NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
Department of Electrical Engineering
End Sem Examination
(for final year students and students on extended semester),
2020-2021(Autumn)
Program: B.Tech.
Semester: 5th
Subject Name: Power Generation, Transmission and Distribution
Subject Code: EE 3103
Number of Pages: 2 Full Marks: 50 Duration: 2 Hr.
Figures at the right hand margin indicate marks.
All symbols carry usual meaning. Assume standard value for any missing data.
Q. Instruction regarding questions Marks
No. Answer all questions [Time]
1i) A part of the transposition cycle of a 3 phase double circuit line is shown in Fig. below. 6+6
Radius of each conductor is 12 mm. The conductors are solid copper. Determine GMD, [30 Min.]
GMR and calculate the inductance per km per phase of the line.
7.5 m c’
a
4m b b’
9m
c a’
4m
7.5 m
A 10 km long 3-phase overhead transmission line delivers 5 MW at 0.8 lagging pf. Line loss
ii) is 12 % of power delivered. Line inductance 1.2 mH per km per phase. Find sending end
voltage and voltage regulation.
2 i) Each of the three insulators forming a string has a self capacitance of ‘C’ farads. The 6+6
shunting capacitance of the connecting metal work of each insulator is 0.2 C to earth [30 Min.]
and 0.1 C to the line. A guard ring increases the capacitance to the line of the metal
work of the lowest insulator to 0.25 C. Calculate the string efficiency of this
arrangement with the guard ring.
ii) A transmission line conductor having a diameter of 18 mm weighs 0.8 kg/m. The span
is 270 metres. The wind pressure is 40 kg/m2 of projected area with ice coating of 12
mm. The ultimate strength of conductor is 6000 kg. Calculate the maximum sag, if
factor of safety is 2 and ice weighs 912 kg/m3.
3 i) Find the critical disruptive voltage and corona loss for a 3-phase line which is operating at 220 6+6
kV, 50 Hz frequency. The line has conductor of 1.3 cm diameter arranged in a 3 metre delta [30 Min.]
connection. Assume air density factor of 0.96 and dielectric strength of air to be 21.1 kV/cm.
P.T.O
1
ii) What do you mean by grading of dielectric cables ?
What are the different methods used for grading of cables?
4 i) A 2-wire dc distributor AB, 900m long is fed at A at 400V & loads of 50A, 100A & 6+8
150A are tapped off from C, D & E which are at distance of 200m, 500m & 800m from [30 Min.]
point A respectively. The distributor is also loaded uniformly at the rate of 0.5A/m. If
resistance of distributor per metre (go & return) is 0.0001Ω, calculate voltage
i) at point B & ii) at point D.
ii) Write short notes on any two of the followings
(i) Effect of earth on capacitance of line
(ii) Synchronous condenser method of voltage control with vector diagram
(iii) Transmission line voltage and current wave equations
Wish you all the Best
