FDTD法に基づく汎用サージ解析プログラムの開発

抄録

This paper presents the development of a general surge analysis program named VSTL (Virtual Surge Test Lab.) based on the FDTD (finite-difference time-domain) method. The FDTD method divides the space of interest into cubic cells and directly calculates the electric and magnetic fields of the cells by discretizing the Maxwell Equations of electromagnetic fields, where the derivatives with respect to time and space are replaced by a numerical difference. By use of the FDTD method, the developed program is inherently able to take into account the geometrical features of a simulated structure, unlike EMTP-type circuit-based transient programs. Thus, the program is advantageous to solve problems: (i) surge propagation on a three-dimensional skeleton structure, and (ii) surge propagation insideathree-dimensional imperfectly conducting medium such as earth soil.
The method of moments (MoM) also numerically solves the Maxwell Equations, and NEC-2 is awell-known program based on MoM. Although MoM efficiently solves the problem (i), it cannot solve the problem (ii) except very simple cases, because it cannot deal with three-dimensional current distribution in the imperfectly conducting medium. On the other hand, FDTD is able to solve both the problems. One weak pointof FDTD is the treatment of a thin wire. Thus, a field correction method to accurately treat the radius of the thin wire is proposed in this paper. Starting from the description of VSTL's solution method, benchmark simulations and comparisons with experimental results are presented in this paper.