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To calculate the iron loss in an electric machine accurately, the anomalous eddy current loss generated by domain wall motion should be considered. A simple numeric modeling of anomalous eddy current loss by modifying the conductivity of steel plates is sometimes used. However, investigation on this method in detail has not been carried out. In this paper, this method is investigated in two iron-loss models neglecting and including the skin effect and then applied to the loss calculation of various kinds of nonoriented and oriented silicon steel plates. Then, the dependence of the modified conductivity on the amplitude and frequency of the induction magnetic field for each material is obtained and the appropriate iron-loss model and method for modifying the conductivity are proposed for the nonoriented and oriented silicon steel plates. The calculated iron losses using the appropriate iron-loss model with modified conductivity are compared with the measured data. It is clarified that for nonoriented materials, the iron-loss model including the skin effect with constant modified conductivity shows good agreement. And for oriented materials, the model neglecting the skin effect with the modified conductivity depending on frequency is better.