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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..