Degradation of insulating materials under electrical stress

An avalanche of physical and physicochemical phenomena, often self-sustaine d, leads to the end of life of an insulating material. The collapse of the insulating role of a material is mostly due to the electrical field stress. The path leading from the catastrophic situation, the breakdown, back to i ts origin is followed in the present paper. A defect, pre-existing or creat ed by the in-service stresses, gives rise to an ionization process in a vol ume bounded by insulating walls. With time the process does not remain iden tical due to both changes in the material and gas evolution, which makes it difficult to interpret the detected electrical signal. The end of life wil l occur through microcracks in which new discharges are initiated, activati ng the propagation of these structural failures. This change of structure o f the insulating material when due to the existence of water molecules will lead to the same kind of final degradation. The polymeric insulating mater ials could contain additives but they lead only to a partial healing. From polymers as little complex as the PE used in cables, assuming that there is no pre-existing defect, one endeavors to understand how a microstructure r eacts with a local field or accumulated charges. The present paper summariz es the thoughts of the author pertaining to the problems of aging and diele ctric breakdown in organic insulating materials, processes often given a co ncrete form through experiments.