Dielectric Response During Thermal-Oxidative Aging of Low-Voltage Cable Insulation Analyzed by Davidson-Cole
Wang Jingran1, Wang Yingjie2, Zhuang Hongwei3, Ji Minzun1, Liu Wenfeng1
1. State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong University Xi’an 710049 China; 2. Suzhou Nuclear Power Research Institute Suzhou 215004 China; 3. Guangxi Fangchenggang Nuclear Power Co. Ltd Fangchenggang 538001 China
Abstract The low-voltage(LV) cables in nuclear power plants would be affected by heat and oxygen under actual operation, and the cable materials would gradually deteriorate with the increase of service time. The most common standard traditionally used to evaluate the insulation state of LV cables was the mechanical parameter, mainly elongation at break (EAB), however, the tensile experiments were destructive. Rencently, frequency domain spectroscopy (FDS), as one new non-destructive diagnostic technology, had the advantages of being non-destructive and simple, and was suitable for the characterization of the overall insulation state of the cables. However, the vast majority of studies focused on qualitatively analyzing the variation of the FDS with various influencing factors. Therefore, one scientific dielectric model was used to quantitatively analyze the dielectric response characteristics of LV cables, and the correlation between the dielectric parameters and the physical, chemical, mechanical properties of the materials was discussed. Firstly, the accelerated aging experiments were carried out on the cross-linked polyethylene (PE)/ ethylene-vinyl acetate copolymer (EVA) specimens at 165℃ to obtain the samples with different degrees of deterioration. The changes in physical and chemical properties of PE/EVA specimens were tested through the Fourier transform infrared (FTIR) spectroscopy and the gel content. The deterioration of the mechanical property was investigated through the EAB experiment, and the dielectric properties were analyzed through the FDS at 100℃. The PE/EVA specimens had two relaxation processes form the analysis of FDS, and the DC conductance was considered at the same time. Therefore, the complex permittivity spectra of the PE/EVA samples with different aging degrees were fitted by the Davison-Cole dielectric model to extract the characteristic parameters of polarization and conductance. The results showed that the re-crosslinking reaction of the specimens occurs during the whole aging process, which increased the three-dimensional network structure. The carbonyl index of PE/EVA showed a trend of decreasing at the beginning and then increasing, which was caused by the degradation of vinyl acetate groups at the early stage and the oxidation reaction after 504 h. It was found that the relaxation strength Δεα due to the motion of segmental chains, the thermionic polarization strength Δεδ as well as the DC conductivity σdc gradually decreased with the increase of aging time through the Davidson-Cole dielectric model. The decrease of Δεα and σdc slowed down due to the accelerated oxidation reaction after 504 h. The preliminary fitting of the characteristic parameters Δεα, Δεδ, σdc of the dielectric model and the traditional state evaluation criteria EAB showed a positive correlation. The following conclusions can be drawn from the analysis of experimental and fitting results: (1) The degree of cross-linking, as the key parameter during the aging process, is the most important determinant of the consistency between the dielectric parameters and the mechanical parameter. The increase in the degree of cross-linking of PE/EVA inhibits the migration of ions, so that the DC conductivity σdc and the relaxation strength of the samples decrease with the aging time. The free volume of PE/EVA specimens is reduced due to the augment of the macromolecular network structure, which weakens the movement of the molecular segments. At the same time, the increase of the degree of cross-linking reduces the flexibility of macromolecules of PE/EVA, and then the EAB decreases during the aging process. (2) It is found that the quantitative analysis of the frequency domain spectroscopy can not only characterize the dielectric response mechanism of the materials, but also has a strong correlation with the elongation at break, which can be better applied in the evaluation of the state and life of the LV cables.
Wang Jingran,Wang Yingjie,Zhuang Hongwei等. Dielectric Response During Thermal-Oxidative Aging of Low-Voltage Cable Insulation Analyzed by Davidson-Cole[J]. Transactions of China Electrotechnical Society, 2023, 38(15): 4030-4039.
[1] Powers W F.The basics of power cable[J]. IEEE Transactions on Industry Applications, 1994, 30(3): 506-509. [2] Suraci S V, Fabiani D, Xu A, et al.Ageing assessment of XLPE LV cables for nuclear applications through physico-chemical and electrical measurements[J]. IEEE Access, 2020, 8: 27086-27096. [3] 周涛, 秦雪猛, 李子超, 等. 核电缆发展分析研究[J]. 黑龙江电力, 2018, 40(4): 283-286. Zhou Tao, Qin Xuemeng, Li Zichao, et al.Analysis and research of nuclear cable development[J]. Heilongjiang Electric Power, 2018, 40(4): 283-286. [4] Chi Xiaohong, Li Jianxi, Ji Minzun, et al.Thermal-oxidative aging effects on the dielectric properties of nuclear cable insulation[J]. Materials, 2020, 13(10): 2215. [5] 曹丹, 孙彬, 单永东, 等. 核电用交联三元乙丙绝缘材料热氧老化状态的评估[J]. 合成材料老化与应用, 2019, 48(3): 1-5, 63. Cao Dan, Sun Bin, Shan Yongdong, et al.Evaluation of thermal oxygen aging status of crosslinked EPDM insulation materials for nuclear power[J]. Synthetic Materials Aging and Application, 2019, 48(3): 1-5, 63. [6] Suraci S V, Fabiani D, Roland S, et al.Multi scale aging assessment of low-voltage cables subjected to radio-chemical aging: towards an electrical diagnostic technique[J]. Polymer Testing, 2021, 103: 107352. [7] 杜伯学, 韩晨磊, 李进, 等. 高压直流电缆聚乙烯绝缘材料研究现状[J]. 电工技术学报, 2019, 34(1): 179-191. Du Boxue, Han Chenlei, Li Jin, et al.Research status of polyethylene insulation for high voltage direct current cables[J]. Transactions of China Electro-technical Society, 2019, 34(1):179-191. [8] 周凯, 李诗雨, 尹游, 等. 退运中压XLPE和EPR电缆老化特性分析[J]. 电工技术学报, 2020, 35(24): 5197-5206. Zhou Kai, Li Shiyu, Yin You, et al.Analysis of aging characteristics of medium voltage XLPE and EPR retired cables[J]. Transactions of China Electro-technical Society, 2020, 35(24): 5197-5206. [9] Glass S W, Fifield L S, Dib G, et al.State of the art assessment of NDE techniques for aging cable management in nuclear power plants FY2015[R]. Pacific Northwest National Lab, Richland, WA, USA, 2015. [10] Linde E, Verardi L, Fabiani D, et al.Dielectric spectroscopy as a condition monitoring technique for cable insulation based on crosslinked polyethylene[J]. Polymer Testing, 2015, 44: 135-142. [11] 刘刚, 刘斯亮, 金尚儿, 等. 基于理、化、电特性的110 kV XLPE绝缘电缆剩余寿命的综合评估[J]. 电工技术学报, 2016, 31(12): 72-79, 107. Liu Gang, Liu Siliang, Jin Shanger, et al.Comprehensive evaluation of remaining life of 110 kV XLPE insulated cable based on physical, chemical and electrical properties[J]. Transactions of China Electrotechnical Society, 2016, 31(12): 72-79, 107. [12] 张益舟, 龚智明, 王雷, 等. 基于介电性能的电缆热老化及辐照老化检测技术研究[J]. 绝缘材料, 2017, 50(9): 62-67. Zhang Yizhou, Gong Zhiming, Wang Lei, et al.Thermal and irradiation ageing detection technology of cables based on dielectric properties[J]. Insulating Materials, 2017, 50(9): 62-67. [13] 单秉亮, 李舒宁, 杨霄, 等. XLPE配电电缆缺陷诊断与定位技术面临的关键问题[J]. 电工技术学报, 2021, 36(22): 4809-4819. Shan Bingliang, Li Shuning, Yang Xiao, et al.Key problems faced by defect diagnosis and location technologies for XLPE distribution cables[J]. Transactions of China Electrotechnical Society, 2021, 36(22): 4809-4819. [14] 王昊月, 李成榕, 王伟, 等. 高压频域介电谱诊断XLPE电缆局部绝缘老化缺陷的研究[J]. 电工技术学报, 2022, 37(6): 1542-1553. Wang Haoyue, Li Chengrong, Wang Wei, et al.Local aging diagnosis of XLPE cables using high voltage frequency domain dielectric spectroscopy[J]. Transactions of China Electrotechnical Society, 2022, 37(6): 1542-1553. [15] 刘涛, 李欢, 徐磊, 等. 热老化对XLPE微观结构及介电性能的影响机制综述[J]. 陕西理工大学学报(自然科学版), 2021, 37(4): 1-9, 31. Liu Tao, Li Huan, Xu Lei, et al.Review of effects of thermal aging on micro-structure and performance of cross-linked polyethylene cable insulation[J]. Journal of Shaanxi University of Technology (Natural Science Edition), 2021, 37(4): 1-9, 31. [16] Zhou Haolong, Hanafusa W, Udo K, et al.Aging behavior of flame-retardant cross-linked polyolefin under thermal and radiation stresses[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(1): 303-309. [17] Cole R H.Dielectric polarization and relaxation[M]// Molecular Liquids. Dordrecht: Springer Netherlands, 1984: 59-110. [18] 杨丽君, 齐超亮, 邓帮飞, 等. 采用修正Cole-Cole模型提取油纸绝缘频域介电谱的特征参量方法[J]. 高电压技术, 2013, 39(2): 310-317. Yang Lijun, Qi Chaoliang, Deng Bangfei, et al.Application of modified Cole-Cole model to extract characteristics of frequency dielectric spectroscopy of oil-paper insulation[J]. High Voltage Engineering, 2013, 39(2): 310-317. [19] 杨丽君, 高思航, 高竣, 等. 油纸绝缘频域介电谱的修正Cole-Cole模型特征参量提取及水分含量评估方法[J]. 电工技术学报, 2016, 31(10): 26-33. Yang Lijun, Gao Sihang, Gao Jun, et al.Characteristic parameters extracted from modified Cole-Cole model and moisture content assessment methods study on frequency-domain dielectric spectroscopy of oil-paper insulation[J]. Transactions of China Electrotechnical Society, 2016, 31(10): 26-33. [20] 刘骥, 尹梦涵, 李秀婧, 等. 油纸绝缘老化评估的Davidson-Cole模型参数提取方法[J]. 电机与控制学报, 2017, 21(3): 63-70. Liu Ji, Yin Menghan, Li Xiujing, et al.Parameters extraction of Davidson-Cole model on aging assessment of oil-paper insulation[J]. Electric Machines and Control, 2017, 21(3): 63-70. [21] Min Daomin, Li Shengtao, Hirai N, et al.Dielectric spectroscopic analysis of degradation in ethylene-propylene-diene copolymer[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2016, 23(6): 3620-3630. [22] Min Daomin, Yan Chenyu, Huang Yin, et al.Dielectric and carrier transport properties of silicone rubber degraded by gamma irradiation[J]. Polymers, 2017, 9(10): 533. [23] 马以正, 侯海林. 辐射交联无卤阻燃聚烯烃复合材料的研究[J]. 核技术, 1997, 20(7): 408-412. Ma Yizheng, Hou Hailin.Preparation of non-halogen flame retardant polyolefin complex by radiation crosslinking[J]. Nuclear Techniques, 1997, 20(7): 408-412. [24] 丁圆, 张宏, 刘琪, 等. PE/EVA共混改性研究进展[J]. 化工时刊, 2020, 34(10): 22-24, 59. Ding Yuan, Zhang Hong, Liu Qi, et al.Research progress of PE/EVA blending modification[J]. Chemical Industry Times, 2020, 34(10): 22-24, 59. [25] Colombani J, Sidi A, Larché J F, et al.Thermooxidative degradation of crosslinked EVA/EPDM copolymers: impact of Aluminium TriHydrate (ATH) filler incorporation[J]. Polymer Degradation and Stability, 2018, 153: 130-144. [26] 雷清泉. 高聚物的结构与电性能[M]. 武汉: 华中理工大学出版社, 1990. [27] 林生军, 黄印, 谢东日, 等. 环氧树脂高温分子链松弛与玻璃化转变特性[J]. 物理学报, 2016, 65(7): 304-310. Lin Shengjun, Huang Yin, Xie Dongri, et al.Molecular relaxation and glass transition properties of epoxy resin at high temperature[J]. Acta Physica Sinica, 2016, 65(7): 304-310. [28] 康文斌, 蒙绍兴, 李世军, 等. 硅橡胶绝缘介质的分子链运动与电极极化特性[J]. 高电压技术, 2018, 44(12): 3798-3807. Kang Wenbin, Meng Shaoxing, Li Shijun, et al.Molecular chain motion and electrode polarization properties of silicone rubber[J]. High Voltage Engineering, 2018, 44(12): 3798-3807. [29] Ohki Y.Broadband complex permittivity and electric modulus spectra for dielectric materials research[J]. IEEJ Transactions on Electrical and Electronic Engineering, 2022, 17(7): 958-972. [30] Sidi A, Colombani J, Larché J F, et al.Multiscale analysis of the radiooxidative degradation of EVA/EPDM composites. ATH filler and dose rate effect[J]. Radiation Physics and Chemistry, 2018, 142: 14-22. [31] 翁诗甫. 傅里叶变换红外光谱分析[M]. 2版. 北京: 化学工业出版社, 2010. [32] Yamaguchi H, Ishii H, Hirai N, et al.Degradation of mechanical and dielectric properties of flame-retardant ethylene propylene rubber by thermal aging[J]. IEEJ Transactions on Electrical and Electronic Engineering, 2020, 15(4): 488-495. [33] Allen N S, Edge M, Rodriguez M, et al.Aspects of the thermal oxidation of ethylene vinyl acetate copolymer[J]. Polymer Degradation and Stability, 2000, 68(3): 363-371. [34] 何平笙. 新编高聚物的结构与性能[M]. 北京: 科学出版社, 2009. [35] 朱诚身. 聚合物结构分析[M]. 北京: 科学出版社, 2004. [36] 秦书娟, 徐曼, 曹晓珑, 等. EVA/VLDPE/Mg(OH)2阻燃体系介电性能研究[J]. 电线电缆, 2010(3): 31-34, 37. Qin Shujuan, Xu Man, Cao Xiaolong, et al.Study on the dielectric performance of EVA/VLDPE/Mg(OH)2 composite[J]. Electric Wire & Cable, 2010(3): 31-34, 37. [37] International Atomic Energy Agency. Assessment and management of ageing of major nuclear power plant components important to safety: volume Ⅱin-containment instrumentation and control cables[M]. Vienna: International Atomic Energy Agency, 2000. [38] Fabiani D, Suraci S V.Broadband dielectric spectroscopy: a viable technique for aging assessment of low-voltage cable insulation used in nuclear power plants[J]. Polymers, 2021, 13(4): 494.
2023, Vol. 38 
