Insulation Performance Evolution in 500-kV HVDC XLPE Cable Factory Joints: Role of Vulcanization Temperature

To clarify the influence of vulcanization parameters of factory joints on their performance, this study investigates the vulcanization characteristics of return insulation in 500 kV XLPE submarine cable factory joints to optimize insulation performance. Commercial 500 kV XLPE materials were subjected to hot-pressing at temperatures ranging from 160 °C to 240 °C for 4 h. Comprehensive analyses—including differential scanning calorimetry (DSC), gel content, fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), space charge, DC conductivity, and DC breakdown tests—were conducted to evaluate material properties and electrical performance at 30 °C and 70 °C. Results indicate that crosslinking temperature critically influences crystallinity, gel content, and microstructure. Optimal electrical properties are achieved at 180 °C. Temperatures exceeding 200 °C cause severe network degradation, evidenced by reduced gel content, increased C=C bonds, and significant deterioration in insulation performance. These findings provide critical insights for optimizing vulcanization processes in high-voltage DC cable factory joints.