Upda-multiple Choice Questions

(1)

Circuit breaker Circuit breaker

1. A circuit breaker is 1. A circuit breaker is

(A) power factor correcting device (A) power factor correcting device

(B) a device to neutralize the effect of transients (B) a device to neutralize the effect of transients (C) a waveform correcting device

(C) a waveform correcting device (D) a current interrupting device. (D) a current interrupting device. 2. The function of protective relay in

2. The function of protective relay in a circuit breaker isa circuit breaker is (A) to each any stray voltages

(A) to each any stray voltages

(B) to close the contacts when the actuating quantity reaches a certain predetermined value (B) to close the contacts when the actuating quantity reaches a certain predetermined value (C) to limit arcing current

(C) to limit arcing current during the operation of circuit breakerduring the operation of circuit breaker (D) to provide additional safety in the operation of circuit br (D) to provide additional safety in the operation of circuit br eakereaker 3. Low voltage circuit breakers have rated voltage of less than 3. Low voltage circuit breakers have rated voltage of less than (A) 220 V (A) 220 V (B) 400V (B) 400V (C) 1000 V (C) 1000 V (D) 10,000 V. (D) 10,000 V.

4. The fault clearing time of a

4. The fault clearing time of a circuit breaker is usuallycircuit breaker is usually (A) few minutes

(A) few minutes (B) few seconds (B) few seconds (C) one second (C) one second

(D) few cycles of supply voltage. (D) few cycles of supply voltage.

5. The medium employed for extinction of arc

5. The medium employed for extinction of arc in air circuit breaker isin air circuit breaker is (A) SF6 (A) SF6 (B) Oil (B) Oil (C) Air (C) Air (D) Water. (D) Water.

6. Which of the following circuit breakers

6. Which of the following circuit breakers is preferred for EHT applicationis preferred for EHT application (A) Air blast circuit breakers

(A) Air blast circuit breakers (B) Minimum oil circuit breakers (B) Minimum oil circuit breakers (C) Bulk oil circuit breakers (C) Bulk oil circuit breakers (D) SF6 oil circuit breakers. (D) SF6 oil circuit breakers.

7. For high voltage, ac circuit breakers, the rated short circuit current is passed for 7. For high voltage, ac circuit breakers, the rated short circuit current is passed for (A) 0.01 sec (A) 0.01 sec (B) 0.1 sec (B) 0.1 sec (C) 3 seconds (C) 3 seconds (D) 30 seconds. (D) 30 seconds.

8. Which of the following is not a type of the contactor for circuit breakers ? 8. Which of the following is not a type of the contactor for circuit breakers ? (A) Electro-magnetic (A) Electro-magnetic (B) Electro-pneumatic (B) Electro-pneumatic (C) Pneumatic (C) Pneumatic

(2)

(D) Vacuum. (D) Vacuum.

9. Interrupting medium in a contactor may 9. Interrupting medium in a contactor may bebe (A) air (A) air (B) oil (B) oil (C) SF6 gas (C) SF6 gas

(D) any of the above. (D) any of the above.

10. In air blast circuit breakers, the pressure of air is of the order of 10. In air blast circuit breakers, the pressure of air is of the order of (A) 100 mm Hg (A) 100 mm Hg (B) 1 kg/cm2 (B) 1 kg/cm2 (C) 20 to 30 kg/cm2 (C) 20 to 30 kg/cm2 (D) 200 to 300 kg/cm2 . (D) 200 to 300 kg/cm2 . 11. SF6 gas is 11. SF6 gas is

(A) sulphur fluoride (A) sulphur fluoride (B) sulphur difluoride (B) sulphur difluoride (C) sulphur hexafluorine (C) sulphur hexafluorine (D) sulphur hexafluoride. (D) sulphur hexafluoride. 12. SF6 gas 12. SF6 gas

(A) is yellow in color (A) is yellow in color (B) has pungent odor (B) has pungent odor (C) is highly toxic (C) is highly toxic (D) is (D) is non-inflammable.non-inflammable. 13. SF6 gas 13. SF6 gas

(A) is lighter than hydrogen (A) is lighter than hydrogen (B) is lighter than air

(B) is lighter than air

(C) has density 2-times as compared to

(C) has density 2-times as compared to that of airthat of air (D) has density 5 limes as compared to

(D) has density 5 limes as compared to that of air.that of air.

14. The pressure of SF6 gas in circuit breakers is of the order of 14. The pressure of SF6 gas in circuit breakers is of the order of (A) 100 mm Hg (A) 100 mm Hg (B) 1 kg/cm2 (B) 1 kg/cm2 (C) 3 to 5 kg/cm2 (C) 3 to 5 kg/cm2 (D) 30 to 50 kg/cm2. (D) 30 to 50 kg/cm2. 15. While selecting a gas

15. While selecting a gas for circuit breaker, the for circuit breaker, the property of gas that should be considered isproperty of gas that should be considered is (A) high dielectric strength

(A) high dielectric strength (B) non-inflammability (B) non-inflammability (C) non-toxicity

(C) non-toxicity (D) all of the above. (D) all of the above.

16. Out of the following circuit breakers,

16. Out of the following circuit breakers, which one has the lowest voltage range ?which one has the lowest voltage range ? (A) Air-break circuit breaker

(3)

(B) Tank type oil circuit breaker (B) Tank type oil circuit breaker (C) Air-blast circuit breaker (C) Air-blast circuit breaker (D) SF6 circuit breaker. (D) SF6 circuit breaker.

17. Which of the following circuit breaker

17. Which of the following circuit breaker can be installed on 400 kV linecan be installed on 400 kV line (A) Tank type oil circuit breaker

(A) Tank type oil circuit breaker (B) Miniature circuit breaker (B) Miniature circuit breaker (C) Vacuum circuit breaker (C) Vacuum circuit breaker (D) Air blast circuit breaker. (D) Air blast circuit breaker.

18. In a vacuum circuit breaker, the vacuum is of the order of 18. In a vacuum circuit breaker, the vacuum is of the order of (A) 10mm Hg (A) 10mm Hg (B)10-2mmHg (B)10-2mmHg (C) l0-6 mmHg (C) l0-6 mmHg (D)10-9mmHg. (D)10-9mmHg.

19. In modem EHV circuit breake

19. In modem EHV circuit breakers, the operating time between instant of rs, the operating time between instant of receiving trip signal and finalreceiving trip signal and final contact separation is, of the order of

contact separation is, of the order of (A) 0.001 sec (A) 0.001 sec (B) 0.015 sec (B) 0.015 sec (C) 0.003 sec (C) 0.003 sec (D) 0.03 sec. (D) 0.03 sec. 20. In a HRC

20. In a HRC fuse the time between cut-off and fuse the time between cut-off and final current zero, is known asfinal current zero, is known as (A) total operating time

(A) total operating time (B) arcing time

(B) arcing time (C) pre-arcing time (C) pre-arcing time (D) any of the above. (D) any of the above.

21. Fusing factor for a HRC fuse is 21. Fusing factor for a HRC fuse is

(A) Minimum fusing current / Current rating (A) Minimum fusing current / Current rating

(B) Minimum fusing current / Minimum rupturing time (B) Minimum fusing current / Minimum rupturing time (C) Maximum fusing current / Minimum fusing current (C) Maximum fusing current / Minimum fusing current (D) Minimum fusing current / Prospective current of c (D) Minimum fusing current / Prospective current of c ircuit.ircuit. 22. Which of the following circuit breakers

22. Which of the following circuit breakers does not use pneumatic operating mechanismdoes not use pneumatic operating mechanism (A) Air blast circuit breaker

(A) Air blast circuit breaker (B) SF6 blast circuit breaker (B) SF6 blast circuit breaker (C) Air break circuit breaker (C) Air break circuit breaker (D) Bulk-oil circuit breaker. (D) Bulk-oil circuit breaker.

23. The contact resistance of a circuit breaker is. of the order of 23. The contact resistance of a circuit breaker is. of the order of (A) 20 micro ohms ± 10

(A) 20 micro ohms ± 10 (B) 20milli ohms ± 10 (B) 20milli ohms ± 10 (C) 20 ohms ± 10 (C) 20 ohms ± 10 (D) 200 ohms ± 10. (D) 200 ohms ± 10.

24. The insulation resistance of high voltage circuit breaker 24. The insulation resistance of high voltage circuit breaker isis

(4)

(A) 1k Ohm (A) 1k Ohm (B) 10 k Ohm (B) 10 k Ohm (C) 20 Mega ohms (C) 20 Mega ohms (D) 2000 Mega ohm. (D) 2000 Mega ohm.

25. There is definite objection to

25. There is definite objection to use of which of the following medium for extinguishing the arc use of which of the following medium for extinguishing the arc in casein case of a circuit breaker ? of a circuit breaker ? (A) Air (A) Air (B) SF6 gas (B) SF6 gas (C) Vacuum (C) Vacuum (D) Water. (D) Water. 26. In a circuit

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

than the specified limit, the probable cause could be (A) moisture

(A) moisture

(B) dirty insulation surface (B) dirty insulation surface

(C) carbon or copper particles sticking to the internal surface (C) carbon or copper particles sticking to the internal surface (D) any of the above.

(D) any of the above.

27. If a circuit breaker does not operate on electrical compound, the probable reason could be 27. If a circuit breaker does not operate on electrical compound, the probable reason could be (A) spring defective

(A) spring defective (B) trip circuit open (B) trip circuit open (C) trip latch defective (C) trip latch defective (D) any of the above. (D) any of the above.

28. The normal frequency rms voltage that

28. The normal frequency rms voltage that appears across the breaker poles after appears across the breaker poles after final arc extinction hasfinal arc extinction has occurred, is

occurred, is

(A) recovery voltage (A) recovery voltage (B) re striking voltage (B) re striking voltage (C) supply voltage (C) supply voltage (D) peak voltage. (D) peak voltage.

29. The transient voltage that appears across

29. The transient voltage that appears across the contacts at the instant of the contacts at the instant of arc extinction is calledarc extinction is called (A) recovery voltage

(A) recovery voltage (B) re striking voltage (B) re striking voltage (C) supply voltage (C) supply voltage (D) peak voltage. (D) peak voltage.

30. In a circuit breaker the active recovery voltage depends upon 30. In a circuit breaker the active recovery voltage depends upon (A) power factor

(A) power factor (B) armature reaction (B) armature reaction (C) circuit conditions (C) circuit conditions (D) all of the above. (D) all of the above.

31. The following figure shows the voltage waveform across t

31. The following figure shows the voltage waveform across t he pole of a circuit breaker; Ihe pole of a circuit breaker; In this voltagen this voltage R represents

(5)

(A) System voltage (A) System voltage (B) Re striking voltage (B) Re striking voltage (C) Recovery voltage (C) Recovery voltage (D) Extinction of arc. (D) Extinction of arc.

32. In the above figure, D represents 32. In the above figure, D represents (A) Recovery voltage

(A) Recovery voltage (B) Re striking voltage (B) Re striking voltage (C) System voltage (C) System voltage (D) Extinction of arc. (D) Extinction of arc.

33. Best protection is provided by HRC

33. Best protection is provided by HRC fuses in case offuses in case of (A) Open circuits

(A) Open circuits (B) Short circuits (B) Short circuits (C) Overloads (C) Overloads

(D) None of the above. (D) None of the above.

34. For motor circuit breakers, the time of closing the cycle is 34. For motor circuit breakers, the time of closing the cycle is (A) 0.001 sec (A) 0.001 sec (B) 0.01 sec (B) 0.01 sec (C) 0.10 sec (C) 0.10 sec (D) 0.003 sec. (D) 0.003 sec.

35. A relay used for

35. A relay used for protection of motors against overload isprotection of motors against overload is (A) Impedance relay

(A) Impedance relay

(B) Electromagnetic attraction type (B) Electromagnetic attraction type (C) Thermal relay

(C) Thermal relay (D) Buchholz's relay. (D) Buchholz's relay.

36. Which curve in the figure represents inverse time characteristics ? 36. Which curve in the figure represents inverse time characteristics ?

(6)

(A) Curve A (A) Curve A (B) Curve B (B) Curve B (C) Curve C (C) Curve C (D) Curve D. (D) Curve D.

37. Fuse protection is used for current ratings up to 37. Fuse protection is used for current ratings up to (A) 10 A (A) 10 A (B) 20 A (B) 20 A (C) 50 A (C) 50 A (D) 100 A. (D) 100 A.

38. The fuse current in amperes is related with fuse wire diameter D as 38. The fuse current in amperes is related with fuse wire diameter D as (A) I ∞ I/D (A) I ∞ I/D (B) I ∞ D (B) I ∞ D (C) I ∞ D3/2 (C) I ∞ D3/2 (D) I ∞ D2. (D) I ∞ D2.

39. The acting contacts for a circuit breakers are made of 39. The acting contacts for a circuit breakers are made of (A) Stainless steel

(A) Stainless steel

(B) Hard pressed carbon (B) Hard pressed carbon (C) Porcelain

(C) Porcelain

(D) Copper tungsten alloy. (D) Copper tungsten alloy.

40. Ionization in a circuit breaker is

40. Ionization in a circuit breaker is not facilitated bynot facilitated by (A) high temperature of surrounding medium

(A) high temperature of surrounding medium (B) material of contacts

(B) material of contacts (C) increase of field strength (C) increase of field strength (D) increase of mean free (D) increase of mean free path.path.

41. Which circuit breaker is g

41. Which circuit breaker is generally used in railway traction ?enerally used in railway traction ? (A) SF6 gas circuit breaker

(A) SF6 gas circuit breaker (B) Air break circuit breaker (B) Air break circuit breaker (C) Vacuum circuit breaker (C) Vacuum circuit breaker (D) Minimum oil circuit breaker. (D) Minimum oil circuit breaker.

(7)

42. A fuse wire

42. A fuse wire should haveshould have

(A) Low specific resistance and high melting (A) Low specific resistance and high melting pointpoint (B) Low specific resistance and low melting point (B) Low specific resistance and low melting point (C) High specific resistance and high 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.

43. Fuse wire, protection, system

43. Fuse wire, protection, system is usually not used beyondis usually not used beyond (A) 10 A (A) 10 A (B) 25 A (B) 25 A (C) 50 A (C) 50 A (D)100A. (D)100A.

44. For extra high voltage lines which circuit breaker is preferred 44. For extra high voltage lines which circuit breaker is preferred (A) Bulk oil circuit breaker

(A) Bulk oil circuit breaker (B) Vacuum circuit breaker (B) Vacuum circuit breaker (C) SF6 gas circuit breaker (C) SF6 gas circuit breaker (D) Minimum oil circuit breaker. (D) Minimum oil circuit breaker.

45. The number of cycles in which a

45. The number of cycles in which a high speed circuit breaker can complete its operathigh speed circuit breaker can complete its operat ion ision is (A) 3 to 8 (A) 3 to 8 (B) 10 to 18 (B) 10 to 18 (C) 20 to 30 (C) 20 to 30 (D) 40 to 50. (D) 40 to 50. 46. When D is the

46. When D is the diameter of fuse wire, the fusing current diameter of fuse wire, the fusing current will be proportional towill be proportional to (A) 1/D (A) 1/D (B) 1/D2 (B) 1/D2 (C) D3/2 (C) D3/2 (D) D1/2 . (D) D1/2 .

47. A material best suited for manufacturing of

47. A material best suited for manufacturing of fuse wire isfuse wire is (A) Aluminium (A) Aluminium (B) Silver (B) Silver (C) Lead (C) Lead (D) Copper. (D) Copper.

(8)

48. In a circuit breaker the current which exists at the instant of contact separation is known as 48. In a circuit breaker the current which exists at the instant of contact separation is known as (A) re striking current

(A) re striking current (B) surge current (B) surge current (C) breaking current (C) breaking current (D) recovery current. (D) recovery current. 49. A Merz-price protection is

49. A Merz-price protection is suitable forsuitable for (A) transformers (A) transformers (B) alternators (B) alternators (C) feeders (C) feeders (D) transmission lines. (D) transmission lines. 50. 'Kick fuse' has 50. 'Kick fuse' has

(A) square law characteristics (A) square law characteristics (B) linear characteristics (B) linear characteristics (C) inverse characteristics. (C) inverse characteristics.

51. Air blast circuit breakers for 400 kV. Power system are designed to operate in 51. Air blast circuit breakers for 400 kV. Power system are designed to operate in (A) 50 micro seconds

(A) 50 micro seconds (B) 50 milli seconds (B) 50 milli seconds (C) 500 milli seconds (C) 500 milli seconds (D) 50 seconds. (D) 50 seconds.

52. Breaking capacity of a circuit

52. Breaking capacity of a circuit breaker is usually expressed in terms ofbreaker is usually expressed in terms of (A) Amperes (A) Amperes (B) Volts (B) Volts (C) MW (C) MW (D) MVA. (D) MVA. 53. Sulphur hexafluoride is a 53. Sulphur hexafluoride is a (A) Conductor of electricity (A) Conductor of electricity (B) Semi-conductor (B) Semi-conductor (C) Inactive gas (C) Inactive gas (D) Dielectric. (D) Dielectric.

54. The contact resistance is least affected by 54. The contact resistance is least affected by (A) the mechanical force applied

(A) the mechanical force applied (B) the shape of the contact faces (B) the shape of the contact faces

(C) the amount of surface contamination (C) the amount of surface contamination (D) the ambient temperature.

(D) the ambient temperature.

55. The arc voltage produced in ac circuit breaker is 55. The arc voltage produced in ac circuit breaker is (A) leading the arc current by 90°

(A) leading the arc current by 90° (B) lagging the arc current by 90° (B) lagging the arc current by 90° (C) In phase with the arc current (C) In phase with the arc current (D) In phase opposition to the arc

(9)

Questions 56 to 59 refer

Questions 56 to 59 refer to the following figure :to the following figure :

56. Various forms of contacts are

56. Various forms of contacts are shown in the figure above. Point contact is (are) reshown in the figure above. Point contact is (are) re presented bypresented by (A) A only

(A) A only (B) A and B only (B) A and B only (C) A, B and C (C) A, B and C onlyonly (D) A, B, C and D. (D) A, B, C and D.

57. Which contact surface provides line contact o 57. Which contact surface provides line contact o nly?nly? (A) A (A) A (B) B (B) B (C) C (C) C (D) D. (D) D.

58. Which form of contact are

58. Which form of contact are widely used in switchgear particle ?widely used in switchgear particle ? (A) A and B only

(A) A and B only (B) A and C only (B) A and C only (C) C and D only (C) C and D only (D) B, C and D only. (D) B, C and D only.

59. For the various types of co

59. For the various types of contacts Shown, for the same force, ntacts Shown, for the same force, F, the contact resistance will be F, the contact resistance will be least inleast in case of case of (A) A (A) A (B) B (B) B (C) C (C) C (D) D. (D) D.

(10)

60. As the force on contact is increased, the contact resistance will 60. As the force on contact is increased, the contact resistance will (A) increase linearly

(A) increase linearly (B) increase exponentially (B) increase exponentially (C) remain unaltered (C) remain unaltered (D) decrease. (D) decrease.

61. The heat produced at the

61. The heat produced at the contact point, due to passage of currcontact point, due to passage of curr ent, will least depend onent, will least depend on (A) contact resistance

(A) contact resistance

(B) time during which the current (B) time during which the current flowsflows (C) current flowing

(C) current flowing

(D) temperature of the surrounding medium. (D) temperature of the surrounding medium. 62. For the contact

62. For the contact and their material, which of the following should have low valueand their material, which of the following should have low value (A) Contact resistance

(A) Contact resistance (B) Thermal capacity (B) Thermal capacity (C) Thermal conductivity (C) Thermal conductivity (D) All of the above. (D) All of the above.

63. Minimum arcing voltage will be least in case o 63. Minimum arcing voltage will be least in case o ff (A) carbon (A) carbon (B) graphite (B) graphite (C) tungsten (C) tungsten (D) silver. (D) silver.

64. Minimum arcing voltage for platinum is 16 V. It

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

below 16 V

(A) it will not be possible to interrupt

(A) it will not be possible to interrupt the circuitthe circuit (B) it will not be possible to pass the

(B) it will not be possible to pass the currentcurrent (C) it will be possible to interrupt any value o

(C) it will be possible to interrupt any value o f current without arcingf current without arcing (D) it will be possible to interrupt any value

(D) it will be possible to interrupt any value of current without bringing contact closer tof current without bringing contact closer t o one another.o one another. 65. Oil immersion of contacts is the method of

65. Oil immersion of contacts is the method of (A) arc dispersion

(A) arc dispersion (B) arc prevention (B) arc prevention (C) de ionization (C) de ionization (D) none of the above. (D) none of the above.

66. Which of the following is not the

66. Which of the following is not the method of arc dispersion ?method of arc dispersion ? (A) Oil immersion of contacts

(A) Oil immersion of contacts (B) Magnetic blow out of arc (B) Magnetic blow out of arc (C) Use of rectifiers

(C) Use of rectifiers

(D) De ionization of arc path. (D) De ionization of arc path.

67. Which of the following contact point metals has

67. Which of the following contact point metals has the highest melting point ?the highest melting point ? (A) Silver (A) Silver (B) Tungsten (B) Tungsten (C) Gold (C) Gold (D) Copper (D) Copper

(11)

68. The arc voltage produced in the circuit breaker is always 68. The arc voltage produced in the circuit breaker is always (A) in phase with arc current

(A) in phase with arc current (B) leading the arc current by 90° (B) leading the arc current by 90° (C) lagging the arc current by 90° . (C) lagging the arc current by 90° .

69. Which of the following figure represents the voltage-current characteristics of arc in a circuit breaker 69. Which of the following figure represents the voltage-current characteristics of arc in a circuit breaker ? ? (A) Figure A (A) Figure A (B) Figure B (B) Figure B (C) Figure C (C) Figure C (D) Figure D. (D) Figure D.

70. Ionization process during arc is ge

70. Ionization process during arc is ge nerally accompanied by emission ofnerally accompanied by emission of (A) light (A) light (B) heat (B) heat (C) sound (C) sound

(D) all of the above. (D) all of the above.

71. Sparking between contacts can be reduced by 71. Sparking between contacts can be reduced by ( A) inserting resistance in the line

( A) inserting resistance in the line (B) inserting a capacitor in series with

(B) inserting a capacitor in series with the contactsthe contacts (C) inserting a capacitor in parallel with the

(C) inserting a capacitor in parallel with the contacts.contacts. 72. For magnetic blow out of

72. For magnetic blow out of arc the magnetic field is producedarc the magnetic field is produced (A) in the load circuit

(A) in the load circuit

(B) parallel to the axis of the arc (B) parallel to the axis of the arc

(C) at right angles to the axis of the arc. (C) at right angles to the axis of the arc.

(12)

73. Cool gases are solids brought into the arc stream assist in quenching the arc mainly by 73. Cool gases are solids brought into the arc stream assist in quenching the arc mainly by (A) reducing current density

(A) reducing current density (B) providing arc shield (B) providing arc shield (C) De ionization

(C) De ionization

(D) providing parallel paths. (D) providing parallel paths.

74. Sparking occurs when a load is switched o

74. Sparking occurs when a load is switched o ff because the circuit hasff because the circuit has (A) high inductance

(A) high inductance (B) high capacitance (B) high capacitance (C) high resistance. (C) high resistance. 75. HRC fuses are 75. HRC fuses are

(A) High resistance and Capacitance fuses (A) High resistance and Capacitance fuses (B) Heat reflecting cool fuses

(B) Heat reflecting cool fuses

(C) Holding and Resisting current fuses (C) Holding and Resisting current fuses (D) High rupturing capacity fuses. (D) High rupturing capacity fuses.

76. Which of the following metals does not

76. Which of the following metals does not amalgamate with mercury ?amalgamate with mercury ? (A) Tungsten (A) Tungsten (B) Molybdenum (B) Molybdenum (C) Nickel alloy (C) Nickel alloy (D) All of the above. (D) All of the above. 77. For the same c

77. For the same c urrent, which of the following fuse wires will have turrent, which of the following fuse wires will have t he least fusing time ?he least fusing time ? (A) 18 SWG TIN - 12.5 A (A) 18 SWG TIN - 12.5 A (B) 20 SWG TIN - 10 A (B) 20 SWG TIN - 10 A (C) 22 SWG TIN-7.5 A (C) 22 SWG TIN-7.5 A (D) 24 SWG TIN-5 A. (D) 24 SWG TIN-5 A.

78. An automatic device that operates

78. An automatic device that operates at present values is known asat present values is known as (A) mercury switch

(A) mercury switch (B) relay (B) relay (C) fuse (C) fuse (D) contactor. (D) contactor.

79. The basic function of a circuit br

79. The basic function of a circuit br eaker is toeaker is to (A) produce the arc

(A) produce the arc

(B) ionize the surrounding air (B) ionize the surrounding air (C) transmit voltage by arcing (C) transmit voltage by arcing (D) extinguish the arc.

(D) extinguish the arc.

80. In a circuit breaker the arc is indicated by the process of 80. In a circuit breaker the arc is indicated by the process of I. Thermal emission

I. Thermal emission II. Ionization of oil II. Ionization of oil

III. High temperature of air III. High temperature of air IV. Field emission

IV. Field emission (A) I and II only (A) I and II only (B) I, II and III only (B) I, II and III only

(13)

(C) II, III and IV only (C) II, III and IV only (D) I and IV only. (D) I and IV only.

81. The power factor of the arc in circuit breaker is 81. The power factor of the arc in circuit breaker is (A) always zero

(A) always zero (B) always unity (B) always unity (C) always lagging (C) always lagging (D) always leading. (D) always leading.

82. Air blast circuit breakers are

82. Air blast circuit breakers are usually used forusually used for (A) instantaneous duty

(A) instantaneous duty (B) permanent break (B) permanent break (C) intermittent duty (C) intermittent duty (D) repeated duty. (D) repeated duty.

83. Flame proof switch gears are

83. Flame proof switch gears are usually preferredusually preferred (A) on transmission lines of low voltage

(A) on transmission lines of low voltage (B) substations

(B) substations (C) in mines (C) in mines

(D) in high MVA capacity circuits. (D) in high MVA capacity circuits. 84. Pressure of air

84. Pressure of air in air blast circuit breakers is usuallyin air blast circuit breakers is usually (A) 1 - 5 kg/cm2 (A) 1 - 5 kg/cm2 (B) 5 - 10 kg/cm2 (B) 5 - 10 kg/cm2 (C) 10-30 kg/cm2 (C) 10-30 kg/cm2 (D) 35-100 kg/cm2. (D) 35-100 kg/cm2.

85. Air used in air blast circuit breaker 85. Air used in air blast circuit breaker (A) must have least carbon dioxide (A) must have least carbon dioxide (B) must be ionized

(B) must be ionized (C) must have oil mist (C) must have oil mist

(D) must be free from moisture. (D) must be free from moisture. 86. In a circuit

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

coil is known as (A) lag time (A) lag time (B) lead time (B) lead time (C) protection time (C) protection time (D) operation time. (D) operation time. 87. In a circuit

87. In a circuit breaker the lime duration from the instant of the breaker the lime duration from the instant of the fault to the extinction of arc fault to the extinction of arc is known asis known as (A) operation time

(A) operation time (B) total clearing time (B) total clearing time (C) lag time

(C) lag time (D) lead time. (D) lead time.

(14)

88. In a circuit breaker the lime duration from the instant of fault to the instant of closing of contact is 88. In a circuit breaker the lime duration from the instant of fault to the instant of closing of contact is known as

known as

(A) Recycle time (A) Recycle time (B) Total time (B) Total time (C) Gross time (C) Gross time (D) Re closing time. (D) Re closing time.

89. For high speed circuit breakers the total lime is nearly 89. For high speed circuit breakers the total lime is nearly (A) Half cycle

(A) Half cycle (B) One cycle (B) One cycle (C) Few cycles (C) Few cycles (D) Ten cycles. (D) Ten cycles.

90. For a high speed circuit breaker the total clearing time is nearly 90. For a high speed circuit breaker the total clearing time is nearly (A) 1 to 2 cycles (A) 1 to 2 cycles (B) 5 to 10 cycles (B) 5 to 10 cycles (C) 10 to 15 cycles (C) 10 to 15 cycles (D) less than 50 cycles. (D) less than 50 cycles.

91. If the power factor is zero, the active recovery voltage will be 91. If the power factor is zero, the active recovery voltage will be (A) minimum (A) minimum (B) 0.5 (B) 0.5 (C) 0.707 (C) 0.707 (D) maximum. (D) maximum.

92. Which of the following is not a

92. Which of the following is not a part of the circuit breaker ?part of the circuit breaker ? (A) Explosion pot

(A) Explosion pot

(B) Fixed and moving contacts (B) Fixed and moving contacts (C) Conservator

(C) Conservator

(D) Operating mechanism. (D) Operating mechanism. 93. A circuit breaker

93. A circuit breaker will normally operatewill normally operate (A) When the switch is put on

(A) When the switch is put on (B) When the line is to be checked (B) When the line is to be checked (C) When the power is t

(C) When the power is to be suppliedo be supplied (D) Whenever fault in the line occurs. (D) Whenever fault in the line occurs. 94. Which of the following circuit breaker

94. Which of the following circuit breaker will produce the least arc energy will produce the least arc energy ? (A) Minimum oil circuit? (A) Minimum oil circuit breaker

breaker

(B) Air blast circuit breaker (B) Air blast circuit breaker (C) Plain oil circuit breaker (C) Plain oil circuit breaker

(D) All will produce same energy. (D) All will produce same energy. 95. For a circuit breaker 'break time' is 95. For a circuit breaker 'break time' is (A) same as opening time

(A) same as opening time (B) opening time + arc duration (B) opening time + arc duration (C) opening time + arc duration + re

(15)

96. The breaking capacity of a circuit breaker in MVA (3 phase) is given by 96. The breaking capacity of a circuit breaker in MVA (3 phase) is given by (A) rated service voltage x rated symmetrical current

(A) rated service voltage x rated symmetrical current (B) 1.1 x rated service voltage x rated symmetrical current (B) 1.1 x rated service voltage x rated symmetrical current (C) (2)1/2 x rated service voltage x rated symmetrical current (C) (2)1/2 x rated service voltage x rated symmetrical current (D) (3)1/2x rated service voltage x rated symmetrical current. (D) (3)1/2x rated service voltage x rated symmetrical current. 97. Which relay is used for fee

97. Which relay is used for feeders ?ders ? (A) MHO relay

(A) MHO relay (B) Translay relay (B) Translay relay

(C) Merz price protection (C) Merz price protection (D) Buchholz relay.

(D) Buchholz relay.

98. Which of the following relays is used on

98. Which of the following relays is used on transformers ?transformers ? (A) Buchholz relay

(A) Buchholz relay (B) MHO relay (B) MHO relay (C) Merz price relay (C) Merz price relay (D) None of the above. (D) None of the above. 99. MHO relay is used for 99. MHO relay is used for (A) rectifiers (A) rectifiers (B) circuit breakers (B) circuit breakers (C) transmission lines (C) transmission lines (D) feeders. (D) feeders.

100. Merz-price protection is used on 100. Merz-price protection is used on (A) substations (A) substations (B) capacitor bank (B) capacitor bank (C) induction motor (C) induction motor (D) generators. (D) generators.

101. Match the following : 101. Match the following :

Relay Operation

(a)

(a) Static Static relay relay (i) (i) Responds Responds to to vector vector difference difference between between two two electrical electrical quantitiesquantities (b)

(b) Over Over current current relay relay (ii) (ii) Quick Quick operationoperation (c)

(c) Differential Differential relay relay (iii) (iii) Responds Responds to to increase increase in in currentcurrent (d)

(d) Instantaneous Instantaneous (iv) (iv) No No moving moving parts parts relayrelay

(A) a - (i), b- (ii), c

(A) a - (i), b- (ii), c - (iii), d - (iv)- (iii), d - (iv) (B) a - (iv), b -

(B) a - (iv), b - (iii), c - (i), d- (iv)(iii), c - (i), d- (iv) (C) a - (ii), b -

(C) a - (ii), b - (i) c- (iii), d - (iv)(i) c- (iii), d - (iv) (D) a - (iii), b - (ii), c

(D) a - (iii), b - (ii), c - (i), d - (iv).- (i), d - (iv). 102. The values of fault current

102. The values of fault current depend ondepend on (A) voltage at the faulty point

(A) voltage at the faulty point (B) total impedance up to the fault (B) total impedance up to the fault (C) both (A) and (B) above

(C) both (A) and (B) above (D) none of the above (D) none of the above

(16)

103. The advantage of neutral earthing is 103. The advantage of neutral earthing is (A) simplified design of earth fault protection (A) simplified design of earth fault protection

(B) over-voltages due to lightning can be discharged to

(B) over-voltages due to lightning can be discharged to the earththe earth (C) freedom from persistent arcing gr

(C) freedom from persistent arcing gr oundsounds (D) all of the above.

(D) all of the above.

104. Match the following : 104. Match the following :

Material

Material used used in in circuit circuit breaker breaker ApplicationApplication (a)

(a) Poly Poly tetra tetra (i) Bearing (i) Bearing surfaces surfaces fluoroethylene fluoroethylene and and sliding sliding partsparts (b)

(b) SF6 SF6 gas gas (ii) Insulating (ii) Insulating mediummedium (c)

(c) Electrolytic Electrolytic (iii) Main (iii) Main contacts contacts coppercopper (d)

(d) Dielectric Dielectric oil oil (iv) (iv) Quenching Quenching mediummedium

(A) a- (i), b - (ii), c

(A) a- (i), b - (ii), c - (iii), d - (iv)- (iii), d - (iv) (B) a - (ii), b -

(B) a - (ii), b - (i), c - (iii), d - (iv)(i), c - (iii), d - (iv) (C) a - (iii), b - (ii),

(C) a - (iii), b - (ii), c - (i), d - (iv)c - (i), d - (iv) (D) a - (iv), b - (iii), c

(D) a - (iv), b - (iii), c - (ii), d - (i).- (ii), d - (i). 105. Match the following: 105. Match the following:

(A) a - (i), b -(ii), c

(A) a - (i), b -(ii), c - (iii), d - (iv)- (iii), d - (iv) (B) a - (ii). b - (iii), c

(B) a - (ii). b - (iii), c - (i), d - (iv)- (i), d - (iv) (C) a - (iii), b - (i),

(C) a - (iii), b - (i), c - (iv), d - (ii)c - (iv), d - (ii) (D) a - (iv), b - (iii), c

(D) a - (iv), b - (iii), c - (ii), d - (i).- (ii), d - (i).

106. The over-voltage surges in power

106. The over-voltage surges in power systems may be caused bysystems may be caused by (A) lightning (A) lightning (B) switching (B) switching (C) resonance (C) resonance

(17)

107. The protection against over-voltage due to lightening is provided by 107. The protection against over-voltage due to lightening is provided by (A) use of surge diverters

(A) use of surge diverters

(B) low tower footing resistance (B) low tower footing resistance (C) use of overhead ground wires (C) use of overhead ground wires (D) any of the above.

108. Which of the following is a conducting medium for

108. Which of the following is a conducting medium for electric current ?electric current ? (A) Low temperature gas

(A) Low temperature gas (B) High temperature gas (B) High temperature gas (C) Dissociated gas

(C) Dissociated gas (D) Plasma.

(D) Plasma.

109. In circuit-breakers the c

109. In circuit-breakers the contact space is ionized byontact space is ionized by (A) thermal ionization of gas

(A) thermal ionization of gas

(B) thermal emission from surface of contacts (B) thermal emission from surface of contacts (C) field emission from the surface of contacts (C) field emission from the surface of contacts (D) any of the above.

110. Which of the following are air-break

110. Which of the following are air-break switching devices ?switching devices ? (A) Isolator (A) Isolator (B) Limit switch (B) Limit switch (C) Earthing switch (C) Earthing switch (D) All of the above. (D) All of the above.

111. Which of the following statement about SF6

111. Which of the following statement about SF6 gas is incorrect ?gas is incorrect ? (A) It is non-toxic gas

(A) It is non-toxic gas (B) It

(B) It is non-inflammableis non-inflammable

(C) It has density 5 times that of air at 200C (C) It has density 5 times that of air at 200C (D) It has dark yellow color.

(D) It has dark yellow color.

112. SF6 gas is

112. SF6 gas is transported intransported in (A) gas cylinders

(A) gas cylinders

(B) liquid form in cylinders (B) liquid form in cylinders (C) solid form in boxes (C) solid form in boxes (D) air cylinders. (D) air cylinders.

113. During arc extinction SF6 gas 113. During arc extinction SF6 gas

(18)

(A) decomposes into S and F ions (A) decomposes into S and F ions (B) decomposes into SF4and SF2 (B) decomposes into SF4and SF2 (C) gets oxidized (C) gets oxidized (D) reduces to SF3. (D) reduces to SF3. 114. Dielectric strength of SF6 is 114. Dielectric strength of SF6 is (A) less than that of air at

(A) less than that of air at atmospheric pressureatmospheric pressure (B) less than that of oil used in OCB

(B) less than that of oil used in OCB (C) more than that of oil used

(C) more than that of oil used in OCBin OCB (D) more at lower pressure and low

(D) more at lower pressure and low at higher pressures.at higher pressures.

115. Which of the following is the demerit of SF6 circuit breakers ? 115. Which of the following is the demerit of SF6 circuit breakers ? (A) sealing problem of gas

(A) sealing problem of gas (B) In flux of moisture in the

(B) In flux of moisture in the gas system is dangerousgas system is dangerous (C) Deterioration of quality of circuit breaker

(C) Deterioration of quality of circuit breaker affects reliability of circuit breakeraffects reliability of circuit breaker (D) All of the above.

(D) All of the above.

116. Sphere gaps are used for 116. Sphere gaps are used for

(A) measurement of high dc voltages (A) measurement of high dc voltages (B) measurement of high ac voltages (B) measurement of high ac voltages (C) measurement of impulse voltages (C) measurement of impulse voltages (D) all of the above.

(D) all of the above.

117. Flash point of dielectric is usually above 117. Flash point of dielectric is usually above (A) 80°C (A) 80°C (B) 100°C (B) 100°C (C) 140°C (C) 140°C (D) 240°C. (D) 240°C. 118. A fuse is normally a 118. A fuse is normally a (A) current limiting device (A) current limiting device (B) voltage limiting device (B) voltage limiting device (C) power limiting device (C) power limiting device

(D) power factor correcting device. (D) power factor correcting device.

119. Most of the fuses operate due to 119. Most of the fuses operate due to

(19)

(A) heating effect of current (A) heating effect of current (B) magnetic effect of current (B) magnetic effect of current (C) electrostatic effect of current (C) electrostatic effect of current (D) none of the above.

(D) none of the above.

120. Normally the fuse elements are

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

melting point of tin bridge is (A) 35°C (A) 35°C (B) 88°C (B) 88°C (C) 230°C (C) 230°C (D) 540°C. (D) 540°C.

121. The material used for bus bars should have 121. The material used for bus bars should have (A) low resistivity

(A) low resistivity

(B) higher softening temperature (B) higher softening temperature (C) low cost

(C) low cost

122. Insulation resistance of HV circuit breaker

122. Insulation resistance of HV circuit breaker is more thanis more than (A) 100 Ohms (A) 100 Ohms (B) 1 M Ohms (B) 1 M Ohms (C) 500 kOhms (C) 500 kOhms (D)100M Ohms. (D)100M Ohms.

123. The isolator is interlocked with circuit

123. The isolator is interlocked with circuit breaker and earthing switch. While opening the cbreaker and earthing switch. While opening the c ircuitircuit ...

... opens first, then ... opens first, then the ... and only after the ... and only after this the...this the... can .. can closeclose (A) isolator c

(A) isolator circuit breaker...ircuit breaker... earthing switch... earthing switch (B) earthing

(B) earthing switch ...switch ... isolator... isolator... circuit .... circuit breakerbreaker (C) circuit

(C) circuit breaker...breaker... earthing switch ... earthing switch ... isolator.... isolator (D) circuit

(D) circuit breaker ...breaker ... isolator . isolator ... .. earthing ... .. earthing switch.switch.

124. The main factor in favour of t

124. The main factor in favour of t he use of aluminium as bus bar material ishe use of aluminium as bus bar material is (A) its low melting point

(A) its low melting point (B) its high resistivity (B) its high resistivity (C) its low cost

(C) its low cost (D) its low density. (D) its low density.

125. Over-current protection for motor

125. Over-current protection for motor is provided byis provided by (A) cartridge fuses

(20)

(B) high resistance fuses (B) high resistance fuses (C) over-current relay (C) over-current relay (D) all of the above. (D) all of the above.

126. Fuse in motor circ

126. Fuse in motor circuit providesuit provides (A) over current protection

(A) over current protection (B) short-circuit protection (B) short-circuit protection (C) open-circuit protection (C) open-circuit protection (D) none of the above. (D) none of the above.

127. In which method of starting a

127. In which method of starting a motor, the starting current is tmotor, the starting current is the maximum ?he maximum ? (A) Auto-transformer

(A) Auto-transformer (B) Star-delta starter (B) Star-delta starter (C) Stator rotor starter (C) Stator rotor starter (D) Direct-on-line. (D) Direct-on-line.

Questions 128 and 129 refer to data given below : Questions 128 and 129 refer to data given below :

Transformers 250 kVA, 11/0.415 kV percentage impedance 4.75%. Transformers 250 kVA, 11/0.415 kV percentage impedance 4.75%. 128. The rated current for LV side fuse should be

128. The rated current for LV side fuse should be (A) 100 A (A) 100 A (B) 174 A (B) 174 A (C) 200 A (C) 200 A (D) 348 A. (D) 348 A.

129. The rated current

129. The rated current for HV side fuse should befor HV side fuse should be (A) 13.1 A (A) 13.1 A (B) 23.0 A (B) 23.0 A (C) 48 A (C) 48 A (D) 55.5 A. (D) 55.5 A.

130. Which of the following are the

130. Which of the following are the voltage waves of magnitude higher than the desirable value ?voltage waves of magnitude higher than the desirable value ? (A) Over-voltages (A) Over-voltages (B) Surges (B) Surges (C) Transients (C) Transients (D) All of the above. (D) All of the above.

(21)

131. Over-voltage transients may occur due to 131. Over-voltage transients may occur due to (A) lightning (A) lightning (B) switching (B) switching (C) arcing grounds (C) arcing grounds (D) any of the above. (D) any of the above.

132. Which of the following protective devices c

132. Which of the following protective devices c an be used against lightning surges ?an be used against lightning surges ? (A) Horn gap

(A) Horn gap (B) Surge diverters (B) Surge diverters (C) Lightning arresters (C) Lightning arresters (D) Any of the above. (D) Any of the above.

133. Switching surges may be caused 133. Switching surges may be caused byby (A) closing of unchanged line

(A) closing of unchanged line

(B) load shedding at receiving end of line (B) load shedding at receiving end of line (C) switching of magnetizing current (C) switching of magnetizing current (D) any of the above.

134. Surge impedance of over

134. Surge impedance of over-head transmission lines is of the order of-head transmission lines is of the order of (A) 20 to 30 ohms (A) 20 to 30 ohms (B) 300 to 500 ohms (B) 300 to 500 ohms (C) 3000 to 5000 ohms (C) 3000 to 5000 ohms (D) 30 k ohm to 60 k ohm. (D) 30 k ohm to 60 k ohm.

135. The surge impedance of under-ground cables is of

135. The surge impedance of under-ground cables is of the order ofthe order of (A) 20 to 60 ohms (A) 20 to 60 ohms (B) 200 to 600 ohms (B) 200 to 600 ohms (C) 2 k ohm to 5 k ohm (C) 2 k ohm to 5 k ohm (D) 20 k ohm to 60 k ohm. (D) 20 k ohm to 60 k ohm.

136. Which statement is correct 136. Which statement is correct (A) SF6 gas is nontoxic

(A) SF6 gas is nontoxic (B) SF6 gas is lighter than air (B) SF6 gas is lighter than air (C) SF6 gas has pungent (C) SF6 gas has pungent smellsmell (D) SF6 gas is yellow in

(D) SF6 gas is yellow in color.color.

137. The surge impedance, of a

(22)

(A) (LC)1/2 (A) (LC)1/2 (B) (C/L)1/2 (B) (C/L)1/2 (C) (L/C)1/2 (C) (L/C)1/2 (D) (L+C)1/2 . (D) (L+C)1/2 .

138. Surge modifiers are used to 138. Surge modifiers are used to (A) reduce the current of wave-front (A) reduce the current of wave-front (B) reduce the voltage of wave-front (B) reduce the voltage of wave-front (C) reduce the steepness of wave-front (C) reduce the steepness of wave-front (D) modify the shape of wave-front. (D) modify the shape of wave-front.

139. The steepness of the wave-front can be reduced by 139. The steepness of the wave-front can be reduced by (A) connecting a capacitance between line

(A) connecting a capacitance between line and earthand earth (B) connecting an inductor in series with the line (B) connecting an inductor in series with the line (C) either of (A) or (B)

(C) either of (A) or (B) aboveabove

(D) connecting an inductor between line and eart

(D) connecting an inductor between line and eart h and connecting a capacitor in series with h and connecting a capacitor in series with the line.the line.

140. In the circuit breaker, the arcing contacts are made of 140. In the circuit breaker, the arcing contacts are made of (A) electrolytic copper

(A) electrolytic copper (B) copper tungsten alloy (B) copper tungsten alloy (C) aluminium alloy (C) aluminium alloy (D) porcelain. (D) porcelain.

141. The disadvantage offered by ungrounded systems is 141. The disadvantage offered by ungrounded systems is (A) frequent arcing grounds

(A) frequent arcing grounds (B) difficult earth fault relaying (B) difficult earth fault relaying (C) voltage oscillations

(C) voltage oscillations (D) all of the above. (D) all of the above.

142. Solid grounding is used for voltages 142. Solid grounding is used for voltages (A) above 220 kV (A) above 220 kV (B) above 11 kV (B) above 11 kV (C) below 660 V (C) below 660 V (D) below 115 V. (D) below 115 V.

143. Resistance grounding is used for voltages 143. Resistance grounding is used for voltages

(23)

(A) below 220 V (A) below 220 V (B) up to 660 V (B) up to 660 V (C) between 3.3 kV to 11 kV (C) between 3.3 kV to 11 kV (D) above 66 kV. (D) above 66 kV.

144. Switching over-voltages are more

144. Switching over-voltages are more hazardous than lightning surges in case ofhazardous than lightning surges in case of (A) Low voltage systems

(A) Low voltage systems (B) 11 kV systems

(B) 11 kV systems

(C) Unbalanced systems (C) Unbalanced systems (D) EHV and UHV systems. (D) EHV and UHV systems.

145. Current limiting reactors may be 145. Current limiting reactors may be (A) air cooled, air cored

(A) air cooled, air cored

(B) oil immersed magnetically shielded (B) oil immersed magnetically shielded (C) oil immersed

(C) oil immersed non-magnetically shieldednon-magnetically shielded (D) any of the above.

146. Series reactors are installed at strategic locations of power systems to 146. Series reactors are installed at strategic locations of power systems to (A) bring down the fault level within the c

(A) bring down the fault level within the c apacity of switchgearapacity of switchgear (B) directly pass the fault surges to

(B) directly pass the fault surges to groundground (C) pass neutralizing surges of opposite nature (C) pass neutralizing surges of opposite nature (D) discharge the capacitors.

(D) discharge the capacitors.

147. Fault diverters 147. Fault diverters

(A) divert the current to earth in the event of short-circuits (A) divert the current to earth in the event of short-circuits (B) neutralize the surges by resistors

(B) neutralize the surges by resistors (C) modify the surge wave shapes (C) modify the surge wave shapes (D) none of the above.

(D) none of the above.

148. In star connected system without neutral grounding, zero sequence currents are 148. In star connected system without neutral grounding, zero sequence currents are (A) same as peak value of phase curre

(A) same as peak value of phase curre ntnt (B) same as rms value of phase currents (B) same as rms value of phase currents (C) vector sum of phase currents

(C) vector sum of phase currents (D) zero.

(D) zero.

149. In which portion of the

(24)

(A) Transformers (A) Transformers (B) Overhead lines (B) Overhead lines (C) Alternators (C) Alternators (D) Underground cables. (D) Underground cables.

150. Bulk-oil circuit breaker is suitable for voltages up 150. Bulk-oil circuit breaker is suitable for voltages up toto (A)10kV (A)10kV (B) 16 kV (B) 16 kV (C) 26 kV (C) 26 kV (D) 36 kV. (D) 36 kV.

151. The ohmic value of impedance to be

151. The ohmic value of impedance to be connected in the neutral to grconnected in the neutral to ground circuit of a 2000 kVAound circuit of a 2000 kVA transformer with earth fault relay set to 40%, with respect to 400 V side will be

transformer with earth fault relay set to 40%, with respect to 400 V side will be (A) 0.2 ohm (A) 0.2 ohm (B) 2.0 ohms (B) 2.0 ohms (C) 20 ohms (C) 20 ohms (D) 200 ohms. (D) 200 ohms.

Questions 152 and 153 refer

Questions 152 and 153 refer to data given below:to data given below:

A 3-phase, 5000 kVA, 6.6 kV generator having 12% sub-transient reactance. A 3-phase short-circuit A 3-phase, 5000 kVA, 6.6 kV generator having 12% sub-transient reactance. A 3-phase short-circuit occurs at its terminals.

occurs at its terminals. 152. Fault MVA is 152. Fault MVA is (A) 21.5 (A) 21.5 (B) 41.66 (B) 41.66 (C) 53.33 (C) 53.33 (D) 75.75. (D) 75.75. 153. Fault current is 153. Fault current is (A) 3640 A (A) 3640 A (B) 2460 A (B) 2460 A (C) frequency (C) frequency (D) 880 A. (D) 880 A.

154. The actuating quantity for the re

154. The actuating quantity for the re lays can belays can be (A) magnitude

(A) magnitude (B) phase angle (B) phase angle

(25)

(C) frequency (C) frequency

155. Electro-magnetic relays may be operate 155. Electro-magnetic relays may be operate d byd by (A) electro-magnetic attraction

(A) electro-magnetic attraction (B) electro-magnetic induction (B) electro-magnetic induction (C) thermal effect

(C) thermal effect (D) any of the above. (D) any of the above.

156. Which of the following is not a

156. Which of the following is not a relay using electromagnetic forcerelay using electromagnetic force (A) Buchholz relay

(A) Buchholz relay (B) Induction cup relay (B) Induction cup relay (C) Balanced beam relay (C) Balanced beam relay

(D) Attracted armature type relay. (D) Attracted armature type relay.

157. Buchholz relay is operated by 157. Buchholz relay is operated by (A) Eddy currents

(A) Eddy currents (B) Gas pressure (B) Gas pressure (C) Electro-magnetic induction (C) Electro-magnetic induction (D) Electro-static induction. (D) Electro-static induction.

158. Thermal relays are often used 158. Thermal relays are often used inin (A) generator protection

(A) generator protection (B) transformer protection (B) transformer protection (C) motor starters

(C) motor starters (D) none of the above. (D) none of the above.

159. A bimetal strip consists of two met

159. A bimetal strip consists of two met al strips have differental strips have different (A) thermal diffusivity

(A) thermal diffusivity (B) thermal conductivity (B) thermal conductivity (C) specific beat

(C) specific beat (D) coefficient of e

(D) coefficient of e xpansion.xpansion.

160. Differential protection principle is used in the protection of 160. Differential protection principle is used in the protection of (A) generators

(A) generators (B) transformers (B) transformers

(26)

(C) feeders (C) feeders

TRUE OR FALSE TRUE OR FALSE

1. The voltage across the circuit breaker pole after final current zero is recovery voltage. 1. The voltage across the circuit breaker pole after final current zero is recovery voltage.

A True A True B False B False

2. Air circuit breakers are used for voltages above 12 kV. 2. Air circuit breakers are used for voltages above 12 kV.

3. Double pressure type SF6

3. Double pressure type SF6 circuit breaker is also known as Puffer type.circuit breaker is also known as Puffer type. A True

A True B False B False

4. Air blast circuit breakers and SF

4. Air blast circuit breakers and SF6 circuit breakers are 6 circuit breakers are preferred for EHV applications.preferred for EHV applications. A True

5. Arcing contacts of circ

5. Arcing contacts of circuit-breakers are generally made of copper uit-breakers are generally made of copper tungsten alloy.tungsten alloy. A True

6. The are plays important role

6. The are plays important role in the behavior of circuit breaker.in the behavior of circuit breaker. A True

(27)

B B FalseFalse

7. The arc has a brightly burning core of high temperature ranging from 6000 K to 25000 K. 7. The arc has a brightly burning core of high temperature ranging from 6000 K to 25000 K.

8. SF6 is a

8. SF6 is a heavy, colorless and chemically inert gas.heavy, colorless and chemically inert gas. A True A True B False B False 9. SF6 gas is electro-positive. 9. SF6 gas is electro-positive. A True A True B False B False

10. In oil circuit breakers

10. In oil circuit breakers transformer oil is used.transformer oil is used. A True

11. . An isolator does not have

11. . An isolator does not have any current making or current breaking capacity.any current making or current breaking capacity. A True

12. SF6 circuit breaker

12. SF6 circuit breaker takes minimum time for installation.takes minimum time for installation. A True

(28)

13. A triple pole isolator has thre

13. A triple pole isolator has three identical poles, with operate simultaneously.e identical poles, with operate simultaneously. A True

14. Isolators operate under no

14. Isolators operate under no current conditions.current conditions.

15. Non-linear resistors are used in lightning arresters. 15. Non-linear resistors are used in lightning arresters.

16. Switching over-voltages are proportional to system voltages. 16. Switching over-voltages are proportional to system voltages.

17. Switching over-voltages arise from energizing of

17. Switching over-voltages arise from energizing of uncharged line can be reduced by the uncharged line can be reduced by the use of highuse of high voltage shunt reactors.

voltage shunt reactors. A True

18. The damage caused by surge

18. The damage caused by surge depends on steepness of the wave-front.depends on steepness of the wave-front. A True

19. Bulk oil circuit breaker is used

19. Bulk oil circuit breaker is used for outdoor UHV application.for outdoor UHV application. A True

(29)

B B FalseFalse

20. In electro-magnetic relays t

20. In electro-magnetic relays the restraining torque is given by springs.he restraining torque is given by springs. A True

21. For remote operation c

21. For remote operation circuit-must breaker be equipped with shunt trip.ircuit-must breaker be equipped with shunt trip. A True

22. A protective system which re

22. A protective system which responds to vector difference between two sponds to vector difference between two electrical quantities is knownelectrical quantities is known as differential protection. as differential protection. A True A True B False B False

23. Protective systems prevent faults by disconnecting an equipment in

23. Protective systems prevent faults by disconnecting an equipment in the event of abnormalthe event of abnormal condition. condition. A True A True B False B False

24. Selectivity is the property

24. Selectivity is the property by virtue of which the protective relaying system distinguishes betweenby virtue of which the protective relaying system distinguishes between normal condition and abnormal condition.

normal condition and abnormal condition.

A True A True

(30)

B B FalseFalse

25. Frequency relays are used in generator protection. 25. Frequency relays are used in generator protection.

26. SF6 circuit breaker

26. SF6 circuit breaker has high reliability and negligible maintenance.has high reliability and negligible maintenance.

27. Tripping relays are slow and generally attracting

27. Tripping relays are slow and generally attracting armature type.armature type.

28. The over-current relays are

28. The over-current relays are connected to the system normally by means of CT's.connected to the system normally by means of CT's.

29. Core balance CT's are

29. Core balance CT's are used for earth-fault protection.used for earth-fault protection. A True

(31)

30. Short circuit tests are conducted on circuit breakers to prove the ratings of the circuit-breakers. 30. Short circuit tests are conducted on circuit breakers to prove the ratings of the circuit-breakers.

31. Fusing factor is the r

31. Fusing factor is the ratio of minimum fusing current to the current atio of minimum fusing current to the current rating.rating. A True

32. The distance protection responds to the

32. The distance protection responds to the ratio V/I.ratio V/I. A True

33. Graded time lag and grade current over-current protection is used for single radial feeder where 33. Graded time lag and grade current over-current protection is used for single radial feeder where time lag can be permitted.

time lag can be permitted. A True

34. Distance relaying is based on measurement o

(32)

A A TrueTrue B False B False

35. Distance relay is used where time lag can be permitted. 35. Distance relay is used where time lag can be permitted.

36. Pilot wire differential relaying is used for

36. Pilot wire differential relaying is used for lines up to 40 km of length.lines up to 40 km of length. A True

37. In motor starter,

37. In motor starter, thermal relay provides overload protection as well as single phasing protection.thermal relay provides overload protection as well as single phasing protection.

38. Protection against unbalanced supply voltage is provided by negative phase sequence

38. Protection against unbalanced supply voltage is provided by negative phase sequence relays.relays. A True

(33)

39. Breaking current of a pole on a circuit breaker is the current in that pole at the instant of contact 39. Breaking current of a pole on a circuit breaker is the current in that pole at the instant of contact separation. separation. A True A True B False B False

40. Most of the alternators are

40. Most of the alternators are provided with Buchholz relay in addition to differential protection.provided with Buchholz relay in addition to differential protection. A True

1. A sudden short-circuit in an ac

1. A sudden short-circuit in an ac system causes a rise in __________ in the short-circuited phase.system causes a rise in __________ in the short-circuited phase.

2. The voltage appearing across the

2. The voltage appearing across the circuit breaker pole after final currcircuit breaker pole after final curr ent zero is called __________ent zero is called __________ voltage.

voltage.

3. Thermal ionization of gases occurs at temperature ar

3. Thermal ionization of gases occurs at temperature ar ound ________ound __________ C.__ C.

4. The electron emission from contact surface

4. The electron emission from contact surface caused by incidence of light energy is caused by incidence of light energy is called __________called __________..

5. De ionization can take place by t

5. De ionization can take place by t he processes of recombination or attachment as well as he processes of recombination or attachment as well as by process ofby process of __________ a

__________ and _________nd __________._.

6. The behavior of arc in high vacuum is

(34)

7. Sphere gaps are used for measurement of __________. 7. Sphere gaps are used for measurement of __________.

8. Current breakers are

8. Current breakers are generally overhauled every __________ years.generally overhauled every __________ years.

9. In circuit breakers,

9. In circuit breakers, arc is extinguished either by __________ the arc __________ the arc orarc is extinguished either by __________ the arc __________ the arc or __________ th

__________ the arc.e arc.

10. Deterioration of dielectric oil is g

10. Deterioration of dielectric oil is g overned by __________ color.overned by __________ color.

11. The characteristics of a fuse

11. The characteristics of a fuse is governed by material and __________ of the fuse element.is governed by material and __________ of the fuse element.

12. A fuse should generally have a normal r

12. A fuse should generally have a normal r ating 25 to 50 percent above ating 25 to 50 percent above the normal full load current tothe normal full load current to lake care of

lake care of __________________.__.

13. Skin effect is absent

13. Skin effect is absent in case of __________ current.in case of __________ current.

14. Insulators operate

14. Insulators operate under __________ conditionunder __________ conditions.s.

15. Melting point of

15. Melting point of aluminium is _________aluminium is __________._.

16. Density of

16. Density of aluminium is nearly __________ of the density of copper.aluminium is nearly __________ of the density of copper.

17. Melting point of

17. Melting point of copper is __________ 0C.copper is __________ 0C.

18. Pantograph isolator is preferred for circ

(35)

19. __________ current is the rms value of the current which a

19. __________ current is the rms value of the current which a breaker must carry for breaker must carry for a stated time.a stated time.

20. The insulation requirements of switchgear are

20. The insulation requirements of switchgear are determined by __________ vdetermined by __________ voltage.oltage.

21. In horn gaps the

21. In horn gaps the arc is produced at the __________ during high voltage surge.arc is produced at the __________ during high voltage surge.

22. Secondary type lightning arresters ar

22. Secondary type lightning arresters ar e used for the protection of __________ transformers.e used for the protection of __________ transformers.

23. The non-linear resistor in lightning arrester offers __________ resistance to the flow of discharge 23. The non-linear resistor in lightning arrester offers __________ resistance to the flow of discharge currents and __________ resistance to power frequency voltage.

currents and __________ resistance to power frequency voltage.

24. The surge current w

24. The surge current which flows through the lightning arrester after the hich flows through the lightning arrester after the spark over is expressed inspark over is expressed in terms of __________ value.

terms of __________ value.

25. The most severe cause

25. The most severe cause of switching over-voltages is __________.of switching over-voltages is __________. 26 __________ type lightening arresters are designed to discharge the 26 __________ type lightening arresters are designed to discharge the switching over-voltage as well as lightning over-voltages.

switching over-voltage as well as lightning over-voltages.

27. Traveling wave gets reflected

27. Traveling wave gets reflected from short circuited line with reflected from short circuited line with reflected current wave of __________current wave of __________ polarity and voltage wave

polarity and voltage wave of the __________ polarity.of the __________ polarity.

28. Peterson coil is the

28. Peterson coil is the reactance used in __________ earthing.reactance used in __________ earthing.

29. The phenomena of arcing grounds is commonly experienced w

(36)

30. In solid grounding system, the neutral is connected to ground without any __________ between 30. In solid grounding system, the neutral is connected to ground without any __________ between neutral and ground.

neutral and ground.

31. The grounding is generally at the __________ end. 31. The grounding is generally at the __________ end.

32. Insulation co-ordination of EHV

32. Insulation co-ordination of EHV and UHV line is and UHV line is based on __________.based on __________.

33. In delta connected load, the

33. In delta connected load, the line current return path. Hence line curreline current return path. Hence line curre nts __________ zero sequencents __________ zero sequence component.

component.

34. The negative sequence network

34. The negative sequence network has only negative sequence __________.has only negative sequence __________.

35. The smallest value of actuating quantity at which protection star

35. The smallest value of actuating quantity at which protection star ts operating in relation with thets operating in relation with the minimum value of fault current in the protected

minimum value of fault current in the protected zone, is known as __________ of the protectivezone, is known as __________ of the protective scheme.

scheme.

36. Trip circuit

36. Trip circuit is normally a part of is normally a part of ___________________._.

37. The time elapsed between the

37. The time elapsed between the instant of occurrence of fault and instant of final arc instant of occurrence of fault and instant of final arc extinction inextinction in circuit breaker

circuit breaker is known as __________.is known as __________.

38. The time interval between oc

38. The time interval between occurrence of fault and closure of recurrence of fault and closure of re lay contacts is known as __________.lay contacts is known as __________.

39. The lime interval between closure o

39. The lime interval between closure o f trip circuit and final arc interrf trip circuit and final arc interruption is known as ________uption is known as __________.__.

40. Acting ground

(37)

41. Phase fault

41. Phase fault is __________ fault.is __________ fault.

42. A relay which responds to

42. A relay which responds to increase in current is known as __________.increase in current is known as __________.

43. Power line carrier

43. Power line carrier is a __________ signal sent through the power line conductors.is a __________ signal sent through the power line conductors.

44. Static

44. Static relays _________relays __________ moving parts._ moving parts.

45. An electro-magnetic relay will operate

45. An electro-magnetic relay will operate when operating force is __________ restraining force.when operating force is __________ restraining force.

46. __________ is suitable for outdoor UHV and HV traction system. 46. __________ is suitable for outdoor UHV and HV traction system.

47. The drop off value to pick-up value of

47. The drop off value to pick-up value of a relay is also known as __________.a relay is also known as __________.

48. The holding ratio

48. The holding ratio of a relay of a relay is usually __________is usually __________..

49. A bimetal strip consists of two

49. A bimetal strip consists of two metal strips having different __________.metal strips having different __________.

Upda-multiple Choice Questions

1.D --- 2.B --- 3.C

1.D --- 2.B --- 3.C --- 4.D --- 5.C --- 6.D --- 7.C

--- 4.D --- 5.C --- 6.D --- 7.C --- 8.D ---9.D ---10.C ---

8.D 9.D 10.C

11.D 12.D 13.D 14.C 15.D 16.A 17.D 18.D 19.D

11.D 12.D 13.D 14.C 15.D 16.A 17.D 18.D 19.D