Magnetic circuits with D-C magnetization and high alternating induction

A fairly simple theory is given and criteria have been established for analysis or design of magnetic circuits in which there are an unbalanced or d-c magnetization and a high alternating induction. High values of alternating induction and a nonlinear relation between induction B and field strength H are characteristics of magnetic circuits in power apparatus, in contrast to magnetic circuits in audio components. The relation between induction and field strength during cyclic variation is given approximately by the d-c magnetization curve of the magnetic circuit. Maximum and minimum values of induction correspond to maximum and minimum values of field strength, but the average values of B and H are not simply related. The demagnetizing effect of an alternating field superimposed upon a direct field is the reduction of average induction after the application of the alternating field. This effect is due to the nonlinearity of the magnetization function. A simple circuit using the test sample and an auxiliary transformer has been devised for obtaining data on magnetic cores by direct measurement. Test results for representative cores have been organized in a manner suitable for design use. Excitation volt-amperes, optimum per-cent gap, and core loss may be found as a function of a-c induction and unbalanced field strength. The data on magnetic materials are applicable to reactors and to transformers with unbalanced direct current such as units for supplying half-wave rectifiers. Analysis of the frequency components aids in understanding the operation of half-wave supply circuit. Only the induced voltage of the primary winding and the average secondary current affect the magnetic circuit.