A study of the behaviour of earth electrodes connected together in resonant earthed neutral systems

Inside urban areas the earth electrodes of the MV/lv substations are often electrically connected together so as to form a single extended earthing system. The advantages of the realization of an extended earthing system are the reduction of the current that each substation earth electrode injects in the soil during the fault and a better uniformity of the voltages to earth inside the urban area. In previous works, models for the study of extended earthing systems have been proposed. These models were valid for the case of single-line-to earth fault in isolated neutral MV networks. In this paper, the extended earthing system is analyzed in the case of a resonant earthed neutral MV network. The mathematical model used for the analysis and an application example are shown and a comparison with the case of isolated neutral system is done.