Dielectric Materials and Electrostatics E-Book

Olivier Gallot-Lavallee

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 230

Veröffentlichungsjahr: 2013

Beschreibung

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

Leseprobe

Table of Contents

Foreword

Chapter 1 Mathematical Examination of Dielectrics

1.1. Introduction to dielectrics

1.2. Perfect dielectrics

1.3. Forces exerted on polarized dielectrics

1.4. Dielectric losses

1.5. Residual charges

1.6. Electrets

1.7. Characteristics of an insulator

1.8. Pyro and piezo-electricity

1.9. Currents in extended conductors

Chapter 2 Physical Examination of Dielectrics

2.1. Gaseous dielectrics

2.2. Liquid and solid dielectrics

Bibliography

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

The Authors

Index

First published 2013 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd

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London SW19 4EU

UK

www.iste.co.uk

John Wiley & Sons, Inc.

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USA

www.wiley.com

© ISTE Ltd 2013

The rights of Olivier Gallot-Lavallée to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Control Number: 2013937862

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN: 978-1-84821-604-4

Foreword

Often, people overlook or undervalue the crucial role played by electrical insulation in the operation of equipment for production, transport, distribution and usage of electrical energy. Generally speaking, electrical insulation must be put in place at any juncture where there are conductors – or substances – with different electrical potentials. The basic questions about electrical insulation – particularly the electrical properties of dielectric materials – are often dealt with as annexes to the subject of electrostatics. As electrostatics is sometimes perceived as an “ancient” science and the teaching of it is often formal, engineers and scientists find themselves rather poorly equipped to deal with practical problems and numerous electrostatic phenomena which require a mode of thinking which has precious little to do with formal presentations and Maxwell’s equations.

This book is not a systematic treatise on electrical insulators, presenting all current knowledge and usage; rather, it is presented as an introduction for engineering students and practitioners who are likely to encounter insulation problems, and its aim is to clearly identify the principles and physical mechanisms that need to be taken into account in order to comprehend the phenomena and behaviors and to control them. This presentation is based on the notes of N. Félici, who taught electrical engineering students at Grenoble from the 1960s to 1980s with the goal of providing them with an accurate and practical view of the problems encountered in the field of electrical insulation. What was special about Félici’s course was that he used a manner – which was fairly uncommon at the time – of presenting a highly technical subject in a lively and vibrant way, using images and simple physical facts to explain complex behaviors and usages.

O. Gallot-Lavallée initiated and wrote this book under the guidance of N. Félici around a year before the latter’s sad passing. Dielectric Materials and Electrostatics is a faithful re-transcription of N. Félici’s vision of the subject. This carefully-worked edition presents simple ideas and concepts, constructing a solid basis from which to approach phenomena which are complex and sometimes difficult to predict, such as the lifespan of an insulator, for instance. I am certain that students and practitioners using this book will be able to profit from it, and will appreciate the work of the authors.

Pierre ATTENÉcole Polytechnique (Paris)Director of research at CNRS (Grenoble)

Chapter 1

Mathematical Examination of Dielectrics

1.1. Introduction to dielectrics

The ideal insulator is a substance with infinite resistivity. In the real world, insulators have resistivity values which are very high, but finite. Table 1.1 gives an indication of the resistivity of a number of insulators, expressed using the MKSA (Meter, Kilogram, Second, Ampere) system.

Table 1.1.Resistivity of a number of dehydrated insulators expressed in [Ω.m] at 20°C

For many applications, the value which best characterizes a material’s insulating capacity is its relaxation time – the time constant of a condenser of any form using that material. This time is given by the following equation [1.1]:

[1.1]

where ε is the permittivity and ρ the resistivity.

The relaxation time is directly involved in the value of the electrical loss angle δ with alternating current (AC). Indeed, if conduction is the only cause of loss, and if the time constant τ is around a second, the loss angle will be too great for long-term operation at industrial frequencies without the risk of accident [1.2]:

[1.2]

Whilst solid insulators, both organic and mineral-based, can easily deliver sufficiently high relaxation times, liquids are usually far too conductive to be usable. Only a very few aromatic hydrocarbons, including the infamous PolyChloroBiphenyl (PCB or pyralene) or the Mono-Dibenzyl-Toluene (used by Jarylec in Isère) have taken their place in industry, alongside mineral-based oils; other liquids, such as a1cohol, acetone and nitrobenzene, rarely reach values above 10 or l0 [.] due to their sensitivity to the slightest electrolytic contamination.