Level, Class and Prospected Safety Performance of a Lightning Protection System for a Complex of Structures (LPCS)

The recent standard IEC 62305 provides advanced information for the design of Lightning Protection of Structures (LPS). In determining the position of the air-termination system two methods are generally suggested: the protective angle method and the rolling sphere method. Adopting a 3D graphical simulation, the "rolling sphere" method allows: -to analyze the protected volume at the building roof inside of the rolling ply surface, -to verify the behavior of the designed air termination system, -to evaluate the contribution of the surrounding structures in limiting the lightning current flowing in the down-conductors. This current affects the probability of dangerous sparking and the separation distance for the protection of internal installations. The paper presents this approach by a case study of a building in a complex of structures: it highlights particularly the worst cases of the lightning impact related to the designed air-termination system.