The effect of flux distribution on iron losses

Abstract

The classical formula used to compute eddy-current losses in magnetic sheet steel is derived from Maxwell's field equations based on the conditions of constant permeability. This Condition of constant permeability is unfounded since in each cycle the permeability of modern materials will undergo changes of at least 1 to 100. Large differences between actual losses and the losses computed according to the classical formula have been noted. These differences could be attributed to the assumption of constant permeability. This paper attempts to determine approximate solutions for Maxwell's field equations under the condition of variable permeability that will lead to a modified formula for determining the eddy-current losses. Since rough approximations were used, final conclusions cannot be made. However, the results indicate that the error in the classical formula (the assumption of constant permeability) accounts for only a small part of the discrepancy between calculated and actual eddy-current losses. Experiments were conducted that confirmed the concept of changing flux distribution. These experiments also indicated that other mathematical approaches could be used for more accurate approximations.