| Gas insulated switchgear and gas insulated transmission line are important equipments of high voltage direct current transmission,in which SF6 is adopted as insulation gas and the phenomenon of surface flashover restricts the miniaturization and safe operation of the equipments.The greenhouse effect of SF6 and safe operation are gradually being concerned by the power research and operation department.N2 and mixed gas of SF6/N2 with high pressure is the best alternative to pure SF6.This paper is supported by Natural Science Foundation of Hebei Province?E2015502081?“Study on the surface characteristics of epoxy resin in SF6/N2 with high pressure before and after surface flashover”,Fundamental Research Funds for the Central Universities?2016ZZD07?“Research and application of surface morphology and chemical modification of insulating material”,State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources?LAPS16009?“Effect of aging damage on the surface charge accumulation of insulating materials under DC voltage”.The surface flashover performance of epoxy resin in SF6,N2 and their mixed gas was studied.The main research contents are as follows:Firstly,the existing surface flashover test platform was improved,study on the factors of flashover voltage was carried out and the experimental operation scheme was determined.The effects of different locations on the surface of the epoxy resin and the different flashover times,boost rate,time interval of the applied voltage and the mixing time of the mixed gas on the flashover voltage were studied.The specific scheme of each factor was determined in the experiment.Secondly,in N2,SF6 and their mixed gas,the experimental study on the flashover characteristics of epoxy resin under different types of electric field and different gas pressure was carried out.In the environment of N2 and SF6,four kinds of electric field with different uniformity were formed by rod-rod,rod-plate,pin-pin and pin-plate electrode.Different electrode distance,different gas pressure and different power supply were set up to explore the change rule of flashover voltage.By changing the proportion and pressure of the two gases,the flashover performance of the mixed gas was obtained.The flashover voltage was obtained under different conditions,and the insulation strength of the pure SF6 gas can be obtained by properly increasing the pressure of the mixed gas.And then,surface physical and chemical properties of epoxy resin were analyzed based on the morphology and chemical testing methods.SEM and AFM were used to test the surface topography of different damage degree and different damage locations.Then the main chemical groups and chemical elements on the surface of epoxy resin were tested by FTIR and EDS.The results showed that there were significant differences in the surface morphology of N2 and SF6;with the increase of the number of flashover,the organic chemical groups on the surface of epoxy resin gradually decreased,and inorganic filler of material surface was gradually highlighted;the surface damage of epoxy resin was caused by the surface flashover,flashover voltage was slightly reduced.Finally,based on the AFM test data,fractal,surface power spectrum density method and wavelet method were used to analyze the microstructure of the surface of the material.The AFM test chart was converted to grayscale,and then the changes of morphology from different angles were reflected by the three methods.The calculated results showed that the fractal dimension decreased with the increase of the number of flashover,and the self similarity of the surface topography was improved;the surface power spectrum was increased and there was an obvious difference in the electrode connecting direction and perpendicular to electrode connection direction after flashover;the energy value of each node was increased after wavelet decomposition. |
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