Electrical tree propagation along barrier-interfaces in epoxy resin

The propagation of electrical trees along interfaces in epoxy resin is described. The electrical trees grew in needle-plane samples with and without internal barriers up to the final breakdown. The barrier materials glass, mica and PTFE had been chosen because they have significantly different bond mechanisms to the epoxy resin as well as being common materials in various composite high voltage insulation systems. The mechanical strength of the epoxy resin-barrier material systems was determined for the materials tested. The results show that the propagation of the tree along the barrier is dependent on the type of chemical bond and the shear strength between the epoxy resin and the barrier material. The higher the bond strength between the barrier and the epoxy the higher the resistance to electrical tree propagation. Furthermore it appears that the wettability of the barrier materials plays a minor role in tree propagation along them. The results give a better understanding of the failure mechanism of certain composite insulating materials exposed to high voltage.