The effect of frequency dependence of soil electrical parameters on the lightning performance of typical wind-turbine grounding systems

The impact of the frequency dependence of soil electrical parameters on the lightning response of a typical grounding arrangement of wind-turbine systems is assessed, based on experimental and simulated results. It was found that the frequency dependence of soil parameters is responsible for decreasing the grounding potential rise of grounding system and, thus, its impulse impedance and its impulse coefficient. This effect is more pronounced with increasing soil resistivity and for typical currents of subsequent strokes. It is also shown that, considering wind-turbine grounding arrangements of typical dimensions, their impulse impedance is expected to be lower than the low-frequency grounding resistance, considering lightning currents representative of first and subsequent strokes.