Resistivity and core size dependencies of eddy current loss for Fe-Si compressed cores

In this study resistivity and core size dependencies of eddy current loss for Fe-Si compressed cores are systematically investigated, and the mechanism of the eddy current generation is discussed. FeSi powders are made by atomizing process with chemical composition of 3 mass% Si and balance Fe. Annealing at 1223 K in H₂ atmosphere is done. Forming pressure of 1.96 GPa in pressing method is used to form ring shaped specimens with outer diameter of 28 mm and inner diameter of 20 mm. Core loss is measured between 1 kHz and 100 kHz at fixed magnetic flux density of 0.2 T and is separated into eddy current loss and hysteresis loss. Eddy current loss shows approximately constant value independently on core height below 1173 K but over 1173 K it increases rapidly with raising of heat treatment temperature. When resistivity is over about 0.01 Ωm, eddy current runs only inside particles and eddy current loss is constant independently on the resistivity. Lower than about 0.01 Ωm, eddy current loss increases as core height becomes thick.