Effect of Vulcanization Time on Electrical Properties of 500 kV EHVDC XLPE Cable Factory Joints

To investigate the performance variation of 500 kV extra high voltage direct current (EHVDC) subsea cable factory joints at different vulcanization times, this study utilizes commercial 500 kV cross-linked polyethylene (XLPE) cable pellets to prepare double-layer XLPE joint samples with varying vulcanization times. These samples were subjected to conductivity tests, surface charge decay tests, and DC breakdown tests at different temperatures. The results indicate that increasing the vulcanization time consistently improves the DC breakdown strength of the samples, regardless of the testing temperature. The conductivity of the samples showed a positive correlation with the electric field intensity. When the temperature was 50 °C or below, a reduction in vulcanization time increased the conductivity, whereas at 70 °C, shortening the vulcanization time led to a decrease in conductivity, thereby improving the insulation performance. Analysis of the surface potential decay curves revealed that, for any sample, an increase in temperature rapidly accelerated the dissipation of surface charges. At temperatures of 50 °C or below, an increase in vulcanization time enhanced the absolute value of the initial potential, whereas at 70 °C, the vulcanization time was negatively correlated with the initial potential of the sample. The experimental data provides theoretical support and engineering application references for the development of factory joints for 500 kV EHVDC XLPE subsea cables.