Influence of high DC electrical fields on some aging properties of XLPE

The influence of high DC electrical fields (above 40 kV/mm) on some electrical properties and on the morphology of polyethylene (PE) is discussed from published experimental data. As it is well known, the polarization currents obtained under such fields are controlled by space charges. It is then possible to deduce the electrons mobility and concentration as a function of field. We show that the charge concentration thus calculated is in excellent agreement with space charge measurements performed with a modern and sophisticated equipment. The same calculation shows that the significance of the so-called thresholds fields is, at best, debatable. Old polarization measurements predicting recent observations of very strong charge injection are also briefly discussed. IR and positron spectroscopy measurements as well as capacitance measurements tend to suggest that the polymer morphology is modified by high fields. The possible relation with the submicrocavity formation proposed in our aging model is discussed