Probability of surge protective device systems to reduce the risk of failure of apparatus due direct flashes to overhead low voltage lines

Aim of the paper is to investigate on the probability of a coordinated surge protective device (SPD) system to reduce the risk of failure of electrical and electronic equipment within a structure against lightning surges due to direct lightning stroke to the connected low voltage overhead lines (source of damage S3 according to IEC standard 62305). Two SPD systems are considered, namely SPD system type SL, consisting of a SPD1 switching type and a SPD2 limiting type, and an SPD system type LL, consisting of a SPD1 and a SPD2 limiting type. The approach here presented and discussed takes into account the type of SPD system and the characteristics of the upstream power line and of the downstream protected circuit. The analysis has been performed by several simulations obtained by means of the transient software EMTP-RV. The results are compared with those obtained with only one SPD (switching or limiting type) installed for the protection of apparatus within the structure.