Electrical Treeing Breakdown Characteristics of Epoxy/ TiO 2 Nanocomposites Influenced by Aggregates of Nano‐Sized TiO 2

Inorganic fillers and additives are commonly used as polymer insulating materials such as an epoxy resin (EP) to enhance the thermal, mechanical, and, in some cases, electrical characteristics. The electrical treeing breakdown test is conducted to investigate the filler addition effect on EP's electrical features containing titanium oxide with nano‐size (nTiO 2 ) and the submicron—a few micros‐sized aggregates of nTiO 2 . EP with a nTiO 2 content of 1 vol% has about a 60% higher treeing breakdown voltage under an AC ramp voltage application and a longer insulation lifetime under a constant AC voltage application than those of EP. Furthermore, the treeing breakdown tests in the multi‐insulation configuration adapted to the practical rotating machine were performed. The enhancement effect caused by adding the nTiO 2 is also confirmed in the multi‐insulation configuration containing the mica sheet and the EP/nTiO 2 nanocomposite. The nTiO 2 filler may capture an electron, leading to the generation and growth of an electron avalanche. The submicron—a few micron‐sized aggregates of nTiO 2 may also improve the treeing property by the field relaxation effects caused by many tree branching, and the increasing impact of the effective distance between electrodes due to the nTiO 2 aggregates as well as the electron capture effect and the barrier effect on the tree channel by filling nTiO 2 . © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.