Resistance to earth of substation earth electrodes in uniform and two-layer soils

The resistance to earth of square and rectangular grid and combined grid-multiple rods earth electrodes buried in uniform and two-layer soils has been analyzed for a wide set of electrodes and soil parameters. Novel approximate expressions for earth resistance are deduced based upon the data obtained by exact computer modelling. These expressions and a set of diagrams provided can be used in the preliminary design stage of substations earthing systems for assessing the effects of various earthing system and soil parameters.