Understanding electrical trees in solids: from experiment to theory

The author reviews how far we have advanced in being able to relate experimental observation to physical theories. He concentrates on the inception process and the first stage of propagation because these are the areas in which most progress has been made, although even here there are unresolved problems. It is convenient, as well as conventional, to start at the beginning with tree inception. In this way the various mechanisms whereby energy can be transferred to the solid polymer to create damaged regions, can be introduced and discussed in the light of experimental data. For the propagation of the tree structures, this prior discussion is used to provide the background to the mechanistic features involved, so that we can concentrate upon the fascinating topic as to why tree structures have the form that they do.