Roll No.__________________
05 March, 2015
Sarhad University, Peshawar
(Distance Education)
Paper
: Power Transmission & Distribution-EE254
Examination: Final, Fall 2014
Total Marks: 70, Passing Marks (35)
Time Allowed : 03 hours
NOTE: Q.1 is compulsory, attempt any four questions from the remaining. All questions carry equal marks
Phones and other Electronic Gadgets are not allowed. Draw neat and clean diagram where necessary.
Q.1
i.
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iii.
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viii.
ix.
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xii.
xiii.
xiv.
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The maximum value of power factor is...............
Primary transmission is done by 3-phase ...............wire a.c. system
If the spacing between the conductors is increased, then corona effect is................
If the length of a transmission line increases, its inductance is....................... .
The d.c. resistance of a line conductor is ................... than its a.c. resistance.
If the supply frequency increases, then skin effect is....................
[increases, decreased]
If the conductor diameter decreases, inductance of the line is..........
[increased, decreased]
In any transmission line, AD − BC =..............................
When the regulation is positive, then receiving end voltage (VR) is .......... than sending end voltage (VS).
[more, less]
If the length of a cable is doubled, its capacitance is..................
[doubled, halved, quadrupled]
Voids in the layers of impregnated paper insulation................. the breakdown voltage of the cable.
[Increase, decrease]
The main consideration in the design of a feeder is the.............
[Current carrying capacity, voltage drop]
The difference in level between points of supports and the lowest point on the conductor is
called................
The most commonly used material for insulators of overhead lines is...........
Q.2
(a) Discuss in detail different types Insulators used in power system?
(b) Define Kelvin Law and mention its few limitations?
Q.3
(a) Draw the T-Model and Pi Model of the Medium Transmission Line?
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(b) A single phase overhead transmission line delivers 1100 kW at 33 kV at 0.8 p.f. lagging. The total
resistance and inductive reactance of the line are 10 Ω and 15 Ω respectively. Determine: (i) sending
end voltage (ii) sending end power factor and (iii) transmission efficiency.
Q.4
The conductors of 220kV, 50Hz three phase overhead transmission line are arranged in equilateral
triangle fashion with spacing between phases conductor is 5.5m. If overall diameter of each conductor is
3cm with surface irregularity factor of 0.9 for both Audio and Visual Corona. Assume that air pressure is
65 cm of Hg and temperature of 100C. Find:
a) Peak value of critical Disruptive voltage.
b) Peak value of Visual critical disruptive voltage.
c) Total power loss due to corona if length of the conductor is 100km.
Power Transmission & Distribution-EE254 Fall-2014
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Roll No.__________________
05 March, 2015
Q.5
An insulator string consists of three units, each having a safe working voltage of 15 kV. The ratio of selfcapacitance to shunt capacitance of each unit is 8: 1. Find the maximum safe working voltage of the
string. Also find the string efficiency. What are the different methods used for improving string
Efficiency (Write name only) and mention which method is practically applied in transmission system.
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Q.6
A transmission line has a span of 150 m between level supports. The conductor has a cross-sectional area
of 2 cm2. The tension in the conductor is 2000 kg. If the specific gravity of the conductor material is 9.9
gm/cm3 and ice coating of 0.1cm thickness on the conductor. Calculate the sag. Take the Density of ice
0.91gm/cm3.
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Q.7
(a) What is skin effect? Why is it absent in the d.c. system?
(b) The three conductors of a 3-phase line are arranged at the corners of a triangle of sides 2 m, 2.5 m and
4.5 m. Calculate the inductance per km and Capacitance per km of the line when the conductors are
regularly transposed. The diameter of each conductor is 1.24 cm.
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Q.8
Write Short note on any two of the following:
a) What are the main Line constant. Define each with mathematical formula?
b) Distribution System
c) Corona and its factors which affect corona.
Power Transmission & Distribution-EE254 Fall-2014
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