Rotational Magnetic Losses in Nonoriented Fe–Si and Fe–Co Laminations up to the kilohertz Range

Literature data on the energy loss behavior of steel sheets under rotating induction are restricted to quite low frequencies, i.e., up to a few hundreds of hertz. This is not sufficient to predict the loss in high-speed electrical machines, where frequencies in the kilohertz range are commonly encountered. We have overcome this difficulty by making loss measurements under alternating and circular induction in 0.2 mm thick Fe-(3 wt%)Si and Fe₄₉Co₄₉V₂ sheets using a specially designed experimental setup. Peak polarization levels and frequencies up to 1.6 T at 2 kHz have been reached in the Fe-Si laminations, whereas the Fe-Co alloy, endowed with much higher permeability, has been characterized up to 2.1 T at 5 kHz. In the first part of this paper, the measured loss behavior versus peak polarization and magnetizing frequency is presented. In the second part, a loss model for circular induction is proposed, considering the skin effect. To this end, we have derived a simple magnetic constitutive law for the material, assumed to be isotropic, and we have introduced it into the electromagnetic diffusion equation. The solution of this equation by an iterative algorithm provides the induction profile across the sample thickness and eventually the classical loss component, which represents the major contribution to the total loss at high frequencies. Good agreement with the experiments is obtained.