Ageing, Space Charge and Nanodielectrics: Ten Things We Don't Know About Dielectrics

Three areas of considerable progress are identified in the area of polymeric insulation since the mid 1990s (i.e. since the inception of the Eric O. Forster Memorial Lectures): the understanding of ageing, the measurement of space charge, and the development of nanodielectrics. The paper proposes a typology to distinguish and define electrical ageing, degradation and breakdown. With reference to the principal theories of thermo-ageing, it is concluded that there is little direct evidence for ageing even though it is likely to exist, at least above a critical field. The capability to measure space charge has improved considerably and this shows considerable potential as a diagnostic tool. Space charge behaviour is extremely difficult to analyse and general predictions may be impossible in practice. It is, however, necessary to control space charge accumulation in HVDC systems. Nanodielectrics continue to offer promise and understanding is improving in this area, particularly in the development of models of interaction zones around nanoparticles.