The physico-chemical origins and nature of space charge in insulating solids under electrical stress

There is increasing interest in understanding the characteristics of excess charge in insulating polymeric materials. This interest arises not only from the conviction that such charge is conducive to failure of the insulation but also from the increasing ease and sophistication with which the spatial distribution of such charge can be detected under techniques with acronyms such as LIPP, LIMM, PEA and PWP. In spite of this growth of interest the descriptive models for the charge and its interaction with the polymeric environment frequently lack detail and tend to be confined to macroscopic concepts based on Poisson's equation and the classical ideas of conduction. The present aim is to consider in more detail how charge might exist and move in the insulating solid polyethylene and how it might transfer across the polyethylene-metal interface at an electrode. Polyethylene is chosen, not only because of its importance as a high-voltage insulation but also because its complex morphology introduces features, which are very much at variance with the classical concepts of a bland dielectric.