## Description

High voltage engineering is a vast subject, extending from basic knowledge in physics, chemistry, andmaterial science to applications in the insulation design of high-voltage transmission lines and substation equipment. Although high voltage engineering applications extend to medicine and nuclear science, these topics are beyond the scope of this book. The book is targeted towards those in the electric power profession. The selection of what material to include is a difficult decision. To limit the scope even further, it was decided to exclude material on the design and testing of high-voltage switchgear, a subject of great scientific and practical interest that is usually dealt with under the designation: high power engineering.

There are some compelling reasons to write a new book on high voltage engineering. Firstly, there is a new revival of worldwide interest in EHV and UHV power transmission. UHV ac transmission lines have been operating for the last two decades in Russia, and more recently, in China. UHV ac lines of 1200 kV are also being planned in India. UHV dc transmission lines of ±750 and ±800 kV have been operating in Russia and, more recently, in China and are presently in the planning stage in India. A ±1000 kV UHV dc line is being designed in China, with commercial operation foreseen in about two years. Second, many experts in high voltage engineering have retired in the last decade, and it would be helpful for the sake of a new generation of engineers to conserve some of that experience.

The book comprises 14 chapters. Insulation systems of transmission lines and power equipment are exposed to stresses caused by operating voltage as well as those due to internal and external overvoltages. Chapter 1 provides a brief review of power system overvoltages. It starts with simple lumped circuits that can be treated by direct solution of differential equations or by Laplace transforms. Analysis is then extended to long transmission lines with distributed parameters. Temporary overvoltages (TOV) are addressed first, with an emphasis on the effects of neutral grounding and shunt reactor compensation. Symmetrical components are introduced to deal with unsymmetrical faults. Traveling waves follow from the solution of the wave equation of a single lossless line under unit step energization. This was later extended to account for generalized input. Special attention is paid to the important case of energization of an open line with and without surge arrester termination. Three-phase lines are dealt with using modal analysis. However, all through the emphasis is on understanding the overvoltage generation mechanism rather than the completeness or sophistication of the computational procedure, which is covered in more specialized texts. Special attention is paid to overvoltages caused by interruption of small inductive andcapacitive currents. The chapter concludes with a brief summary of the EMTP. An example is given on the energization of an open 735 kV transmission line.

Electric field calculations are essential, since ionization phenomena in electrical insulation systems are very sensitive to electrical stresses. This is covered in Chapter 2, which deals with electrostatic fields. In the absence of space charge, the problem amounts to solution of Laplace equation under appropriate boundary conditions. In the presence of space charge, we deal with Poisson’s equation. In general, these equations are three dimensional, but considerable simplification results in symmetrical configurations. Analytical solutions for simple geometries are introduced. Uniform field electrodes are also introduced for single and composite dielectrics. Cylindrical geometry is discussed, with a focus on coaxial cables. Prolate spheroidal coordinates are presented, with application to spheroidal electrodes and dielectric particles. A hyperboidal field is introduced with particular reference to the basic rod-plane gap often dealt with in long air gap tests. Different methods of transformation are described, with an emphasis on the method of images. Among the electrodes dealt with is the sphere– sphere configuration, historically used as a high-voltage measuring device. Numerical methods for field computation are briefly reviewed. The method of successive images is of particular importance in handling electric fields of multiconductor systems. This is followed by a discussion of the charge simulation method, which is applied to a coaxial SF6 cable with epoxy spacers. Finally, the chapter presents a brief account of the methods of finite differences and finite elements.

Recognition of the statistical nature of ionization and breakdown phenomena is essential for proper planning of high-voltage tests and for interpretation of test results. This is covered in Chapter 3, which describes the characterization of a set of test results. The chapter then introduces discrete and continuous statistical distributions, including the binomial, Poisson, Maxwell, and normal distributions. For low breakdown probability, a number of extreme-value distributions are important. The chapter therefore describes the Gumbel extreme-value distribution as well as the Weibull distribution, which is likely to be more familiar to high voltage engineers. Methods of selection for the appropriate distribution to characterize a certain population are introduced, including the concepts of 50% value, standard deviation, and confidence limits, which are of obvious practical importance. The practical use of special graphic paper, which often simplifies statistical treatment of test results, is also emphasized. Different examples on the planning and interpretation of high-voltage tests are given. Reference is also made to relevant recommendations of international test standards.