Realistic and accurate model for analyzing substation grounding systems buried in various backfill material

The design of a substation grounding system that is surrounded by a number of backfill material (finite volumes of soil) with distinct resistivity values, such as a thin surface layer of crushed rock and paved surfaces is particularly complicated. The effects of such arbitrary finite volumes of backfill material and heterogeneous soil have been studied in this paper. The numerical solution of a boundary element based method and the exact analytical solution for a hemispheroidal soil model are used in this study. Computation results for a realistic case are presented by comparing several approaches. The analysis demonstrates that it is necessary to model such arbitrary volumes accurately in order to determine the grid GPR, touch and step voltages realistically and to avoid unsafe or costly designs.