Grounding impedance characteristcs of gravity foundations of offshore wind turbines

Wind power is considered as a potential energy to solve the power shortage. The wind farm and wind power generation develop quickly these years. Due to the influence of the tides which determined sea level, the grounding impedance of wind turbines will be in a greater fluctuation and even reach a dangerous figure. So it is necessary to research on the grounding impedance of offshore wind turbines especially in intertidal zone. In this paper, steel gravity foundations of offshore wind turbines were selected as calculation models using CDEGS software. Various affecting factors were considered, including depth of seawater caused by tide, soil resistivity, thickness of claypan and gravel according to the characteristics of area of wind farm. Different size, material, and installation method of gravity foundations are also considered and calculated. Simulation results show that grounding impedance is influenced most severely by depth of seawater. On the basis of calculation, the limit values of grounding impedance in some kinds of area that wind farms locate in are given. The following shows relations between grounding impedance and depth of sea water in different soil resistivity area for example.