High Voltage Engineering

LAXMI INSTITUTE OF TECHNOLOGY

SARIGAM

COURSE FILE

Faculty Name : Mr. Prakash I Pandav

Subject Name : High Voltage Engineering

Subject Code : 2160904

Course Name : B.E (Electrical Engineering)

Semester : VI

Session : Dec - April 2019

DEPARTMENT OF ELECTRICAL ENGINEERING GUJARAT TECHNOLOGICAL UNIVERSITY

ELECTRICAL ENGINEERING (09) HIGH VOLTAGE ENGINEERING SUBJECT CODE: 2160904 B.E. 6th SEMESTER

Type of course: Engineering Science (Electrical)

Prerequisite: NA

Rationale:NA.

Teaching and Examination Scheme:

Teaching Scheme Credits Examination Marks Total L T P C Theory Marks Practical Marks Marks ESE PA (M) ESE (V) PA (E) PA ALA ESE OEP (I) 3 0 2 5 70 20 10 20 10 20 150

Content:

Sr. No. Content Total % Hrs Weightage 1. Electrostatic fields and field stress control : 04 08 Electrical field distribution and breakdown strength of insulating materials - fields in homogeneous, isotropic materials - fields in multi-dielectric, isotropic materials - numerical method: Finite Element Method (FEM), charge simulation method (CSM) 2. Electrical breakdown in gases 05 12 Gases as insulating media - ionization and decay processes, Townsend first ionization coefficient, photoionization, ionization by interaction of metastable with atoms, thermal ionization, deionization by recombination, deionization by attachment–negative ion formation, examples - cathode processes – secondary effects, photoelectric emission, electron emission by positive ion and excited atom impact, thermionic emission, field emission, Townsend second ionization coefficient, secondary electron emission by photon impact, examples - transition from non-self-sustained discharges to breakdown, the Townsend mechanism, examples - the streamer or ‘kanal’ mechanism of spark, examples - the sparking voltage–Paschen’s law, penning effect, the breakdown field strength, breakdown in non-uniform fields- partial breakdown, corona discharges, 3. Breakdown in liquid and solid dielectrics 07 16 Liquid as insulators, breakdown in liquids - electronic breakdown, suspended solid particle mechanism, cavity breakdown, examples - static electrification in power transformers, transformer oil filtration, transformer oil test, alternative liquid insulations like vegetable oils, esters and silicon oils - breakdown in solids, intrinsic breakdown, streamer breakdown, electromechanical breakdown, edge breakdown and treeing, thermal breakdown, erosion breakdown, tracking - breakdown of solid dielectrics in practice, partial discharges in solid insulation, solid dielectrics used in practice 4. Generation of high voltages : 07 16 Generation of high direct voltages, half and full wave rectifier circuits, voltage multiplier circuits, Van de Graff generators, electrostatic generators, examples - generation of alternating voltages, testing transformers, cascaded transformers, resonant transformers, examples - impulse voltages, Standard lightning and switching surge and associated parameters and their corrections, impulse voltage generator circuits, Marx circuit, operation, design and construction of impulse generators, examples - impulse current generator - control systems 5. Measurement of high voltages : 06 16 High direct voltage measurement, peak voltage measurements by spark gaps, sphere gaps, reference measuring systems, uniform field gaps, rod gaps, factors affecting sphere gap measurements, examples - electrostatic voltmeters - ammeter in series with high ohmic resistors and high ohmic resistor voltage dividers - generating voltmeters and field sensors - the measurement of peak voltages, the Chubb–Fortescue method, high- voltage capacitors for measuring circuits - voltage dividing systems and impulse voltage measurements, digital recorders, errors inherent in digital recorders 6. Over voltages, testing procedures and insulation coordination : 04 10 The lightning mechanism, energy in lightning, nature of danger - laboratory high-voltage testing procedures and statistical treatment of results, examples - insulation coordination, insulation level, statistical approach to insulation coordination, correlation between insulation and protection levels - modern power systems protection devices, MOA – metal oxide arresters 7. Non-destructive insulation test techniques : 05 12 Measurement of d.c. resistivity - dielectric loss and capacitance measurements, the Schering bridge, current comparator bridges, Tan Delta measurement, null detectors - partial-discharge (PD) measurements, the basic PD test circuit, PD currents, PD measuring systems within the PD test circuit, measuring systems for apparent charge, sources and reduction of disturbances, other PD quantities, calibration of PD detectors in a complete test circuit, digital PD instruments 8 High voltage testing: 0 4 10 Testing of insulators and bushings, testing of isolators and circuit breakers Testing of cables, testing of transformers - testing of surge diverters - radio interference measurements - design, planning and layout of high voltage laboratory Note: 1. 10%-20% weightage should be given to the Examples and Short/Multiple choice questions. 2. The institutes which does not have proper High Voltage Laboratory are advised to visit nearby High Voltage laboratory

Suggested Specification table with Marks (Theory):

Distribution of Theory Marks

R Level U Level A Level N Level E Level C Level 20% 20% 20% 20% 20% 0%

Legends: R: Remembrance; U: Understanding; A: Application, N: Analyze and E: Evaluate C: Create and above Levels (Revised Bloom’s Taxonomy)

Note: This specification table shall be treated as a general guideline for students and teachers. The actual distribution of marks in the question paper may vary slightly from above table.

Reference Books:

1. Kuffel, E., Zaengl W.S., Kuffel J., “High Voltage Engineering: Fundamentals” Butterworth- Heinmann (A division of Reed Educational & Profession Publishing Limited), 2nd Edition, 2000. 2. Naidu M. S. and Kamaraju V., “High Voltage Engineering”, fourth Edition, Tata McGraw- Hill Publishing Company Limited, New Delhi, 2009. 3. Rakosh Das Begamudre, “High Voltage Engineering, Problems and Solutions”, New Age International Publishers, New Delhi, 2010. 4. Dieter Kind, Kurt Feser, “High Voltage Test Techniques”, Reed educational and professional publishing ltd. (Indian edition), New Delhi-2001 5. M. Khalifa, "High Voltage Engineering-Theory and Practice", Marcel Dekker, Inc. New York and Basel,1990. 6. Hugh M. Ryan, “High Voltage Engineering and Testing”, 2nd edition, The Institution of Electrical Engineers, London, United Kingdom, 2001. 7. Wadhwa C.L., "High Voltage Engineering", third edition, New Age publishers, New Delhi, 2010.

Course Outcome:

After learning the course the students should be able to

1. Understand the basic generation and measurement of High voltage and High current for testing purposes 2. Comprehend Breakdown phenomenon in air, solid and liquid insulation 3. Test high voltage electrical Equipment with various testing devices.

List of Experiments:

1. Testing of transformer oil according to IS:6792 2. Testing of solid insulation with tape electrodes 3. Generation High D.C. Voltages and measurement through sphere gaps 4. Generation High A. C. voltages and measurement through sphere gaps 5. Generation of High A. C. voltages through cascaded transformers 6. Impulse voltage generation through Marx generator 7. Impulse voltage generation though simulation 8. Trace the field through electrolytic tank 9. Generation and visualization of corona in corona cage 10. Capacitance and loss factor measurement 11. A report on visit to high voltage laboratory

Note: At least eight practicals shall be performed depending on availability of the equipment

Design based Problems (DP)/Open Ended Problem:

1. Design of impulse generator with various combination of wave shaping resistor and capacitor 2. Design of CW type voltage multiplier with various stages 3. Design of tesla coil 4. Design of Generating voltmeter These problems may be done on paper by hand and/or using some simulation software.

Major Equipment:

1. Multi stage Impulse voltage generator 2. Multi stage Impulse current generator 3. High voltage AC and DC generating source (Min 100 kV) 4. Partial Discharge Measurement set up 5. Corona setup 6. Electrostatic generator 7. Cascade transformer 8. Resonant Transformer 9. Two to three sets of sphere gap assembly of various diameters 10. Faraday cage 11. Oil test kit 12. Solid insulation test kit\ 13. Schering bridge 14. DC resistivity measurement test kit 15. Surface resistance measurement test kit 16. Paschen’s law test kit

List of Open Source Software/learning website:

Open source software: 1. Finite Element Method Magnetics FEMM 2. LTSpice for circuit simulation, 3. KiCAD for CAD application

Web-based tools for design: 1. http://www.fairchildsemi.com/support/design-tools/power-supply-webdesigner/ 2. http://www.ti.com/lsds/ti/analog/webench/overview.page

Circuit Lab: 1. https://www.circuitlab.com/editor/

Open source Math Tools: 1. http://maxima.sourceforge.net/ 2. http://www.sagemath.org/ 3. http://www.scilab.org/ 4. http://www.gnu.org/software/octave/

Online Experiment Portal 1. http://vlab-ee1.iitkgp.ernet.in

Learning website 1. http://www.electrical-engineering-portal.com/ 2. http://nptel.iitm.ac.in/courses.php

Standards

1. “IEEE Standard Techniques for High-Voltage Testing”, 6th edition, IEEE Std. 4-1978. 2. “High-voltage test techniques, Part 1: General definitions and test requirements”, IEC 60060-1, 1989. 3. “High Voltage Test Techniques, Part 2: Measuring Systems”, IEC Publication 60060-2, 1994. 4. “High Voltage Test Techniques, Part 3: Measuring Devices”, IEC Publication 60060-3, 1976. 5. “High Voltage Test Techniques, Part 4: Application Guide for Measuring Devices”, 1st ed., IEC Publication 60060-4, 1977. 6. Indian Standard specifications for High Voltage test techniques”, Bureau of Indian Standard, IS 2071, New Delhi, 1991.

ACTIVE LEARNING ASSIGNMENTS: Preparation of power-point slides, which include videos, animations, pictures, graphics for better understanding theory and practical work – The faculty will allocate chapters/ parts of chapters to groups of students so that the entire syllabus to be covered. The power-point slides should be put up on the web-site of the College/ Institute, along with the names of the students of the group, the name of the faculty, Department and College on the first slide. The best three works should submit to GTU. High Voltage Engineering (2160904)

Assignment/Question Bank

Q.1. Give the answers of Short Questions. 1. Which of following gas is a electronegative gas? (a) Air (b) O2 (c) SF6 (d) Both O2 and SF6 2. State expression for Paschen’s Law. 3. Ionization coefficient α ,γ are function of (a) applied voltage (b) Pressure and Temperature (c) electric field (d) ratio of electric field to pressure.

4. For a 1cm gap in air at 760 mm pressure and 20°C temperature, the breakdown voltage is (a) 24 KV (b) 30.3 KV (c) 22.92 KV (d) 40 KV 5.The process of ionization brought about by (a) positive ion only (b) photon only (c) metastable particle (d) all of above6.The breakdown duo to internal discharges develops (a) in milliseconds (b) in few seconds (c) over a long duration of several days (d) all of above

Q.2. Explain Electric discharge in gas with CORONA discharge/partial discharge Q.3. What is Electric stress? Explain Electric field stress in homogeneous isotropic materials. Q.4. Explain how a sphere gap can be used to measure the peak value of voltages. And what are the parameter and factors that influence voltage measurement by sphere gap? Q.5. Explain time lags for breakdown of gas. Q.6. Explain Charge Simulation Method for solving Field Problems and Estimation of potential distribution. Q. 7. Explain various factors influencing the break down in gases Q. 8. Explain and Derive Townsend’s current growth equation for first ionization coefficient Q. 9. Explain and Derive Townsend’s current growth equation considering with primary and secondary ionization. Q. 10. Explain and Derive Paschen’s law Q. 11. Explain in detail concept of Breakdown in Vaccume.

Q.12. If a Steady State current of a certain gas is 5.4×10 A at 8 kV at a distance of 0.4 cm between the plane electrodes. Keeping the Field constant and reducing the distance to 0.1 cm results in a current of 5.5×10A. Calculate Townsend’s primary ionization coefficient α. Also find value of γ at 0.9 cm. High Voltage Engineering (2160904)

Assignment/Question Bank

Centre Code: 086 Examination : Mid Semester Examination Branch: Electrical Semester: 6th Sub Code: 2160904 Sub: HEE Date: 02/02/2019 Time:- 9:00 to 10:00Am Marks: 20 Note: Attempt any four from given questions marks Q. Explain Electric discharge in gas with CORONA discharge/partial discharge 5 Q. Explain various factors influencing the break down in gases 5 Q. Explain and Derive Townsend’s current growth equation for first ionization coefficient 5 Q. Explain and Derive Townsend’s current growth equation considering with primary and 5 secondary ionization. Q. Explain and Derive Paschen’s law 5 Q. Explain in detail concept of Breakdown in Vaccume. 5

Laxmi Institute of Technology , Sarigam Approved by AICTE, New Delhi; Affiliated to Gujarat Technological University, Ahmedabad Academic Year 2018-19

Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) EXAMINATION – WINTER 2018 Subject Code:2160904 Date:30/11/2018 Subject Name:High Voltage Engineering Time: 02:30 PM TO 05:00 PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

MARKS Q.1 (a) State & Explain Paschen’s Law. 03 (b) Explain Finite Element Method. 04 (c) Define Townsend’s first and second ionization coefficients. Obtain 07 Current growth equation due to first and second ionization.

Q.2 (a) What is Thermal breakdown in solid dielectric. 03 (b) Discuss properties of good solid dielectric. 04 (c) Explain Purification and Breakdown tests for liquid Dielectric. 07 OR (c) What is Electric stress? Explain Electric field stress in homogeneous isotropic 07 materials. Q.3 (a) Draw & explain characteristics of Lightning Impulse Voltage wave. 03 (b) What is difference between Marx circuit and modified Marx circuit. 04 (c) An impulse generator has eight stages with each condenser rated for 0.16 µF and 07 125 KV. The load capacitor available is 1000 pF. Find the series resistance and the damping resistance needed to produce 1.2/50 µs impulse wave. What is the maximum output voltage of the generator, if the charging voltage is 120 KV ?

OR Q.3 (a) List out different techniques to measure high voltages. 03 (b) What is the principle of operation of resonant transformer? List out advantages 04 and disadvantages of it. (c) Explain capacitance voltage Transformer with its schematic representation, 07 Equivalent circuit and its phasor diagram. Q.4 (a) Explain principle of Electrostatic voltmeter and limitation of it for high voltage 03 measurement. (b) List out the Difference between Uniform field and Non-uniform field. 04 (c) What is meant by insulation co-ordination ? How are the protective devices 07 chosen for optimal insulation level in a power system? OR Q.4 (a) Discuss Rod Gap Arrester. 03 (b) Discuss Digital PD instrument. 04 (c) Discuss measurement of Dielectric constant and loss tangent of capacitor. 07

Q.5 (a) Draw & Discuss Equivalent circuit of partial discharge. 03 (b) Explain High ohmic series Resistance with Micro-ammeter with its advantages 04 and disadvantages for High Voltage DC measurement. (c) Explain high voltage Testing on Insulators. 07 OR

1 Q.5 (a) What is a Tesla coil? How are damped high-frequency oscillations obtained from 03 Tesla coil ? (b) Give the schematic arrangement of an impulse potential divider with an 04 oscilloscope connected for measuring impulse voltages. (c) Explain Classification of High Voltage Laboratories. 07

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2 Seat No.: ______Enrolment No.______GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2018 Subject Code: 2160904 Date: 05/05/2018 Subject Name: High Voltage Engineering Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 (a) Define Townsend’s first and second ionization coefficients. State 03 condition for breakdown obtained in Townsend discharge. (b) Explain purification test cell system related to liquids. 04 (c) Describe with a neat sketch, the working of a Van de Graff generator. 07

Q.2 (a) Explain how a sphere gap can be used to measure the peak value of 03 voltages. (b) What are the parameter and factors that influence voltage 04 measurement by sphere gap? (c) Explain Electrostatic Voltmeter for high voltage measurement. 07 OR (c) What is Paschen’s law? Explain minimum voltage for breakdown 07 under a given ‘p x d’ condition.

Q.3 (a) Explain front and tail times of an impulse wave with neat sketch. 03 (b) Explain with neat sketch, testing transformer construction. 04 (c) A 12 stage impulse generator has 0.126µF capacitors. The wave front and 07 wave tail resistances connected are 800Ω and 5000Ω respectively. If the load capacitor is 1000pF, find the front and tail times of the impulse wave produced. OR Q.3 (a) Enlist components used in Modified Marx circuit. 03 (b) Explain Trigatron gap. 04 (c) Discuss the “Charge Simulation Method “for solving field problems 07 and estimation of potential distribution.

Q.4 (a) Define statistical time lag, formative time lag and total time lag. 03 (b) Explain drawbacks of Townsend mechanism. 04 (c) A steady current of 600µA flows through the plane electrodes 07 separated by a distance of 0.5cm when a voltage of 10kV is applied. Determine the Townsend’s first ionization constant if a current of 60µA flows when the distance of separation is reduced to 0.1cm and the field is kept constant at previous value. OR Q.4 (a) What are the commercial liquids? 03 (b) Enlist factors affecting ionization process and state processes 04 responsible for gaseous breakdown. (c) Explain treeing and tracking related to solid breakdown. 07 Q.5 (a) What is surge arrester? 03 (b) Discuss the importance of grounding in High Voltage Lab. 04 (c) Discuss the method of balanced detection for locating partial 07 discharges in electrical equipments.

OR Q.5 (a) List out the common test facilities available in High Voltage Lab. 03 (b) Explain Metal Oxide Arrestor. 04 (c) Explain insulation coordination and statistical approach to it. 07

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Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) EXAMINATION – WINTER 2017 Subject Code: 2160904 Date: 16/11/2017 Subject Name:High Voltage Engineering Time:02:30 PM TO 05:00PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

MARKS Q.1 (a) Explain time lags for breakdown of gas. 03

(b) Define Townsend’s first ionization coefficients. Obtain current 04 growth equation due to first ionization. (c) Draw and explain Marx circuit and modified Marx circuit of 07 multistage impulse generator.

Q.2 (a) Explain Transformer oil testing. 03 (b) Explain cultivation and bubble theory for liquid breakdown. 04 (c) What are treeing and tracking ? Explain this two phenomenon in solid 07 dielectrics. OR (c) A 10-stage Cockcroft Walton circuit has all capacitors of 0.06 µF. 07 The secondary voltage of the supply transformer is 100 KV at a frequency of 150 Hz. If the load current is 1mA, determine: (1) voltage regulation (2) The ripple (3) The optimum number of stages for maximum output voltage. Q.3 (a) List advantages, disadvantages and applications of Van de Graaff 03 generator. (b) What is impulse voltage? Discuss characteristic of it. 04 (c) Describe the principle of Generating Voltmeter operation. List out 07 advantages and disadvantages of Generating Voltmeter.

OR Q.3 (a) Discuss Principle of Electrostatic Voltmeter 03 (b) Draw circuit of series capacitor peak voltmeter. Describe different 04 sources that contribute error in it. (c) Discuss the factor affecting spark over voltage of sphere gaps. 07 Q.4 (a) Explain metal oxide lightning arrester. 03 (b) Discuss dielectric constant and loss factor. 04 (c) Describe high voltage Schering bridge. 07 OR Q.4 (a) Draw block diagram of Digital PD Analyser. 03 (b) Explain equivalent circuit of partial discharge. 04 (c) Explain testing of cables. 07

Q.5 (a) Describe Test facility provided in high voltage laboratory. 03 (b) What is insulation co-ordination ? 04 (c) Explain capacitance voltage transformer with advantages and 07 disadvantages. OR Q.5 (a) Give comparison between positive corona and negative corona. 03 1 (b) Discuss Hall effect in Hall generator. 04 (c) An impulse generator has 8 stages with each condenser rated for 07 0.16 µF and 125KV. The load capacitor available is 1000 PF. Find the series resistance and damping resistor needed to produce 1.2/50 µs impulse wave. What is the maximum output voltage of generator, if the charging voltage is 120 KV ?

2 Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2017 Subject Code: 2160904 Date: 05/05/2017 Subject Name: High Voltage Engineering Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

MARKS Q.1 Short Question OR Multiple Choice Questions 14 1. Which of following gas is a electronegative gas? (a) Air (b) O2 (c) SF6 (d) Both O2 and SF6 2. State (b) expression for Paschen’s Law. 3. Ionization coefficient α ,γ are function of (a) applied voltage (b) Pressure and Temperature (c) electric field (d) ratio of electric field to pressure 4. For a 1cm gap in air at 760 mm pressure and 20°C temperature, the breakdown voltage is (a) 24 KV (b) 30.3 KV (c) 22.92 KV (d) 40 KV 5. The process of ionization brought about by (a) positive ion only (b) photon only (c) metastable particle (d) all of above 6. The breakdown duo to internal discharges develops (a) in milliseconds (b) in few seconds (c) over a long duration of several days (d) all of above 7. A trigetron gap is used with (a)cascade transformer unit (b) impulse current generator (c) impulse voltage generator (d) dc voltage doubler unit 8. In testing with a resonant transformer, the output voltage is (a) rectangular wave (b) triangular wave (c) trapezoidal wave (d) pure sine wave 9. A generating voltmeter is used to measure (a) dc voltages (b) ac voltages (c) impulse voltages (d) high-frequency ac voltages 10. Compensated capacitance divider for high voltage (1MV) generally has a bandwidth of (a) 100 MHZ (b) 1 MHZ (c) 10 MHZ (d) 1000 MHZ 11. The peak value of lightning stroke currents are of order of (a) 100 A (b) 1000 A (c) 10 to 100 KA (d) 106 A 12. The equivalent circuit of a lossy capacitor or dielectric is (a) R-C series circuit (b) L-C series circuit (c) R-C parallel circuit (d) L-C parallel circuit 13. Most important tests conducted on isolators and circuit breaker are (a) voltage withstand tests (b) short circuit tests (c) high current test (d) temperature rise tests

1 14. Fault location in an HV cable is done by (a) Voltage withstand tests (b) partial discharge scanning tests (c) life test (d) impulse testing Q.2 (a) Explain Tesla coil with its circuit & Waveform 03 (b) Differentiate between Marx & modified Marx circuit for 04 multistage impulse generators with circuit. (c) A 10 stage Cockcroft-Walton circuit has all capacitors of 07 0.06 μF. The secondary voltage of the supply transformer is100 KV at a frequency of 150Hz.If the load current is 1mA, determine: (1) percentage voltage regulation.(2) The ripple (c) The optimum number of stages for maximum output voltage. OR (c) Explain with neat diagram the principle & construction of 07 of an electrostatic voltmeter. Q.3 (a) Explain advantages and disadvantages of capacitance 03 voltage Transformer with equivalent circuit (b) Discuss how to measure ac voltage using sphere gap. 04 (c) A steady current of 600 μA flows through the plane 07 electrodes separated by a distance of 0.5 cm when a voltage of 10 KV is applied. Determine the Townsend’s first ionization coefficient if a current of 60 μA flows when the distance of separation is reduced to 0.1 cm and the field is kept constant at previous value. OR Q.3 (a) Explain breakdown test for Transformer oil. 03 (b) What is stressed oil volume theory ? How does it explain 04 breakdown in large volumes of commercial liquid dielectrics? (c) Explain solid breakdown due to treeing & tracking. 07 Q.4 (a) Explain Thermal breakdown in solid dielectrics 03 (b) Give comparison between uniform and non-uniform field. 04 (c) Explain corona discharge. What are different factor 07 affecting Corona losses. How Corona loss can be eliminated? OR Q.4 (a) Define and explain the terms: Statistical time lag, 03 formative time lag, total time. (b) Discuss Measurement of Dielectric constant and loss 04 tangent of capacitor. (c) Explain High voltage Schering bridge for tan δ and 07 capacitance measurement of Insulators. Q.5 (a) Discuss power frequency tests of insulator. 03 (b) What is Finite Element Method? Brief it for solving the 04 field problems (c) Give classification of high voltage laboratory. 07 OR Q.5 (a) Write a comprehensive note on metal oxide arrestors. 03 (b) Discuss origin of switching surges and its characteristics. 04 (c) Explain the partial discharge tests for cables. 07

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2 Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE – SEMESTER – VI (NEW).EXAMINATION – WINTER 2016

Subject Code: 2160904 Date: 26/10/2016 Subject Name: High Voltage Engineering Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 (a) If a Steady State current of a certain gas is A at 8 kV at a distance of 0.4 cm between the plane electrodes. Keeping the Field constant and reducing the distance to 0.1 cm results in a current of A. Calculate Townsend’s primary ionization coefficient . Also find value of at 0.9 cm. (b) Explain Charge Simulation Method for solving Field Problems and Estimation 07 of potential distribution.

Q.2 (a) Explain the phenomenon ‘Treeing and Tracking’ in solid insulating materials 07 under electrical stress. How does it lead to breakdown? (b) Explain the working of ‘Van de Graff Generator’ with neat sketch. What are the 07 factors that limit the maximum voltage obtained? OR (b) Explain Voltage Multiplier Circuit for generation of High Voltage. 07

Q.3 (a) What is Paschen’s Law? How do you account for the minimum voltage for 07 breakdown under a given ‘p x d’ condition? (b) A 12- stage Impulse generator has 0.126 µF capacitors. The wave front and the 07 wave tail resistances connected are 800 ohms and 5000 ohms respectively. If the load capacitors is 1000 pF, find the front and tail times of the impulse wave produced. OR Q.3 (a) What is Capacitance Voltage Transformer? Explain with phasor diagram how a 07 tuned capacitance voltage transformer can be used for voltage measurements in power systems. (b) Design a peak reading voltmeter along with a suitable micro-ammeter such that 07 it will be able to read voltages, up to 100 kV (peak). The capacitance potential divider available is of the ration 1000 : 1

Q.4 (a) What is ‘Stressed Oil Volume Theory’? How does it explain breakdown in 07 large volumes of commercial liquid dielectrics? (b) Discuss the different methods of measuring high D.C. voltages. What are the 07 limitation in each method? OR Q.4 (a) Briefly explain the methods used for calibrating the partial discharge detectors. 07 (b) What are the different methods and means for purification of liquid dielectrics? 07

Q.5 (a) Explain the importance of RIV measurements for EHV power apparatus. 07 (b) What is composite insulation? How does short term breakdown differ from long 07 term breakdown? OR Q.5 (a) What is meant by insulation co-ordination? How are the protective devices 07 chosen for optimal insulation level in a power system? (b) What is Finite Element Method? Brief it for solving the field problems 07

************* 1 Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2016 Subject Code:2160904 Date:13/05/2016 Subject Name: High Voltage Engineering Time: 10:30 AM to 01:00 PM Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 (a) Describe the working of Van de Graff generator with neat diagram. 07 (b) Define Townsend’s first and second ionization coefficient. Explain Townsend’s 07 discharge.

Q.2 (a) Explain vacuum breakdown. 07 (b) Explain various theories for breakdown in commercial liquids. 07 OR (b) Explain solid breakdown due to treeing and tracking. 07

Q.3 (a) Draw and explain Marx circuit and modified Marx circuit of multistage impulse 07 generator. (b) What is principle of operation of a resonant transformer? List out its advantages 07 and disadvantages. OR Q.3 (a) A ten stage Cockcroft-Walton circuit has all capacitors of 0.06 µF. The 07 secondary voltage of the supply transformer is 100 kV at a frequency of 150 Hz. If the load current is 1mA determine: 1.Voltage Regulation, 2.The Ripple, 3. The optimum number of stages for maximum output voltage

(b) Explain cascade connection for producing ac high voltage. Explain use of 07 isolating transformer.

Q.4 (a) What are different methods of high DC voltage measurement? Explain 07 Generating voltmeter method in detail. (b) Explain capacitive voltage transformer with its schematic representation, 07 equivalent circuit and phasor diagram. OR Q.4 (a) Explain series capacitor peak voltmeter. 07 (b) What is meant by insulation co-ordination? How are the protective devices 07 chosen for optimal insulation level in a power system?

Q.5 (a) Explain with neat sketch the mechanism of lightning discharge. 07 (b) What are partial discharges and how are they detected under power frequency 07 operating conditions? OR Q.5 (a) Explain impulse testing of power transformer? 07 (b) Explain test facilities and layout of high voltage laboratory. 07

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1 Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE – SEMESTER – VI EXAMINATION – WINTER 2015

Subject Code:160904 Date:14/12/ 2015 Subject Name: High Voltage Engineering Time: 2:30pm to 5:00pm Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 (a) Explain “Treeing” and “Tracking” clearly the two processes in solid dielectrics. 07 (b) Explain how a sphere gap can be used to measure the peak value of voltages. 07 What are the parameters and factors that influence such voltage measurement?

Q.2 (a) Explain with neat diagram the principle of operation of an electrostatic 07 voltmeter. Discuss its advantages and limitations for high voltage measurement. (b) What is meant by insulation co-ordination? How are the protective devices 07 chosen for optimal insulation level in a power system? OR (b) What is Paschen’s law? Explain significance of existence of minimum sparking 07 potential in paschen’s curve.

Q.3 (a) Draw & Explain Marx circuit and Modified Marx circuit of multistage impulse 07 generator. Discuss differences between these two. (b) Discuss measurement of dielectric constant and loss tangent of capacitor. 07 OR Q.3 (a) Explain test facilities and testing equipments in high voltage Laboratories 07 (b) Explain Tesla coil for producing high frequency high voltages with its 07 derivation of output voltage.

Q.4 (a) Explain principle, working, advantages & disadvantages of Generating 07 voltmeters. (b) Explain series capacitor peak voltmeter 07 OR Q.4 (a) Discuss High voltage Schering Bridge. 07 (b) Explain corona discharge. 07

Q.5 (a) Explain potential dividers for impulse voltage measurement by CRO. Suggest 07 arrangement to minimize errors. (b) Explain Purification & Breakdown tests for Liquid Dielectric. 07 OR Q.5 (a) Explain the working of Cockcroft-Walton circuit with schematic diagram. 07 (b) Explain how are switching impulse generated in Laboratory. 07

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1 Seat No.: ______Enrolment No.______

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI • EXAMINATION – SUMMER • 2015

Subject Code: 160904 Date:14/05/2015 Subject Name: High Voltage Engineering Time: 10.30am-01.00pm Total Marks: 70 Instructions: 1. Attempt all questions. 2. Make suitable assumptions wherever necessary. 3. Figures to the right indicate full marks.

Q.1 (a) Define Townsend’s first and second ionization coefficients. Obtain current growth 07 equation due to first and second ionization. (b) Describe the working of a Van de Graff generator with a neat sketch. 07

Q.2 (a) Describe the principle of Generating Voltmeter operation. List out advantages 07 and disadvantages of Generating Voltmeter. (b) Explain Corona discharge. 07 OR (b) Define and explain the terms: Statistical time lag, formative time lag, total time. 07

Q.3 (a) Explain intrinsic breakdown mechanism of solid dielectric material. 07 (b) A solid dielectric material of dielectric strength of 6.0 has an internal void of 07 thickness 1 mm. The specimen is 1 cm thick and is subjected to rms voltage of 10 kV. If the void is filled with air (breakdown strength of air = 3 kV/mm), give remark on occurrence of internal discharge. OR Q.3 (a) Explain cultivation and the bubble theory for breakdown of liquid dielectric. 07 (b) The capacitive voltage divider is used in electrostatic voltmeter for measurement 07 of high voltage ac. A three terminal standard compressed air capacitor of 1nF and mica capacitor of 1μF are available. If 100V ac voltmeter is connected across mica capacitor, what will the maximum available reading of voltmeter? Ignore capacitance of meter.

Q.4 (a) Explain cascade transformer unit with isolating transformers for high alternating 07 voltage generation. (b) How sphere gap can be used to measure the peak value of voltages. What are the 07 parameters and factors that influence such voltage measurement? OR Q.4 (a) What is the principle of operation of a resonant transformer? List out its 07 advantages and disadvantages of it. (b) Describe hall generator for measuring high dc currents. 07

Q.5 (a) Explain the mechanism of lightning strokes. 07 (b) Explain the high voltage schering bridge for tan δ and capacitance measurement 07 of insulators. OR Q.5 (a) Briefly explain how partial discharges in insulation can be detected and display. 07 (b) Explain the insulation testing of insulators. 07

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