Verifying the Computational Method of Transient Performance with Respect to Grounding Systems based on the FD-TD Method.

Abstract

Lightning strikes on bulk transmission lines and distribution lines frequently cause serious accidents involving electrical apparatus. It is strongly desired to analyze transient performance in terms of the transient electric potential, transient current, and transient grounding resistance of grounding systems of electrical apparatus in order to establish accident prevention. The transmission line approach, which was brought to practical applicability by Sunde and the electromagnetic field approach based on the method of moments have been conventionally used to analyze the transient performance, however, both are insufficient in general practical usage because the former can only deal with TEM waves and the latter can only analyze grounding systems in homogeneous earth. Hence, one of the authors has already proposed a novel method for computational analysis of transient performance based on the finite-difference time-domain, (FD-TD) method (FD-TD CMTP).This paper presents both experimental results of transient performance with respect to a grounding electrode of a rectangular parallelepiped electrode, which is a model of a foot of the transmission towers, and a square loop electrode, which is an element of a grounding grid, and the calculated results obtained using FD-TD CMTP. The calculated results agree very well with experimental results. This confirms the validity of using FD-TD CMTP to analyze transient performance of grounding systems of electrical apparatus.The FD-TD CMTP is expected to facilitate the rational design of grounding systems.