Investigation of relaxation processes in thermally-aged XLPE cable models

The results of thermally stimulated discharging current (TSDC) and DC isothermal charging/discharging current measurement, performed on pretreated and thermally aged XLPE (cross-linked polyethylene) cable models, are presented. A β relaxation, related to the glass-rubber transition of the amorphous region, and a high-temperature peak, likely due to charge polarization and related to the melting of the crystalline region, were found in the TSDC spectra. A TSDC peak with a maximum at 55°C appeared with thermal aging. This process was also pointed out by isothermal discharging current measurement and was mainly ascribed to charge polarization. Correlations between the changes of intensity and temperature location of TSDC peaks with aging and changes of other properties as well (melting enthalpy and temperature, glass-transition temperature, etc.) were established