Impact Mechanism Of Salt Fog Contamination On The Lightning Protection Performance Of Offshore Wind Turbine Blades

Offshore wind power has a broad development prospect in the future.However,the development of large-scale offshore wind turbines meets challenges due to the limits from lightning protection.On the one hand,offshore wind turbines are more likely to be struck by lightning because they are usually located in open environment,with high towers and long wind turbine blades.One the other hand,the blades of offshore wind turbines are prone to be adhered with salt fog after long-time exposure in the marine-atmosphere environment,which will reduce the efficiency of the lightning protection system and pose a serious challenge to the normal operation of wind turbines.In order to improve the efficiency of the lightning protection system,further study about the distribution of lightning striking probability(LSP)for wind turbine blades and the influence of salt fog contamination on LSP is urgently needed.Based on finite element analysis,the co-simulation platform is established by COMSOL&MATLAB.For simplified wind turbine blade model,the development process of downward and upward leader is simulated in the paper.A quantitative characterization method,called lightning striking probability model,is established to calculate the LSP base on the average electric field between downward leader and potential attachment point on blade surface before the return stroke.This model has the universality and is independent of the shape of blades.The simulation results indicate that the areas of highest LSP are distributed in the receptor and conductor area close to the receptor,and the areas nearby receptor and conductor are more likely to get struck by lightning than any other areas on the blade.The positive discharge experiments were carried out,and the experimental results verify the validity of this model.Both simulation and enperimental results indicate that,in the progress of positive discharge,a plenty of charged particles will be accumulated nearby salt fog area due to higher electric field intensity and conductivity,which will improve the LSP of salt fog area,and reduce the efficiency of the receptor.The influence of salt fog on LSP will be more obvious if the salt fog is close to the receptor area.Similarly,the impact of salt fog on LSP is more obvious with the increasing of the scope of salt fog area.Based on the lightning striking probability model,the influence of external factors on LSP is also discussed in the paper.The receptor could protect the blade from being struck by lightning efficiently if the lateral distance between the tip of downward leader and receptor is small.More and more lightning discharges will strike on the receptor area with the increasing of angle of blade.The distribution of lightning striking points is markedly affected by voltage polarity.For negative discharge experiments,all lightning discharges strike on the receptor area,whether the wind turbine blade is contaminated by salt fog or not.