Practical method for the analysis of earthing systems with long external electrodes

The earthing problem of distribution stations that supply consumers through a radial underground network, with cables having unisulated outer sheaths, is solved efficiently and in a satisfactory manner, even when all the other relevant factors are very unfavourable. In a wide area surrounding these stations, the cable lines spontaneously form a large network of earthing conductors, which incorporate other types of underground metallic structures typical of urban areas. All this significantly improves the characteristics of the earthing system, but, at the same time, makes it very complex, so that the analysis of such an earthing system often represents a serious and difficult task. The paper describes a practical method which, by certain idealisations and simplifications of the actual physical model, enables the solution of the problem in a series of practical situations, using a quick and cheap procedure.