Transient analysis of wind turbine grounding system: Comparison between interconnected overhead ground wire and underground bare conductor in wind farms

Abstract:
Wind turbines (WTs) are exposed to lightning strikes due to their height and location on high terrains. In order to minimize the overvoltages caused by lightning strikes in WTs, each wind turbine ground system (WTGS) is usually interconnected by bare conductors buried under the soil. Alternatively, some wind farms have their WTGS interconnected by an overhead ground wire (OHGW) on the top of a medium-voltage network (MVN), as seen in Brazil. This paper investigates the performance of WTGS interconnected by an OHGW, in comparison with the traditional WTGS usually interconnected by bare conductors for five distinct values of soil resistivity. The study analyzes the transient currents and ground potential rise (GPR) generated at four distinct points of the grounding base of the transition poles when a single wind turbine is hit by a lightning strike of first positive impulse (FPI) of 100 kA 10/350 mus. All the transient responses are assessed employing the full-wave electromagnetic software XGSLab(r) using the Partial Element Equivalent Circuit (PEEC) method. Results indicate that the WTGS interconnected by an OHGW generated higher transient currents and GPR on the grounding base of the adjacent transition poles of the hit WT compared with the traditional interconnected grounding system with bare conductors.