Comparative assessment of enhancements to wind turbine earthing systems

In this paper, earthing system models for wind turbines are developed under variable frequency and transient conditions. Under high frequency and high resistivity, a fall in the earth potential rise occurs which suggests a strong capacitive effect at these frequencies. For on-shore windfarms, it was found that earthing interconnection of adjacent wind turbine structures is beneficial in reducing transient earth potential rise (TEPR) under impulse conditions. For the on-shore scenario, the benefits of interconnection extend to at least three turbines either side of the struck turbine. However, in an off-shore environment, the benefits of interconnection are less significant due to the low resistivity of the water which limits the effective length to less than that of a typical inter-turbine spacing. It was established that, for high frequency and transient conditions, the magnitude of the potential rise, seen from the point of injection, is significantly higher when the above-ground structure is taken into account. More importantly, the transient earth potential rise at the turbine base is also higher when the model includes the above-ground structure. Enhancements to the wind turbine earthing system are introduced using an insulated conductor in parallel with bare horizontal earth.