Effects of inorganic fillers on withstanding short-time breakdown and long-time electrical aging of epoxy composites

Inorganic fillers were added to epoxy resin for preparing micro and nano filler/epoxy composite, and then the breakdown strengths, depths of erosion caused by partial discharge, and electrical tree experiments of composites were investigated. It was found that the loading of micro fillers usually decreases the short-time breakdown strength (breakdown under a continuously rising voltage) of the composites. On the contrary, it increases the ability to withstand long-time electrical aging (erosion or breakdown caused by electrical tree under a discontinuously rising voltage or constant voltage) of the composites. The effect of inorganic fillers in suppressing the electrical tree or erosion channel propagation in the composite is different during the process of withstanding short-time breakdown and long-time electrical aging. Defects are introduced during the mixing of fillers and epoxy resin, which play a role to decrease the short-time breakdown strength and accelerate long-time electrical aging. It is concluded that micro and nano inorganic fillers can suppress the electrical tree channel propagation and erosion caused by partial discharge, whereas defects play the opposite role in composites. Two opposite effects of inorganic fillers and defects exist simultaneously during the process of electrical aging and breakdown; whereas inorganic fillers play a primary role in long-time electrical aging, defects play a primary role in short-time breakdown. (C) 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.