Effects of Thermo-Oxidative Aging on the Dielectric Property and Electrical Breakdown of Epoxy Resin Using in High-Voltage Equipment

In this article, the effects of thermo-oxidative aging on the dielectric properties of epoxy resin are investigated at 180 °C under different durations. In the early stage of aging (0–168 h), the dielectric properties of epoxy resin are slightly improved, which are characterized by the reduction of dielectric loss and conductivity and the slightly enhancement of breakdown strength. These are attributed to the molecular rearrangement and postcuring reactions inside the epoxy resin, as evidenced by the improved glass transition temperature. With the continuous increase of thermal aging time, oxidative decomposition and scission reactions start to dominate. The cross-linked network of epoxy resin is gradually destroyed, leading to the increase of carrier quantity and the reduction of trap energy level and density. The dielectric polarization and charge injection are intensified, while the partial discharge initiation voltage (PDIV) and breakdown strength are decreased significantly. After aging for 1440 h, the conductivity could be increased by 59.64%, and the breakdown strength is decreased by 18.14%. The insulation performance of epoxy resin is determined by the competition results of the molecular rearrangement, postcuring, and oxidative cleavage reactions during thermal aging, which could provide a theoretical basis for the aging assessment of epoxy resin for high-voltage applications.