Code No:310203

III-B-Tech I-Semester Supplementary Examinations

June-2003
Set No. 1

POWER SYSTEM – II

(Electrical and Electronics Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) Write a short notes on the following types of over head line conductors (i) ACSR (ii) Bundled conductors (iii) Hollow conductors (iv) AAC conductors.

b) Find the loop inductance and reactance per km of a single phase overhead line consisting of two conductors each 1.213cm diameter. Te spacing between conductors is 1.25meters and frequency is 50Hz.

2. a) What is symmetrical and asymmetrical spacing of conductors? What is the significance of symmetrical spacing of conductors?

b) What is Radio Interference? Why it occurs explain.

c) What is transposition? Explain the method of transposition.

3. a) Discuss why equivalent pi circuit of a long line is preferred over the equivalent T CIRCUIT.

b) A three phase 50Hz transmission line is 150 km ling and delivers 25MW at 0.85 power factor lagging and at 110KV. The resistance and reactance of the line per conductor per km are 0.3ohms and 0.9ohms respectively. The line charging admittance is 0.3 x 10^-6 mho per km per phase. Compute by applying the nominal pi method the voltage regulation and transmission efficiency.

4. a) What is skin effect?

b) A 3phase, 50Hz, 100km long transmission line delivers a load of 20000KW at 110KV at 0.9 power factor lagging. The copper conductors of the line are 1.2 cm in diameter and are spaced equilaterally, so that the distance between then is 2m. Using nominal pi method, calculate the sending end voltage, current, power factor, regulation and efficiency of the line. Neglect the leakage.

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

b) How are the sag and tension of the conductor affected by an extreme fall of temperature?

6. a) What are all the insulating materials used in U.G. Cables? Explain in detail about different kinds of insulating materials.

b) Determine the economical size of a single core cable working on 220KV,3 phase system. The maximum permissible stress in the dielectric is not to exceed 250KV/cm.

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.

c) List the power factor improvement equipment and briefly explain.

8. a) Compare the merits and demerits of various methods of p.f. Improvement methods

b) A single phase motor connected to a 240V, 50Hz supply takes 20A at a.p.f. Of 0.75 (lag) A capacitor is shunted across the motor terminals to improve the p.f.to 0.9 (log). Determine the capacitance of the capacitor to be used.