3D MACC Modelling of Instantaneous Magnetic Flux Distributions in Epstein Tester

Magnetic energy losses of silicon iron (SiFe) sheets are determined by the standardized methods of single sheet tester (SST) or Epstein tester (ET). The ET is much more compact and can be applied in a large range of frequency. However, it suffers from several sources of systematic errors. The most severe one is given by the magnetic cores flux distribution that shows a strong degree of inhomogeneity. This fact is highly evident. However, it never has been investigated in detail so far. Herein, we report results of a 3-D modeling, performed by magnetic anisotropic circuit calculation (MACC), considering non-linearity in connection with anisotropy, for both non-oriented (NO) steel and grain-oriented (GO) steel. The results reveal substantial differences of the corresponding flux distributions. NO steel proves to be characterized by high homogeneity of induction in rolling direction in the middle sections of the four limbs. However, the four corners show strong inhomogeneity in instants of low global induction, while a transition to more balanced flux arises at peak magnetization. On the other hand, this transition is much less pronounced for GO steel. As a conclusion for the evaluation of losses, a distinction is needed for the two different types of material.