Research On Optimization Of Shed Parameters And DC Pollution Flashover Performance For Composite Post Insulators At High Altitude

In order to improve the pollution flashover performance of composite post insulators,increase the outdoor insulation degree of UHV convert stations, this paper had systemicoptimized shed parameters of composite post insulator under the condiction of DC voltage athigh altitude areas, and comprehensive investigated the DC pollution flashover performance oflarge-size composite post insulator (5composite post insulators series connection) at highaltitude. The main contents are as follows:(1) Based on the theory of electromagnetic field and finite element method by usingsoftware ANSYS, the simulation models of large-size contaminated composite post insulators(5composite post insulators series connection) with different shed shapes were estabilished.By analysising the change of surface’s average electric field and the non-uniform electric fieldcoefficient, the relationship between the sheds parameters of composite post insulators and theelectric field distribution along the insulator surface were studied, and the range of shedparameter’s optimal value has been given, provided the theoretical basis for the experimentalstudy on shed parameters optimization.(2) Based on the optimal range of simulation, the specimens of composite post insulatorswith different shed parameters and material were made, and the natural contamination tests ofthese specimens were carried out in National Engineering Laboratory for Ultra High VoltageEngineering Technology (Kunming) at high altitude area (2100m), all the specimens wereplaced in the natural environment9months. By comparing the difference of value of surfacecontamination, the relationship between the sheds parameters and the nature contaminationperformance were analyzed, investgated the shed parameters and material how to effect on thenature contamination performance, and provides optimal plan for the selection and design ofcomposite post insulator.(3)50kinds of composite post insulator with different shed parameters were presented,and artificial pollution tests were carried out on these specimens in National EngineeringLaboratory for Ultra High Voltage Engineering Technology (Kunming). By analysising theresult of artificial pollution tests, the relationship between shed parameters and DC flashovervoltage had in-depth studied, the most optimal value of shed parameters has been given, put forward the optimum ratio value of large shed overhang and large shed spacing. Based on theminimum mean square error method, the quadratic function relationship between shendoverhang, shed spacing and dc pollution flashover voltage was built and fitted. This paper alsodiscussed the mechanism of which how the shed parameters effect on dc pollution flashoverby analysising the ultraviolet discharge characteristic, the development of arcs along theinsulators surface and the utilization of creepage distance.(4) Take the composite post insulator of most optimal shed parameters as specimens, thedc pollution flashover performance of large-size composite post insulator (5composite postinsulators series connection) was comprehensive investigated, the curve of dc pollutionwithstand voltage of large-size composite post insulator with two types shed shapes wasobtained, analysised the relationship between the pollution factors (ESDD、NSDD andpollution uneven distribution) and the dc pollution withstand voltage, then compared the curveof dc pollution withstand voltage of short-size specimen and large-size specimen, discussedthe relationship between the length of composite post insulator and the DC pollution flashovervoltage. Meawhile discussed the mechanism of which how pollution factors effect on dcpollution flashover by analysising the ultraviolet discharge characteristic, the development ofarcs along the insulators surface.(5) Determine the contamination level of convert stations by analysising the compositionof contamination, then according to the result of optimal studies, and using the test date oflarge-size composite post insulator (5composite post insulators series connection), theinsulation distances of composite post insulator for ChuXiong±800kV UHV DC convertstations has been designed, and the insulation distances of composite post insulator for FuNingand YongRen±500kV DC convert stations also were estimated by pollution withstand voltagemethod.