The high-voltage characteristics of earth resistances

This paper concerns the behaviour of earth resistances under h.v. currents. The author has tried to contribute to the explanation of the phenomena causing the decrease of the earth resistance and to check the effectiveness of giving to the earth electrodes the properties of edges or points. An explanation is given for the ¿breakdown¿ of the soil, based on the results obtained from the theoretical treatment of model earths. The analysis of the experimental results obtained on model earths leads to favourable conclusions as regards the use in practice of electrodes having the properties stated above. The direct discharges on the ground surface during lightning strokes and falls of overhead h.v. line conductors are considered and the corresponding resistances and currents are estimated. The results obtained lead to the suggestion that in some cases the special earthing of h.v. line poles is not necessary, either for the protection of these lines against lightning strokes or for the operation of the line-disconnecting devices during short-circuits to earth.