A boundary element numerical approach for earthing grid computation

Abstract

[Abstract] Analysis and design of substation earthing involves computing the equivalent resistance of grounding systems, as well as distribution of potentials on the earth surface due to fault currents [1,2]. While very crude approximations were available in the sixties, several methods have been proposed in the last two decades, most of them on the basis of intuitive ideas such as superposition of punctual current sources and error averaging [3,4]. Although these techniques represented a significant improvement in the area of earthing analysis, a number of problems have been reported; namely: large computational requirements, unrealistic results when segmentation of conductors is increased, and uncertainty in the margin of error [4]. A Boundary Element approach for the numerical computation of substation grounding systems is presented in this paper. Several widespread intuitive methods (such as the Average Potential Method) can be identified in this general formulation as the result of suitable assumptions introduced in the BEM formulation to reduce computational cost for specific choices of the test and trial functions. On the other hand, this general approach allows the use of linear and parabolic leakage current elements to increase accuracy. Efforts have been particularly made in getting a drastic reduction in computing time by means of new completely analytical integration techniques, while semi-iterative methods have proven to be specially efficient for solving the involved system of linear equations. This BEM formulation has been implemented in a specific Computer Aided Design system for grounding analysis developed within the last years. The feasibility of this approach is finally demonstrated by means of its application to two real problems.