Code No:310203

III-B-Tech I-Semester Regular Examinations

November-2003
Set No. 2

POWER SYSTEM – II

(Electronics and Instrumentation Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) Write a short notes on 'overhead line conductors' bringing out the reasons for using ACSR conductors.

b) What is a bundled conductors? Why it is used? Give a few configurations of such conductors commonly employed.

C) Why Hollow conductors are required for EHV and UHV applications?

d) Find the loop inductance and reactance per km of a single phase overhead line consisting of two conductors, each 1.3cm diameter. The spacing between conductors is 1.4meters and frequency is 50Hz.

2. a) How do we find line to neutral capacitance in a 3-phase system? b) The three conductors R, Y and B of a 3-phase line are arranged in a horizontal place with D_RY=1.5mtr; D_YB=2mtr and D_BR=3.5 mtr. Find line to neutral capacitance per km if dia of each conductor 1.2cm. The conductors are transposed at regular intervals. Also calculate line capacitance per km length.

3. a) Discuss the effect of load power factor on voltage regulation and efficiency of a transmission line.

b) What is skin and proximity effects?

c) A 10km long 3 phase line delivers 1 MW at 0.8 lagging power factor. The series impedance of the line is 0.5+j0.56 ohms per km phase. The ending end voltage is 11KV. Find the line current, receiving end voltage and transmission efficiency.

4. a) Each conductor of a 33KV, 3-phase system is suspended by a string of three similar insulators, the capacitance of each disc is nine times the capacitance to ground. Calculate the voltage across each insulator. Determine the string efficiency.

b) A string of eight suspension insulators is to be graded to obtain uniform distribution of voltage across the string. If the capacitance of the top unit is 10 times the capacitance to ground of each unit determine the capacitance of the remaining seven units.

5. a) What is a sag-template? Explain how this is useful for location of towers and stringing of power conductors.

b) What is a stringing chart? Explain clearly the procedure adopted for stringing the power conductors on the supports.

6. a) What are the limitations of solid type cables. How are these overcome in pressure cables?

b) A single core cable has conductor of 40mm and the internal diameter of the lead sheath of 90mm. The cable is provided with two different insulating materials having relative permittivities 4.5 (inner), and 3.5 (outer) respectively. The corresponding maximum permissible electric stresses are 4.5 and 3.5 kv/mm.

i) Determine the radial thickness of the insulating materials required to confirm with the above specifications.
ii) Also find the safe operating voltage of the cable.

7. a) Why the improvement of power factor is very important for both consumers and generating stations?

b) List the various causes of low power factor and explain.

8. The currents in a 3-phase unbalanced system are:

I_R=(12+j6); I_Y=(12-j12)A
I_B(-15+j10)A

The phase sequence is RYB. Calculate the zero, positive and negative components of the currents.