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High-Voltage Engineering High-Voltage Engineering About the Authors M S Naidu was Professor in the Department of High-Voltage Engineering, Indian Institute of Science, Bangalore. A PhD from the University of Liverpool, he served as a visiting scientist at the High- Voltage Laboratory of the Eindhove...

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High-Voltage Engineering

High-Voltage Engineering

About the Authors

M S Naidu was Professor in the Department of High-Voltage Engineering, Indian Institute of Science, Bangalore. A PhD from the University of Liverpool, he served as a visiting scientist at the HighVoltage Laboratory of the Eindhoven University of Technology, Netherlands. He had also given lectures at many high-voltage laboratories in West Germany, Switzerland and France. Professor Naidu was a Chartered Engineer, a Fellow of the Institution Of Engineers (India) and also a Fellow of the National Academy of Engineering. His research interests included gaseous insulation, circuit-breaker arcs, pollution under HVDC, etc. He published many research papers and authored Advances in High Voltage Breakdown and Arc Interruption in SF6 and Vacuum (Pergamon Press, 1981). Recently, a book on Gas Insulated Substations that had been authored by him, was published in 2008. Professor Naidu passed away in February 2002.

V Kamaraju obtained his PhD in High-Voltage Engineering from the Indian Institute of Science, Bangalore. He was formerly a Professor and Principal at the JNTU College of Engineering, Kakinada, Andhra Pradesh. He was a visiting professor at Middle East Technical University, Gaziantep, Turkey, during 1981-82. Professor Kamaraju is a Chartered Engineer and a Fellow of the Institution of Engineers (India). He has published many research papers and has been a consultant to various industries and to the Andhra Pradesh State Electricity Board. He has published Electrical Distribution Systems and Linear Systems: Analysis and Applications during 2006-2008 and High Voltage Direct Current Transmission in 2011, all by McGrawHill Education (India). He received the Best Teacher award from Government of Andhra Pradesh, India, in 2001. At present, he is Professor in the Department of Electrical Engineering at Mahavir Institute of Science and Technology, Hyderabad, Andhra Pradesh, India. Professor Kamaraju has done extensive research in the areas of liquid and solid dielectrics, composite insulation and partial discharges.

High-Voltage Engineering

(Late) M S Naidu Formerly, Professor in Department of High Voltage Engineering Indian Institute of Science, Bangalore V Kamaraju Formerly, Principal and Professor of Electrical Engineering JNT University College of Engineering Kakinada, Andhra Pradesh

Published by McGraw Hill Education (India) Private Limited P-24, Green Park Extension, New Delhi 110 016 High-Voltage Engineering, 5e Copyright © 2013,2009,2004,1993,1982 by McGraw Hill Education (India) Private Limited. No part of this publication may be reproduced or distributed in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise or stored in a database or retrieval system without the prior written permission of the publishers. The program listings (if any) may be entered, stored and executed in a computer system, but they may not be reproduced for publication. This edition can be exported from India only by the publishers, McGraw Hill Education (India) Private Limited. Print Book: ISBN-13: 978-1-25-906289-6 ISBN-10: 1-25-906289-9 Ebook Book: ISBN-13: 978-93-392-0318-4 ISBN-10: 93-392-0318-6 Vice President and Managing Director: Ajay Shukla Head—Higher Education (Publishing and Marketing): Vibha Mahajan Publishing Manager (SEM & Tech. Ed.): Shalini Jha Editorial Executive: Koyel Ghosh Manager—Production Systems: Satinder S Baveja Assistant Manager—Editorial Services: Sohini Mukherjee Senior Production Executive: Suhaib Ali Assistant General Manager (Marketing)—Higher Education: Vijay Sarathi Senior Product Specialist: Tina Jajoriya Senior Graphic Designer—Cover: Meenu Raghav General Manager—Production: Rajender P Ghansela Manager—Production: Reji Kumar Information contained in this work has been obtained by McGraw Hill Education (India), from sources believed to be reliable. However, neither McGraw Hill Education (India) nor its authors guarantee the accuracy or completeness of any information published herein, and neither McGraw Hill Education (India) nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that McGraw Hill Education (India) and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. Typeset at Tej Composers, WZ 391, Madipur, New Delhi 110 063 and printed at Magic International Pvt. Ltd., Plot No. 26E, Sector-31 (INDUSTRIAL), Site-IV, Greater Noida - 201306 Cover Printer: Magic International Pvt. Ltd. DZZYYRCORCYLX

To Our Children May their world be filled with understanding, love and peace

Preface Overview The demand for the generation and transmission of large amounts of electric power today, necessitates transmission at extra-high voltages. In developed countries like the USA, power transmission voltages have reached 765 kV to 1100 kV, and 1500 kV systems are also being built. In our country, 750 kV ac power systems have already come into operation, and in another 10 years’ time, every state is expected to be linked by a National Power Grid operating at 750 kV to 1100 kV.

Target Audience In the current industrial scenario, a practicing electrical engineer or a student of electrical engineering is expected to possess knowledge of high-voltage techniques and should have sufficient background in high-voltage engineering. Unfortunately, at present, very few textbooks in high-voltage engineering are available, compared to those in other areas of electrical engineering. Even among these, no single book has covered the entire range of topics in high-voltage engineering in depth and presented the material in a lucid manner. Therefore, an attempt has been made in this book, to bring together different topics in high-voltage engineering to serve as a single-semester course for final-year undergraduate students or postgraduate students studying Electrical Engineering, Electronics Engineering, and Applied Physics. This book is also intended to serve power engineers in the industry who are involved in the design and development of electrical equipment as well as engineers in the electricity supply and utility establishments. It provides all the latest information on insulating materials, breakdown phenomena, overvoltage, and testing techniques. It is useful for self-study by engineers in the field of electricity utilities and design, development testing of electrical apparatus, transmission line hardware, particle acceleration, etc.

About the Book The material in this book has been organized into five sections, namely (i) insulating materials and their applications in electrical and electronic engineering, (ii) breakdown phenomena in insulating materials—solids, liquids, and gases, (iii) generation and measurement of high dc, ac, and impulse voltages and currents, (iv) overvoltage phenomena in electrical power transmission systems and insulation coordination, and (v) high-voltage testing techniques, testing of apparatus and equipment, and planning of high-voltage laboratories. Much of the information on these topics has been drawn from standard textbooks and reference books and have been simplified and reorganized to suit the needs of the students and graduate engineers. Many research publications have also been referred to, and relevant standard specifications have been quoted to help the reader gain easy access to the original references.

Salient Features • Includes latest industry inputs on HV Construction Kits • HVDC Systems and Testing expanded to cover the updates in technology, such as

º Surge Arresters for EHV systems º HVDC Divider for HVDC Transmission Systems º Testing of HVDC valves and systems • Dedicated chapter on Design, Planning and Layout of High-Voltage Laboratories • Pedagogy enhanced and revised to suit examination requirements: º 47 Worked Examples º 14 Short-Answer Questions º 140 Review Questions º 34 Problems º 199 Multiple-Choice Questions

Chapter Organization The text is organized in 11 concise chapters. Chapter 1 introduces the basic concepts of high-voltage engineering and includes numerical methods for electric field computations (viz., FEM, CSM, BEM techniques) Chapter 2 is on conduction and breakdown in gases and has been revised to include the basics of collisions processes; breakdown phenomenon in SF6 and SF6—air mixtures. This chapter also has a completely revised section on Paschen’s Law with supporting problems. Chapter 3 is on conduction and breakdown in liquid dielectrics and contains information on the recent developments in liquid insulents. Chapters 4 and 5 are on breakdown in solid dielectrics and applications of insulating materials respectively, and incorporate the latest solid insulating materials and their applications in electric power apparatus. Chapter 6 discusses the generation of high voltages and currents, while Chapter 7 deals with measurement of high voltages and currents. This chapter also explains electric field (E) measurements, field intensity meters, impulse test and measuring systems. Chapter 8 is on overvoltage phenomenon and insulation coordination in electric power systems. Over voltages and testing of Gas Insulated Substation (GIS) has been added in this edition (chapters 5 and 8). Chapter 9 discusses non-destructive testing of materials and electric apparatus, and Chapter 10 is on high-voltage testing of electric apparatus. Finally, Chapter 11 is on design, planning and layout of high-voltage laboratories. It also includes the recent developments in HV testing laboratories and includes a brief description of the UHV laboratory, CPRI, Hyderabad. Details of high-voltage laboratories across the world have also been made up-to-date. (Table 11.6).

Further testing of HVDC Valves and equipment is added in the present edition. This edition offers almost 100 fresh problems in different sets such as multiple-choice questions, review questions, solved and unsolved problems to help students in self-study and understanding. Updates in the text have been made wherever necessary.

Online Learning Centre The text is accompanied by an exhaustive Online Learning Centre which can be accessed at http://www.mhhe.com/hve5

It contains the following material:

For Students • Interactive Quiz • Useful Web links for further reading

For Instructors • Solution Manual (for selected problems) • PowerPoint Slides with figures from text

Acknowledgements First, the authors wish to express their gratitude to all the reviewers who took out time to review the book. The authors acknowledge, with thanks, for the permission given by º Central Power Research Institute, UHV Laboratory, Hyderabad, to refer to the details of their institute º Ms Emile Haefely and Co. Ltd., Switzerland, to include the photographs of their equipment º MWB HV TEST SYSTEMS, Bangalore The authors express their sincere gratitude to the Director, Indian Institute of Science, Bangalore, and Vice Chancellor, Jawaharlal Nehru Technological University, Hyderabad, for their constant encouragement. It is hoped that students, readers, academicians and engineers will continue to favor and patronize the book.

Feedback Suggestions for further improvement of the book are welcome and every effort will be made to incorporate them in the next edition. (Late) M S Naidu and V Kamaraju

Publisher's Note Do you have any further request or a suggestion? We are always open to new ideas (the best ones come from you!). You may send your comments to [email protected] Piracy-related issues may also be reported!

Contents Preface 1. Introduction 1.1 Electric Field Stresses 1.2 Gas/Vacuum as Insulator 1.3 Liquid Dielectrics 1.4 Solids and Composites 1.5 Estimation and Control of Electric Stress 1.6 Numerical Methods for Electric Field Computation 1.7 Surge Voltages, their Distribution, and Control Key Terms Multiple-Choice Questions Review Questions Short Questions References 2. Conduction and Breakdown in Gases 2.1 Gases as Insulating Media 2.2 Collision Processes 2.3 Ionization Processes 2.4 Townsend’s Current Growth Equation 2.5 Current Growth in the Presence of Secondary Processes 2.6 Townsend’s Criterion for Breakdown 2.7 Experimental Determination of Coefficients α and γ 2.8 Break down in Electro negative Gases 2.9 Time Lags for Breakdown 2.10 Streamer Theory of Breakdown in Gases 2.11 Paschen’s Law 2.12 Breakdown in Non-Uniform Fields and Corona Discharges 2.13 Post-Breakdown Phenomena and Applications 2.14 Practical Considerations in using Gases and Gas Mixtures for Insulation Purposes 2.15 Vacuum Insulation Key Terms Worked Examples Multiple Choice Questions Review Questions Problems References 3. Conduction and Breakdown in Liquid Dielectrics 3.1 Liquids as Insulators 3.2 Pure Liquids and Commercial Liquids

3.3 Conduction and Breakdown in Pure Liquids 3.4 Conduction and Breakdown in Commercial Liquids 3.5 Testing of Insulating Oils (Fluids):Transformer Fluids 3.6 Conclusions Key Terms Worked Examples Multiple-Choice Questions Review Questions References 4. Breakdown in Solid Dielectrics 4.1 Introduction 4.2 Intrinsic Breakdown 4.3 Electromechanical Breakdown 4.4 Thermal Breakdown 4.5 Breakdown of Solid Dielectrics in Practice 4.6 Breakdown in Composite Dielectrics 4.7 Solid Dielectrics used in Practice Key Terms Worked Examples Multiple-Choice Questions Review Questions References 5. Applications of Insulating Materials 5.1 Introduction 5.2 Applications in Power Transformers 5.3 Applications in Rotating Machines 5.4 Applications in Circuit Breakers 5.5 Applications in Cables 5.6 Applications in Power Capacitors 5.7 Applications in High-Voltage Bushings 5.8 Applications in Fractional Horse Power Motors Key Terms Multiple-Choice Questions Review Questions References 6. Generation of High Voltages and Currents 6.1 Generation of High Direct-Current Voltages 6.2 Generation of High Alternating Voltages 6.3 Generation of Impulse Voltages 6.4 Generation of Impulse Currents 6.5 Tripping and Control of Impulse Generators Key Terms

Worked Examples Multiple-Choice Questions Review Questions Problems References 7. Measurement of High Voltages and Currents 7.1 Measurement of High Direct-Current Voltages 7.2 Measurement of High AC and Impulse Voltages 7.3 Measurement of High Currents—Direct, Alternating and Impulse 7.4 Cathode-Ray Oscillographs for Impulse Voltage and Current Measurements Key Terms Worked Examples Multiple-Choice Questions Review Questions Problems References 8. Overvoltage Phenomenon and Insulation Coordination in Electric Power Systems 8.1 Natural Causes for Over voltages—Lightning Phenomenon 8.2 Overvoltage due to Switching Surges, System Faults and other Abnormal Conditions 8.3 Principles of Insulation Coordination on High-Voltage and Extra High-Voltage Power Systems Key Terms Worked Examples Multiple-Choice Questions Review Questions Problems References 9. Non-Destructive Testing of Materials and Electrical Apparatus 9.1 Introduction 9.2 Measurement of Direct Current Resistivity 9.3 Measurement of Dielectric Constant and Loss Factor 9.4 Partial Discharge Measurements Key Terms Worked Examples Multiple-Choice Questions Review Questions References

10. High-Voltage Testing of Electrical Apparatus 10.1 Testing of Insulators and Bushings 10.2 Testing of Isolators and Circuit Breakers 10.3 Testing of Cables 10.4 Testing of Transformers

10.5 Testing of Surge Arresters 10.6 Radio Interference Measurements 10.7 Testing of HVDC Valves and Equipment Key Terms Multiple-Choice Questions Review Questions References

11. Design, Planning and Layout of High-Voltage Laboratories 11.1 Introduction 11.2 Test Facilities Provided in High-Voltage Laboratories 11.3 Activities and Studies in High-Voltage and UHV Laboratories 11.4 Classification of High-Voltage Laboratories 11.5 Size and Ratings of Large Size High-Voltage Laboratories 11.6 Grounding of Impulse Testing Laboratories Key Terms Multiple-Choice Questions Review Questions Problems References Appendix : Important Formulae Author Index Subject Index

CHAPTER

1 Introduction In modern times, high voltages are used for a wide variety of applications covering the power systems, industry, and research laboratories. Such applications have become essential to sustain modern civilization. High voltages are applied in laboratories in nuclear research, in particle accelerators, and Van de Graaff generators. For transmission of large bulks of power over long distances, high voltages are indispensable. Also, voltages up to 100 kV are used in electrostatic precipitators, in automobile ignition coils, etc. X-ray equipment for medical and industrial applications also use high voltages. Modern high-voltage test laboratories employ voltages up to 6 MV or more. The diverse conditions under which a high-voltage apparatus is used necessitate careful design of its insulation and the electrostatic field profiles. The principal media of insulation used are gases, vacuum, solid, and liquid, or a combination of these. For achieving reliability and economy, a knowledge of the causes of deterioration is essential, and the tendency to increase the voltage stress for optimum design calls for judicious selection of insulation in relation to the dielectric strength, corona discharges, and other relevant factors. In this chapter, some of the general principles used in high-voltage technology are discussed.

1.1 ELECTRIC FIELD STRESSES Like in mechanical designs where the criterion for design depends on the mechanical strength of the materials and the stresses that are generated during their operation, in high-voltage applications, the dielectric strength of insulating materials and the electric field stresses developed in them when subjected to high voltages are the important factors in high-voltage systems. In a high-voltage apparatus, the important materials used are conductors and insulators. While the conductors carry the current, the insulators prevent the flow of currents in undesired paths. The electric stress to which an insulating material is subjected to is numerically equal to the voltage gradient, and is equal to the electric field intensity,

where E is the electric field intensity, φ is the applied potential, and ∇ (read del) operator is defined as

where ax, ay, and az are components of position vector r = ax X + ayY + azZ. As already mentioned, the most important material used in a high-voltage apparatus is the insulation. The dielectric strength of an insulating material can be defined as the maximum dielectric stress which the material can withstand. It can also be defined as the voltage at which the current starts increasing to very high values unless controlled by the external impedance of the circuit. The electric breakdown strength of insulating materials depends on a variety of parameters, such as pressure, temperature, humidity, field configurations, nature of applied voltage, imperfections in dielectric materials, material of electrodes, and surface conditions of electrodes, etc. An understanding of the failure of the insulation will be possible by the study of the possible mechanisms by which the failure can occur. The most common cause of insulation failure is the presence of discharges either within the voids in the insulation or over the surface of the insulation. The probability of failure will be greatly reduced if such discharges could be eliminated at the normal working voltage. Then, failure can occur as a result of thermal or electrochemical deterioration of the insulation.

1.2 GAS/VACUUM AS INSULATOR Air at atmospheric pressure is the most common gaseous insulation. The breakdown of air is of considerable practical importance to the design engineers of power transmission lines and power apparatus. Breakdown occurs in gases due to the process of collisional ionization. El...