DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING QUESTION BANK SUBJECT CODE & NAME : EE 1402 HIGH VOLTAGE ENGINEERING UNIT I

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1 DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING QUESTION BANK SUBJECT CODE & NAME : EE 1402 HIGH VOLTAGE ENGINEERING YEAR / SEM : IV / VII UNIT I OVER VOLTAGES IN ELECTRICAL POWER SYSTEMS 1. What are the causes of power frequency over voltages?(2) 2. What are the causes of over voltages in power system? (2) 3. What are the different types of fault that may occur on power lines? (2) 4. What are harmful effects of lightning? (2) 5. Name the sources of switching surges? (2) 6. What is voltage surge? Draw a typical lightning voltage surge. (2) 7. Name the sources of switching surges. (2) 1. Explain the selection of surge arresters for E.H.V. system. Explain the V-I Characteristics of typical surge diverters. 2. What are the methods used to control of over voltages due to switching? Explain briefly. 3. What are the causes for power frequency over voltage? How they are controlled in power systems? 4. What are the causes for switching over voltage? How they are controlled in power systems? 5. What are the different methods employed for lightning protection of overhead lines? 6. Explain the characteristics of switching surges with typical wave shapes clearly. 7. Give the mathematical model of lightning discharges and explain them

2 8. With neat sketches, describe the two types of lightning strokes. 9. A transmission line has the following line constants R = 0.1 ohm/km, L=1.26 mh/km, C = µf/km, and G = 0. if the line is a 3 phase line and is charged from one end at a line voltage of 230 KV, find the rise in voltage at the other end, if the line length is 400Km. 10. A 3 phase single circuit transmission line is 400 Km long. If the line is rated for 220 KV and has the parameters, R = 0.1 ohms/km, L=1.26 mh/km, C = µf/km, and G = 0, find (a) the surge impedance and (b) the velocity of propagation neglecting the resistance of the line. If a surge of 150 KV and infinitely long tail strikes at one end of the line, what is the time taken for the surge to travel the other end of the line? UNIT II ELECTRICAL BREAKDOWN IN GASES, SOLIDS AND LIQUIDS 1. Define Gas law. (2) 2. State paschen s law(2) 3. Which insulation is used in high voltage circuit breakers of large power rating? (2) 4. What are electronegative gases? Give example(2) 5. What is time lag in the break down of dielectric mediums? (2) 6. Name the different secondary ionization processes. (2) 7. Name the three properties of composite dielectrics that are important to their performance. (2) 8. Name the various mechanism of vacuum breakdown. (2) 1. Deduce the Townsend s break down criteria. Also define the Townsend s primary and secondary ionization coefficients. 2. Explain clearly breakdown in non uniform fields and corona discharges. 3. Explain the various theories of breakdown mechanism of the commercial liquid dielectrics. 4. Explain the characteristics of liquid dielectrics. 5. Explain the different mechanism by which breakdown occurs in solid dielectric in practice. 6. Classify the various breakdown mechanisms occurring on solid dielectrics and explain them briefly.

3 7. In an experiment of gas, it was found that at steady current of 5.5 X 10-8 A with 0.4 cm separation between the plates. For constant field, if the separation reduces to 0.1 cm, results in a current of 5.5 X 10-9 A. find Townsend s primary ionization coefficient. 8. What will be the breakdown strength of air be for small gaps (1 mm) and large gaps (20 cm) under uniform field conditions and standard atmospheric conditions? 9. A solid specimen of dielectric has a dielectric constant of 4.2, and tan del = at a frequency of 50Hz. If it is subjected to an alternating field of 50 KV/cm, calculate the heat generated in the specimen due to the dielectric loss. UNIT III GENERATION OF HIGH VOLTAGES AND HIGH CURRENTS 1. Give some uses of HVDC(2) 2. What are the applications of impulse current wave forms of high magnitude? (2) 3. How are capacitances connected in an impulse current generator? (2) 4. What type of wave form will be available in impulse current generator output? (2) 5. Draw a circuit diagram of a simple voltage doubler. (2) 6. Write the expressions to find the optimum no. of stages and % ripple in a voltage multiplier circuits. (2) 7. Draw a simple Tesla Coil equivalent circuit for generation of high frequency A.C high voltage. (2) 8. Write an expression to find the % ripple and % voltage regulation in a multi stage voltage multiplier circuit. (2) 9. What are the advantages of high frequency resonant transformer used in HVAC generation? (2) 10. Find the percentage ripple in the output voltage produced by a 8 stage Cockcroft-Walton multiplier circuit with a capacitance all equal to 0.05 µf. The supply transformer secondary voltage is 125 KV at a frequency of 150 Hz and the load current is 5 ma. (2) 11. A Cockcroft-Walton type voltage multiplier has eight stages with capacitances all equal to 0.05 µf. The supply transformer secondary voltage is 125 KV at a frequency of 150 Hz and the load current is 5 ma. Find the optimum no. of stages for minimum voltage regulation. (2)

4 12. A Tesla coil has a primary winding rated for 10 KV with 2 µf capacitance on primary side and 1nF capacitance on the secondary side. If the energy efficiency is 5%, calculate the output voltage. (2) 13. A 12 stage impulse generator has µf capacitors. The wave front and wave tail resistances connected are 800 ohms and 5000 ohms respectively. If the load capacitor is 1000 pf, find the front and tail times of the impulse wave produced. (2) 14. What is a voltage multiplier circuits? (2) 15. Distinguish between electromagnetic and electrostatic machines. (2) 1. Describe the cascade transformer connection to generate high alternating voltages. 2. With neat sketch explain the working principle of a Cockcroft Walton voltage multiplier circuits. 3. Describe with neat diagram the principle of operation, advantages, limitations and applications of Van de Graff generator. 4. Give the Marx circuit arrangement for multistage impulse generators. How is the basic arrangement modified to accommodate the wave time control resistances? 5. What is Tesla coil? How are damped high frequency oscillations obtained from a Tesla coil? 6. Explain any one method of generating HV AC at power frequency and discuss its limitation/feature. 7. What are the different forms of high voltages classified? Explain any one method of voltage multiplier circuits. 8. Draw and explain the circuits for producing impulse waves. 9. A 100 KVA, 400V/250 KV testing transformer has 8% leakage reactance and 2% resistance on 100KVA base. A cable has to be tested at 500 KV using the above transformer as a resonant transformer at 50 Hz. If the charging current of the cable at 500 KV is 0.4 A, find the series inductance required. Assume 2% resistance for the inductor to be used and the connecting leads. Neglect dielectric loss of the cable. What will be the input voltage to the transformer?

5 UNIT IV MEASUREMENT OF HIGH VOLTAGES AND HIGH CURRENTS 1. What are the general methods used for measurement of high frequency and impulse currents? (2) 2. What are the high voltage d.c measurement techniques used? (2) 3. For what measurement are Hall generators normally used? (2) 4. What type of measuring devices are preferred for measurement of impulse currents of short duration? (2) 5. Draw the simple circuit of peak reading voltmeter and it s equivalent. (2) 6. List the factors that are influencing the peak voltage measurement using sphere gap. (2) 7. What are the advantages of CVT measurement in HVAC? (2) 8. What are the limitations of generating voltmeter? (2) 9. State the demerits of CVT measurement for HVAC measurements. (2) 1. Tabulate the high voltage and high current measurement techniques for different types of voltage and current. 2. Explain sphere gap for measurement of high voltage with diagrams. 3. With a neat sketch explain the principle of operation of an electrostatic voltmeter for HVAC measurement. What are the merits and demerits? 4. What is CVT? Explain through phasor diagram how a tuned CVT can be used for HV AC measurement in substations. 5. Discuss the various techniques for the measurement of impulse voltage. 6. The effective diameter of the moving disc of an Electrostatic voltmeter is 15 cm with an separation of 1.5 cm. Find the weight in grams that is necessary to be added to balance the moving plate when measuring a voltage of 50 KV d.c. Derive any formula used. What is force of attraction between the plates when they are balanced? 7. A rogowski coil is required to measure impulse current of 8 KA having rate of change of current of A/sec. The voltmeter is connected across the integrating circuit which reads 8 volts for full scale deflection. The input to integrating circuit is from Rogowski coil. Determine the mutual inductance of coil, R and C for integrating circuit. 8. Describe a new scheme of current transformer measurement introducing elector optical technique for EHV systems. 9. Explain with diagram the extended series resistance for high a.c. voltage measurements.

6 UNIT V HIGH VOLTAGE TESTING AND INSULATING COORDINATION 1. What are test conducted on insulators? (2) 2. What are test conducted on Bushings? (2) 3. Define withstand voltage. (2) 4. Define impulse voltage. (2) 5. Differentiate type test and routine test. (2) 6. Give the values of reference atmospheric conditions as per I.S specifications. (2) 7. Define Disruptive discharge voltage. (2) 8. What are the demerits of synthetic testing of circuit breakers? (2) 9. Define creepage distance. (2) 10. What is insulation co ordination? (2) 1. With a neat sketch explain the impulse testing on the power transformer. 2. Discuss the various test carried out in a circuit breaker at HV labs. 3. What are the different power frequency tests done on bushings? Mention the procedure for testing. 4. Briefly discuss the various tests carried out the insulator. 5. What is meant by insulation coordination? How are the protective devices chosen for optimal insulation level in a power system? 6. 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. 7. 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. 8. (i) What are the tests conducted on circuit breakers and isolator switches? Explain about any one of the tests.(8) (ii) What are different tests conducted on cables? Explain any one of them. (8)

ROEVER ENGINEERING COLLEGE ELAMBALUR, PERAMBALUR DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

ROEVER ENGINEERING COLLEGE ELAMBALUR, PERAMBALUR 621 212 DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING EE1003 HIGH VOLTAGE ENGINEERING QUESTION BANK UNIT-I OVER VOLTAGES IN ELECTRICAL POWER SYSTEM