Influence of humidity treatment on electrical tree propagation in epoxy resin

The electrical insulation performance of polymeric materials is degraded by humidity treatments or water absorption. An electrical tree is a pre-breakdown phenomenon and constitutes one of the main contributing factors to the degradation of polymers. In this work, the structure and length of the electrical tree in epoxy resin, with/without humidity treatment during curing, was determined by high-resolution X-ray computed tomography (X-CT), using synchrotron radiation. It is revealed from X-CT that the deterioration of the epoxy resin is associated with the conditions of humidity treatment. In particular, the treatment has an effect of enlarging and extending on electrical tree. The ionization potential of material is essential for evaluating the tree-propagation rate in the discharge-avalanche (DA) model. In this study, the ionization potential of the epoxy molecule, with/without water solvent effect, was calculated using by the density functional theory (DFT). The characteristic times of the electrical tree (with/without the humidity effect) were computed, via the DA model and DFT calculations, and these values corresponded closely to the X-CT results.