| Oil-paper insulation, as the most important component of inner insulation of power transformers, endures electricity-thermal-moisture combined aging stress in the long run operation process. The insulation lifetime will decrease, which gives a direct threat to the safe operation of the power transformers. The research about aging characteristic mostly focus on single aging factor currently, but electrical aging characteristic and lifetime model of vegetable oil-paper insulation combined with multi-factor have not attached great attention. Consequently, electrical aging characteristics and lifetime model of vegetable oil-paper insulation influenced by multi-factor were studied, and the primary content of the dissertation includes:①The electrical breakdown and accelerated electrical aging experiments of vegetable oil-paper insulation with different test temperature and moisture content were conducted, and the times to breakdown of oil impregnated paper were obtained. The two parameter Weibull distribution was used to statistic analysis, and the rules of electric filed distribution influenced by temperature and moisture have been revealed. The results show that temperature and moisture have much significant impact on relative permittivity of inslating paper than that of insulating oil gap. Electric field intensity focus more on oil gap whose electric strength is weak, thus it leads to the decrease of breakdown voltage. Electrical aging lifetime data meets all the assumptions and obeys Weibull distribution.②The rules of electrical aging lifetime influenced by temperature and moisture have been analyzed, the lifetime models of vegetable oil-paper insulation considering temperature or moisture content were established, respectively. The results indicate that FALLOU model consider synthetically the effect of electricity and thermal, which is suited to predict the lifetime of oil-paper insulation combined with temperature, prediction error is below 5%. The lifetime curves of oil-paper insulation move left with moisture content increasing. The relationship between the voltage endurance coefficient and moisture content in paper is linear correlation, that is to say electrical aging lifetime of vegetable oil-paper insulation decrease exponentially with moisture content.③The collaborative effect of temperature and moisture on electrical aging lifetime was analyzed. The lifetime general equation of vegetable oil-paper insulation considering temperature and moisture content was established on that basis of two parameter lifetime model. Stepwise regression was used to screen the best lifetime model combining with experiment data. The results show that the acceleration effect of temperature to lifetime attenuation become obvious with the increase of moisture content, and it is the same when it comes to the increase of temperature. It exists synergistic effect between temperature and moisture. The lifetime of paper is influenced exponentially by voltage, temperature and moisture, and lifetime model considering temperature and moisture content fit well with test results. |
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