Dielectric Materials and Electrostatics

An introduction to the physics of electrical insulation, this book presents the physical foundations of this discipline and the resulting applications. It is structured in two parts. The first part presents a mathematical and intuitive approach to dielectrics; various concepts, including polarization, induction, forces and losses are discussed. The second part provides readers with the keys to understanding the physics of solid, liquid and gas insulation. It comprises a phenomenological description of discharges in gas and its resulting applications. Finally, the main electrical properties of liquids and solids are presented, in order to explain the phenomena of electrical degradation, dissipation and breakdown.

Contents

1. Mathematical Examination of Dielectrics
2. Physical Examination of Dielectrics
Appendix 1. List of Figures
Appendix 2. List of Symbols
Appendix 3. List of Useful Values
Appendix 4. Reminder about Dielectric Spectroscopy
Appendix 5. Reminder about Transitory Currents

Foreword ix

Chapter 1 Mathematical Examination of Dielectrics 1

1.1.Introduction to dielectrics 1

1.1.1.Polarization 3

1.1.2.Ionization 4

1.1.3.Polarized dielectrics 5

1.1.4.Electrical induction 10

1.1.5.Move from one dielectric to another 11

1.1.6.Move from a dielectric to a conductor 12

1.1.7.Energy contained in a dielectric 13

1.2.Perfect dielectrics 15

1.2.1.Refraction of force-and induction-lines 16

1.2.2. Field in the vicinity of a charged conductor. 19

1.2.3 Electrostatic pressure 20

1.2.4.Corresponding elements 21

1.2.5.Equilibrium in a system of conductors 22

1.2.6.Capacities and influence coefficients 23

1.2.7.Calculation of the interstitial field 25

1.2.8.Depolarizing field 27

1.3.Forces exerted on polarized dielectrics 34

1.3.1 Forces exerted on a rigidly-polarized solid dielectric 34

1.3.2. Forces exerted on a solid perfect dielectric 37

1.3.3 Forces exerted on a liquid dielectric 41

1.3.4.Electrostriction 44

1.4 Dielectric losses 45

1.5.Residual charges 50

1.6.Electrets 51

1.7.Characteristics of an insulator 52

1.8.Pyro and piezo-electricity 54

1.8.1.Pyroelectricity 55

1.8.2.Piezoelectricity 56

1.9.Currents in extended conductors 63

1.9.1.Current density 63

1.9.2 Expression of Ohm’s law in an extended conductor 65

1.9.3.Conservation of current density 67

1.9.4 Distribution of current in an extended medium 67

1.9.5.Power dissipated by the Joule effect 70

1.9.6.Resistance of the conductive medium 70

1.9.7 Deviation of the electrical current when crossing the surface separating two conductors 77

Chapter 2. Physical Examination of Dielectrics 81

2.1.Gaseous dielectrics 81

2.1.1.Reminder of the properties of gases 81

2.1.2.Ionization 89

2.1.3 Examination of the conditions of initiation of self-sustaining discharge 95

2.1.4.Corona discharge effect 110

2.1.5.Use of gases as insulators 134

2.2.Liquid and solid dielectrics 138

2.2.1.Conductivity 138

2.2.2.Physics of polarization 141

2.2.3.Dielectric losses 155

2.2.4.Breakdown of solid dielectrics 161

Bibliography 185

Appendix 1 List of Figures 187

Appendix 2 List of Symbols 193

Appendix 3 List of Useful Values 197

Appendix 4 Reminder about Dielectric Spectroscopy 199

Appendix 5 Reminder about Transitory Currents 201

The Authors 203

Index 205