Research On Lightning Leader Characteristics And Polarity Effects In The Process Of Fan Blade Flashing

With the rapid development of the economy,the demand for electricity is increasing.As a clean renewable energy generation method,wind power has achieved rapid and large-scale development in the world in recent years.However,the lightning disasters have also become increasingly destructive to large-capacity wind turbines in wind farms.Since 90%of the lightning in nature is negative,most of the lightning protection systems are based on negative lightning,and there is very little research on the positive lightning.According to the research and setting of the negative-voltage lightning protection,when the positive lightning is encountered,the problem of insufficient protection margin may occur.Therefore,it is necessary to study the polarity effect of the fan blade flashing process.In this paper,the long gap discharge experiment of solid fan blades is designed and implemented.The experimental results show that the polarity effect is obvious,the discharge path of the positive lightning is relatively scattered,and it is easier to hit away from the tip of the blade.The lightning arrester has high failure rate.The rotation angle of the blade and the position of the high voltage electrode will affect the distribution of the lightning strike point and the discharge channel.That is,the larger the blade rotation angle and the larger the side distance,the higher the interception failure efficiency of the lightning receptor.It has a greater influence on the positive polarity.The conclusions obtained provide a reference for lightning protection design of lightning from different directions for different polarities.The mode in which the line charge and the point charge are combined represents the distribution of charge in the descending pilot channel of the lightning.The stochastic development model of negative lightning pilot is established according to the geometric characteristics of natural lightning and the theory of gas discharge fractal.The simulation results satisfy the geometric characteristics of the lightning pilot discharge,and the validity of the model is verified.According to the development characteristics and polarity effects of lightning pilots,the critical critical breakdown field strength and fractal coefficient are modified,and the positive-state lightning downlink pilot development model is established.The validity of the model was verified by long gap discharge experiments.The model established in this paper can provide a theoretical basis for the optimization and improvement of wind turbine blades lightning protection system design.Based on the long gap discharge experiment,the initial and development processes of the positive and negative leader are summarized.In the case of positive lightning,the upstream leader is the negative leader of the discontinuous step development.In the case of negative lightning,the upstream pilot is a continuously developing positive polarity leader.The reason for the polarity effect is that the upward leader is difficult to start for positive lightning,and it is difficult to develop,and the attraction to the downlink leader is small.The long gap discharge experiment of 1:30 shrinkage 3MW wind turbine model was designed to verify the correctness of the conclusion.In order to study the influence of polarity effect on wind farm layout,the electrical geometry model of multiple turbines is established based on the electrical geometry model of single turbine,and the criterion of lightning shielding between two fans is given.Further research using the criterion shows that when the lightning is positive,the maximum shielding distance between the two fans is small,and the positive lightning protection needs to take stronger measures.The research content of this paper involves many common problems in the process of lightning strike fan blades,and adapts to the major technical requirements of the。current large-scale development of wind farms.The research results enrich the basic theory of wind turbine blade lightning process,and provide theoretical basis and analysis method for the optimization and improvement of wind turbine blade lightning protection system design,which provides a new idea for the layout of large-scale wind farm.