The Shell Finite Element Method Of Magnetic Fields Shielding With Sheet At Power Frequency

There is much difficulty in doing mesh generation and calculating precisely when we use traditional finite element method(FEM) to deal with the problem of shielding with sheet in the 3D eddy current field. To solve this problem, this paper presents the shell FEM which only need to overcome mesh generation in the shell of sheet, but express the effect of current upon eddy area with integration. When the thickness of shielding plate is far less than penetration depth, the volumetric current density is essentially uniform in the thickness direction, in this case where the sheet model can be simplified as the shell model which makes it easy to reduce the difficulty of mesh generation.The shell FEM introduces a vector potential T which is perpendicular to the plane of sheet, and surface current density can be expressed as the curl of T. According to the coupling between eddy current area and coil current, we can obtain the Poisson equation of vector potential T. According to vertical dimension of the vector potential T and the sheet, the Poisson equation can be simplified as the one of scalar potential T, and we express it in phasor form. Scalar potential T can be obtained by solving the Poisson equation, and the surface current density on the shielding sheet can also be calculated. With the values of the coil current and the surface current density on the sheet, we can calculate the magnetic induction strength of any point in free space before and after the shielding, so as to calculate shielding efficiency.The shell FEM of magnetic fields shielding with sheet at power frequency is derived in detail and programmed with Fortran program, and the method is proven. We calculate the surface current density of an axisymmetric disk model, and compare it to be effect with the results calculated by ANSYS software. In addition, we model and calculate the shielding of electromagnetic interference of three-phase reactors in substation, the computed results are compared with the measured ones. It is shown that the method is accurate and effectual by two ways.