Influence of filler added into one side of insulation layers on electrical treeing characteristics

To understand the electrical treeing properties at the interface, the treeing breakdown test was performed. The effect of the filler added into one side of the insulation layers on the treeing breakdown was investigated. Time to breakdown of the epoxy/epoxy sample including the silica fillers at upper epoxy resin layer became shorter than that not-including the silica filler as the filler content increased. The addition of the filler increased the propagation speed with a few branches, accelerating tree propagation. As the filler content further increased, the time to breakdown epoxy/epoxy sample including the silica fillers at upper epoxy resin layer became longer than that not-including the silica. The increase in the effective length between electrodes, field relaxation of tree tip and dispersion of discharge energy were caused by the many branches due to high filler content. From these results, it was clarified that the filler on the insulation layer caused the change of the tree structure around the interface of the multilayer.