12608683-Electrical-Machines-and-Drives-Systems

12608683-Electrical-Machines-and-Drives-Systems - 1...

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Unformatted text preview: 1 Introduction and review of basic theory 1.1 Aim of the book On entering the world of electrical machines, the student meets many conceptual difficulties not experienced for example in the early studies of digital systems, with their simple and precise 2-state operation. More assistance is required to permit the new-comer to gain confidence in dealing with non-linear, 3-dimensional, rotating electromagnetic devices. The purpose of this book is to provide this aid to understanding by showing how, with a limited number of equations derived from basic considerations of power flow and elementary circuit and electromagnetic theory, the electromechanical performance can be explained and pre-dicted with reasonable accuracy. Such an aim, which will permit the calculation of power-input/output c haracteristics almost close enough in engineering terms to those of the device itself, can be achieved by representing the machine as a simple electrical circuit - the equivalent-circuit model. This concept is explained in many books, for example in the author's companion volume Electrical Machines and Their Applications. Though more detailed theoretical treat-ment is given there, substantial portions of the present text may be regarded as suitable revision material. This expanded 3rd edition can, as a whole, be considered as a textbook with particular, but not exclusive, emphasis on Electrical Drives, taught through worked examples, for a reader having some familiarity with basic machine theory. Perhaps it is appropriate to point out that complete and exact analysis of machine performance is so complex as to be virtually impossible. The additional accuracy achieved by attempts to approach such methods is primarily of interest to the spet designer who must ensure that his 2 Electrical Machines and Drive Systems (1.1) product will meet the user's needs without breakdown and he must judge when the analytical complication is justified. For the user, and for the engineering student who is not yet a spet, the simpler methods are adequate for general understanding and provide a lead-in if necessary for later speation. There are many features of all machine types which are common, the obvious example being the mechanical shaft equations. But apart from these and the fundamental electromagnetic laws, the input/output relationships and modes of operation have many similarities. These are brought together where possible and also in this first chapter, some elementary mechanical, magnetic and circuit theory is discussed briefly, as a reminder of the basic knowledge required. Students should beware of underestimating the vital importance of this material, since experience shows that it is these very points, improperly understood, which hold back progress in coming to feel at ease with machines problems....
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