Degradation Model of Oil-paper Insulation Regarding Levelling-off DP and Time-varying Temperatures

The Degree of Polymerization (DP) of oil-paper insulation decreases gradually during thermal ageing, determining its remaining service life. Previous studies have found that under certain aging conditions, there is a lower limit value for DP called Levelling-off DP (LODP), which significantly impacts the thermal life of oil-paper insulation. Although many studies have used second-order kinetic models for cellulose degradation to describe the changes in DP with aging time, there needs to be more research on the factors affecting LODP. This article analyzes the influence of material types and aging temperature on LODP and finds that the initial aging rate k10 and ratio k10/k2 in the second-order kinetic model satisfy the Arrhenius equation concerning aging temperature. Therefore, an improved kinetic model considering LODP values has been proposed and can be used to quantitatively calculate the variation of DP with time-varying temperatures, thereby predicting the insulation life loss of transformer hotspots under time-varying loads.