Electrochemical Changes in Epoxy Resin Due to Thermal Aging and Their Effect on Electrical Tree Growth

Thermal aging causes electrochemical changes in a polymeric dielectric, instigating the formation of microvoids and oxidized carbonaceous layers. These voids increase in number and size with aging time. This and other chemical changes result in weight reduction, change in dielectric constant of the sample, and affect electrical tree growth inside the polymer. The current work aims to understand the electrochemical changes in epoxy resin due to thermal aging and their effect on electrical tree growth. Physicochemical analysis is performed using field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The formation of carboxyl groups and voids encourages space charge accumulation resulting in local field enhancement. Inception of trees occurs in the regions of high field stress. Carbonization of tree tubules due to aging makes the walls conducting and promotes tree growth. Furthermore, thermal aging leads to gap formation and carbonization at the metal–dielectric interface, which also affects the nature of electrical tree growth in aged insulation.