In this investigation, four kinds of epoxy/silica nanocomposites with different sizes of nano-fillers were experimentally investigated on treeing breakdown lifetime. The nanocomposite specimens used included 3 wt% nano-fillers of 12, 40, 90 and 300 nm in size, and were prepared with and without silane-coupling agents for evaluation. According to SEM observation, nano-fillers were considered to be well dispersed in all the specimens used. As a result, it was found that the nanocomposite specimens with 12 nm size fillers own much longer tree breakdown time than neat epoxy and other epoxy nanocomposite specimens under applied voltage of 10 to 30 kVrms. Difference in lifetime between neat epoxy and nanocomposites with 12 nm size fillers tends to be enlarged, as applied voltage is lowered. Furthermore, it was confirmed that the addition of coupling agents would help increase lifetime. The coupling in the interfaces is considered to suppress tree propagation in this process.
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