Second Special Case: Static Magnetic Fields

Electrical machines use the properties of magnetic fields in ferromagnetic materials. This chapter describes the details of the energy transfer between the currents, the fields, and the electrons in the iron. In this manner, material properties are connected to machine efficiencies. It is shown that, depending on how magnetically active substances are distributed in space, the magnetic potential must fulfil different equations. This helps to understand why Boit-Savart’s law for calculating magnetic fields is not always applicable. It is shown that torques act on closed current loops of any shape and that the dipole moments characterising the loops have similarities with electric dipole moments. Multipole expansions are introduced. The chapter also discusses the use and validity of magnetic circuits. It ends with some remarks on inductances.