NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
Department of Electrical Engineering
End sem Examination, 2022-2023(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: 3 Hrs.
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
1 A 3-phase, 50 Hz, 100 km transmission line has the following constants: 5
Resistance/phase/km = 0.1 Ω
Reactance/phase/km = 0.5 Ω
Susceptance/phase/km = 10-5 S
If the line supplies a load of 20 MW at 0.9 pf lagging at 66 kV at the receiving end,
calculate by using nominal πmethod:
(i) sending end current (ii) line value of sending end voltage (iii) sending end power
factor (iv) regulation
2 It is required to grade a string having seven suspension insulators. If the pin to earth 5
capacitances are all equal to C, determine the line to pin capacitances that would give
the same voltage across each insulator of the string.
3 An overhead transmission line at a river crossing is supported from two towers at heights 5
of 50 m and 100 m above the water level. The horizontal distance between the towers is
400 m. If the maximum allowable tension is 1800 kg and the conductor weighs 1 kg/m.
Find the clearance between the conductor and water at a point mid-way between the
supports.
4 What do you mean by corona in overhead transmission line? Derive the expression of 5
critical disruptive voltage between two circular wires having surface irregularity factor
m and air density correction factor δ.
5 A single-core cable has a conductor diameter of 2,5 cm and a sheath of inside diameter 5
of 6 cm, Calculate the maximum stress. It is desired to reduce the maximum stress by
using two intersheaths. Determine their best positions, the maximum stress and the
voltage on each. System voltage is 66 kV, 3-phase
6 A 3-core, 3-phase metal sheathed cable had i) capacitance of 1µF between shorted 5
conductors and sheath and ii) capacitance between two conductors shorted with the
sheath and the third conductor is 0.6 µF. Find the capacitance i) between any two
conductors ii) between any two shorted conductors and the third conductor.
P.T.O.
7 A distortion less line has characteristic impedance Z0= 50 Ω, attenuation constant α = 25 5
mNp/m, velocity of wave v = 0.5 C, C: speed of light in vaccum.
Find resistance R, inductance L, conductance G, capacitance C and wavelength λ at
frequency of 80 MHz.
8 A two-wire dc distributor AB is 300 m long. The end A is fed at 205 V and end B is fed 5
at 200 V. The distributor is uniformly loaded at 0.15 A/metre length and has concentrated
loads of 50 A, 60 A and 40 A at points distant 75, 175 and 225 m respectively from end
A. The resistance of each conductor is 0.15 Ω per kilometre. Calculate
i) the point of minimum potential
ii) current fed at ends A and B
9 Determine the most economical size of a 3-phase line which supplies the following loads 5
at 10 kV
i) 100 kW at 0.8 pf (lag) for 10 hours
ii) 500 kW at 0.9 pf (lag) for 8 hours
iii) 100 kW at unity pf for 6 hours
The above gives the daily load cycle. The cost per km of the completely erected line
is Rs. (8000a+1500) where a is area of cross section of each conductor. The
combined interest and depreciation is 10 % per annum per capital cost. Cost of
energy loss is 5 paise per kWh. Resistivity of conductor material = 1.72×10-6 Ωcm.
10 Explain any two of the followings: 2×2,5
=5
i) Effect of earth on capacitance of line
ii) Voltage control by auto transformer tap-changing
iii) Power factor improvement using Phase Advancers
Wish you all the best
