Analysis of Earth Electrodes of Wind Turbine Generator Grounding System Under Lightning Discharge Currents

This paper presents an analysis of various earthing electrode configurations for the lightning protection of a wind turbine earthing system. The IEC 61400-24 standard recommends a type B earthing arrangement for the protection of wind turbines from lightning discharge currents. However, we show that the required impedance cannot be achieved with the recommended electrode lengths of the standard when typical soil resistivity values are taken into account. We analyse different earth electrode configurations and lengths for lightning discharge current frequencies for different soil resistivity values based on frequency independent and dependent soil parameters. The results show a reduction of up to 85% of the wind turbine earth impedance at higher frequencies with frequency-dependent soil parameters. Amongst the studied electrode configurations, the configuration with ring and horizontal electrodes provides the lowest impedance path for lightning discharge currents.