Research On Accelerated Aging Test Method And Lifetime Prediction Of GIS Seal Rings

Over the last few years,the problem of the aging of seal rings in gas-insulated switchgear(GIS)applications has led to an increasing rate of SF₆ gas leakage defects.However,traditional test and lifetime prediction methods has the shortage of 1)lack of standard test methods,2)mismatch between the aging factors of the accelerated aging test and the actual operating conditions of GIS seal ring,3)lack of an objective sealing failure criterion.In order to solve these problem,the research on accelerated aging test method and lifetime prediction of GIS seal rings was conducted.In this dissertation,a new method of the mechanical property test of GIS seal rings was proposed.The insights for the inconsistency between mechanical and chemical aging rate was studied.The three-factor accelerated aging test method of heat,compression,pressured SF₆ and the leakage rate test method of GIS seal ring were proposed,and the corre-sponding test platform and system were established.The degradation law of the mechanical properties and the leakage rate of GIS seal rings under three-factor accelerated aging conditions were obtained.The sealing failure criterion of GIS seal ring based on compression set was obtained.Details of the work are as follows:1)the research on the test methods of compression set,sealing force and Shore hardness of GIS seal ring.First,the cross-sectional characteristics of the GIS seal rings that has been in operation for 30 years were analyzed.The method of measuring the cross-sectional diameter in the actual compression direction of the seal is studied with a rubber thickness gauge,and is used as the recovered thickness of the seal in the calculation of the compression set.Independ-ent repeated experiments and sensitivity analysis were used to obtain the error of the test method.Then,a special compression fitting with its upper and lower parts automatically paral-leled themselves were developed and installed on the universal testing machine.The attenuation of the compressive force with time when compressing the seal rings was analyzed.The thermal-compression treatment method was studied to accelerate the physical stress relaxation process.Finally,the test method of Shore hardness on the GIS seal rings was studied.The method was to mark a specific position on the seal ring and read after 20 seconds.The error of the test was analyzed through experiments.2)the research on the degradation law under two-factor accelerated aging test.First,the levels of aging factors under the operating conditions of GIS seal rings,including the compres-sion factor,the thermal factor,and the chemical factor were analyzed.Then,the two-factor accelerated aging test platform of thermal and compression for GIS seal rings was built.Seals of two commercial EPDM formula were studied through experiments.The degradation of the mechanical properties of the seal rings were obtained under the accelerated aging test.Then,the residual compression ratio was used to characterize the remaining utility of the compression factor during the aging of the seal rings.The compression set under unit residual compression ratio was derived to explain the inconsistency between the mechanical aging rate and the chem-ical aging rate.Finally,the effect of temperature on the compression set was analyzed.3)the research on three-factor accelerated aging test method and leakage rate test of GIS seal rings.First,a pressured aging vessel(PAV)that can be filled with SF₆ gas during the aging of GIS seal rings was developed.The temperature of the oven was calibrated,and the safety monitoring system was configured.Thus,the three-factor accelerated aging test platform of heat,compression and pressured SF₆ was built.Then,the simulated chamber and the fix-volume cover were developed.A leakage rate test system was established and the novel accumulation method of fix volume covering was proposed.The accuracy of the leakage rate test was then studied through the three-factor accelerated aging test.Finally,the evolution of compression set and leakage rate with aging time were studied under the accelerated aging test where the aging conditions were the combination of the temperature of 120?,105?,90?,the compression rate of 20%,25%,30%and the SF₆ gas pressure of 0.3 MPa.The degradation of the properties was compared to those aged by traditional two-factor accelerated aging.4)the research on the key parameters of the lifetime prediction model including the Ar-rhenius activation energy and the sealing failure criterion.First,the chemical kenetic analysis of seal rings was studied.The Arrhenius activation energy of a certain commercial GIS seal rings under two-factor and three-factor accelerated aging conditions was investigated and cor-rected by the kinetic curve method and the time-temperature superposition method.The failure test of the seal ring was carried out.Under the two-factor accelerated aging test with samples compressed by flanges,4 seal rings leaked and failed.The correlation between the leakage rate and the compression set was analyzed.The end-of-life criterion of GIS seal ring based on com-pression set was then proposed.Finally,the lifetime of the GIS seals under their typical operat-ing temperature was calculated and discussed through multiple test conditions.