Effect of moisture on treeing phenomenon in epoxy resin with filler under AC voltage

Epoxy resin is widely used as an insulating material for many electrical apparatuses because of its excellent electrical and manufactural characteristics. It is usually mixed with filler to improve mechanical and thermal properties. From the viewpoint of the insulation system reliability in various electrical apparatuses, it is very important to investigate the relation between the microstructure of these composite materials and the treeing phenomenon. We have studied the effect of moisture on treeing phenomenon in epoxy resin with fillers under AC voltage. In order to clarify the effect of moisture and fillers on the treeing phenomenon, tree propagation was observed under humid conditions. Moisture accelerated the tree propagation. It is suggested that moisture would weaken the electric strength of the resin, leading to the acceleration of tree propagation. In addition, it was found in the filled specimen that the interface easily splits when moisture was introduced. However, even when the specimen contained moisture, it is seen that the filler still suppresses the tree propagation.