Q2Electrical Machine Design
Question
Q.2. Why hysteresis loss is less in the case of a soft magnetic material when compared to that of a hard magnetic material?
Answer
Soft magnetic materials have a narrow hysteresis loop (low coercivity), so the area enclosed (representing energy dissipated per cycle) is small, unlike hard magnetic materials which have wide loops and high coercivity.
Hysteresis loss per cycle is proportional to the area enclosed by the material's B-H hysteresis loop. Soft magnetic materials (e.g., silicon steel used in transformer/motor cores) have low coercivity and remanence, producing a narrow, thin hysteresis loop with small enclosed area, resulting in low hysteresis loss — essential since these materials undergo continuous cyclic magnetization at supply frequency. Hard magnetic materials (used for permanent magnets) have high coercivity, producing a wide loop with large enclosed area and hence much higher hysteresis loss per cycle, which is acceptable since permanent magnets are not intended to be repeatedly cycled through magnetization reversal during normal operation.