Power System MCQ With Answers PDF

61. Installation of capacitors at suitable locations and of optimum size in a distribution system results in

1. improved voltage regulation.
2. reduction in distribution power losses.
3. reduction of kVA rating of distribution transformers.

Select the correct answer from the codes given below :
(a) 1 alone
(b) 1 and 2
(c) 1, 2 and 3
(d) 3 alone

62. Insulation coordination for UHV lines (above 500 kV) is done based on

(a) lightning surges.
(b) lightning surges and switching surges.
(c) switching surges.
(d) none of the above.

63. As compared to ac transmission dc transmission is free from

(a) inductance.
(b) capacitance.
(c) phase displacement.
(d) all of the above.

64. In a dc transmission line

(a) it is necessary for the sending end and receiving end to be operated in synchronism.
(b) the effects of inductive and capacitive reactances are greater than in an ac transmission line of the same rating.
(c) there are no effects due to inductive and capacitive reactances.
(d) power transfer capability is limited by stability considerations.

65. HVDC transmission is preferred to HVAC because

(a) HVDC terminal equipment are inexpensive.
(b) VAR compensation is not required in HVDC system.
(c) system stability can be improved.
(d) harmonics problem is avoided.

66. High Voltage DC (HVDC) transmission is mainly used for

(a) bulk power transmission over very long distances.
(b) interconnecting two systems with the same nominal frequency.
(c) eliminating reactive power requirement in the operation.
(d) minimizing harmonics at the converter stations.

67. Consider the following statements regarding HVDC power transmission:

1. The modern HVDC systems use 12-pulse converters.
2. DC systems never use ground or sea return.
3. Most of present-day dc schemes are two-terminal links.

Which of the statements given above is/are correct?
(a) 1, 2 and 3.
(b) 1 only.
(c) 2 and 3 only.
(d) 1 and 3 only.

68. Choose the appropriate auxiliary components of HVDC transmission system from the following

1. DC line inductor.
2. AC line inductor.
3. Reactive power sources.
4. Distance relays on dc line.
5. Series capacitance on AC line.

(a) 1 and 2
(b) 1 and 3
(c) 2 and 4
(d) 4 and 5

69. Bulk power transmission over long HVDC lines are preferred on account of

(a) low cost of HVDC terminals.
(b) no harmonic problems.
(c) minimum line power losses.
(d) simple protection.

70. Consider the following statements: HVDC transmission is superior to HVAC transmission due to

1. Lack of reliable dc circuit breakers.
2. Lesser number of conductors for same power carrying capacity.
3. Non-synchronous link between two different systems simplifying the problem of voltage stability and frequency.
4. No costly terminal equipments such as converters and inverters are required.

Which of the above statements is; are correct?
(a) 4 only.
(b) 4 and 3.
(c) 1 and 2.
(d) 2 and 3.

71. For bulk power transmission over long distance HVDC transmission is

(a) is economically and technically superior to ac transmission.
(b) not good alternative to ac transmission.
(c) not economically viable.

72. Corona loss in a dc line is

(a) less than that in ac line operating at same rms voltage.
(b) more than that in ac line at the same rms voltage.
(c) same as in ac line at equal rms voltage.

73. In the case of an HVDC system, there is

(a) charging current but no skin effect.
(b) no charging current but skin effect.
(c) neither charging current nor skin effect.
(d) both charging current and skin effect.

74. Which one of the following statements in respect of HVDC transmission line is not correct ?

(a) The power transmission capability of bipolar line is almost the same as that of single circuit ac line.
(b) HVDC link can operate between ac systems whose frequencies need not be equal.
(c) There is no distance limitation for HVDC transmission by UG cable.
(d) Corona loss is much higher in HVDC transmission line.

75. A dc line carries

(a) less power than an equivalent ac line.
(b) more power than the ac line.
(c) same power as an ac line.

76. Back to back HVDC is used to

(a) increase the transmission capability.
(b) decrease line losses.
(c) provide stable interconnection.
(d) reduce voltage drop.

77. HVDC transmission needs

(a) pulse converters.
(b) dc generators.
(c) ac filters.
(d) dc filters.
(e)transformers.

78. In an HVDC link, power flows

(a) from the rectifier end to the inverter end.
(b) from the inverter end to the rectifier end.

79. In HVDC system a converter acts as a rectifier when the firing angle α has a value

(a) 0 < α <120^o
(b) 0 < α <90^o
(c) 90^o < α <180^o

80. In a 3-phase converter used in HVDC transmission, the three anodes conduct sequentially. Due to overlap caused by circuit inductance, two anodes conduct simultaneously during overlap period. The output voltage waveform during this period is the

(a) voltage of the 1st anode, because the second anode has not completely taken over.
(b) mean of the two anode voltages, as they conduct together.
(c) voltage of second anode, because the voltage of this anode is greater than that of the 1st.
(d) sum of 1st and the second anode voltages because both the anodes are conducting.

81. The capital cost on a HVDC converter is

(a) less than ac substation.
(b) more than ac substation.
(c) same as that of ac substation.

82. Consider the following statements regarding the suitable choice of HVDC converter configuration:

1. Pulse number should be high.
2. Ratio of peak inverse voltage to no-load dc output voltage should be as high as possible.
3. Transformer utilization factor should be nearly unity.

Which of the statements given above are correct?
(a) 1 and 2
(b) 1, 2 and 3
(c) 2 and 3
(d) 1 and 3

83. Consider the following statements: The suitable configuration of HVDC converter is decided on the requirements of

1. high pulse number.
2. converter transformer utilization factor should be near to unity.

Which of the above statements is/are correct?
(a) 1 only.
(b) Both 1 and 2.
(c) Neither 1 nor 2.
(d) 2 only.

84. In HVDC transmission there are predominant

(a) voltage harmonics on dc side and current harmonics on ac side of converters.
(b) current harmonics on dc side and voltage harmonics on ac side of converters.
(c) current harmonics only on the dc side of converters.
(d) voltage harmonics only on the ac side of converters.

85. High voltage dc transmission requires filters for

(a) current harmonics on ac side and voltage harmonics on dc side.
(b) voltage harmonics on ac side and current harmonics on dc side.
(c) voltage harmonics on both ac and de sides.
(d) current harmonics on both ac and dc sides.

86. An HVDC link consists of rectifier, inverter, transmission line and other equipments. Which one of the following is true for this link?

(a) The transmission line produces/supplies reactive power.
(b) The rectifier consumes reactive power and the inverter supplies reactive power from/to the respective connected ac systems.
(c) Rectifier supplies reactive power and the inverter consumes reactive power to/from the respective connected ac systems.
(d) Both the converters (rectifier and inverter) consume reactive power from the respective connected ac systems.

 

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