Treeing in Solid Extruded Electrical Insulation

A survey of the literature on the subject of treeing in solid dielectrics is presented. The purpose is to provide an introduction to the subject, some background for the current research work, and a list of references to some of the more rigorous treatments which in most cases have a narrower scope. The trees which grow in insulating materials can be considered in three classifications; electrical trees, water trees, and electrochemical trees. They are all initiated at sites of high and divergent electrical stress and may be aggravated by the presence of moisture, chemical environment, and contaminants. It has been shown that trees will grow in any organic dielectric under appropriate conditions. However, the major portion of the work sUmmarized here has been carried out on polyethylene. This is not because polyethylene is most subject to treeing, but because it is the most popular modern insulating material. It has excellent electrical properties, and an enviable service record. Recent development of improved constructions for electrical insulating systems, including high voltage power cables, and research on formulation of materials and voltage stabilizing additives have shown that improved resistance to treeing is possible.