A theoretical and analogue approach to stray eddy-current loss in laminated magnetic cores

A method of obtaining the interlaminar eddy-current loss in laminated magnetic cores is devised by using a resistance-network analogy. It is assumed that in a laminated-core section the flux distribution is uniform, that there is a uniform resistivity in the direction across the laminations and that the IR drops in the direction along the planes of the laminations are negligible compared with those in the perpendicular direction. The stray eddy-current loss is derived as a function of the resistivity ratio between the two directions. The network analogy leads to the subsequent estimation of the effect on core loss of any short-circuiting paths in the section. An experimental technique was developed to investigate the eddycurrent distribution in any conductive network through which a uniform alternating magnetic flux passes. The eddy-current distribution for an isotropic section was first obtained. An analogy to the laminated-core section from the point of view of conductivity was effected using a differential wire network whose resistivity in one direction was of the order of 104 times that in the perpendicular direction. The eddy-current distribution in such a network under an alternating magnetic field was found to confirm the theoretical calculations for core sections with and without interlaminar short-circuits.