B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2011
Electrical and Electronics Engineering
EE 2353 — HIGH VOLTAGE ENGINEERING (Regulation 2008)
Time : Three hours
Maximum : 100 marks
Answer ALL questions
PART A — (10 × 2 = 20 marks)
1. What is known as Isokeraunic Level?
2. A transmission line of surge impedance 250 is connected to a cable of surge impedance 50 at the other end, if a surge of 400 kV travels along the line to the junction point, find the voltage build at the junction.
3. State and explain Paschen’s law.
4. What do you mean by ‘Intrinsic strength’ of a solid dielectric?
5. What are the drawbacks of single stage circuit for the generation of very high impulse voltage?
6. What is a cascaded transformer?
7. What is the effect of nearby earthed objects on the measurements using sphere gaps?
8. An electrostatic voltmeter has two parallel plates. The movable plate is 10 cm
in diameter. With 8 kV between the plates the pull is 5 × 10–3 N. Determine the change in capacitance for a movement of 1 mm of movable plate.
9. List out various tests to be carried out on insulator and give a brief account of each test.
10. What are the significances of power factor tests?
PART B — (5 × 16 = 80 marks)
11. (a) (i) An underground cable of inductance 0.150 mH/km and of capacitance 0.2 µF/km is connected to an overhead line having an inductance of 1.2 mH/km and capacitance of 0.006 µF/km. Calculate the transmitted and reflected voltage and current waves at the junction, if a surge of 200 kV travels to the junction, (1) along the cable and (2) along the overhead line. (8)
(ii) Describe about various types of shunt protected devices used for overhead lines against lightning stroke. (8)
(b) (i) Discuss about the various control techniques for switching and power frequency over voltages. (8)
(ii) Explain the different theories of charge formation in clouds. (8)
12. (a) (i) Explain clearly various processes which explain electric breakdown in vacuum. (8)
(ii) Discuss about the properties of composite dielectrics. (8) Or
(b) (i) Explain briefly various theories of breakdown in liquid dielectrics. (10)
(ii) Explain the Townsends criterion for a spark. (6)
13. (a) (i) A ten stage Cockraft-Walton circuit has all capacitors of 0.04 µF. The secondary voltage of the supply transformer is 120 kV at a frequency of 150 Hz. If the load current is 1.2 mA, determine
(1) voltage regulation (2) the ripple (3) the optimum number of stages for maximum output voltage (4) the maximum output voltage. (8)
(ii) Explain the Marx circuit arrangement for multistage impulse generators. How is the basic arrangements modified to accommodate the wave time control resistances? (8)
(b) (i) Explain the basic principle of operation of an electrostatic generator. (6)
(ii) Draw a typical impulse current generator circuit and explain its operation and application. (10)
132 132 132
14. (a) (i) Explain with neat diagram how rod gaps can be used for measurement of high voltages. Compare its performance with a sphere gap. (8)
(ii) Explain with neat diagram the principle of operation of an Electrostatic Voltmeter. Discuss its advantages and limitations for high voltage measurements. (8)
(b) A Rogowski coil is required to measure impulse current of 8 kA having rate of change of current of 1010 A/sec. The voltmeter is connected across the integrating circuit which reads 8 volts for full scale deflection. The input to the integrating circuit is from the Rogowski Coil. Determine the mutual inductance of coil, R and C of the integrating circuit. (16)
15. (a) Explain the method of impulse testing of high voltage transformers. What is the procedure adopted for locating the failure? (16)
(b) Explain the different aspects of insulation design and insulation co-ordination adopted for EHV systems. (16)