Comprehensive diagnostic and aging assessment method of solid insulation in transformer

Up to now, the diagnostic methods and criteria for operating oil-immersed power transformers are still under research. Besides the investigation of diagnostic methods for solid insulation in transformer, quite a lot of data collected from the in-service transformers under different condition included the data of failed or defected transformers have been analyzed systematically in this paper, such as its furfural concentrations, dissolved gases in oil, the degree of polymerization of insulating paper and pressboard, etc. Statistic analyses or the membership functions had been carried out to reveal the relationship between the contents of furfural or gases in oil and the aging of solid insulation. And the life expectancy of power transformer is studied. Finally a comprehensive diagnostic method is put forward for the aging assessment of solid insulation. The examples of application show the method is effective and easy to apply for the operating transformers.