| Surface flashover on epoxy resin in GIS driven by very fast transient overvoltage(VFTO)may cause a certain degree of damage on the insulating material surface,which can further affect the insulating performance of the equipment.In this paper,epoxy resin was taken as the research object,and characteristics of surface flashover driven by microsecond pulses in air and SF6 were studied.Furthermore,physical and chemical properties of the material surface after surface flashover under different conditions were investigated.Firstly,an experiment setup used to study the surface flashover characteristics of epoxy resin was built.The results showed that in air and SF6 environment,the flashover voltage of epoxy resin increased with the increment of electrode distance and gas pressure,but decreased with the augment of power supply repetition frequency.In the process of surface flashover,it was found that the developing path of electrical arc along epoxy resin surface was confined to an oval,and there were about 20 percent of arcs which did not develop cling to the material surface.With the increase of applied voltage,the spectral intensity became stronger,and the number of charged particles included in the reaction increased,leading to more serious damages on the epoxy resin surface.In addition,physical properties of epoxy resin were tested by AFM and SEM after surface flashover under microsecond pulses.The results showed that after the surface flashover in air,granular bulges were generated on the material surface.With the accumulation of aging energy on material surface,the particles increased both in number and size,leading to the growing of surface roughness.In the aging process,the molecular chains of epoxy resin on the surface were broken,resulting in the occurrence of oxidation and carbonization.During the aging of epoxy resin in SF6,the morphology transformation of material surface was a dynamic process,which could sequentially evolve into crack zone,then changed to granular zone,flocculent-granular zone,and flocculent zone.What’s more,the damage of discharge aging occurring at the area in front of the electrode was serious,whereas the material surface below the electrode was hardly affected.Even so,under the impact of arc,there was little change to the crystal distribution of alumina particles as the packing of epoxy resin.The insulating performance and charge of epoxy resin surface were tested and then analysis their relationship with the surface properties.Results showed that the flashover aging treatment had a different effect to the surface charge dissipation rate,with the negative higher than the positive.Though surface flashover on material surface caused some degree of damage on the material,the insulating performance of insulator were scarcely influenced.What’s more,in the process of epoxy resin’s aging under the condition of air,the macromolecular chain on the material surface ruptured,resulting in reacting with oxygen in air and generating some chemical groups with low trap level on the material surface.To some extent,that would speed up dissipating surface charge,and the insulating performance of materials could be enhanced.The surface of epoxy resin was divided into no-particle area and particle area after aging in SF6,which showed that no-particle area on the surface was less damaged,but the particles area had huge change in element content.More specifically speaking,in the early process of aging,oxidation and decomposition on particles area of epoxy resin occurred,with oxygen content gradually rising.Along with the development of aging,fluoride phenomenon for organics was more serious,and the charge dissipation rate on material surface was accelerated.In conclusion,the given environment,properties of material surface and the point of junction between material and electrode collectively determined the change of the insulation performance.Therefore,study related to the repercussions of surface flashover and aging characteristics of epoxy resin has important practical significance for assessing the impact of flashover on insulating materials within GIS. |
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