Code No:310203

III-B-Tech I-Semester Regular Examinations

November-2003
Set No. 4

POWER SYSTEM – II

(Electronics and Instrumentation Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) Develop an expression for the inductance of a single phase transmission line taking into account the internal flux linkages. Assume the conductors are solid.

b) Calculate the inductance per km per phase of a p-phase transposed line, with distance between any two conductors being 4m, 4m and 8meter respectively.

2. a) Will capacitance of a transmission line depend upon the ground effect? If so explain.

b) Explain the method of images.

c) Derive the formula for capacitance between two charged conductors with method of images.

3. a) How a corona formation does affect the efficiency of the line? Give Peterson's formula to determine the power loss due to corona?

b) A 1 phase transmission line has a resistance of 0.2ohm and an inductive reactance of 0.4 ohm. Find the voltage at the sending end to give 500KVA at 2KV at the receiving end at load power factors of (i) unity (ii) 0.7.7 lagging. Illustrate with suitable phasor diagrams.

4. The potential across the 6 units of the string is equalize the potential, calculate the capacitance of the top insulator is 8Cand that of pin-to-earth is C. Calculated the capacitance of the other units.

If instead of graded insulators, a guard ring is used to equalize the potential, calculated the capacitance of each link to conductors. Assume that the insulator used in the string are similar to that of the top.

5. A transmission line conductor at a river crossing is supported from two towers at height of 50 and 80 meters above water level. The horizontal distance between the towers is 300metres. If the tension in the conductor is 2000Kgs, find the clearance between the conductor and water at a point midway between the towers. Weight of conductor per meter =0.844Kg. Assume that the conductor takes the shape of parabolic curve.

6. a) Derive an expression for the capacitance of a single core cable.

b) The insulation resistance of a single core cable is 495MΩ/km. If the core diameter is 2.5cm and resistivity of insulation is 4.5x10¹⁴Ω-cm. Find the insulation thickness.

7. a) What is most economical power factor? Why it is needed?

b) List the methods to improve power factor and explain briefly.

c) Show that the most economical power factor depends upon the relative costs of supply and p.f. correction equipment.

8. Three resistors of 5 ohm, 10 ohm and 20 ohm are connected in Delta across the three phases of a balanced 100 volts supply. What are the sequence currents in the resistors and in the supply lines?