Abstract
In general, a polymer insulator applied high voltage reaches a complete breakdown through a propagation of electrical trees. We showed in previous paper that magnesium hydroxide has a suppressive effect on the growth of an electrical tree and that the lifetime of the polymer insulator can be improved. Hydrated alumina, metal hydroxide, also has the property of releasing crystallization water at a high temperature. Therefore, we have studied the effects of the hydrated alumina on treeing this time. As a result, it was confirmed that the voltage lifetime of epoxy resin with 30 phr of aluminum hydroxide was approximately 100 times longer than that of the neat epoxy resin. Moreover, amorphous part of hydrated alumina was detected by the electron beam diffraction analysis of the fillers located contiguous to electrical tree, and it showed that a endothermic reaction of hydroxide alumina was took place. The suppression of the tree growth by fillers was generally explained by a barrier effect, but the fillers such as hydrated alumina that generated the endothermic reaction have another mechanism for suppression of tree growth.
