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Posted By: prashanth beerelli Member Level: Diamond Posted Date: 04 Sep 2008
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2006 Jawaharlal Nehru Technological University Electrical and Electronics Engineering III B.Tech I Semester Regular Examinations, November 2006 POWER SYSTEMS-II Question paper
Code No: RR310203 Set No. 4
III B.Tech I Semester Regular Examinations, November 2006
POWER SYSTEMS-II
(Electrical & Electronic Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Input to a single-phase short line is 2000kW at 0.8 lagging power factor. The
line has a series impedance of (0.4 + j 0.4 ) ohms. If the load voltage is 3kV,
find the receiving end power factor and supply voltage. [8+8]
(b) Derive the equivalent ABCD parameters considering nominal T network.
2. (a) Give brief description of corona phenomenon. [8+8]
(b) Derive the expression for potential gradient at the surface of a conductor of
1-phase transmission line.
3. The line conductor of a transmission line has an overall diameter of 19.53mm,
weights 0.844 kgf/m, and an ultimate breaking strength of 7950 kgf. If the factor
of safety is to be 2 when the conductor has an ice load of 1kgf/m and a horizontal
wind pressure of 1:5 kgf/m, find approximately the vertical sag which corresponds
to this loading for a 300m span between level supports. [16]
4. (a) What do you mean by grading of Cables? Explain briefly different types of
grading of cables. [6]
(b) A conductor of 1 cm diameter passes centrally through a porcelain cylinder
of internal diameter 2cms and external diaeter 7cms. The cylinder is sur-
rounded by a tightly fitting metal sheath. The permittivity of porcelain is 5
and the peak voltage gradient in air must not exceed 34kV/cm. Determine
the maximum safe working voltage. [10]
5. (a) What are the advantages and disadvantages of static capacitors used for power
factor improvement. [8+8]
(b) Explain the effect of power factor on transmission line conductor size and KVA
rating of the equipment.
6. What are the various methods of voltage control in a power system, explain with
neat sketches and vector diagrams. [16]
7. (a) What are the different symmetrical faults and compare their properties. [6]
(b) The section bus bar A and B are linked by a bus-bar reactor rated at 5000KVA
with 10% reactance. On bus-bar A there are two generators each of 10000KVA
with 10% reactance and on B two generators each of 8000KVA with 12%
reactance .Find the steady MVA fed into a dead short circuit between all
phases on A and on B with bus-bar reactor in the circuit.
8. (a) Draw the positive , negative and zero sequence networks for the system de-
scribed as follows. The system consists of a 3-f star connected alternator
is supplying power to the 3-f star connected synchronous motor through a
delta-star step up transformer , a transmission line and a star- delta step
down transformer .The neutral points of the machine windings are solidly
grounded and the transformer winding neutrals are un grounded . [10+6]
(b) Explain the concept of sequence impedances of a 3-f star connected rotating
load whose neutral is grounded through some impedance and draw its sequence
impedance networks
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