Influence of absorbed water on volume resistivity of epoxy resin insulators

Water absorption behavior of disk-like mineral filled epoxy resin insulators is determined by measuring the change of weight at different relative air humidity. Bulk current measurements with epoxy resin samples which have reached their absorption equilibrium during storage at various relative humidity are carried out and a significant decrease of the volume resistivity is observed with increasing water content. Water absorption into the epoxy samples follows Fick´s Diffusion Law (diffusion coefficient D = (5±3)·10^-9 cm²S^-1). A model based on Fickian diffusion has been developed which allows for the simulation of the dynamic degradation of the volume resistivity during humidity storage. The results of simulation are verified by periodic volume resistivity measurements with epoxy resin samples during 99% relative humidity storage.