Electrical engineering practice MCQ : Transmission and Distribution (Part 2)

For previous part, check the previous post,








51. Which of the following is usually not the generating voltage ?

(a) 6.6 kV

(b) 8.8 kV

(c) 11 kV

(d) 13.2 kV

Ans: b

52. For an overhead line, the surge impedance is taken as

(a) 20-30 ohms

(b) 70—80 ohms

(c) 100—200 ohms

(d) 500—1000 ohms

(e) none of the above

Ans: c

53. The presence of ozone due to corona is harmful because it

(a) reduces power factor

(b) corrodes the material

(c) gives odour

(d) transfer energy to the ground

(e) none of the above

Ans: b

54. A feeder, in a transmission system, feeds power to

(a) distributors

(b) generating stations

(c) service mains

(d) all of the above

Ans: a

55. The power transmitted will be maximum when

(a) corona losses are minimum

(b) reactance is high

(c) sending end voltage is more

(d) receiving end voltage is more

Ans: c

56. A 3-phase 4 wire system is commonly used on

(a) primary transmission

(b) secondary transmission

(c) primary distribution

(d) secondary distribution Ans: d

57. Which of the following materials is used for overhead transmission lines ?

(a) Steel cored aluminium

(b) Galvanised steel

(c) Cadmium copper

(d) Any of the above Ans: d

58. Which of the following is not a constituent for making porcelain insulators ?

(a) Quartz

(b) Kaolin

(c) Felspar

(d) Silica

Ans: d

59. There is a greater possibility of occurence of corona during

(a) dry weather

(b) winter

(c) summer heat

(d) humid weather

(e) none of the aboveAns: d

60. Which of the following relays is used on long transmission lines ?

(a) Impedance relay

(b) Mho's relay

(c) Reactance relay

(d) None of the above

Ans: b

61. The steel used in steel cored conductors is usually

(a) alloy steel

(b) stainless steel

(c) mild steel

(d) high speed steel

(e) all of the aboveAns: c

62. Which of the following distribution systems is more reliable ?

(a) Radial system

(b) Tree system

(c) Ring main system

(d) All are equally reliable

Ans: c

63. Which of the following characteristics should the line supports for transmission lines possess ?

(a) Low cost

(b) High mechanical strength

(c) Longer life

(d) All of the above

Ans: d

64. Transmission voltage of llkV is normally used for distances upto

(a) 20—25 km

(b) 40—50 km

(c) 60—70 km

(d) 80—100 km Ans: a

65. Which of the following regulations is considered best?

(a) 50%

(b) 20%

(c) 10%

(d) 2%

Ans: d

66. Skin effect is proportional to

(a) (conductor diameter)

(b) (conductor diameter)

(c) (conductor diameter)

(d) (conductor diameter)

(e) none of the above

Ans: c

67. A conductor, due to sag between two supports, takes the form of

(a) semi-circle

(b) triangle

(c) ellipse

(d) catenary

Ans: d

68. In AC.S.R. conductors, the insulation between aluminium and steel conductors is

(a) insulin

(b) bitumen

(c) varnish

(d) no insulation is required

Ans: d

69. Which of the followingbus-bar schemes has the lowest cost ?

(a) Ring bus-bar scheme

(b) Single bus-bar scheme

(c) Breaker and a half scheme

(d) Main and transfer scheme Ans: b

70. Owing to skin effect

(a) current flows through the half cross-section of the conductor

(b) portion of the conductor near the surface carries more current and core of theconductor carries less current

(c) portion of the conductor near the surface carries less current and core of the conductor carries more current (d) any of the above

(e) none of the above Ans: b

71. By which of the following methods string efficiency can be improved ?

(a) Using a guard ring

(b) Grading the insulator

(c) Using long cross arm

(d) Any of the above

(e) None of the above

Ans: d

72. In aluminium conductors, steel core is provided to

(a) compensate for skin effect

(b) neutralise proximity effect

(c) reduce line inductance

(d) increase the tensile strength Ans: d

73. By which of the following a bus-bar is rated ?

(a) Current only

(b) Current and voltage

(c) Current, voltage and frequency

(d) Current, voltage, frequency and short time current Ans: d

74. A circuit is disconnected by isolators when

(a) line is energized

(b) there is no current in the line

(c) line is on full load

(d) circuit breaker is not open

Ans: b

75. For which of the following equipment current rating is not necessary ?

(a) Circuit breakers

(b) Isolators

(c) Load break switch

(d) Circuit breakers and load break switches Ans: b

76. In a substation the following equipment is not installed

(a) exciters

(b) series capacitors

(c) shunt reactors

(d) voltatre transformers

Ans: a

77. jCorona usually occurs when the electrostatic stress in air around the conductor exceeds

(a) 6.6 kV (r.m.s. value)/cm

(b) 11 kV (r.m.s. value)/cm

(c) 22 kV (maximum value)/cm

(d) 30 kV (maximum v^lue)/cm

Ans: d

78. The voltage drop, for constant voltage transmission is compensated by installing

(a) inductors

(b) capacitors

(c) synchronous motors

(d) all of above

(e) none of the above

Ans: c

79. The use of strain type insulators is made where the conductors are

(a) dead ended

(b) at intermediate anchor towers

(c) any of the above

(d) none of the above

Ans: c

80. The current drawn by the line due to corona losses is

(a) non-sinusoidal

(b) sinusoidal

(c) triangular

(d) square

Ans: a

81. Pin type insulators are generally not used for voltages beyond

(a) 1 kV

(b) 11 kV

(c) 22 kV

(d) 33 kV

Ans: d

82. Aluminium has a specific gravity of

(a) 1.5

(b) 2.7

(c) 4.2

(d) 7.8

Ans: b

83. For transmission of power over a distance of 200 km, the transmission voltage should be

(a) 132 kV

(b) 66 kV

(c) 33 kV

(d) 11 kVAns: a

84. For aluminium, as compared to copper, all the following factors have higher values except

(a) specific volume

(6) electrical conductivity

(c) co-efficient of linear expansion

(d) resistance per unit length for same cross-section Ans: b

85. Which of the following equipment, for regulating the voltage in distribution feeder, will be most economical ? (a) Static condenser

(b) Synchronous condenser

(c) Tap changing transformer

(d) Booster transformer

Ans: d

86. In a tap changing transformer, the tappings are provided on

(a) primary winding

(b) secondary winding

(c) high voltage winding

(d) any of the above

Ans: b

87. Constant voltage transmission entails the following disadvantage

(a) large conductor area is required for same power transmission

(b) short-circuit current of the system is increased

(c) either of the above

(d) none of the above Ans: b

88. On which of the following factors skin effect depends ?

(a) Frequency of the current

(b) Size of the conductor

(c) Resistivity of the conductor material

(d) All of the above

Ans: d

89. The effect of corona can be detected by

(a) presence of zone detected by odour

(b) hissing sound

(c) faint luminous glow of bluish colour

(d) all of the above

Ans: d

90. For transmission of power over a distance of 500 km, the transmission voltage should be in the range (a) 150 to 220 kV

(b) 100 to 120 kV

(c) 60 to 100 kV

(d) 20 to 50 kVAns: a

91. In the analysis of which of the following lines shunt capacitance is neglected ?

(a) Short transmission lines

(b) Medium transmission lines

(c) Long transmission lines

(d) Medium as well as long transmission lines Ans: a

92. When the interconnector between two stations has large reactance

(a) the transfer of power will take place with voltage fluctuation and noise

(b) the transfer of power will take place with least loss

(c) the stations will fall out of step because of large angular displacement between thestations

(d) none of the above

Ans: c

93. The frequency of voltage generated, in case of generators, can be increased by

(a) using reactors

(b) increasing the load

(c) adjusting the governor

(d) reducing the terminal voltage

(e) none of the above

Ans: c

94. When an alternator connected to the bus-bar is shut down the bus-bar voltage will

(a) fall

(b) rise

(c) remain unchanged

(d) none of the above

Ans: c

95. The angular displacement between two interconnected stations is mainly due to

(a) armature reactance of both alternators

(b) reactance of the interconnector

(c) synchronous reactance of both the alternators

(d) all of the above

Ans: a

96. Electro-mechanical voltage regulators are generally used in

(a) reactors

(b) generators

(c) transformers

(d) all of the above

Ans: b

97. Series capacitors on transmission lines are of little use when the load VAR requirement is

(a) large

(b) small

(b) fluctuating

(d) any of the above

Ans: b

98. The voltage regulation in magnetic amplifier type voltage regulator is effected by

(a) electromagnetic induction

(b) varying the resistance

(c) varying the reactance

(d) variable transformer

Ans: c

99. When a conductor carries more current on the surface as compared to core, it is due to

(a) permeability variation

(b) corona

(c) skin effect

(d) unsymmetrical fault

(e) none of the above

Ans: c

100. The following system is not generally used

(a) 1-phase 3 wire

(b) 1-phase 4 wire

(c) 3-phase 3 wire

(d) 3-phase 4 wire

Ans: a

101. The skin effect of a conductor will reduce as the

(a) resistivity of conductor material increases

(b) permeability of conductor material increases

(c) diameter increases

(d) frequency increases

Ans: a

102. When a live conductor of public electric supply breaks down and touches the earth which of the following will happen ?

(a) Current will flow to earth

(b) Supply voltage will drop

(c) Supply voltage will increase

(d) No current will flow in the conductor

(e) None of the above

Ans: a