Effect of nano-sized layered silicate on AC electrical treeing behavior of epoxy/layered silicate nanocomposite in needle-plate electrodes

A layered silicate at 1-10 wt% was incorporated into an epoxy matrix in order to prepare an insulation material for heavy electric equipments using a three roll mill for nanoparticle dispersion, and then alternating current (AC) electrical treeing and breakdown tests were carried out. Wide-angle X-ray diffraction (WAXD) analysis and transmission electron microscopy (TEM) observation showed that the multilayered silicate at 1 wt% was fully exfoliated into nano-sized monolayers in the epoxy matrix, however the silicate layers at over 3 wt% were in an intercalated state. When 1 wt% nano-sized silicate layers were incorporated, the tree initiation time in the needle-plate electrodes geometry was 18.0 times longer and the breakdown time was 16.7 times longer than those of the neat epoxy resin under the applied electrical field of 520.9 kV mm−1 at 30 °C. But these values were in great decline at over 3 wt% of the layered silicate content. These results meant that the exfoliated nano silicates blocked the tree initiation and propagation processes effectively, however the effect largely decreased with the increasing silicate content in the intercalated state.