Comparison of insulation states between new and operated EHV XLPE cables

Analysis of high voltage out of service cables elucidates the state of cable insulation after several years of operation. Operated cables are obtained from the Beijing state grid, China. The characteristic of the electrical tree growth and the corresponding partial discharge (PD) of cross-linked polyethylene slices at 11 kV and 13 kV are simultaneously monitored. Morphology structures of these slices are examined by differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR) and mechanical property analysis. Results of the electrical tree experiment show that new and operated cables have similar electrical tree shapes; Operated cables have shorter initiation time, and larger PD magnitude than new cables. DSC results indicate that the left limit temperature of the melting peak for operated cables decreases relative to that of the new cables, and the crystallization rate increases. Thermal stability analysis by TG and FTIR indicate almost no change to operated samples except for one exhibiting a certain extent of thermal oxidation aging. Statistical mechanical property parameters of operated cable are within the normal range.