Research On Electrical Tree Of Epoxy Resin Insulation Material

Epoxy resin is widely used in dry-type transformers, current transformers, SF6high-voltage switchgear and GIS combination electrical insulation parts because of excellent electrical insulation and chemical resistance. With the increase of power transmission capacity and voltage level, electrical tree aging problem of insulation materials become more crucial outstanding. In this paper, the author does experimental research to study the impact of curing temperature, curing time, SiO2additive, thermal aging time and air gap on electrical tree growth characteristics in epoxy resin, it is very important to valuating insulation performance.Experiment uses the needle-plate discharge model, the sample is immersed in transformer oil, digital CCD camera records the growth process of electrical tree. The same curing time, different curing temperature and the same curing temperature, different curing time, analysis the impact of curing temperature and curing time on the electrical tree. It was found that:the characteristic parameters of electrical tree in epoxy resin cured in temperature110℃is better than the ones cured in temperature90℃and130℃; the characteristic parameters of electrical tree in epoxy resin cured in time8hours is better than the ones cured in time10hours and12hours. Epoxy resin is filled with different mass fraction of SiO2, and takes electrical tree experimental and frequency breakdown experiments to analysis the impact of SiO2mass fraction on insulation performance of epoxy resin. It is found that:with the addition of SiO2, the characteristic parameters of electrical tree in epoxy resin is better than the samples without SiO2; with the increase of SiO2content, frequency breakdown voltage of epoxy resin firstly increase and then decrease, and the SiO2mass fraction is3%, frequency breakdown voltage becomes maximum. The epoxy resin samples are thermally aged at90℃temperature for30hours,50hours,100hours and200hours, and takes electrical tree experimental and frequency breakdown experiments to analysis the impact of thermal aging time on insulation performance of epoxy resin. It is found that:With the increase of thermal aging time, the performance of electrical tree and frequency breakdown voltage is decreased. The sample with air-gap in needle electrode takes electrical tree experiment to analysis the impact of air-gap on insulation performance of epoxy resin. It is found that:with the addition of air gap, the electrical tree becomes darker, electrical tree growth becomes faster, the electrical tree has obvious thick pine dry channel, and the dense branched electrical trees develop from the thick pine dry channel.Experiments and date analysis results show that:(1)the moderate curing temperature is helpful to the migration of curing agent and the curing of epoxy resin to make the respond between curing agent and epoxy more fully;(2) With high temperature curing time increased, residual stress after the epoxy curing reaction becomes stronger, and thus affects the performance of the material;(3) Scattering theory and trap model explains the reason why the epoxy resin insulation performance with addition of SiO2becomes better, the role of reunion in SiO2particles makes epoxy insulation decreased with content of SiO2continue increased;(4) with the process of thermal aging time, due to high temperature the structure of materials damage, leading to a decrease in insulation;(5) With air-gap in needle electrode, thermal effects, chemical corrosion and mechanical stress caused by partial discharge is the main reason of the insulation materials damage.