From thermodynamic to phenomenological multi-stress models for insulating materials without or with evidence of threshold (XLPE cables)

Abstract

In this paper, the relationships between phenomenological and thermodynamic models used for characterization of insulating materials aged under multiple thermal-electrical stresses are derived. Phenomenological models fitting life lines for insulating materials that show or do not show a tendency to threshold are considered and compared with appropriate thermodynamic models. The thermodynamic models account for the electrical field action with an activation-energy-lowering factor that differs for threshold and non-threshold materials. The dependence of this factor on applied stresses is thoroughly explained. The models are applied to results of life tests performed on XLPE cables. The comparison shows very good agreement of test data with the threshold model when a suitable temperature-dependence of model parameters is assumed.