A New Method for Calculating Earth Electrode Length for a Wind Turbine Generator Grounding System based on a Two-Layer Soil Structure

The earthing system is a crucial component of the lightning protection system in a wind turbine generator. In particular, the length of the earth electrodes has a significant role in the wind turbine earthing resistance value. The state of the art standard IEC 61400-24 provides guidance on the design of the earthing system. However, this method assumes uniform soil resistivity. This paper proposes a more accurate method to calculate the minimum length of the earth electrode for a two-layer soil model considering electrode dimension, burying depth and frequency. The proposed method is implemented for measured values of soil resistivity for three wind turbine sites and compared to results from traditional methods. We found that using the proposed method results in a decrease in the lightning generated ground potential rise of up to 64% compared to the conventional method.