Abstract :
The fundamental considerations involved in defining the incremental magnetic properties of a material are briefly reviewed, and methods of measuring the properties are described. Measured values at 50 c/s and 800 c/s for the various grades of hot-rolled silicon-iron in common use are tabulated. These measurements were obtained on samples representing the best and the worst (as judged by total power loss at 50 c/s and magnetic flux density of 10 000 and 13 000 gauss) for each grade of material, specially selected from production by the manufacturer. It is shown that the apparent reluctivity of a magnetic circuit, with an air-gap which is optimum for the particular conditions of incremental magnetization, can be related to the apparent polarizing magnetizing force by an empirical equation. This equation is sufficiently accurate for most practical applications, and its use enables a purely analytical method of design of air-gapped smoothing chokes to be evolved. Formulae are developed for designs where the polarizing current and incremental inductance, together with either the d.c. voltage drop or the temperature rise, are specified. Typical values of design parameters used in actual manufactured chokes are given. For comparison, a small number of measurements of incremental properties of two grades of nickel-iron alloys are included in an Appendix.
