| The excellent performance of HVDC transmission in the process of large-scale power transmission across regions has effectively alleviated the problem of uneven resource distribution and economic development in China.It is foreseeable that HVDC transmission technology will be further promoted and applied.However,the electromagnetic environment problems brought by the HVDC projects are worthy of attention.The increase in HVDC transmission lines has caused more and more frequent situations in which HVDC transmission lines are adjacent to agricultural greenhouses.When the HVDC transmission lines are adjacent to the agricultural greenhouse,a large amount of space charges generated by corona discharge will move directionally under the action of electric field.Due to the blocking characteristics of the dielectric film to ion current,the generated charges will accumulate on the surface of the dielectric film,resulting in distortion of the total electric field on the ground.At present,although experimental studies and simulation calculations have been carried out on the charging characteristics of the dielectric film in the ion flow field.However,the lack of research on the influence of different factors on the charging characteristics of the dielectric film has caused errors in the calculation and the actual situation.In order to improve the accuracy of ion flow field prediction when adjacent to agricultural greenhouses,and to reveal the influence mechanism of different factors on dielectric film charging,this paper studies the factors affecting the dielectric film charging characteristics in ion flow field.Based on the parallel plate ion flow generator,this paper builds a uniform ion flow field experimental platform suitable for the study of dielectric film charging characteristics.In order to avoid the measurement error caused by the charge dissipation during the surface potential measurement,a potential regression calculation method based on the single-point potential dissipation curve is proposed,which improves the accuracy of the surface charge distribution measurement.This paper proposes an ion flow field calculation method based on the Upstream FEM(finite element method),which takes dielectric film into account and is suitable for the parallel plate ion current generator,and the validity of the calculation method is verified by experiments.The calculation and analysis of the influence of the dielectric film height on the charging characteristics show that as the height increases,the total electric field decreases significantly.The total electric field is further divided into three components and analyzed separately by using the charge distribution results,revealing the mechanism of the influence of height on the charging characteristics of the dielectric film.Using an artificial climate chamber with controllable temperature and humidity,the influence of humidity on the charging characteristics of the dielectric film is studied.The ion flow field is regulated by adjusting the corona wire voltage,and the electric field at the lower electrode plate is used as a reference to ensure the constant ion flow field under different humidity.Experiments have found that as the relative humidity increases,the surface charge of the film decreases,and total electric field also decreases.By fitting the potential decay curve under the film,the influence of humidity on the surface charge dissipation of the dielectric film is analyzed,and it is found that the higher the relative humidity,the faster the charge dissipation rate and the faster the negative charge under the same conditions.In addition,it is also proved through experiments that the adhesion of droplets on the inner surface of the dielectric film will cause the reduction of the electric field under the film,and the more severe the adhesion of the droplets,the stronger the weakening of the electric field. |
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