Abstract：Cross-linked polyethylene (XLPE) has been widely utilized as a high-voltage direct current (HVDC) cable insulation material. However, in the context of the growing demand for extra-high voltage direct current cables that require larger capacity and broader operating temperature ranges, XLPE insulation must address the challenges posed by space charge accumulation and the temperature sensitivity of conductivity, which can lead to electric field distortion. To tackle this issue, graft modification introducing deep trap groups can effectively capture charges, suppress carrier transport, and enhance the DC electrical performance of XLPE. Moreover, through the rational combination of organic functional groups, constructing functional graftable molecules capable of effectively introducing deep charge traps, and subsequently grafting them onto XLPE, results in a graft-modified XLPE insulation material with extremely low temperature sensitivity of electrical conductivity. To investigate the charge transport mechanisms in graft-modified XLPE over a broad field range and explore the regulatory behavior of deep traps introduced by the graft modification on the internal charge in XLPE under varying temperatures and electric fields, this study focuses on two materials: the pristine XLPE before modification and the graft-modified XLPE (GXLPE) developed by our research team, which exhibits excellent DC electrical performance. Tests on the space charge distribution and conductivity current of both materials are conducted over a wide range of electric field strengths and temperatures. The study analyzes how graft modification affects charge transport in XLPE under high electric fields and provides insights into the impact of graft modification on the electrical performance of XLPE from the perspective of charge transport. The space charge distribution test results indicate a severe charge packet migration behavior within XLPE at high electric fields during the stepwise voltage increase, and this behavior occurs at lower threshold field strengths with increasing temperature. With the increasing of the temperature, charge packet migration can be observed at as low as 15 kV/mm at 70℃. In the grafted XLPE, however, the majority of charges remain confined near the electrodes within the specimen, even under high temperature and high field conditions, with very few charges injected into the material's interior, thus preventing high-density charge packet migration. The conductivity current test results show that the conductivity behavior in XLPE generally follows the space charge-limited current regime, transitioning from a charge-free Ohmic region to a trap-limited space charge limited current (TL-SCLC) region, and eventually to a trap-filled space charge limited (TF-SCLC) region under high temperature and high fields. In graft-modified XLPE, only the Ohmic and TL-SCLC regions can be observed due to its high trap density and low carrier mobility, which can prevent traps from becoming fully filled, resulting in the absence of a TF-SCLC region within the tested electric field range. The deep traps formed by graft modification effectively improve the material's spatial charge and conductivity characteristics over a wide field range, inhibiting space charge packet migration and conductivity current. Even under combined electrothermal field conditions of 120 kV/mm, the deep traps are able to efficiently capture and restrain carriers, demonstrating a stable improvement in DC electrical performance.
杨旭, 程功, 张城城, 杨佳明, 李春阳, 赵洪, 王暄. 接枝改性XLPE绝缘材料宽场域下的空间电荷与电导特性[J]. 电工技术学报, 2025, 40(21): 6882-6893.
Yang Xu, Cheng Gong, Zhang Chengcheng, Yang Jiaming, Li Chunyang, Zhao Hong, Wang Xuan. Space Charge and Conductance Characteristics of Grafted XLPE Insulation Material in Wide Field Range. Transactions of China Electrotechnical Society, 2025, 40(21): 6882-6893.
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