Evaluation of hysteresis loss and eddy-current loss in induction motor stator cores using the excitation inner core method

It is well known that the magnetic properties of a stator core in a rotating machine such as an induction motor are influenced by residual stress and external force. Residual stress is generated during manufacturing processes such as punch, laminate, and shrink fit processes. Magnetic properties such as iron loss of the stator core increases dramatically during the punching process and the shrink fit process. However, it is not easy to evaluate the magnetic properties of the actual stator core which has a complex shape. To evaluate the growth rate of iron loss in an actual stator core by manufacturing processes, the excitation inner core method was developed. The excitation inner core method can successfully evaluate changes in magnetic properties in an actual stator core. Then, the excitation inner core method was applied to examine the influence given to iron loss of the stress that caused by a motor frame. Moreover, iron loss consists of hysteresis loss and eddy-current loss. The iron loss measured using the excitation inner core method was separated into hysteresis loss and eddy-current loss by the dual frequency method. Experiments showed the compressive stress from a motor frame greatly influenced hysteresis loss, but the influence of this stress on eddy-current loss was small.