Eddy current losses in solid iron pieces under three-dimensional magnetic field

Abstract

This paper deals with a method to compute eddy losses in the massive magnetic pieces of electrical machines when the magnetic field near the material surface has three components. The flux outside the massive pieces is computed assuming that there are no eddy currents. This is normally satisfactory because the very weak coupling between magnetic and non-magnetic areas. Time dependence is neglected and only peak values are considered. Inside the material, the eddy currents concentrate the flux in a very thin skin depth. The local losses depend on that flux or the associated magnetic field. They are analytically calculated assuming a one-directional geometry. Time dependence, which may be sinusoidal or not, and the iron saturation is now considered. The internal flux path is determined, taking into account the iron piece shape, by solving a two-dimensional quasi-Poissonian equation. Computed and experimental figures of magnetic field and losses are compared at the same locations in a 20 MVA transformer.