1
Introduction

The subject, “High Voltage Engineering,” is the knowledge of the behavior of dielectrics—electrical insulation when subjected to high voltage. Performance of dielectrics is electric field dependent. The electric field configuration, to which a dielectric is subjected, determines its life and function in the long run. It is always desirable to minimize the volume of the electrical insulation requirements yet a long and trouble‐free life of all high voltage apparatus should be ensured. For an apparatus to be economically viable, its desirable life expectancy is 30–40 years, depending upon the cost and technology of production involved.

The world has seen rapid advancement in the technology applied in high voltage apparatus in the second half of the twentieth century. Manufacturing of gas insulated sub‐stations (GIS), power transformers, cables, and switchgears at the highest rated voltages up to 1100 kV involve the most sophisticated technologies. Such a development has taken place with dedicated efforts to understand the behavior of dielectrics, gaseous, solid, liquid, and vacuum.

The last half century has also seen prominent advancement in the technology of dielectric finishes on equipment. To a limited extent, insulating materials with better dielectric properties and performance have been developed. Knowledge of electric field dependent behavior of dielectrics has led to better use of the insulating materials. Advancement in techniques of evaluating the quality of the finish of electrical insulation in an apparatus has contributed to producing quality power apparatus with more reliability up to the highest rated voltages. The non‐destructive testing and condition monitoring techniques of equipment/insulation have improved considerably. The high voltage test apparatus and measuring instrumentation and their respective technologies have also made big advances. These have led to the production of more dependable and economical high voltage apparatus with sophisticated technologies.

The contents of this book was initially developed at the High Voltage Laboratory of Technische Universität Dresden, Germany, which is well known in the continent of Europe for its dedicated research and development work for more than one and a half centuries. These were published for the first time in English in our earlier book, “High Voltage Insulation Engineering,” in 1995. Advances in this subject, at TU Dresden, Germany and Indian Institute of Technology Kanpur (India) and in many other countries in the world, are being incorporated into this second book.

While delivering the lectures based on our first book, interaction with the students revealed a number of lacunae in interpreting the basic concepts essential for understanding the behavior of dielectrics. Hence, some fundamental terminologies used commonly in this subject are explained in the following pages. Explanation of these terms has been mainly derived from various English‐language dictionaries [1–4] that describe the same terminology in slightly different ways. Hence, a number of similar expressions available for a particular term are compiled. These descriptions are bulleted in the following text. A clear interpretation of these terms will help the reader to better understand the high voltage phenomena.

1.1 Electric Charge, Discharge, Current, and Potential

Electron

• an elementary particle consisting of negative charge, found outside the nucleus of an atom
• negatively charged sub‐atomic particle found in all atoms and acting as the primary carrier of electricity in solids

Proton

• a subatomic particle with a positive electric charge occurring in all atomic nuclei‐origin Greek, “first thing”
• a nuclear particle with positive charge equal and opposite to that of an electron negative charge

Ion

• an electrified atom having either a positive or negative charge
• an electrified atom which has increased or decreased its number of electrons after electrolysis (ionization)
• an atom or molecule with a net electric charge produced through loss or gain of electrons

Ionize

• convert an atom, molecule, or substance into an ion or ions
• to convert into an ion form
• to convert wholly or partly into ions—to become ionized

Ionization

• the process of formation of ions

Electric Charge

• the presence of an uncancelled excess of either positive subatomic particles (protons), or negative subatomic particles (electrons) in a substance
• electricity in free subatomic particles of a polarity, positive or negative

The behavior of electric charge can be explained with the following typical characteristics:

• ionization is a process by which charges build up
• accumulation of charge (q) builds up potential ϕ
• concentration of like polarity charge (in dielectrics) is known as “space charge”
• when the positive and the negative charges are uniformly distributed in a dielectric, the volume charge density “ρv,” is equal to zero
• on the contrary, when there is a concentration of any one polarity charge, ρv is not equal to zero
• the electric charge is at rest in dielectrics; however, it is restless in conductors
• the electric charge always acquires the least resistance path to flow
• flow of charge is electric current
• the electric charge finds its ultimate peace only inside the earth, the mother earth

Electric Discharge

• to get rid of a charge of electricity
• withdrawing or transference of an electric charge
• release or neutralize the electric charge
• a flow of electricity through the air or other gas
• a sudden movement of charge

Electric Current

• the rate of flow of electric charge carriers, or the charged particles, over a point or a region
• flow of one coulomb of charge per second is a measure of one “ampere” of current in SI units

Electric Potential

• the amount of work done per unit charge to move the charge from a point of reference to a specified point
• the work done measured in “joules per coulomb” is known as “volts”

The electric discharge process can be typically described by the following:

• ionization is the process by which electric charges—hence potential builds up; while discharge involves movement of charge—hence loss of potential
• ionization builds up potential on a body while discharge tends to lose it
• electric discharge leads to equalization of the difference of electric potential built by the charge between any two bodies/electrodes

1.2 Electric and Magnetic Fields

Field is a quantity that is a function of space. The presence of a field is sensed by the force exerted on a particle or body. A wave can be defined as a function of both time and space [5,6].

Electric Field

• a quantitative description of the attraction or repulsion of one electric charge by another at any one point
• the ratio of the force exerted on a positive test charge, placed at that point, to the magnitude of the charge
• the source of electric field intensity is electric charge

Magnetic Field

• the portion of space near a magnetic body or a current carrying body in which the forces from the body or current can be detected
• a region around a magnet within which the force of magnetism acts
• any space or region in which magnetic forces are present, as the space or region in or around a piece of magnetized steel, or in or around an electrical current

1.3 Electromagnetism

Electromagnetism is defined as an interaction between electricity and magnetism. For example, when a changing magnetic field generates an electric field or vice versa. It is also explained as:

• magnetism developed by a current of electricity
• branch of physical science that deals with the physical relations between electricity and magnetism
• the study of the relation between electric currents and magnetism
• magnetism caused by electric current

Electromagnetic

• relating to the inter‐relation of electric and magnetic fields
• pertaining to electromagnetism or an electromagnet

Electromagnetic Radiation

• radiation in which electric and magnetic fields vary at the same time

Electromagnetic Wave

• a wave whose characteristics are variations of electric and magnetic fields, such as a radio wave or a light wave
• one of the waves that are propagated by simultaneous periodic variations of electric and magnetic field intensity and that include radio wave, infrared, visible light, ultraviolet, X‐rays, and gamma rays

Electromagnetic waves can also be explained as follows:

• time varying magnetic field produces an electric field (Maxwell's equation)
• time varying electric field also produces a magnetic field, even in the absence of flow of electric current
• time varying electric and magnetic fields form electromagnetic waves that are...