Impacts of Earthing Arrangement on Lightning Protection Efficiency of Grid Connected PV System

This paper investigates the potential and current distribution of a grid-connected (PV) system with surge protective devices connected according to the European Commission for Electrotechnical Standardization (CENELEC) under various values of grounding resistance for isolated and integrated AC and DC earthing systems. A 400 kW PV system is implemented using PSCAD/EMTDC software, where the system is connected to a 33 kV grid through a boost transformer. The simulation results were obtained for negative subsequent lightning stroke (50% value), developed by Heidler function. The current was injected separately into both the DC and the AC sides of the PV inverter. The values of resistance of the earthing systems have been varied over a set of combinations. The results show that when the AC and DC sides are separately earthed for non-zero values of resistance, the line potentials reach very high values posing a severe risk of a system to earth arcing. The situation is worse when the lightning strikes the DC side and when the DC side earth resistance has high values. The situation improves significantly when the earthing systems are integrated. It is advisable to achieve an earth resistance below 5 Ω for the integrated earthing system.