Three-dimensional magnetic properties measurement of the laminated silicon steels

Silicon steels are widely applied in the magnetic cores design, such as power transformer, electrical machine, and magnet. Magnetic properties of the silicon steel are key factors in design and performance optimization of the electrical apparatus. In the past several decades, one and two dimensional (2-D) magnetic properties testing methods have been developed for single sheet silicon steel specimen [1]. Their testing and analyzing scopes were confined in some direction or one plane. While in application, the silicon steels are usually in lamination, which may cause magnetic interaction between the vicinity layers. Magnetic properties along the perpendicular rolling direction and effects of the laminated layers might be ignored in the traditional testing methods. In this condition, big error may occur in material modeling and core loss calculation. Also, rotational magnetic fields are testified comprehensively in cores of rotating AC machines and T-joints of three-phase transformers, which cause rotational core losses may amount to more than 50% of the total core losses [2]. Therefore, 3-D magnetic properties of the laminated silicon steel in the complex rotating magnetization conditions should be taken into account. The first 3-D testing system with core-yoke excitation structure was designed mainly for isotropic soft magnetic composite (SMC) materials [3, 4]. For the junctions of laminated yokes and cores cannot be kept in uniform in any axis, this excitation structure can make asymmetric flux distributions in three axes. In order to perform relatively uniform and symmetrical magnetization of the laminated silicon steel specimen, the authors have been done a number of valuable benchmarking studies on a novel 3-D magnetization structure with 'C-type' cores as shown in Fig. 1.