Assessment of the Transient Response of Wind Turbine Grounding Systems to Upward Negative Lightning

This paper presents some results of simulation of the resulting ground potential rise (GPR) in wind turbine grounding systems in response to typical current pulses pertinent to upward negative lightning. The analyses consider two different current pulses, which are defined based on measured currents of upward flashes initiated from the instrumented Säntis Tower in Switzerland, namely: i) a fast pulse, similar to return strokes observed in downward negative lightning, and ii) a slow pulse associated with M-componenttype pulses. The GPR in response to the fast current pulse is characterized by high steepness and is strongly attenuated at points distant from the current injection point, while the GPR in response to the M-component-type current pulse presents a slow rate of rise and long duration, and can be transferred to more distant points without significant attenuation. The results obtained in this paper highlight the importance of considering upward flashes in the design of the lightning protection system of wind farms.