| With the proposal of my country’s "carbon peak" and "carbon neutral" dual carbon goals,ultra-high voltage and ultra-high voltage direct current transmission,as the key technology of energy transmission in my country,has been vigorously developed.As one of the important electrical equipments in the DC transmission system,the safety and stability of the insulation of the converter transformer directly affects the safe and stable operation of the power grid.Dry-type insulating bushing with epoxy resin impregnated paper as insulating material is widely used in converter transformers because of its advantages of oil-free,maintenance-free and high safety compared with traditional oilpaper insulating bushings.At present,the research on epoxy resin impregnated paper materials mainly focuses on the dielectric properties,the influence of ambient temperature and humidity on it,and the creepage-related research mainly focuses on oil-paper insulation.There are few studies on electrical properties.Therefore,based on laboratory epoxy resin impregnated paper material model specimens,this paper conducts related experimental research on interlayer creepage and interlayer creepage after thermaloxidative aging.First of all,this paper designs and builds the interlayer creepage test platform of epoxy resin impregnated paper,which mainly includes the interlayer creepage simulation platform and the interlayer creepage detection and acquisition platform.At the same time,the epoxy resin impregnated paper test sample model was prepared,and the structure of the pressure electrode was designed.After that,the pressure method and method of interlayer creepage test of epoxy resin impregnated paper insulation were determined,and the process of interlayer creepage test and partial discharge data were studied.Through image processing analysis and surface topography analysis,the law and microscopic characteristics of creepage between epoxy resin impregnated paper layers were studied.Finally,a thermo-oxidative aging test method is designed.Through partial discharge analysis,micro-morphology analysis,and surface element analysis,the creepage law and micro-characteristics between the thermal-oxidative aging epoxy resin impregnated paper insulation layers are studied.The main research results show that:(1)The carbon marks of the first three layers of epoxy impregnated paper insulation develop obviously,the first layer has the highest level of carbon marks,and the fourth and fifth layers have very low levels of carbon marks at each stage.In the initial stage of discharge,the first layer of the sample was obviously damaged,with fiber breakage and holes,while the second layer was less damaged,accompanied by a small number of holes.When developing to the discharge burst period,large-area holes and surface cracks appeared in the first and second layers of the sample,and more carbonized holes and surface cracks appeared in the third layer.(2)With the extension of thermal-oxidative aging time,the discharge amount and the number of discharges of epoxy resin-impregnated paper insulation gradually increased.Compared with the microscopic analysis of the interlayer creepage surface without thermal oxidation aging,the thermal oxidation aging of 4 and 8 days has little effect on the interlayer creepage characteristics of the insulation,and the thermal oxidation aging of 16 days and 32 days has little effect on the epoxy resin.The interlayer creepage of impregnated paper insulation has a significant effect.The length of thermal-oxidative aging has the greatest impact on the first layer of epoxy resin impregnated paper insulation,and the effect of thermaloxidative aging time gradually weakens with the number of layers from the inside to the outside. |
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