Tree Propagation and Partial Discharge Phenomena of Nanocomposite Epoxy

Tree propagation and partial discharge phenomena in nano-filled epoxy under the application of 50-Hz sinusoidal wave are studied. Silica particles whose diameters are 12 nm are filled in epoxy samples by 5 wt% and 10 wt%. Trees in a pure sample and a 5-wt% sample propagate and approach close to the grounded electrode. On the other hand, a tree in a 10-wt% sample stopped without approaching close to the ground. Luminescence of a partial discharge is also investigated. In a pure sample and a 5-wt% sample, luminescence of partial discharges is observed at the only tree tip. On the other hand, luminescence of a partial discharge in a 10-wt% sample is observed from the needle tip to the tree tip. The result suggests that conductivity of trees in nanocomposite epoxy becomes lower than that in pure epoxy. The difference of conductivity is an important factor to suppress propagation of electrical trees. SEM observation of tree walls shows that nano particles are attached to the tree walls in a nanocomposite sample. With these results, we propose the suppression model of tree propagation in a nanocomposite sample. In a nanocomposite sample, nano particles on tree walls prevent trees from carbonization, in other words, becoming conductive. Therefore, energy of a partial discharge hardly concentrates only at the tree tip in a nanocomposite sample because partial discharges in trees occur from the needle tip to the tree tip.