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The Role of Theory in Understanding Space Charge Distributions

Space charge generation in insulating polymers is a complex process involving many interlocking synergistic processes, which make the understanding of its equilibrium distributions and their evolution a very challenging problem. It is argued that the general features at equilibrium can be determined from fundamental physics, though the details depend upon many factors that are incompletely known and may even vary from sample to sample. The difference between dynamic and thermodynamic equilibrium is explored, bringing into prominence the limited timescale of laboratory experiments compared to time under service stress. The major importance of the electrode contacts of an insulating system is highlighted and it is shown that our understanding is not yet sufficient to describe injection and extraction in a simple mathematical manner. It is suggested that a way forward is to define an intermediate zone between the electrode material and bulk polymer. The effect of contact charge and carrier barriers at dielectric-dielectric interfaces is briefly touched upon, and the perils of ambiguous interpretation outlined. Finally a route map for the future is presented.