Abstract
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.
