Lumped Mechanism for Polymeric Dielectric Degradation Under High Electrical Fields

Abstract

Since the introduction of the first synthetic polymeric dielectrics, several improvements have been introduced in the field of electrical insulation at the same pace that electrical apparatuses have evolved in complexity throughout time. The implementation of polyethylene as an electric insulator in the early 1960s marked an important breakthrough allowing to pass from low-voltage (a few kilovolts) to high-voltage applications (>15 kV) thanks to diverse contributions from engineers, physicist and chemists. Even though the significant improvements achieved in the field, the mechanism responsible for the degradation or aging of polymeric dielectrics is not completely clear as the material is under several types of stresses (e.g. electrical, chemical and mechanical). In the present study a possible mechanism for the degradation of polymeric dielectrics from a chemical perspective is introduced. It is supported on the hypothesis of the occurrence of ionic and excited species inside the microscopic voids present in the material which are caused by the high voltage field the dielectric is typically subject to. Then, we put into consideration the numerous effects of such ionic/excited species on the backbone chain of the polymeric dielectric, and in particular on polyethylene as it is one of the most employed dielectrics on electrical insulation and to its simple molecular structure. A model of the mechanism is subsequently introduced based on a streamer discharge with the inclusion of the surface boundary chemical phenomena.