This report shows the effects of a direct lightning strike to an air terminal installed on top of a building which is connected to a buried earthing system.

The Annex H in IEEE Standard 80-2013 contains benchmark case results for comparing and evaluating software tools and methodologies used for the analysis of substation earthing. The results compare the simple equations from IEEE Std 80 with the results given by some of the commercially available software such as CDEGS, ETAP, SGW, SDWorkstation and WinIGS.

During an earth fault on a substation earth grid, the flow of current to the earth will produce voltage gradients. An earth grid that is properly designed will safely dissipate current into the ground.

This article shows the effects of soil resistivity and thickness of layers on grid resistance for earthing systems in multilayer soils. Increasing the resistivity of soil layers tends to increase the grid resistance, no matter which soil layer that is. Increasing the thickness of any soil layer with high resistivity also increases grid resistance and if the soil layer thickness is increased for a low resistivity layer then the grid resistance will decrease. Software modelling is performed and the results are compared and shown to match well with those from CDEGS software.