The paper develops an efficient computational method for establishing equivalent characteristics of magnetic joints of transformer cores, with special emphasis on step-lap design. By introducing an equivalent material, the method allows the real three-dimensional structure of the laminated thin sheets to be treated computationally as a two-dimensional problem and enables comparative analysis of designs. The characteristics of the equivalent material are established by minimizing the magnetic energy of the system. To verify the proposed approach, a series of experiments have been conducted. First, the anisotropic characteristics of the step-lap were established, and then space components of the flux density at specified positions measured. This enabled detailed analysis of the flux distribution in the step-lap region, in particular the way in which the flux travels between the laminations close to the air-gap steps. Encouraging correlation between the homogenized 2-D model and experiment has been observed.

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This paper proposes an experimental method to characterise magnetic laminations in the direction normal to the sheet plane. The principle, which is based on a static excitation to avoid planar eddy currents, is explained and specific test benches are proposed. Measurements of the flux density are made with a sensor moving in and out of an air-gap. A simple analytical model is derived in order to determine the permeability in the normal direction. The experimental results for grain oriented steel sheets are presented and a comparison is provided with values obtained from literature.

This paper presents the normal permeability μz of different grades of electrical sheets (Grain oriented, non oriented and amorphous). A specific test bench allows determining the intrinsic static B(H) cycle. The magnetization in static mode makes it possible to suppress the eddy current influence, contrary to others classical methods. The B-H curves of different materials are provided up to the saturation and the μz permeability can be directly implemented in Finite Element software applications.

Purpose -The purpose of this paper is to present a comparative analysis concerning the influence of eddy currents on the distribution of the magnetic flux density in the laminated anisotropic structures. Design/methodology/approach -The influence of the magnetic flux normal to the lamination surface is particularly analysed. Several models containing internal air gaps and overlapping are tested. For every structure, the eddy currents are first taken into account and then, they are neglected. At last, the 3D simulation of the anisotropic conductivity permits to analyse separately the longitudinal and normal flux in the structure and the eddy currents induced by those fluxes. Findings -The study leads to a more realistic numerical model with conducting laminations. The results show that the normal flux does not turn at once on lamination. The normal and longitudinal fluxes induce eddy currents which modify the flux distribution in the laminated structure. Practical implications -The results of the presented simulations make it possible to elaborate a more realistic numerical model of homogenized characteristics taking into account eddy currents. Originality/value -The eddy currents induced by the fluxes modifies the field distribution in the structure and should be taken into account. The internal air-gaps higher than 0.1 mm have an influence on the field distribution; the isolation between the laminations of 0.01 mm has a smaller but not negligible effect on the magnetic flux. The direction of the normal flux from one sheet to another one does not change immediately after the entrance of the lamination, the transition is progressive.

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