Research On Rain Characterization Parameters Of DC Composite Post Insulators

The flashover of external insulation equipment caused by rain has become one of the weaknesses of UHV/EHV DC transmission system.There is more precipitation in the area under the jurisdiction of China Southern Power Grid,there are many rainstorm weather in summer,and the rain is mainly short-term heavy rainfall.In recent years,there have been many rain flashover accidents of external insulation equipment in Tianshengqiao,Gaopo,Xingren and Suidong converter stations.The situation of rain flashover prevention for composite external insulation equipment is very severe.The electric field distribution,partial discharge,arc development and rain flashover voltage are greatly influenced by the water columns and droplets on the edge of sheds.The discharge of water columns and droplets between the sheds makes the creepage distance not effectively used is one of the main reasons for rain flashover.Based on the research results of insulator rain flashover,in this paper,the concept of rain characteristics was proposed,and the parameters of the rain characteristics were selected,the test methods of rain characteristics were studied,the rain characteristic tests under different sheds parameters and different precipitation rate conditions were carried out.The statistical characteristics of rain characterization parameters were studied,and the influence of shed parameters and precipitation rate on the frequency distribution of the length of water columns on the edge of large sheds was analyzed.(1)Based on the analysis of weather conditions at the time of flashover accident,the characteristics of short-term heavy rainfall in the southern region and the performance of the artificial rain system in the laboratory,multiple precipitation rates were selected.The overall and local effects of the rain characteristics photos under different exposure time were compared.It was proposed that the exposure time of the camera in the rain characteristics tests should be less than 1/2000 s.The methods and steps for extracting and measuring the characteristic parameters from rain characteristics photos using Image J and Adobe Photoshop were introduced and the calculation formulas were given.(2)The steps of using the Grubbs criteria to test abnormal data of rain characteristics photos were introduced.The probability distribution characteristics of the length of single liquid column at the edge of large shed and the average length of water columns of one shed unit were studied.It was concluded that the length of single liquid column at the edge of large shed conforming to Lognormal distribution,while the average length of water columns of one shed unit conforming to normal distribution.(3)The rain characteristics of different shed units of the same insulator was studied,the results showed that under the same test conditions,the rain characteristic parameters of different umbrella skirt units of the same insulator did not increase or decrease obviously from top to bottom along the insulator axis,but fluctuated around a certain value.(4)The sheds parameters and precipitation rate had influence on the length of water column of large sheds.When the shed spacing increased,the average sheds extended,the diameter of pole increased and the precipitation rate increased,the maximum water column length corresponding to the tail of lognormal distribution fitting curve of large umbrella liquid column length increased.