Simulation on variation of electrical insulation parameters in predictive test caused by insulation aging of power transformer

The lifetime of oil-immersed power transformers is mainly determined by the condition of their own insulation systems. The predictive electrical insulation test is an important routine method to estimate the insulation condition. The test results are generally influenced by the aging of oil-paper insulation in transformers, but the effective study on how and what degree the results are influenced is still not developed at home and abroad. This paper simulates the relationship between the aging condition of oil-paper insulation and the predictive electrical insulation test (insulation resistance R60s, absorption ratio K, polarization index PI, capacitance C and dielectric dissipation factor tan δ) results based on the extended Debye model, with a set of parameter values of the equivalent model from an oil-immersed power transformer deduced by the researcher abroad. The simulation results show that the influence factors on the electrical insulation parameters are complicated, and the aging processes of solid insulating materials and oil have definitely different effects on the parameters. The aging of oil has little effect on the parameter values of R60s, PI and C, increases the value of tan δ a little and that of K. But the aging of solid insulating materials evidently decreases the values of R60s, K and PI, increases the value of tan δ a little, and has little effect on the value of C.