Quiznetik

Testing and Commissioning of Electrical Equipment’s | Set 3

1. For the protection of a large squirrel cage induction motor against single phase normally

Correct : D. Negative sequence current sensitive relay is used

2. The most commonly used method for the protection of three phase feeder is

Correct : B. Differential protection

3. Which is the pilotless protection method for feeder line ?

Correct : B. Carrier current protection

4. Time graded protection of a radial feeder can be achieved by using

Correct : C. Both definite and inverse time relays

5. Pilot-wire protection scheme is the most economical and provides high speed relaying for

Correct : A. Short length of lines upto 15 km

6. Problems associated with differential protection is/are

Correct : D. All of the above

7. For the protection of transformers, harmonic restraint is used to guard against

Correct : A. Magnetising inrush current

8. The types of faults that occur in electric motors are

Correct : D. All of the above

9. The main function of under voltage protective device generally employed with a motor starter is to

Correct : A. Open the supply circuit on failure of power supply

10. The bias factor S in unit protection synchronous generators

Correct : A. Lies between .05 and .1 pu

11. In a balanced voltage pilot wire protection scheme if the pilot circuit gets opened, the relay will

Correct : A. Fail to trip on internal faults

12. In a balanced voltage pilot-wire protection scheme, if the pilot circuit gets shortcircuited, the relay will

Correct : C. Trip on full load

13. The frequency of carrier in the carrier current pilot scheme is in the range of

Correct : D. 50 kHz to 500 kHz

14. The frequency of carrier transmitted by microwave pilot is in the range of

Correct : C. 900 kHz to 6000 kHz

15. In carrier current protection the purpose of the wave trap is for

Correct : B. Trapping high frequency waves entering into generators/ transformer unit

16. As soon as a fault develops in a generator stator, it is essential to suppress field excitation, otherwise

Correct : C. It will continue to supply power to the stator winding fault

17. Distance protection scheme is preferred over graded lime-lag over-current protection in HV and EHV lines because

Correct : A. It is faster in operation

18. Requirements of protection power station buildings against direct strokes are

Correct : D. All of the above

19. The protection against direct lighting strokes and a high-voltage steep waves is provided by

Correct : C. Lightning arresters and ground wires

20. For protection of rotating machines against lightning surge .............is used

Correct : C. Combination of lightning arrester and a capacitor

21. In between the generating station and consumers a number of transformation and switching stations exist, these are called the

Correct : B. Substations

22. With large reactance interconnector between two power stations

Correct : A. The power stations may fall out of step due to large angular displacement between the power stations

23. In a isolated neutral system, when a single line to ground fault occurs

Correct : D. All of the above

24. Tap changing transformers are employed for

Correct : D. Both stepping up and stepping down the voltage

25. Field failure in an alternator occurs due to

Correct : D. Both A and B

26. Large internal faults are protected by

Correct : A. Merz price percentage differential protection

27. Which of the following is the least expensive protection for over current in lowvoltage system ?

Correct : A. Rewireable fuse

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

Correct : C. Interception, conduction and dissipation

29. The line insulation is............. the insulation level at the station equipment

Correct : D. Not directly related with

30. Short-circuit currents are due to

Correct : D. Any of these

31. For which of the following protection from negative sequence current is provided?

Correct : A. Generators

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

Correct : B. Equal to and above 5 MVA

33. Over voltage protection is recommended for

Correct : D. All of the above

34. Overfluxing protection is recommended for

Correct : B. Generator transformer of the power plant

35. Hey switchgear is device used for

Correct : D. Switching, controlling and protecting the electrical circuit and equipment

36. Switching over voltage arc are more hazardous than lighting surges in case of

Correct : D. EHV and UHV systems

37. Least number of faults are generally reported for

Correct : B. Cables

38. Minimum working voltage will be least in case of

Correct : A. Silver

39. In a contactor, interrupting medium may be

Correct : D. Any of the above

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

Correct : C. Restriking

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

Correct : B. Motor

42. SF6 gas

Correct : C. Is non-toxic

43. SF6 gas is transported in

Correct : C. Liquid from in cylinders

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

Correct : D. Impulse voltage

45. The actuating quantity for the relays may be

Correct : D. Any of the above

46. The operating speed of a relay depends upon the

Correct : D. All of these

47. Inverse time current relays are used for the protection of

Correct : D. Both A and B

48. IDMT relays are used to protect the power transformers against

Correct : D. Both A and B

49. In distance protection, the relay measures

Correct : B. Positive sequence impedance of the line from relay up to the fault point

50. The relay used for phase fault protection of short transmission lines is

Correct : A. Reactance relay

51. Where severe synchronising swing occur, the relay employed is

Correct : B. Mho relay

52. For the protection of lines against faults involving variable fault resistance, the preferred relaying scheme is a

Correct : D. Reactance relay

53. For ground fault we prefer

Correct : D. Reactance relay

54. Admittance relay

Correct : B. Directional relay

55. The relay used for feeder protection is

Correct : B. Translay relay

56. Which relay is used to detect and protect internal fault in a transformer ?

Correct : A. Buchholz relay

57. Which one of the following relay has the capability of anticipating the possible major fault in a transformer ?

Correct : C. Buchholz relay

58. Zero sequence current is used for relaying purpose only in the case of

Correct : C. Ground over current relay

59. To prevent mal operation of differentially connected relay while energising a transformer, the relay restraining coil is biased with

Correct : A. Second harmonic current

60. How many relays are used to detect interphase fault of a three line system?

Correct : C. Three

61. Which is the main relay for protecting up to 90% of the transmission line-length in the forward direction?

Correct : B. Mho relay

62. For protection of parallel feeders fed from one end, the relays required are

Correct : A. Nondirectional relays at the source end and directional relay at the load end

63. Relays can be designed to respond to changes in

Correct : D. All of the above

64. DC shunt relays are made of

Correct : C. Many turns of thin wire

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

Correct : D. Have all above properties

66. Interruption of large currents by relay requires

Correct : D. All of the above

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

Correct : C. Both A and B

68. ............. Relays are used for phase faults on long line

Correct : A. Impedance

69. ........ Relays is preferred for phase fault on short transmission line

Correct : B. Reactance

70. The under voltage relay can be used for

Correct : D. All of the above

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

Correct : D. Three phase motors

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

Correct : B. Internal short circuits

73. In a static over current relay, inverse time characteristics are obtained by

Correct : B. An integrating circuit

74. In the case of transmission line protection, over current relay is used

Correct : C. Only up to 50 KV

75. Directional over current relays have two exciting coils connected across

Correct : C. CT and VT secondaries of same phases

76. The domains of power system where directional over current relay is indispensable are

Correct : C. Both A and B

77. In an inverse definite minimum time, electromagnetic type over current relay, the minimum time feature is achieved because of

Correct : A. Saturation of the magnetic circuit

78. Impedance relay can be used for

Correct : A. Phase faults only

79. Impedance relay may use

Correct : D. Either A or B

80. An impedance is relay is a

Correct : A. Voltage restrained over current relay

81. On transient fault OC and impedance relay

Correct : A. Under reaches

82. Threshold characteristics of a plain impedance relay in a complex Z plane is a

Correct : B. Circle with the centre at the origin

83. The structure used in reactance relay is

Correct : D. Either A or B

84. Reactance relay is normally used for protection against

Correct : A. Earth fault only

85. The operating characteristics of the reactance relay in the complex impedance plane is a

Correct : D. Straight line parallel to the X axis

86. A reactance relay is

Correct : C. Directional restrained overcurrent relay

87. Reactance relays are used for phase fault in.......line

Correct : A. Short

88. A differential relay response to

Correct : B. Phasor difference of two or more similar electrical quantities

89. Differential relays are used for protection of

Correct : D. All of the above

90. Differential relays are used for protection of equipments against

Correct : A. Internal faults

91. In a biased differential relay the bias is defined as a ratio of

Correct : B. Operating coil current and restraining coil current

92. Both voltage and current signals are required for

Correct : C. A directional relay