Analysis of the lightning transient response of the earthing system of large-scale ground-mounted PV plants

Large-scale ground-mounted PV plants, because of their large extend and localization, can be subject to lightning strikes. When a lightning strike falls into the area of the PV plant, the earthing system is affected by the current flowing in the lightning channel and potentially dangerous overvoltages may occur. Thus, the investigation on the performance of the grounding system is of paramount interest for the prediction of the potential threats either for people working in (or animals passing through) the solar farm area and for the installed electric and electronic equipments. The analysis of grounding systems is conducted in the frequency domain and an hybrid approach, based on circuit theory and Method of Moments, is adopted in order to fully account for resistive, inductive and capacitive couplings between elements of the ground system. The actual transient behavior is obtained by means of an Inverse Fourier Transform. A real case study grounding system configuration is considered and analyzed. We show that, even if the requirements of the international standards are fulfilled, and touch and step voltages are controlled with special care, overvoltages may cause failures of internal systems.