Earthing calculations using a commercial program

The publication of the American standard IEEE 80 in 1986, which includes abstracts of several useful reference papers, partially lifted the fog of obscurity under which substation earthing engineering had lurked. However, as engineers are only infrequently required to make necessary calculations, there still exists a mystique surrounding the subject. Partly that is due to the extent of alternatives engineers are faced with. The availability of programs that do all the calculations correctly and at the same time present the information in a clear manner can overcome some of the grey areas. Since 1983, additional data from well-constructed tank model grid tests has highlighted some deficiencies in the American and British standards. Those are addressed in one particular program that is referred to in this paper. The paper discusses the basic construction of formulae in use and includes a list of steps of calculation. It describes how the GROD program deals with the often ignored cases of multiple and separated grids and a new concept of identifying the distance to the notifiable distance to the 650 V or 430 V contours. Not having to bother with the mechanics of calculation enhances the overall understanding of the effects of grid size, rods and other facets.