Lightning distribution through earthing systems

Surge protective devices (SPDs) are categorised into lightning current arresters, arresters and suppressors. They must be coordinated taking into account their maximum surge current capacities, the used low-voltage power distribution system, the telephone line, the water pipe, the medium-to-low voltage transformer, the earth electrode impedance and neighbouring residences/buildings. The aim of this study is to determine the sharing of the current, in time domain, and the stress on the various SPD in terms of current or energy. A method for computing the effects of a direct lightning stroke on the protection system of a residence is presented. We used EMTP (electromagnetic transients program) to perform the necessary calculations. For each element we had to use usual models (as for varistors, gaps and lightning rod) or create some models (as for earthing, water pipes and transformer). It has been possible to simulate many cases of course but in order to give indications of the trends we selected some basic cases based on typical French low voltage networks