| In recent years,with the requirement of long-distance and large-capacity power transmission,DC transmission technique shows a booming trend.Due to the high voltage level and complex transmission environment of EH VDC/UHVDC transmission lines,the problem of external insulation pollution has become one of the important factors to determine the insulation level of lines,and the problem of electrical insulation under the condition of pollution has become increasingly prominent.Since the ±660kV Yindong DC transmission line was put into operation,there have been many voltage drop operations caused by insulator discharge.The reduced voltage operation of transmission line will not only cause the waste of transmission load and economic losses,but also the frequent occurrence of abnormal discharge indicates that there is a risk of pollution flashover discharge in this area,which seriously threatens the safe operation of power system.Once a large-scale pollution flashover blackout accident is caused,it will bring great losses to the national economy.Therefore,it is of great significance to study the natural pollution accumulation characteristics of DC transmission line insulators,analyze and master the natural pollution accumulation rules of insulators,accurately and quickly predict the surface pollution degree of insulators,and carry out the research on high performance superhydrophobic insulator coating to ensure the safe and stable operation of transmission lines.In view of the problems related to the pollution accumulation characteristics and anti-pollution flashover key technologies of DC transmission line insulators,the following aspects are studied.Firstly,the main pollution types and pollution sources along Yindong line are investigated and analyzed,and the pollution and humidity characteristics are systematically studied.It is found that the pollution sources along Yindong line show great regional differences.In Northwest Shandong,the main pollution sources are agricultural pollution,in central Shandong,and in eastern Shandong,the main pollution sources are agricultural pollution and sea salt pollution.Considering the characteristics of pollution sources and the grade of pollution area,35 contamination test points were determined in Yindong line to carry out natural contamination test of insulators.Through the on-site pollution degree test,the pollution accumulation characteristics of insulators were systematically studied,and the pollution accumulation characteristic parameters such as saturation pollution accumulation coefficient and power carrying coefficient for different years were put forward.The influence laws of the polarity,electric field,insulator type,electrified or not,upper and lower surface and other factors on pollution accumulation were obtained.The results show that the saturated pollution accumulation time of Yindong DC transmission line is 48 months.The average saturated pollution accumulation coefficients of 24 months and 36 months are 1.34 and 1.07 respectively.The average charged coefficient of ESDD on insulator surface is 1.176,and the average charged coefficient of NSDD is 1.395.The average ESDD and NSDD of positive porcelain insulator are about 18%lower than that of negative porcelain insulator.The average ESDD and NSDD of positive composite insulator are 11.9%and 15.9%lower than that of negative porcelain insulator respectively.The surface ESDD of composite insulator is obviously higher than that of porcelain insulator,while the surface NSDD and ratio of NSDD to ESDD of porcelain insulator are higher than that of composite insulator.The results show that the ESDD and NSDD on the upper and lower surfaces of insulators show a "U" shape distribution with the change of spatial position,and the ESDD and NSDD on the lower surface are higher than those on the upper surface.Secondly,the pollution composition of insulator and the composition of ambient particulate matter were studied.By measuring the pollution particle size and ion composition of insulators,the effects of polarity,spatial position,insulator type and upper and lower surfaces on the pollution particle size distribution and ion distribution on insulator surface are studied.At the same time,PM2.5,PM 10 and TSP particles around the insulator were collected to detect the ion composition and metal element composition of atmospheric particles,and analyze the composition of atmospheric particles.Through the canonical correlation analysis of atmospheric particles and insulator pollution,the influence of atmospheric particles on insulator pollution is analyzed.The results show that the average particle size of the positive line insulator is slightly larger than that of the negative line,the average particle size of the conductor side and cross arm side of the insulator string is lower,and the average particle size of the middle section surface is higher.The average particle size of the porcelain insulator is 48.91%higher than that of the composite insulator,and the average particle size of the upper surface of the insulator is 13.85%higher than that of the lower surface.The main ions in insulator pollution are SO42-,NO3-,NH4+,Ca2+,and the distribution of pollution ions on insulator surface is basically the same in different spatial positions.The main ions of PM2.5 and PM 10 are SO42-,NO3-,NH4+,Ca2+,and the main metals are Na,Mg,K,and Ca.Both PM2.5 and PM 10 have significant influence on the pollution composition of insulators,and PM2.5 and PM 10 are the main factors affecting the pollution accumulation of insulators.Then,according to the research results of insulator natural pollution accumulation characteristics and the analysis results of the influence of atmospheric particles on insulator pollution,the influencing factors of insulator pollution are analyzed and the appropriate original variable data are selected.A combined prediction model of insulator pollution degree based on exploratory factor analysis and least squares support vector machine is established.The model is optimized by using non-dominated sorting genetic algorithm.Parameters are optimized to get the final prediction results.At the same time,eight evaluation indexes of the model are used and visualized by radar chart to verify the effectiveness and accuracy of the model,so as to realize the accurate and rapid prediction of the contamination degree of DC transmission line insulators.Finally,a preparation method of superhydrophobic coating on insulator based on sol-gel process combined with the plasma jet treatment method is proposed.The microstructure analysis,hydrophobicity,surface free energy calculation,self-cleaning test,and stability test of the insulator are carried out.The natural contamination test is carried out.The results show that:the surface of superhydrophobic coating has micro and nano scale rough structure,the static contact angle of the surface is 160.15°,the contact angle lag is 0.60°,the rolling angle is 1.8°,the surface free energy is only 0.1421 mN/m,and the adhesion work of water on the surface is about 3.9 mN/m.The superhydrophobic coating shows good superhydrophobic,self-cleaning,mechanical stability,chemical stability and time stability.The surface ESDD of superhydrophobic insulator is obviously lower than that of ordinary insulator,and its minimum value is only 1/5 of that of ordinary insulator.Due to the good superhydrophobic and self-cleaning properties of superhydrophobic insulators,the influence of rainfall on the surface contamination of superhydrophobic insulators is much greater than that of ordinary insulators.In dry season,the surface ESDD of superhydrophobic insulators is 12%and 8.9%lower than that of porcelain insulators and glass insulators,respectively.In rainy season,the surface ESDD of superhydrophobic insulators is 68.5%and 67.1%lower than that of porcelain insulators and glass insulators,respectively.The superhydrophobic insulator has good anti-pollution performance. |
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