EE2353 High Voltage Engineering
16 Mark Questions
UNIT – I OVER VOLTAGES IN ELECTRICAL POWER SYSTEMS
1. Draw the cross sectional view of non linear resistor lightning arrester (valve type) and explain its operation in detail and its V-I characteristics.
2. Discuss mechanism of lightning stroke and over voltages on transmission lines and give its mathematical model.
3. Write short notes on:
(i) Rod gaps used as protective devices
(ii) Ground wires for protection of overhead lines.
4. Explain different theories of charge formation in clouds.
5. Explain different methods employed for lightning protection of overhead lines.
6. (i) Draw & Explain the procedure to draw Bewley Lattice Diagram for a two substations system .
(ii) Explain briefly about expulsion type arrester.
UNIT– II ELECTRICAL BREAKDOWN IN GASES, SOLIDS AND LIQUIDS
1. Deduce the Townsend’s break down criteria. Also define the Townsend’s Primary and secondary ionization coefficients.
2. (i) Explain clearly breakdown in non-uniform fields & corona discharges. (ii) Explain breakdown in uniform field (streamer mechanism).
3. Explain the various theories of breakdown mechanism of vacuum.
4. State the criteria for sparking potential and hence obtain the relation between sparking potential and (PD) values (Paschens law). Discuss nature of variation of sparking potential with PD values.
5.Explain the various theories of breakdown mechanism of commercial liquid dielectrics.
6.Explain the various breakdown mechanism involving in solid dielectricbreakdown
UNIT–III GENERATION OF HIGH VOLTAGES AND HIGH CURRENTS
1. What is the principle behind the electrostatic method of energy conversion? Explain the construction and operation of vandegraff generator with neat sketch.
2. Starting from basic marx circuit develop the circuit of modern multistage impulse generator and explain its operation. Discuss significance of various parameters.
3. Explain the operation of simple voltage doubler circuit & Cockcroft -Walton voltage multiplier circuit with expression.
4. Explain in detail about cascade transformer connections and resonant transformer to generate high alternating voltage.
5.Explain in detail how the impulse current is generated using capacitor bank & also explain tripping & control of impulse generators with Trigatron gap Arrangement.
6.(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.
7. A 12 stage impulse generator has 0.126microF capacitors .The wave front & wave tail resistance are 800 ohms and 5000 ohms respectively.For a load capacitor of 1000pF,obtain the front and tail times of the impulse wave produced.
8.A 8 stage impulse generator has 0.12microF capacitors rated for 167 KV.What is the maximum discharge energy ? If it has to produce 1/50 micro second waveform across a load capacitor of 1500 Pico Farad ,find the value of front and tail timings.
UNIT – IV MEASUREMENT OF HIGH VOLTAGES AND HIGH CURRENTS
1. Explain measurements of very high voltages using sphere gaps. Mention merits and de merits of using sphere gaps& also explain digital peak voltmeter & rod gaps.
2. With a neat sketch explain the principle of operation of an electrostatic voltmeter for HVAC measurement. What are the merits and demerits?
3. Explain generating voltmeter for measuring high DC voltage.
4. What is CVT? Explain through phasor diagram how a tuned CVT can be used for HVAC measurement in substations. & also expain series capacitor peak voltmeter.
5. Explain the methods of measurement of high frequency current.
6. Explain the methods of measurement of high impulse current.
UNIT – V HIGH VOLTAGE TESTING AND INSULATING COORDINATION
- With a neat sketch explain the impulse testing on the power transformer.
- Discuss the various test carried out in a circuit breaker at HV labs.
- What are the different power frequency tests done on bushings? Mention the procedure for testing.
- Briefly discuss the various tests carried out the insulator.
- What is meant by insulation coordination? How are the protective devices chosen for optimal insulation level in a power system?
- Explain the terms:
(i) With stand voltage
(ii) Flash over voltage
(iii) 50% flash over voltage
(iv) Wet and dry power frequency tests as referred to HV testing.
- Explain the following terms used in HV testing as per the standards:
(i) Disruptive discharge voltage
(ii) Creepage distance
(iii) Impulse voltage
(iv) 100% flash over voltage.
- (i) What are the tests conducted on circuit breakers and isolator switches?
Explain about any one of the tests.
(ii) What are different tests conducted on cables? Explain any one of them.