Grounding impedance calculation of steel monopile foundations of offshore wind turbines in intertidal zone

The wind farm in intertidal zone develops quickly in these years and it is considered as a potential energy to solve the power shortage. There are few successful constructions of wind farms in intertidal zone in the world, therefore China cannot learn advanced international experience from other countries. Due to the influence of the advance and retreat of the tides, the grounding impedance will be in a greater fluctuation in intertidal zone. So it is necessary to research on the grounding impedance of offshore wind turbines especially in intertidal zone. In this paper, steel monopile foundations of offshore wind turbines were selected as calculation models. According to the characteristics of intertidal zone, various affecting factors were considered, including depth of seawater caused by tide, soil resistivity, thickness of claypan and gravel, size and different material of monopile foundations and depth the pile pumped into ground. 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 are given using CDEGS software.