Evaluation of ground resistance of a grounding grid of any shape

A large number of grounding grids in substations have shapes other than a square or a rectangle, whereas the formulas and graphs for the ground resistance of a grounding grid available in the literature are applicable only to nearly square or rectangular grids. A new simple equation for the estimation of ground resistance applicable to any practical shape of the grid is presented. The results obtained with this equation have been compared with accurate results obtained via computer and with the results of analog model tests. The value of ground resistance obtained with the proposed method closely approximates that obtained from elaborate and time-consuming computer methods