Thermoelectric ageing of cable grade XLPE in dry conditions

In the literature there are many papers that allude to the endurance of dielectric materials subjected to electrical stress. Generally it is noted that the endurance performance is reduced by stressing in moist conditions. However, it is important to realise that moisture barriers are often incorporated in cable designs so that the dielectric actually operates in a dry environment. In this paper we present the results on a series of dry thermoelectric ageing experiments. There is clear evidence of curvature associated with the endurance data. We have subsequently fitted our data to three models, the Thermodynamic Ageing model, the Space Charge Life model and the Electrokinetic Ageing model. All models purport to being physically based. The preferred model and the most satisfactory fits are achieved with the Electrokinetic Ageing model. This model predicts threshold ageing fields in excess of 21 kV/mm. The relative merits of each model are discussed.