Design of Rotating Electrical Machines, 2nd Edition

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Design of Magnetic Circuits

The magnetic circuit of an electrical machine generally consists of ferromagnetic materials and air gaps. In an electrical machine, all the windings and possible permanent magnets participate in the magnetizing of the machine. It must also be noted that in a multiple-pole system, the magnetic circuit has several magnetic paths. Normally, an electrical machine has as many magnetic paths as it has poles. In a two-pole system, the magnetic circuit is symmetrically divided into two paths. A possible magnetic anisotropy occurring in the geometry of the magnetic circuit also influences the magnetic state of the machine. In the literature, a magnetic circuit belonging to one pole is usually analyzed in the design of a complete magnetic circuit. This method is employed here also. In other words, according to Equation (2.15), the amplitude of the fundamental component of the current linkage is acting on half of the magnetic path. A complete magnetic path requires two amplitudes; see Figure 2.9.

The design of a magnetic circuit is based on the analysis of the magnetic flux density B and the magnetic field strength H in different parts of the machine. The design of a magnetic circuit is governed by Ampère’s law. First, we select a suitable air-gap flux density Bδ to the machine. Next, we calculate the corresponding field strength values H in different parts of ...