Author(s)

A. Campoccia & G. Zizzo

Abstract

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. Keywords: resonant earthed neutral system, interconnected earthing systems, extended earthing system, MV/lv substations. 1 Introduction The design of the earthing system of the MV/lv substations is often a complicated and onerous task, considering the high values of the fault currents usually present. A measure to reduce the design currents of the earthing systems consists in connecting together all the earth electrodes, using, for example, the metal sheath of the cable lines of the MV network. The presence of numerous interconnected earthing systems creates, however, a number of safety problems, due to the transfer of voltages, which need to be analysed.

Keywords

resonant earthed neutral system, interconnected earthing systems, extended earthing system, MV/lv substations.