to copper? Aluminum is higher

A. resistivity

B. coefficient of linear expansion

C. tensile strength

D. joint resistance

C. tensile strength

76. Over current protection for motor is provided by

A. cartridge fuses

B. kit kat fuses

C. over current relay

D. all of the above

C. over current relay

77. Fuse in motor circuits provides

A. over current protection

B. short-circuit protection

C. open-circuit protection

D. none of the above

B. short-circuit protection

78. In which method of starting a motor, the starting current is the maximum?

A. Auto-transformer

B. Star-delta transformer

C. Stator rotor starter

D. Direct-on-line

D. Direct-on-line

79. Over voltage transients may occur due to

A. lightening

B. switching

C. arcing grounds

D. any of the above

D. any of the above

80. Switching surges may be caused by

A. closing of the unchanged line

B. load shedding or receiving end of line

C. switching of magnetizing current

D. any of the above

D. any of the above

81. The disadvantages offered by underground system is

A. frequent arcing grounds

B. difficult earth fault relaying

C. voltage oscillations

D. all of the above

D. all of the above

82. Solid grounding is used for voltages

A. above 220 kV

B. above 11 kV

C. below 660 V

D. below 115 V

C. below 660 V

83. Switching over voltages are more hazardous than lightening surges in case of

A. low voltage systems

B. 11 kV system

C. unbalanced systems

D. EHV and UHV systems

D. EHV and UHV systems

A. air cooled, air cored

B. oil immersed magnetically shielded

C. oil immersed non-magnetically shielded

D. any of the above

D. any of the above

85. Series reactors are installed at strategic locations of the power systems to

A. bring down the fault level within the capacity of the switchgear

B. directly pass the fault surges to ground

C. pass the neutralizing surges of opposite nature

D. discharge the capacitor

A. bring down the fault level within the capacity of the switchgear

Which of the following generating stations has maximum running cost?

A. thermal power station

B. nuclear power station

C. hydro power station

D. none of these

C. hydro power station

2. Which of the following methods of generating electric power from the sea water is more

advantageous?

A. water power

B. ocean power

C. tidal power

D. none of these

C. tidal power

3. Out of the following, which one is not unconventional source of energy?

A. tidal power

B. geothermal power

C. nuclear energy

D. wind energy

D. wind energy

4. Heating value of coal largely depends on

A. ash content

B. moisture content

C. volatile matter

D. size of coal particles

A. ash content

5. Power plants using coal work closely on which of the following cycle?

A. Rankine cycle

B. Binary vapor cycle

C. Otto cycle

D. Brayton cycle

A. Rankine cycle

6. The efficiency of a thermal power plant improves with

A. increased quantity of coal burnt

B. use of high steam pressures

C. lower load in the plant

D. larger quantity of water used

B. use of high steam pressures

7. Which of the following contributes to improvement of efficiency of Rankine cycle in a thermal powerplant?

A. use of high pressures

B. regeneration use of steam for heating boiler feed water

C. reheating of steam at intermediate stage

D. all of the above

D. all of the above

8. Which of the following is not a high pressure boiler?

A. Loeffer boiler

B. Lancashire boiler

C. Velox boiler

D. La-Mount boiler

B. Lancashire boiler

9. Overall thermal efficiency of a steam power station is in the range

A. 18-24%

B. 30-40%

C. 44-62%

D. 68-79%

A. 18-24%

10. In a steam turbine cycle, the lowest pressure occurs in

A. turbine outlet

B. boiler

C. condenser

D. superheater

D. superheater

11. Chemical composition of coal is given by

A. Proximate analysis

B. Ultimate analysis

C. Orost analysis

D. All of the above

B. Ultimate analysis

12. For low head and high discharge, the hydraulic turbine used is

A. Kaplan turbine

B. Francis turbine

C. Pelton wheel

D. Jonval turbine

A. Kaplan turbine

13. A graphical representation between discharge and time is known as

A. Monograph

B. Hectograph

C. Hydrograph

D. Topograph

C. Hydrograph

14. A Pelton wheel is

A. axial flow impulse turbine

B. inward flow reaction turbine

C. outward flow impulse turbine

D. inward flow impulse turbine

A. axial flow impulse turbine

15. A Francis turbine

A. outward flow impulse turbine

B. outward flow reaction turbine

C. inward flow impulse turbine

D. inward flow reaction turbine

A. outward flow impulse turbine