Influence of coercive force on iron losses at low frequencies

Previous authors have calculated low-frequency eddy-current losses in bars and thin sheets assuming a simple domain structure of plane parallel walls. Use is made of these earlier results to derive a wall equation which includes coercive-force terms, attention being concentrated on the case of large wall excursions. From a comparison of calculated loss curves with previously published experimental work on oriented silicon iron, it is considered that the appropriate representation of coercive force is by a constant term, analogous to dry friction. This suggests that for the simple domain structure considered the hysteresis component of total loss per cycle is independent of frequency for any given peak flux density. Attention is paid to the effect on losses of varying waveshapes of B and H. Differences between practical domain structures and the idealised case are used to explain observed differences between the loss curves, and the conclusion is drawn that in practice the hysteresis loss is likely to be a function of frequency as well as of flux density.