Theoretical Basis for Physically Correct Measurement and Interpretation of Magnetic Energy Losses

This paper discusses fundamental physical mechanisms that are responsible for specific errors of standardized methods of magnetic loss measurements on laminated soft magnetic materials. It is shown that the Poyntings theorem offers an exact distinction between localized loss portions on the one hand and total losses on the other hand. Further, a clear distinction is suggested between mechanisms of hysteresis and eddy currents. The correct applicability of experimental measurements proves to be restricted to cases where the Poynting vector is restricted to normal off-plane components. This represents the only case where total losses can be determined on the basis of surface field and cross-sectional averaged induction. As a consequence, physically “correct” loss measurements are to be restricted to sample regions that exhibit mere axial magnetization, in exact ways. This is attainable with a single sheet tester, the homogeneously magnetized region of which is equipped with an induction coil and a large-area tangential field coil, in consistent ways.