Comparison of two schools of polymeric ageing models: Causes and effects of space charge

One of the most significant current discussions in insulation materials is the influence of space charge on electrical ageing processes. The space charge observed under both dc and ac high voltage makes the role of space charge in electrical ageing increasingly difficult to ignore. A considerable amount of literature has been published on electrical ageing models with different physical mechanisms. This paper will review a number of models in association with the effect of the presence of space charge, but will not seek to treat space charge explicitly. Rather, space charge will be considered implicitly as an ageing effect in some models, even though it can be argued that it is both a cause and a consequence of progressive physical and chemical changes within the material in other aging models. The validity of the model will be examined to analyze their effectiveness and the difficulties that may occur in the prediction process is explained, which may reduce the accuracy of the predictions of each approach. These models are classified to two schools of thoughts which are based on the time function of the Eying rate equation and adjusted to demonstrate the physical mechanism for each model. The models that fall within the scope of this study are fitted with experimental data with appropriate parameters values for each model. Therefore, the physical mechanisms of life-expression of each model cannot be critically valid for all insulation materials.