Analysis of Transients in Electrical Circuits Containing Initially Magnetized Ferromagnetics for Impulse Excitation

Many electrical devices have magnetic cores made of ferromagnetic materials with pronounced nonlinearity. Finding the proper values of equivalent circuit parameters for transient analysis, however, may be difficult or even virtually impossible, due to the nonlinear nature of the current skin effect in ferromagnetic cores. Beland and Gamach1, Davidson2, and MacBain3 have studied experimentally and modelled numerically the transient processes in electrical machines or their parts, taking into account the nonlinearity of the magnetic media, but these investigations have been made with assumptions limiting the shape of the electric currents flowing in the circuit. Fridman4 has proved the range of using an equivalent circuit of transformer type for fixed frequency of current flowing through the exciting winding and core thickness. Wiak5,6 and Zakrzewski5 have proved that it is possible to calculate transients in electrical circuits containing ferromagnetics, in many cases, without using an equivalent circuit idea. Instead, the contribution of the eddy-current field to the total impedance of the system is calculated throughout simultaneous solution of a nonlinear field equation in a ferromagnetic core, and the shape of the circuit is being corrected after each step of numerical iteration. In this paper, the author has successfully applied the “circuit-field method”5 to the circuits containing ferromagnetics with DC initial magnetization of a core.