Effects of saturation on the core loss of thin ferromagnetic plates subjected to alternating flux

An original method is proposed for determining the eddy-current loss in thin ferromagnetic plates taking into account the non-linearity of the mean magnetization curve. To improve the versatility of the method a normalized graphical construction is formulated which is applicable over a wide range of frequencies and for materials of different electric and magnetic properties. This leads to a set of standard curves for predetermining the eddy-current loss in thin plates. As is well known, for thin plates the contribution of the hysteresis loss as a component of the total core loss is great. The method is therefore extended to take account of hysteresis also. The validity of the graphical construction is verified against a set of experimental results. In the experimental measurement of core loss in thin plates a clear distinction exists between the observed loss when the current through the winding is sinusoidal and the loss when the voltage across the winding is sinusoidal. For a sinusoidal magnetizing force at the surface the loss is 40% greater than when the flux is sinusoidal with the same r.m.s. surface magnetizing force. This difference is significant and has not been so explicitly reported before. An attempt is made to explain the phenomenon on the basic assumption that the material is isotropic and homogeneous.