MCQ Questions on Transmission & Distribution

51. A feeder with reactance of 0.2 p.u. has a sending-end voltage of 1.2 p.u. If the reactive power supplied at the receiving end of the feeder is 0.3 p.u., the approximate voltage drop in the feeder will be

(a) 0.042 p.u.
(b) 0.052 p.u.
(c) 0.060 p.u.
(d) 0.070 p.u.

52. The insulation strength of EHV lines is mainly governed by

(a) Switching over voltages
(b) Lightning over voltages
(c) Power frequency over voltages
(d) Dynamic over voltages

53. The power factor of a system on a 460 V, 3 Phase, 60 Hz, in which the ammeter indicates 100 amp and watt meter reads 62 kW will be

(a) 0.95 lag
(b) 0.78 lag
(c) 0.65 lag
(d) 0.55 lag

54. Consider the following statements:

Transient stability of a synchronous generator feeding power to an infinite bus through a transmission line can be increased by

1. Increasing the steam supply to the turbine driving the generator during fault clearing.
2. Connection resistors at the generator terminals during fault conditions.
3. Employing a faster excitation system.
4. Quickly throwing off the generator load. Which of these statements are correct?

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

55. The steady-state stability limit of a synchronous generator can be increased by

(a) An increase in its reactance
(b) An increase in the excitation of the machine
(c) A decrease in the moment of inertia to the machine
(d) An increase in the moment of inertia of the machine

56. Consider the following statements

The calculations performed using short-line approximate model instead of nominal π model for a medium length transmission line delivering lagging load at a given receiving-end voltage always result in higher

1. Sending-end current.
2. Sending-end power.
3. Regulation.
4. Efficiency.

Which of these statements are correct?
(a) 1 and 2
(b) 3 and 4
(c) 1, 2 and 3
(d) 1, 2 and 4

57. A short length of cable is connected between dead-end tower and sub-station at the end of a transmission line. Which of the following will decrease, when voltage wave is entering from overhead line to cable?

1. Velocity of propagation of voltage wave.
2. Steepness of voltage wave
3. Magnitude of voltage wave.

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

58. The receiving end voltage of a three-phase 50 Hz single circuit long power transmission line may exceed the sending end voltage during

(a) Peak load conditions
(b) Intermediate load conditions
(c) Light load conditions
(d) None of these

59. Phase modifiers in AC transmission line are

(a) synchronous machines
(b) induction machines
(c) DC machines
(d) Transformers

60. For nominal π-representation of the transmission lines, the ABCD parameters are related to Z and Y of the line, such that C parameter is given by

(a) C = 1 + (1/2)YZ
(b) C = Z
(c) C = Y(1 + (1/4)YZ)
(d) C = Z(1 + (1/4)YZ)

61. A string insulator has 5 units. The voltage across the bottom-most unit is 25% of the total voltage. The string efficiency is

(a) 25 %
(b) 50 %
(c) 80%
(d) 75 %

62. Consider the following statements with respect to an interconnected power system

1. Frequency will be same at all buses in the system.
2. Voltages can be different at different buses.
3. Both frequency and voltage can be different at different buses.

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

63. The function of the earth wire in an extra high voltage line is to

(a) Prevent earth fault
(b) Provide a safety measure for any high flying object
(c) Provide a shield to the phase conductors from direct lightning stroke
(d) Provide mechanical strength to the towers

64. Capacitance Voltage Transformer (CVT) is used to

(a) Improve the power factor of the transmission
(b) Connect instruments on the LT side
(c) Ground the over voltage surges on transmission lines
(d) Both (b) and (c)

65. The per-unit “regulation” of a short transmission line, having a per-unit resistance voltage drop v_r and a per unit reactance voltage drop of v_x at rated current and, with power-factor cos θ  is given by

(a) (v_r + v_x)cos θ 
(b) (v_r + v_x )sin θ 
(c) v_r cos θ  + v_r sin θ 
(d) v_r sin θ  + v_x cos θ

66. The surge impedance of a 100 km long underground cable is 50 ohms. The surge impedance of a 10 km long similar cable would be

(a) 20 ohms
(b) 50 ohms
(c) 80 ohms
(d) 125 ohms

67. A string insulator has 4 units. The voltage across the bottom-most unit is 33.33% of the total voltage, its string efficiency is

(a) 25 %
(b) 33.33%
(c) 66.67%
(d) 75 %

68. The design of insulation for systems above 400 KV, is based upon

(a) Lightning over voltage
(b) Switching surges
(c) System voltage level
(d) System load level

69. Bundled conductors in EHV transmission systems provide

(a) Increased line reactance
(b) Reduced line capacitance
(c) Reduced voltage gradient
(d) Increased corona loss

70. For a given power delivered, if the working voltage of a distributor line is increased to n times, the cross sectional area A of the distributor line, would be reduced to

(a) A/n
(b) A/n²
(c) A/2n²
(d) A/2n

71. For a transmission line with negligible losses, the lagging reactive power (VAR) delivered at the receiving end, for a given receiving-end voltage, is directly proportional to the

(a) Square of the line voltage drop
(b) Line voltage drop
(c) Line inductive reactance
(d) Line capacitive reactance

72. A voltage control bus is characterized by the specified values of

(a) Real and reactive powers
(b) Real power and voltage phase angle
(c) Real power and voltage magnitude
(d) Reactive power and voltage magnitude

73. The X/R ratio for distribution lines is

(a) Less than unity
(b) More than unity
(c) Equal to unity
(d) None of these

74. Corona loss is minimum in

(a) Monopolar HVDC line
(b) Bipolar HVDC line
(c) Both in Monopolar and Bipolar HVDC lines
(d) EHV AC lines

75. In case of a ‘High Voltage DC’ transmission, how many minimum conductors are required?

(a) One
(b) Two
(c) Three
(d) Four

76. Why are shunt reactors connected at the receiving end of long transmission line system

(a) To increase the terminal voltage
(b) To compensate voltage rise caused by capacitive charging at light load
(c) To improve power factor
(d) None of these [DMRC JE – 2016]

77. The disruptive critical voltage will:

(a) Decrease with the increase of moisture content in air
(b) Increase with the increase of moisture content in air
(c) Increase with the decrease of moisture content in air
(d) Decrease with the decrease of moisture content in air [DMRC JE – 2016]

78. What type of insulator will be used if the direction of the transmission line is to be changed? [DMRC JE 2016]

(a) Pin-type
(b) Suspension type
(c) Strain type
(d) Shackle type

79. How much is the neutral current when loads are perfectly balanced in a three-phase system?

(a) Half of the total current
(b) Zero
(c) Half of the line current
(d) None of these

80. What is the angle of separation of voltages in a 3-phase system?

(a) 150°
(b) 180°
(c) 90°
(d) None of these

81. Find the current rating for the following system.

An outdoor pole-mounted 11 kV/415 V substation has to be installed for supply to an area having a load of 63 kVA. [UPPCL JE – 2014]
(a) 50 A
(b) 88 A
(c) 72 A
(d) 65 A

82. The increase in the height of transmission tower will lead to

(a) increase in the line capacitance but decrease in line inductance
(b) decrease in the line capacitance but increase in line inductance
(c) decrease in the line capacitance but line inductance will remain unaltered
(d) increase in the line capacitance but line inductance will remain unaltered

83. What could be the possible length of the transmission line in order to nullify the effect of capacitance in overhead transmission lines? [IOF 2014, UPPCL JE – 2014]

(a) Less than 200 km
(b) Less than 100 km
(c) Less than 120 km
(d) Less than 80 km

84. When will the effective resistance of a conductor be the same as ohmic resistance? [UPPCL JE – 2014]

(a) When current is in true sine wave form
(b) When voltage is low
(c) When power factor is unity
(d) When current is uniformly distributed in the conductor cross-section.

85. The current in a transmission line under no load conditions is due to

(a) spinning reserve
(b) corona effects
(c) capacitance of the line
(d) back flow from earth [UPPCL JE 2014]

86. For increasing the limit of distance of transmission line,

(a) series resistances are used
(b) synchronous condensers are used
(c) shunt capacitors and series reactors are used
(d) series capacitors and shunt reactors are used [UPPCL JE – 2014]

87. Which one of the following conditions leads to increase in transmission efficiency?

(a) Increase in both voltage and power factor
(b) Decrease in both voltage and power factor
(c) Increase in voltage but decrease in power factor
(d) Decrease in voltage but increase in power factor. [UPPCL JE – 2014]

88. What is the result of Skin Effect? [UPPCL JE 2014]

(a) Reduced effective resistance but increased effective internal reactance of the conductor
(b) Increased effective resistance but reduced effective internal reactance of the conductor
(c) Reduced effective resistance as well as effective internal reactance.
(d) Increased effective resistance as well as effective internal reactance.

89. Which of the following systems of distribution offers the best economy at high voltages? [UPPCL JE 2014]

(a) Direct current system
(b) AC single phase system
(c) AC 3 phase 3 wire system
(d) AC 3 phase 4 wire system

90. What happens when alternating current passes through a conductor? [UPPCL JE – 2014]

(a) it remains uniformly distributed throughout the section of conductor
(b) Portion of conductor near the surface carries more current as compared to the core
(c) Portion of conductor near the surface carries less current as compared to the core
(d) Entire current passes through the core of the conductor.

91. One among the following is the top most conductors in high voltage transmission lines, identify it. [UPPCL JE 2014]

(a) R-phase conductor
(b) Y-phase conductor
(c) B-phase conductor
(d) Earth conductor

92. If voltage across the string is denoted by ‘a’ the number of discs on the string is denoted by ‘b’ and the voltage across disc nearest to the conductor is depicted by ‘c’ then the string efficiency is given by

(a) abc
(b) a/b
(c) a/(bc)
(d) (ab)/c

93. A term is given to a 30 km transmission line which carries power at 33 kV. What is the term? [UPPCL JE 2014]

(a) Short transmission line
(b) Long transmission line
(c) High power line
(d) Ultra high voltage line

94. In transmission lines, the effective resistance of a conductor is increased by

(a) Proximity effect and Skin effect
(b) Corona effect and Proximity effect
(c) Corona effect and Skin effect
(d) Proximity effect only [UPPCL JE 2014]

95. If “X” is the allowable voltage variation in transmission and distribution systems, determine the value of “x”.

(a) ±1%
(b) ±10%
(c) ±0.001%
(d) ±15% [UPPCL JE – 2014]

96. When a high voltage overhead line passes over or adjacent to any building, the vertical clearance between the highest part of the building immediately under such lines, recommended in IE rules is not less than

(a) 1.2 m
(b) 2.8 m
(c) 6 m
(d) 3.7 m [NMRC JE – 2017]

97. Surge impedance of a long loss-less transmission line is given by

(a) Z_o = √L/C
(b) Z_o = √(L/C)
(c) Z_o = 1/√(LC)
(d) Z_o = √(LC) [NMRC JE 2017]

98. Cables in power transmission line are provided with inter sheaths to

(a) Minimize charging current
(b) Minimize stress
(c) Provide uniform stress distribution
(d) Minimize high voltage. [NMRC JE 2017]

99. Hollow conductors are used in the transmission lines to

(a) Improve heat dissipation
(b) Reduce corona loss
(c) Reduce skin effect
(d) Reduce the line inductance [DMRC JE 2014]

100. Corona loss is less when the shape of conductor is

(a) Circular
(b) Flat
(c) Oval
(d) Independent of shape