Non-conventional Electrical Machines E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 239

Veröffentlichungsjahr: 2013

Beschreibung

The developments of electrical machines are due to the convergence of material progress, improved calculation tools, and new feeding sources. Among the many recent machines, the authors have chosen, in this first book, to relate the progress in slow speed machines, high speed machines, and superconducting machines. The first part of the book is dedicated to materials and an overview of magnetism, mechanic, and heat transfer.

Leseprobe

Table of Contents

Introduction

Chapter 1. Theoretical Tools and Materials for Electric Machines

1.1. Theoretical tools

1.2. Materials

1.3. Bibliography

Chapter 2. Low-speed Teeth Coupling Machines

2.1. Introduction

2.2. Positioning of the problem. Outline of the feasibility limits

2.3. Teeth coil winding and toothed pole machines

2.4. Machines with distributed winding and the Vernier effect

2.5. Bibliography

Chapter 3. High-speed Electric Machines

3.1. Interest in high-speed rotational operating

3.2. Criteria and constraints of a high-speed machine

3.3. Types of electric machines

3.4. Examples of applications

3.5. Methodology of high-speed machine optimization

3.6. Bibliography

Chapter 4. Superconducting Machines

4.1. Introduction

4.2. Superconducting materials in electrotechnology

4.3. Superconducting materials used in electric machines

4.4. Losses in the self-field of superconductors

4.5. Cryogenic environment

4.6. Superconducting machines

4.7. Bibliography

List of Authors

Index

First published 2012 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

John Wiley& Sons, Inc.

27-37 St George’s Road

111 River Street

London SW19 4EU

Hoboken, NJ 07030

UK

USA

www.iste.co.uk

www.wiley.com

© ISTE Ltd 2012

The rights of Abderrezak Rezzoug and Mohammed El-Hadi Zaïm to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Non-conventional electrical machines / edited by Abderrezak Rezzoug, Mohammed El-Hadi Zaïm.

p. cm.

Includes bibliographical references and index.

ISBN 978-1-84821-300-5

1. Electric machinery. I. Rezzoug, Abderrezak. II. El Hadi Zaïm, Mohamed.

TK2000.N58 2011

621.31′042--dc23

2011012248

British Library Cataloguing-in-Publication Data

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

ISBN 978-1-84821-300-5

Introduction

The world of electric machines, which is in a constant state of evolution, is seeing its field of application growing every day.

The electric machine, historically connected to a network which supplies it with a constant voltage, is today almost as a matter of course fed by a static terminal converter whose voltage varies at a rapid rate, even when its average value is constant or slowly variable.

If it appears obvious to consider the machine as one element in an electromechanical conversion chain, most of the time with a control system, the fact remains that for each new class of application, the electric machine must be examined as such.

This examination is imposed by the function itself, by the movement to be achieved, the requisite security for each element of the electromechanical conversion chain, the limitation in size, the reduction in weight, the high speed and/or the high acceleration to be reached.

In order to respond to increasingly demanding specifications, machine construction has evolved, first of all, thanks to progress made in the development of constituent materials: magnetic materials (ferromagnetic powders, permanent magnets and massive superconductors) and insulating or conductive materials (superconducting wire).

The tools of calculation, software and material, make up another aspect among those which have allowed progress in the design of machines; we are considering here the tools used to calculate fields (magnetic, electrical, thermal, force and stress fields), 3D modeling tools and optimization tools.

If the representation models progress continually in order to take into account more accurately geometric shapes (including teeth harmonics, mechanical failure), nonlinearity due to magnetic (saturation and hysteresis) or electrical behaviors (law E(J) for superconductors), nothing can replace the experience drawn from the achievements.

Nevertheless, the development of tools and the refinement of modeling allow us to perform numerous simulations leading to substantial economies in the design of prototypes and finished products.

This book aims to tackle a subject where even the definition is difficult to determine. What is a non-conventional machine?

The principles of functioning rely completely on the interaction between a magnetic field and a current (as in the majority of electric machines) or on field-to-field interaction (as in magnetic transmitters).

The movement of another category of electromagnetic motor is due to the distortion of the materials themselves (piezoelectric, shape, memory and magnetostrictive material).

This second category, made more popular, particularly by piezoelectric motors, constitutes a specific family in the area of electromagnetic converters and will not be tackled in this publication.

In the category of electromagnetic machines, non-conventional electromagnetic machines can be defined in several ways, and this is in no way the least of our difficulties.

We can attempt to provide a definition starting from the following points:

– the type of movement produced by the machine itself (rotation, linear movement, alternating movement, etc.);

– the number of degrees of freedom required (rotation or movement on one axis, combination of the two, multi-axis movement, spherical movement, etc.);

– required speeds (high, low);

– the number of coils installed and the distribution of the magnetic field;

– the geometry of the magnetic circuit (structure of the whole machine: cylindrical, flat, hollow, conical, salient or smooth structure, position of the magnets, structure of the teeth-slots);

– the materials utilized (permanent magnets, superconductors, non-ferromagnetic materials, etc.);

– the dynamic characteristics (electrical and mechanical response times, dynamic impedance, etc.);

– the forms of voltage or current delivered by its power source (voltage form and amplitude, quality of the current, etc.).

For any given application, the points outlined above can be combined to give rise to a specific and original machine.

The selection of subjects examined in this book is such that each chapter, dealing with one class of machines, is self-sufficient. The authors have written each chapter to be able to be independent for ease of reading.

An introduction to electrotechnical materials used in electrical machines, a reminder of some fundamental principles and calculation methods make up a first introduction to broach the analysis of the machines studied in Chapters 2 to 4.

This book deals with the following types of machines:

– low-speed machines, which allow us to power a charge, by removing or simplifying the mechanical gear which degrades the efficiency of the whole system. This type of machine is in direct competition with hydraulic systems, which are far better but which require robust and heavyweight channels for the flow of liquid under pressure and which need more maintenance;

– high speed machines for direct drive. The speeds of such systems generally exceed 10,000 revolutions per minute. These types of machines have the opportunity to conquer an important area, namely for high-speed machining, for electrical compression or generation and in systems where compactness and weight play an important part;

– machines with superconducting field excitation providing a high magnetic field so that an iron-free armature can be used. The second characteristic of a superconductor being to internally develop induced currents and sometimes act as either a magnetic screen or as a permanent magnet, these behaviors can be put to good use in the design of original machines.

As not a day goes by without some electromagnetic converter being developed in order to meet a specific requirement or a curiosity of research, this book is only an opened window on some electrical machines which continue to conquer market shares.

Chapter 1

Theoretical Tools and Materials for Electrical machines1

This first chapter reviews a set of tools for the modeling of machines. For some of them, in addition to electromagnetic calculations, the mechanical and/or thermal magnitudes must be evaluated, because they constitute the strongest constraints in the machine design.

The first section of this chapter is made up of a review of the main concepts linked to the design of rotating machines. The second section concerns the different materials used in the construction of machines.

1.1. Theoretical tools

1.1.1. Electromagnetism and rotating machines

It is not essential here to observe all the tools used in the electromagnetic calculation of electrical machines, but to recall some of the stages and methods used to do this.

Flux density B in Tesla, field H in amperes per meter and the magnetic polarization J in Tesla are linked by the following relations:

[1.1]

If the medium is homogeneous, isotropic and linear we could write:

[1.2]

where μr is the relative permeability, a real number whose interesting values range from one unit, or close to it (machine air-gap, or permanent magnets) to several thousand units (ferromagnetic materials).

In fact, the ferromagnetic medium being nonlinear, μ varies with the magnetic field (saturation and hysteresis). To make matters worse, the material which is used in electrical machines can be anisotropic (grain-oriented) so in this case μ is a tensor.

The conservation of flux, which is expressed by , allied to the law of constitution [1.2] allows us to establish that in the case of electrical machines with ferromagnetic circuits, the field in the iron, , can be considered, at least in the first instance, as negligible compared to the magnitude of the field in the air-gap .