Effect of domain-wall motion on power loss in grain-oriented silicon-iron sheet

Loss measurements and domain observations are presented for two types of grain-oriented 3%-silicon-iron sheet having widely differing domain sizes, in order to elucidate the origin of anomalous loss in magnetic materials. An alternative method is presented for separation of eddy current and hysteresis losses, which gives a more realistic representation of the processes of domain magnetisation than the conventional definitions. The large eddy-current and hysteresis losses, under alternating conditions at power frequencies, can be ascribed to the wide variation in domain-wall displacements. At high flux densities most of the anomalous loss is due to the large increase in effective a.c. hysteresis loss. By reducing the spread of wall displacements in commercial grain-oriented silicon iron, the losses at 50 Hz could be reduced by up to 30%, and by up to 50% by a reduction in domain width.