power_system_2009_4_4_0
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B.E (EEE) 4th
Sem
Power System - I
Note: Attempt five questions, selecting at least two questions each from part A and part B.
PART-A
Q1. What is meant by single line diagram. Discuss its benefits. Hence find
the impedance diagram for the following system. Assume a base voltage of
33kV for transmission line. Convert all quantities to per unit values on a
system base of 25mvVA. (20)
Q2. (a) Calculate the capacitance of a two wire line. If the conductors are
spaced equilaterally, how do you calculate the capacitance of three phase
line. (10)
(b) Derive an expression to obtain inductance of composite conductor
lines. Hence explain the concept of transposition in transmission line. (10)
Q3. (a) The Configuration of a 3 220kv, 100km long fully transposed, 50hz
transmission line is shown below. If the radius of the conductor is 20mm,
Y
MVA20
KV6.6
vpx .12.0=
MVA25
KV33/11
..08.0 vp
MVA30
KV22/33
..10.0vpx
=
MVA15
KV11
..15.0 vpx =
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compute the capacitance to neutral of the line and the line charging
current by considering the effect of earth. (12)
(b) Derive an expression to determine electric field strength at
conductor surface of a transmission line. (8)
Q4. (a) A 150km, 230kV, 50hz, 3 line has a positive sequence series
impedance z=0.08+ 0.48/km and a positive sequence shunt admittance
y = j3.33x10-6
s/km . At full load, the line delivers 250mw at 0.99pf. lagging
and at 220kv. Using the nominal circuit, calculate:
(a) The ABCD parameters (15)(b) Sending end voltage and current(c) The percentage voltage regulation
(b) Explain line loadability concept. How does it occur & discuss its effects.
m4
m6
m4
m4
R
B Y
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(5)
PART-B
Q5. (a) A star connected balanced load of 10 each has following voltage
across the terminals; Vab=200 V60 . Calculate the symmetrical components,
of the line voltage, Determine the line currents. (10)
(b) How will the inter connections of the sequence network change, if
neutral point n is connected to ground through Zg. Derive an expression forthe neutral voltage. (10)
Q6. A single line to ground fault(phase a) occurs on the bus 1 of the
system of fig. given. Find fault current, short circuit current on transmission
line in all three phases & short circuit current in phase a of the generator.
Rating of each machine is 1200KVA, 600V with x = x2=10% x0=0.05 .Each 3
transformer is rated 1.2MVA, 600/3300 V /Y with leakage reactance of 5%.
The reactance of transmission line are x1 = x2= 20% and x0=40% on the base
of 1.2MVA, 3.3KV. The reactance of the neutral grounding reactors are 5%
on the KVA and voltage base of the m/c. Use Zbus method to solve.
Y
M
T2
1 2
Y
Y
Y
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(20)
Q7. A synchronous generator is rated 25MVA, 11KV. It is star connected
with neutral point solidly grounded. The generator is operating at no load at
rated voltage. Its reactances are x = x2= 0.20 and x0=0.08 p.o.
Calculate the symmetrical subtransient line current for
(1) SLG fault(2) LLG fault(3) Symmetrical three phase fault. (20)
Q8. Write short notes on any two:
(a) Reaction compensating techniques(b) Bus impedance Matrix & its formation(c) Per-unit sequence models of three phase three winding
transformers. (10, 10)
Disclaimer: Well this looks a little stupid but we are not responsible if any portion of this paper
is not relevant with todays syllabus. Due care has been taken to make this paper error free, but
there always remains a chance of error so please ignore any typographical error if present..
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