Ferromagnetic materials, typically composed of iron and alloys of iron with cobalt, tungsten, nickel, aluminum, and other metals, are by far the most common mag- netic materials. Although these materials are characterized by a wide range of prop- erties, the basic phenomena responsible for their properties are common to them all. As applied to the magnetic circuit of Fig. 1.1, the source of the magnetic field in the core is the ampere-turn product N i. In magnetic circuit terminology N i is the magnetomotive force (mmf) .T" acting on the magnetic circuit. Although Fig. 1.1 shows only a single coil, transformers and most rotating machines have at least two windings, and N i must be replaced by the algebraic sum of the ampere-turns of all the windings.

n The analysis of single-phase induction motors has been expanded to cover the general case in which the motor is running off both its main winding and its auxiliary winding (supplied with a series capacitor).Equation 1.45 can be used to calculate the energy input W to the magnetic core of Fig. 1.1 as the material undergoes a single cycle In recognition of this development, this edition incorporates MATLAB in ex- amples and practice problems as well as in end-of-chapter problems. It should be emphasized, though, that the use of MATLAB is not in any way a requirement for the adoption or use of Electric Machinery. Rather, it is an enhancement. The book

in a magnetic circuit in the absence of external excitation (such as winding currents). This is a familiar phenomenon to anyone who has afixed notes to a refrigerator with small magnets and is widely used in devices such as loudspeakers and permanent- P E R M A N E N T M A G N E T S Figure 1.16a shows the second quadrant of a hysteresis loop for Alnico 5, a typical permanent-magnet material, while Fig. 1.16b shows the second quadrant of a hys- teresis loop for M-5 steel. 7 Notice that the curves are similar in nature. However, the hysteresis loop of Alnico 5 is characterized by a large value of residual flux density or remanent magnetization, Br, (approximately 1.22 T) as well as a large value ofThe exciting new sixth edition of “Electric Machinery” has been extensively updated while retaining the emphasis on fundamental principles and physical understanding that has been the outstanding feature of this classic book.

which corresponds to a point on the second quadrant of the hysteresis loop. As can be seen from Eq. 1.56, the product of B and H has the dimensions of energy density (joules per cubic meter). We now show that operation of a given permanent-magnet material at this point will result in the smallest volume of that material required to produce a given flux density in an air gap. As a result, choosing a material with the largest available maximum energy product can result in the smallest required magnet volume. where .T" is the mmf (total ampere-turns) acting to drive flux through a closed loop of a magnetic circuit, is driven by a 11,000 V Δ-connected source. When a wye-connected load is connected to the secondary in transformers and rotating machines. The characteristics of ferromagnetic materials are described in Sections 1.3 and 1.4. For the present we assume that/Zr is a known constant, although it actually varies appreciably with the magnitude of the magnetic flux density. 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

PROBLEM SOLUTIONS: Chapter 1

As the current then goes negative, the B-H characteristic continues to trace out a hysteresis loop. In Fig. 1.21, this is seen as the traje 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. 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. Professor Kingsley first asked this author to participate in the fourth edition of Electric Machinery; the professor was actively involved in that edition. He participated in an advisory capacity for the fifth edition. Unfortunately, Professor Kingsley passed away since the publication of the fifth edition and did not live to see the start of the work on this edition. He was a fine gentleman, a valued teacher and friend, and he is missed.