Ageing Assessment of XLPE Cable Insulation by Residual Antioxidant Content

To improve the efficiency and accuracy of cable ageing assessment, a new method based on residual antioxidant (AO) content is proposed. Cross-linked polyethylene (XLPE) cable insulation is thermally aged in laboratory at 110, 130 and 140°C from 240 h to 3600 h. The ageing degree of XLPE is characterized by tensile testing, AC breakdown measurement, and Fourier transform infrared spectroscopy. The residual AO content in XLPE is detected by FTIR as well as by oxidation induction time (OIT) measurement. It is observed that residual AO content measured by FTIR decreases monotonously with ageing time while OIT shows a non-monotonic transition. The results demonstrate that thermal deterioration is closely related to residual AO content and a critical value of residual AO content exists. During early stage of thermal ageing, the residual AO content is larger than the critical value and the variation in XLPE properties is relatively small. When the residual AO content decreases below the critical value, significant deterioration occurs. The close relationship between thermal degradation and residual AO content was analyzed by oxidative chain reactions.