Relation between space charge and polymeric insulation ageing: cause and effect

Recent results and speculations regarding the possibilities that space charges cause ageing in polymeric insulating materials subjected to a DC electric field are highlighted. Referring to polyethylene-based materials, data are reported that show the relation between accelerated degradation of insulation, the amount of space charge and the rate of charge decay. A life model is presented. In addition, it is shown that the amount of space charge, as well as its apparent mobility, can be modified significantly by the extent of ageing under electrothermal stress. It is suggested that the quantities extracted from space charge observation can be used as diagnostic markers.