Fitzgerald & Kingsley's Electric Machinery (IRWIN ELEC&COMPUTER ENGINERING)

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Practically all transformers and electric machinery use ferro-magnetic material for shaping and directing the magnetic fields which act as the medium for transfer- ring and converting energy. Permanent-magnet materials are also widely used. With- out these materials, practical implementations of most familiar electromechanical- energy-conversion devices would not be possible. The ability to analyze and describe systems containing these materials is essential for designing and understanding these devices. The power at the terminals of a winding on a magnetic circuit is a measure of the rate of energy flow into the circuit through that particular winding. The power, p, is determined from the product of the voltage and the current The total magnetic stored energy at any given value of ~ can be found from setting X~ equal to zero:

until the relative permeability drops to on the order of 1000. Thus, as long as the effective relative to drive dc machines as well as to provide a controllable dc input to inverters in ac drives. Similarly, techniques for producing stepped and pulse-width-modulated wave- forms of variable amplitudes and frequency are discussed. These techniques are at the heart of variable-speed drive systems which are commonly found in variable-speed ac drives. INTERNATIONAL EDITION ISBN 0-07-112193-5 Copyright ~ 2003. Exclusive rights by The McGraw-Hill Companies, Inc., for manufacture and export. This book cannot be re-exported from the country to which it is sold by McGraw-Hill. The International Edition is not available in North America. Samarium-cobalt represents a significant advance in permanent magnet technol- ogy which began in the 1960s with the discovery of rare earth permanent magnet materials. From Fig. 1.19 it can be seen to have a high residual flux density such as is found with the Alnico materials, while at the same time having a much higher coer- civity and maximum energy product. The newest of the rare earth magnetic materials is the neodymium-iron-boron material. It features even larger residual flux density, coercivity, and maximum energy product than does samarium-cobalt.For example, from Eq. 1.20, under the assumption that the reluctance of the core is negligible as compared to that of the air gap, the inductance of the winding in Fig. 1.2 is equal to I wish to thank a number of my colleagues for their insight and helpful discus- sions during the production of this edition. My friend, Professor Jeffrey Lang, who also provided invaluable insight and advice in the discussion of variable-reluctance machines which first appeared in the fifth edition, was extremely helpful in formu- lating the presentations of power electronics and field-oriented control which appear in this edition. Similarly, Professor Gerald Wilson, who served as my graduate thesis advisor, has been a friend and colleague throughout my career and has been a constant source of valuable advice and insight. This chapter will develop some basic tools for the analysis of magnetic field systems and will provide a brief introduction to the properties of practical magnetic materials. In Chapter 2, these results will then be applied to the analysis of transform- ers. In later chapters they will be used in the analysis of rotating machinery.

From Eq. 1.51, the rms value of a sine wave can be shown to be 1 / ~/2 times its peak value. Thus the rms value of the induced voltage isThe late Arthur E. Fitzgerald was Vice President for Academic Affairs at North- eastern University, a post to which he was appointed after serving first as Professor and Chairman of the Electrical Engineering Department, followed by being named Dean of Faculty. Prior to his time at Northeastern University, Professor Fitzgerald spent more than 20 years at the Massachusetts Institute of Technology, from which he received the S.M. and Sc.D., and where he rose to the rank of Professor of Electrical Engineering. Besides Electric Machinery, Professor Fitzgerald was one of the au- thors of Basic Electrical Engineering, also published by McGraw-Hill. Throughout his career, Professor Fitzgerald was at the forefront in the field of long-range power system planning, working as a consulting engineer in industry both before and after his academic career. Professor Fitzgerald was a member of several professional so- cieties, including Sigma Xi, Tau Beta Pi, and Eta Kappa Nu, and he was a Fellow of the IEEE.

takes place. However, the techniques developed are generally applicable to a wide range of additional devices including linear machines, actuators, and sensors. However, in electromechanical energy conversion devices, inductances are often time- varying, and Eq. 1.41 must be written as This seventh edition of Fitzgerald and Kingsley’s Electric Machinery by Stephen Umans was developed recognizing the strength of this classic text since its first edition has been the emphasis on building an understanding of the fundamental physical principles underlying the performance of electric machines.the magnetic circuit is illustrated in this section and will be seen to apply quite well to many situations in this book. 2 T he objective of this book is to study the devices used in the interconversion of electric and mechanical energy. Emphasis is placed on electromagnetic rotating machinery, by means of which the bulk of this energy conversion