| The external insulation design of existing domestic and international power transmission projects mainly depends on the tolerance characteristics of natural and artificially contaminated insulators.With the development of industry,atmospheric pollution has become increasingly serious.The previous design concepts cannot meet the external insulation requirements of power systems under special circumstances.In particular,in recent years,fog and haze have become more frequent,and external insulation of transmission lines is facing severe challenges.The main performances are as follows:1)The UHV transmission project unavoidably passes through the fog and fog area,and the practical operation experience of the transmission line in the fog and haze-fog environment is very scarce,and the natural contamination accumulation status of the insulator cannot be obtained.In particular,the characteristics of particledeposition on the insulator surface of the transmission line are unclear.2)Under the haze-fog environment,the factors that affect the natural fouling of insulators are relatively complex,and their natural contamination characteristics are difficult to describe by mathematical models.3)The droplets easily adhere to the surface of the insulator under the haze-fog environment,causing electric field distortion of the insulator,reducing the dielectric strength,and prone to pollution flashover.This article focuses on the problems encountered by insulators in a hazy environment and begins the following sections of work.First of all,a long-term,large-scale contamination and atmospheric sampling of the insulators in the haze-fog environment are obtained.The ESDD and NSDD of the insulators under different voltage types,voltage levels and voltage polarities are obtained.The atmospheric parameters of smog along the line were analyzed,including particle size distribution,inorganic ions,and metal particulate content.The results show that the degree of contamination on insulator surface is higher than that under normal air quality in smog environment,and the accumulation of contamination on DC negative insulator is more uniform.The size of contamination particles with more than 90%of DC transmission lines is within 50μm.The contamination particles of AC transmission lines are generally larger than that on HVDC transmission line.When the voltage level increases,the soil in the middle of the insulator string tends to increase.The main water-soluble cations of the pollution are Ca2+ and NH4+,and the anions are mainly NO3-and SO42-.From the actual working environment,the parameters for operating the insulators in a variety of haze-fog environments were obtained,which provided a basis for the laboratory to simulate the haze-fog environment and to study the flashover characteristics of the insulators in the haze-fog environment.Secondly,from the perspective of wind speed,wind dip angle and particle size,the soil fouling characteristics of different parts of the insulator were studied,and a particle impact rate prediction model based on BP(Back Propagation)neural network was established.Through a period of 4 years of natural fouling test,the simulation was verified.The results show that under the haze-fog environment,the force of the electric field will accelerate the deposition of pollutant particles.However,as the wind speed increases,the influence of the electric field force decreases.When the wind speed is less than 1 m/s,the electric field force plays a significant role,when the wind speed is more than 1 m/s and the particle size is less than 80 μm,the wind speed has little effect on the surface area.When the particle size is more than 80 μm,the impact rate of the upper surface particles decreases with the increase of wind speed.When the wind inclination angle is not zero,the airflow increases upwards.The surface particle impact rate increases,and the airflow downwards increases the impact rate of the upper surface particles.Thirdly,the weights of the sixteen impact factors related to ESDD and NSDD were analyzed based on Mutual Information(MI)theory and Random Forests(rfs)algorithm.At the same time,based on the influence factors of high weight,a regression method based on rfs as a function to estimate the natural fouling of insulators was proposed.Based on the natural fouling test,the rfs regression algorithm was verified to predict the reliability of insulators ESDD and NSDD.The results show that:voltage level(vl),voltage type(vt),polarity/phase(pp)have a significant impact on ESDD.Coastline distance(d),wind speed(wv),and rainfall(rf)have a significant impact on NSDD.The trained rfs regression model can effectively predict the insulator ESDD and NSDD.Finally,a surface flshover test platform was built,and the dynamic characteristics of droplets on the surface of silicon rubber under haze and fog environment were recorded using a high speed camera.Combining with Ansys Maxwell,the influence of haze on the electric field distortion of the insulator surface was simulated.Based on the Comsol multiphysics simulation,the droplet movement and splitting characteristics were explained.The results show that after the deposition of the haze-fog,the surface conductivity of the insulator increases,and the flashover voltage along the surface decreases.The droplets deposited on the surface of the silicon rubber are deformed,moved,even split by the electric field force.,the newly formed three-phase junction is prone to discharge,affecting the strength of insulation.This paper summarizes the natural contamination characteristics of insulators of different transmission lines under the haze-fog environment,and derives the weights of the influencing factors of ESDD and NSDD.Through the established regression random forest model,the quantitative prediction of the degree of contamination on the insulator surface is achieved.The rate prediction model analyzes the flow field characteristics of rod-shaped composite insulators under haze-fog environment.Through the built-up surface simulation model of creeping haze,the characteristics of creeping discharge under haze-fog environment are analysed to provide reference for the study of external insulation of transmission lines. |
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