The development of permanent magnets with high energy density has led to increased interest in the use of permanent magnets for DC and synchronous machines. The representation of the magnetization characteristics of magnets is difficult and is still the subject of research. However it is often acceptable to consider the permanent magnet as ideal or linear   .1 Consider the hysteresis characteristics in Figures 3.1 and 3.2. Soft magnetic material is typically what one would find in machine laminations or in a magnetic circuit. These materials are characterized by a narrow hysteresis loop. Hard magnetic materials are characterized by wide loops. The intersection of the loop with the ordinate is called the residual or remanent flux density B r . The intersection of the abscissa and the loop is called the coercive force, H c . Many (but not all) of the magnetic materials commonly used in machines exhibit a linear normal magnetization characteristics in the second quadrant. Since the permanent magnet machine is designed to operate in this region - and in fact must be designed so that even during transients such as short circuits the magnet will not be demagnetized, we normally choose a straight line to represent the magnet characteristic. However we should keep in mind that the magnet is a nonlinear material. If we use a linear model, we should check that the model is valid for all expected operating conditions.
KeywordsPermeability Lamination Salon
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