Abstract：Extra-high-voltage direct-current (EHVDC) cross-linked polyethylene (XLPE) submarine cable factory joints play a central role in long-distance, high-capacity DC transmission systems. However, differences in thermal history during the manufacture of factory joints inevitably give rise to a transition interface between the main insulation and the return insulation, where space charge accumulation can trigger insulation degradation. As a result, the impact of vulcanization pressure on the dielectric behavior of factory joints must be properly evaluated in the development of 500 kV EHVDC submarine cable systems. Commercial XLPE pellets for 500 kV DC submarine cables were used to prepare XLPE transition-layer specimens by hot pressing method. Vulcanization pressures of 0.7, 1.6, 1.9, and 2.5 MPa were selected to match those employed in practical manufacturing of factory joints. The surface morphology and physicochemical properties of the specimens were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and gel content analysis. Electrical performance was evaluated via isothermal surface potential decay, conduction current density test, DC breakdown strength test, and pulsed electro-acoustic (PEA) test at 30, 50, 70, and 90℃, respectively. In addition, a bipolar charge transport model for a factory joint was developed. The model was validated through space charge measurements conducted on a full-sized factory joint, and the effect of vulcanization pressure on space charge behavior in full-sized factory joints was subsequently analyzed. The experimental results show that increasing vulcanization pressure enhances interfacial crosslinking and reduces the amorphous fraction in the specimens, leading to an increase in the energy level of deep electron traps and a reduction in the energy level of deep hole traps, accompanied by an increase in carrier mobility. At a vulcanization pressure of 1.6 MPa, the specimens exhibit the maximum DC breakdown strength at elevated temperature, and a pronounced improvement in interfacial space-charge distribution is observed. When the pressure exceeds 1.6 MPa, interfacial crosslinking continues to improve; however, microvoid defects generated by decomposition of crosslinking by-products increase the amorphous fraction. Consequently, the DC breakdown strength and the space-charge injection threshold decrease significantly, and carrier mobility is simultaneously reduced, leading to pronounced space-charge accumulation at the transition interface. Space charge measurements on the factory joint revealed that the potential barrier formed at the interface between the main insulation and the return insulation inhibits carrier transport, leading to accumulation of positive charges at the interface. The simulated space charge distribution of full-sized factory joint was in close agreement with the experimental observations in both magnitude and spatial location. Simulation results for the full-sized factory joint further demonstrate that space charge accumulation preferentially occurs at the composite interfacial regions located at both ends of the stress cone. An elevated temperature accelerates carrier injection and space charge accumulation, resulting in pronounced electric field distortion at the interfaces. Based on the results, an appropriate vulcanization pressure of 1.6 MPa is beneficial for improving the interfacial dielectric performance of factory joints, and space charge induced insulation degradation at interfaces should be considered in the design and development of EHVDC submarine cable factory joints.
[1] 尚恺, 李加才, 王诗航, 等. 高压电缆交联聚乙烯绝缘料黏度参数对挤出特性影响的仿真研究[J]. 电工技术学报, 2024, 39(3): 810-819. Shang Kai, Li Jiacai, Wang Shihang, et al.Simulation study on the extrusion performances based on the viscosity parameters of cross-linked polyethylene insulating materials for high-voltage cables[J]. Transactions of China Electrotechnical Society, 2024, 39(3): 810-819. [2] 赵皓琳, 刘英, 吴婧, 等. 基于异质异径线芯选型实现载流量优化匹配的高压XLPE海缆系统设计[J]. 电工技术学报, 2025, 40(15): 4954-4965. Zhao Haolin, Liu Ying, Wu Jing, et al.Design of high-voltage XLPE submarine cable system based on ampacity optimized matching of cores with different materials and sizes[J]. Transactions of China Electrotechnical Society, 2025, 40(15): 4954-4965. [3] 张添胤, 陈向荣, 王恩哲, 等. 硫化压力对500kV超高压直流XLPE电缆工厂接头恢复绝缘性能的影响[J]. 电工技术学报, 2025, 40(9): 2931-2943. Zhang Tianyin, Chen Xiangrong, Wang Enzhe, et al.Effect of vulcanization pressure on the return insulation performance of 500 kV EHVDC XLPE cable factory joints[J]. Transactions of China Electro-technical Society, 2025, 40(9): 2931-2943. [4] 李震, 郑海峰, 陈俊岐, 等. 基于磁感应联合加热的高压海缆工厂接头制备技术[J]. 电工技术学报, 2024, 39(3): 820-835. Li Zhen, Zheng Haifeng, Chen Junqi, et al.Manufacture technologies of high-voltage submarine cable factory joint based on magnetic induction combined heating[J]. Transactions of China Electro-technical Society, 2024, 39(3): 820-835. [5] Mazzanti G, Castellon J, Chen G, et al.The insulation of HVDC extruded cable system joints. Part 1: Review of materials, design and testing procedures[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2019, 26(3): 964-972. [6] 鲍国栋, 宋柯, 钱定冬, 等. 极性反转条件下XLPE空间电荷与电场分布特性研究[J]. 高压电器, 2025, 61(8): 146-154. Bao Guodong, Song Ke, Qian Dingdong, et al.Study on space charge and electric field distribution characteristics of XLPE under polarity reversal voltage[J]. High Voltage Apparatus, 2025, 61(8): 146-154. [7] 陈向荣, 夏峰, 高智益, 等. 高压直流交联聚乙烯海底电缆用工厂接头关键技术发展与展望[J]. 高电压技术, 2025, 51(8): 4434-4446. Chen Xiangrong, Xia Feng, Gao Zhiyi, et al.Development and prospect of key technologies for high voltage direct current XLPE sub-marine cable factory joints[J]. High Voltage Engineering, 2025, 51(8): 4434-4446. [8] Li Zhonglei, Zheng Zhong, Wu You, et al.Space charge and electric field characteristics in XLPE-insulated extrusion molded joint for HVDC submarine cables: experiment and simulation[J]. IEEE Transac-tions on Power Delivery, 2024, 39(4): 2317-2326. [9] 张振鹏, 胡列翔, 赵健康, 等. 500 kV海缆工厂接头绝缘恢复过渡区形成过程及电树枝特性[J]. 高电压技术, 2019, 45(11): 3413-3420. Zhang Zhenpeng, Hu Liexiang, Zhao Jiankang, et al.Formation process and electrical tree characteristics of insulation recovery transition zone of factory joints in 500 kV submarine cable[J]. High Voltage Engineering, 2019, 45(11): 3413-3420. [10] 孟繁博, 陈向荣, 徐星, 等. 不同粗糙度界面和脱气处理对500kV XLPE直流电缆工厂接头的影响[J]. 中国电机工程学报, 2022, 42(17): 6499-6510. Meng Fanbo, Chen Xiangrong, Xu Xing, et al.Effect of different roughness interface and degassing treatment on 500kV XLPE DC cable factory joint[J]. Proceedings of the CSEE, 2022, 42(17): 6499-6510. [11] Mazzanti G, Diban B, Tzimas A, et al.Space charge measurements on flexible factory joints for HVDC extruded cables[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2026, 33(1): 528-539. [12] Wang Yani, Wang Yalin, Yang Xingwu, et al.Charge transport in full-size HVDC cable joint with modeling of XLPE/EPDM interface[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(6): 2117-2125. [13] Chen Jiming, Gao Ying, Zhu Mingxiao, et al.Space charge dynamics in double-layered insulation cable under polarity reversal voltage[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2020, 27(2): 622-630. [14] Pourrahimi A M, Hoang T A, Liu Dongming, et al.Highly efficient interfaces in nanocomposites based on polyethylene and ZnO nano/hierarchical particles: a novel approach toward ultralow electrical conductivity insulations[J]. Advanced Materials, 2016, 28(39): 8651-8657. [15] 尹克岩. 高压直流海缆绝缘材料交联和绝缘性能的提升研究[J]. 绝缘材料, 2025, 58(11): 49-57. Yin Keyan.Study on cross-linking and insulating performance improvement of insulating materials for HVDC submarine cables[J]. Insulating Materials, 2025, 58(11): 49-57. [16] 张灵, 陈健宁, 周远翔, 等. 聚合物绝缘空间电荷动力学的理论模型与数值仿真研究进展[J]. 中国电机工程学报, 2022, 42(8): 3037-3054. Zhang Ling, Chen Jianning, Zhou Yuanxiang, et al.Progress on theoretical models and numerical simulation of space charge kinetics in polymeric insulation[J]. Proceedings of the CSEE, 2022, 42(8): 3037-3054. [17] 张昱, 刘德远, 周桂月, 等. 高压直流电缆绝缘二维模型下空间电荷动力学仿真算法研究[J]. 中国电机工程学报, 2019, 39(15): 4615-4622. Zhang Yu, Liu Deyuan, Zhou Guiyue, et al.Research on simulation algorithms for two dimensional models of space charge dynamics in high voltage DC cable insulation[J]. Proceedings of the CSEE, 2019, 39(15): 4615-4622. [18] 兰莉, 吴建东, 王雅妮, 等. 低密度聚乙烯/乙丙橡胶双层介质的界面空间电荷特性[J]. 中国电机工程学报, 2015, 35(5): 1266-1272. Lan Li, Wu Jiandong, Wang Yani, et al.Space charge property at the interface in low density polyethylene/ ethylene propylene rubber double-layered insulation[J]. Proceedings of the CSEE, 2015, 35(5): 1266-1272. [19] 董芸滋, 高嫄, 李秀峰, 等. 交联度对交联聚乙烯/有机化蒙脱土纳米复合材料拉伸性能和介电性能的影响[J]. 电工技术学报, 2023, 38(5): 1154-1165. Dong Yunzi, Gao Yuan, Li Xiufeng, et al.Effect of crosslinking degree on tensile and dielectric properties of cross-linked polyethylene/organic montmorillonite nanocomposite material[J]. Transactions of China Electrotechnical Society, 2023, 38(5): 1154-1165. [20] Li Jianying, Zhou Fusheng, Min Daomin, et al.The energy distribution of trapped charges in polymers based on isothermal surface potential decay model[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2015, 22(3): 1723-1732. [21] Wang Tianyu, Mao Jie, Zhang Boya, et al.Polymeric insulating materials characteristics for high-voltage applications[J]. Nature Reviews Electrical Engineer-ing, 2024, 1(8): 516-528. [22] Jones J P, Llewellyn J P, Lewis T J.The contribution of field-induced morphological change to the electrical aging and breakdown of polyethylene[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2005, 12(5): 951-966. [23] 雷清泉, 刘关宇. 如何理解工程电介质中极化与电导两个基本物理过程及其测量的科学原理与方法[J]. 中国电机工程学报, 2018, 38(23): 6769-6789. Lei Qingquan, Liu Guanyu.How to understand the two basic physical processes of polarization and conductance in engineering dielectrics and scientific principles and methods of their measurement[J]. Proceedings of the CSEE, 2018, 38(23): 6769-6789. [24] Zahra S, Morita S, Utagawa M, et al.Space charge measurement equipment for full-scale HVDC cables using electrically insulating polymeric acoustic coupler[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2022, 29(3): 1053-1061. [25] 侯帅, 范珍友, 徐曼, 等. 预鉴定试验对220 kV交联聚乙烯电缆绝缘材料性能的影响[J]. 电工技术学报, 2025, 40(21): 6871-6881. Hou Shuai, Fan Zhenyou, Xu Man, et al.Investigation on insulation material properties of 220 kV XLPE cables after pre-qualification test[J]. Transactions of China Electrotechnical Society, 2025, 40(21): 6871-6881.
2026, Vol. 41 
