硫化压力对500 kV超高压直流XLPE电缆工厂接头恢复绝缘性能的影响

doi:10.19595/j.cnki.1000-6753.tces.240760

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摘要

为了研究硫化压力变化对500 kV超高压直流交联聚乙烯（XLPE）电缆工厂接头恢复绝缘特性的影响,该文选用商用500 kV超高压直流电缆绝缘颗粒,采用热压法分别在1.3 MPa、1.6 MPa、1.9 MPa和2.5 MPa的压力下对材料进行平板热压,制备了不同硫化压力作用下的XLPE试样。对所得试样进行傅里叶变换红外光谱、凝胶含量、差示扫描量热和X射线衍射测试及分析,并测试了试样的电流密度、空间电荷分布和直流击穿强度。研究结果表明：随着硫化压力的增加,试样的交联度和结晶度逐步增加,空间电荷注入阈值电场强度和直流击穿场强先增大后减小,在1.9 MPa硫化压力下阈值电场强度和直流击穿场强达到最大值。当硫化压力大于1.9 MPa时,不断增多的交联副产物给试样引入更多浅陷阱,同时片晶会因硫化压力的增加而发生热膨胀,晶面间距增加,进而导致试样内部空间电荷明显积聚并加剧电场畸变。提高工厂接头的硫化压力有助于改善其恢复绝缘的电气性能,但过高的硫化压力将不利于工厂接头恢复绝缘性能的增强。

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关键词 ：硫化压力, 交联聚乙烯, 超高压直流电缆, 工厂接头, 恢复绝缘

Abstract：

The increasing distance of offshore wind farms from coastal areas has created an urgent need for the development of long-term extra high voltage direct current (EHVDC) cables. Factory joints are commonly used to connect sections of submarine cables, forming extensive cable systems. Therefore, studying factory joint is crucial for advancing long-length cable lines. This study investigates the physicochemical and dielectric insulation characteristics of XLPE samples under various vulcanization pressures, highlighting the effects of these pressure changes on the properties of 500 kV EHVDC cross-linked polyethylene (XLPE) cable joints.
Commercially available 500 kV EHVDC XLPE pellets were used to prepare the XLPE samples via hot-press method. Initially, a specified quantity of XLPE pellets was distributed between two iron plates. The pellets were preheated at 120℃ for 5 minutes and then heated at 180℃. Cross-linking was subsequently performed under different vulcanization pressures of 1.3 MPa, 1.6 MPa, 1.9 MPa and 2.5 MPa respectively. The fabricated XLPE specimens underwent physical characterization through Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and gel content analysis. While electrical measurements included current density analysis, pulsed electro-acoustic (PEA) analysis, and DC breakdown test.
The physiochemical results indicate that increasing vulcanization pressure enhances the crosslinking degree of XLPE samples, transforming the material from a linear molecular structure to a 3D network structure and breaking macromolecules into smaller, mobile molecules. The increased mobility of these small molecules leads to improved crystallinity, resulting in a higher crystallinity structure. Additionally, the recrystallized macromolecular chains have higher melting temperatures, raising the overall melting temperature of the samples. However, higher vulcanization pressure also produces crosslinking by-products that are difficult to decompose and volatilize. The combination of high temperatures and pressures causes thermal expansion forces perpendicular to the lamellae, increasing lamella spacing, creating more amorphous regions, and effecting the insulation performance of the samples.
Regarding electric insulation performance, the DC breakdown strength and space charge injection threshold strength of the fabricated XLPE samples initially increase and then decrease with the increase in vulcanization pressure. Conversely, conductivity current and average space charge density first decrease and then increase. An optimal vulcanization pressure of 1.9 MPa was identified, at which the XLPE samples exhibited improved electrical insulation properties. Below this pressure, the increased trap energy levels inhibit carrier transport, thereby reducing the number of free carrier paths and hindering the formation of conductive channels, ultimately increasing the breakdown strength of the XLPE samples. However, at vulcanization pressures above 1.9 MPa, the increased crosslinking byproducts create more shallow traps, which lower space charge injection and accumulation, ultimately distorting the sample's internal electric field. Additionally, the increased lamella spacing creates more amorphous regions, reducing the carrier transport barrier and further decrease the breakdown strength of the prepared XLPE samples.
Based on the results, it can be concluded that appropriately increasing the vulcanization pressure of factory joints improves the physicochemical and electrical properties of XLPE. However, excessively high vulcanization pressure can have a detrimental impact on the electrical insulation properties of cable factory joints.

Key words： Vulcanization pressure cross-linked polyethylene extra high voltage direct current cable factory joints return insulation

收稿日期: 2024-05-12

PACS:

TM85

基金资助:

浙江省“尖兵领雁”研发攻关计划（2024C01244(SD2)）和国家自然科学基金（51977187）资助项目

通讯作者: 陈向荣男,1982年生,教授/所长,博士生导师,研究方向为先进电气材料与高压绝缘测试技术,先进电力装备与新型电缆系统,高电压新技术等。E-mail：chenxiangrongxh@zju.edu.cn

作者简介: 张添胤男,2000年生,博士研究生,研究方向为高压交直流电缆系统绝缘测试和状态监测技术。E-mail：zhangtianyin_zju@163.com

引用本文:

张添胤, 陈向荣, 王恩哲, 阴凯, 夏峰, 黄若彬. 硫化压力对500 kV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, 0, (): 2492942-2492942. Zhang Tianyin, Chen Xiangrong, Wang Enzhe, Yin Kai, Xia Feng, Huang Ruobin. Effect of Vulcanization Pressure on the Return Insulation Performance of 500 kV EHVDC XLPE Cable Factory Joints. Transactions of China Electrotechnical Society, 0, (): 2492942-2492942.

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