University of Mumbai 2007-6th Sem B.E Electrical and Electronics Engineering Power Transmission - exam paper
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Con. 4840-07. CD-5538 .
(REVISED COURSE)
( 3 Hours) [Total Marks ; 100
N.B. (1) Question No. 1 is compulsory.
(2) Solve any four questions from remaining six questions.
1. (a) State and explain the Fortescue Theorem' lor the analysis of unbalanced systems 10 (b) Derive the interconnection of sequence network for L-L fault. 10
2. (a) Explain in detail Symmetrical ComponentTransformation". 10 (b) Show the variation of voltage and current in a short ended line for a travelling wave. 10
3. (a) A three-phase transmission line has conductor 1-5 cms in dlamater spaced one meter 12
apart in aquilateral formation. The resistance and leakance are negligible. Calculate
(i) The Natural Impedance of the line
(ii) The line current if a voltage wave of 11 kV travels along the line.
(iii) The rate of energy absorption, the rate of reflection and state and the form of reflection, if the line is terminated through a star connected load of 1000 ohm per phase.
(iv) The value of the terminating resistance for no reflection
(v) The amount of reflected and transmitted power over .if the line is connected to a cable extension with inductance and capacitance per phase per cm of 0-5 x 101 H and 01 x tO-6 micro-farad-respectively.
(b) Explain the advantages and disadvantages of Corona in details. 8
4. (a) Write a detail note on zero sequence network of synchronous generator and three-phase 10
transformer with the help of noat diagrams.
(b) A voltage having a crest value of 3000 kV is travelling on a 750 kV line. The protective 10 level is 1700 kV. The surge impedance of lino is 300 ohm. Calculate :
(i) The current in the line before reaching the arrester
(ii) Current through the arrester
(iii) The value*of arrester resistance for this condition
(iv) Reflected voltage.
5. A synchronous generator is rated at 25 MVA, 11 kV. It is star connected with the 20 neutral-point solidly grounded. The generator Is operating at no load at rated voltage. Its reactances are X" = X2 = 0*2 P.U.; Xg = 0*08 P.U.
Calculate the symmetrical subtransient line current for
(i) Single Line to Ground Fault (if) Double Line to Ground Fault
(iii) Line to Line.
6. (a) A 110 kV, 50 Hz, 3-Phase, Transmission Fault line 175 km fong consisting of three 12
one cm dia stranded copper conductor spaced in three meter delta-arrangement.
Temp. = 26 C and barometric pressure is 74 cm., m = 0-85, Mv for local Corona = 0-72 and M, for General Corona = 0-82. Find
(i) Disruptive critical voltage
(ii) Visual critical voltage
(iii) Power loss using peaks formula for fair weather conditions and stormy weather conditions.
(b) Explain Biopolar-Link type of HVDC system. Give its advantages and Disadvantages. 8
(b) Significance of surgo impedance loading
Af HVDC over EHV-AC
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