Abstract
Offshore wind turbines (WTs) are frequently exposed to the risk from lightning, storm, and waves. As a kind of fixed foundations, jacket foundation can effectively reduce the correlatively risk and loss. In order to provide more information about the lightning protection of jacket foundation, a simulation model has been built by simplifying the hollow steel tubes into a series of solid steel cylinders. And some conclusions on the grounding resistance of jacket foundation have been summarized in this paper by using the GSSAS (Grounding System Safe Analysis Software). According to the simulation results, the actual influential factors of grounding resistance, including the depth of seawater, the thickness of clay layer and the resistivity of gravel layer, have been analysed and compared. It is found that the grounding resistance is influenced most severely by the depth of seawater. In addition, the values of sea surface potential have been calculated by the software GSSAS and the three-dimensional diagrams of potential distribution have been mapped out.
Highlights
The common foundation structures of offshore wind turbines are the monopile and gravity foundation, but they are generally adapted for the depths of seawater about 0~15 m [1]
If an offshore wind turbines (WTs) is struck by lightning, the jacket foundation will be surrounded by the virtual curve of potential on the sea surface, and the high potential may be quite dangerous for people and other offshore WTs
By using the professional GSSAS, the simulation research takes account of the typical factors that influence the value of grounding resistance
Summary
The common foundation structures of offshore wind turbines are the monopile and gravity foundation, but they are generally adapted for the depths of seawater about 0~15 m [1]. The grounding resistance and sea surface potential of jacket foundation need to be closely concerned in the electrical design and protection. It is necessary to explore the grounding resistance and sea surface potential of offshore WTs. The multi-layer structure below sea level is taken into account and the simulation model of jacket foundation has been built by using professional software GSSAS [11,12]. GSSAS is employed to compute the value of grounding resistance according to the influential factors and it is used to draw the three-dimensional distribution diagrams of sea surface potential. Calculation data and simulation results show that the value of grounding resistance and the distribution of sea surface potential are mainly affected by the depth of seawater, the thickness of clay layer and the resistivity of gravel. Additional, the marine environment in different countries and regions is different, and the values of grounding resistance need to be carefully studied according to local conditions
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