Magnetic equivalent circuits for electrical machines

The concept of an equivalent magnetic circuit, analogous to an equivalent electric circuit, in which flux replaces current, m.m.f. replaces e.m.f. and reluctance replaces resistance, is well known and widely used, but the technique is generally restricted to the equivalent of d.c. electric circuits. The paper shows how the technique may be extended to cover a.c. electromagnetic systems, using the concepts of quadrature impedance and mutual inductance in the magnetic case. It is shown that the use of an equivalent magnetic circuit is to be preferred for problems in which more than one magnetic circuit is linked with an electric circuit.