Abstract：In converter valve halls of ultra-high voltage direct current (UHVDC) projects, dry-type metallized film capacitors (MFCs) play important roles, such as damping buffer, voltage support and auxiliary commutation, etc. Dry-type MFCs are mainly composed of polypropylene (PP) film overlapped and wound with evaporation electrode, whose performances depend on the insulation characteristics of the dielectric films. With the improvement of the system voltage level and the development trend of the equipment miniaturization, more stringent requirements have been put forward on the dielectric properties of the insulation for capacitors. This paper focuses on the existing problems of PP films for dry-type capacitors. The evolution law of dielectric properties and insulation failure under complex operating conditions are not completely clear, leading to the lack of the guidance to the cooperative regulation of dielectric loss and breakdown strength of PP films. Based on the evolution process of the micro and macro performances of PP films under DC superimposed harmonics or pulse conditions, this paper summarizes the influence of the microstructure, thermal field, complex electric field and mechanical stress on the dielectric properties of the films. In terms of both internal structure and external environment, the mechanism of the insulation aging and even breakdown failure is thoroughly analyzed. It is found that molecular chain configuration, crystallinity and crystal type have important effects on the crystal growth mode, micro morphology and thermal properties of PP films. The polar functional groups in the ash of the material can intensify the ionization of impurities in the film and increase the conduction loss, which is an important reason for the shortening of the capacitor life. Under DC superimposed harmonic voltage, the increase of harmonic amplitude or frequency will lead to the formation of low density area of thin film medium and accelerate the insulation failure. Pulse overvoltages may cause more damage to insulation than DC or harmonic voltages, which needs more concern in future researches. The high temperature environment promotes the injected charges from the electrode, which will increase the dielectric loss and further aggravate the temperature rise inside the capacitor. The localized electric field near the microscopic defects distorts significantly, which ultimately reduces the breakdown strength of the film. Under the combined field of electric field and mechanical stress, multiple partial discharges further decompose the molecular chain and develop into local cracks, which aggravate the partial discharge and insulation aging. The main methods to improve the insulation performance of dielectric films include ultra-fine production of the granular material, optimization of film stretching process, modification of the film material and whole structure design of capacitors. From the aspects of the physical blending, organic addition, ash suppression, crystallization design, chemical grafting and interface modification, the current research status of film insulation modification at home and abroad is summarized. Several methods of regulating the dielectric properties of PP substrates and films for dry-type capacitors are introduced. The effectiveness of different modified films are analyzed based on simulation and experimental data. Traditional inorganic nano addition, physical blending and chemical copolymerization are comparatively not suitable for micron-thickness films. Compared with inorganic nanoparticles, the dispersion of organic/semi-organic nanomaterials in the matrix are better. The breakdown performance of polyphenyl-ring compounds with capture ability of thermoelectrons is improved by introducing chemical traps. Modified films based on ash suppression and crystal morphology design have also proved to be excellent. The interface processing method needs to be further studied for its industrialization feasibility. Finally, the insulation failure and suppression methods of PP films for DC capacitors are summarized and prospected. This paper can provide a reference for the development of dry-type MFCs based on PP insulation suitable for operating conditions in UHVDC projects.
杜伯学, 冉昭玉, 刘浩梁, 肖萌. 干式直流电容器聚丙烯薄膜绝缘性能及其改进方法研究进展[J]. 电工技术学报, 2023, 38(5): 1363-1374.
Du Boxue, Ran Zhaoyu, Liu Haoliang, Xiao Meng. Research Progress of Dielectric Properties and Improvement Methods of Polypropylene Film for Dry-Type Capacitor. Transactions of China Electrotechnical Society, 2023, 38(5): 1363-1374.
[1] 戴志辉, 刘宁宁, 何永兴, 等. 基于直流滤波环节暂态能量比的高压直流线路纵联保护[J]. 电工技术学报, 2020, 35(9): 1985-1998. Dai Zhihui, Liu Ningning, He Yongxing, et al.High-voltage DC line pilot protection based on the transient energy ratio of the DC filter link[J]. Transactions of China Electrotechnical Society, 2020, 35(9): 1985-1998. [2] 孙晓武. 直流支撑电容器温升影响因素研究[J]. 电气技术, 2020, 21(4): 84-87. Sun Xiaowu.Research on influencing factors of temperature rise of DC support capacitors[J]. Electrical Engineering, 2020, 21(4): 84-87. [3] 王子建, 严飞, 侯智剑, 等. 高压全膜电容器热稳定性能试验条件下的温度场特性[J]. 电工技术学报, 2016, 31(17): 207-216. Wang Zijian, Yan Fei, Hou Zhijian, et al.Temperature field characteristics of high-voltage all-film capacitors under thermal stability test conditions[J]. Transactions of China Electrotechnical Society, 2016, 31(17): 207-216. [4] Du Boxue.Polymer insulation applied for HVDC transmission[M]. Germany: Springer, 2021. [5] 许然然, 杜伯学, 肖谧. 高压直流电容器电介质研究现状[J]. 电气工程学报, 2018, 13(11): 1-10. Xu Ranran, Du Boxue, Xiao Mi.Research status of high voltage DC capacitor dielectrics[J]. Journal of Electrical Engineering, 2018, 13(11): 1-10. [6] 叶建铸, 管春伟, 谢超, 等. 高压直流输电工程用电力电容器故障分析[J]. 电力电容器与无功补偿, 2017, 38(1): 71-75. Ye Jianzhu, Guan Chunwei, Xie Chao, et al.Failure analysis of power capacitors for HVDC transmission projects[J]. Power Capacitor & Reactive Power Compensation, 2017, 38(1): 71-75. [7] 林圣, 牟大林, 刘磊, 等. 基于特征谐波阻抗比值的HVDC直流滤波器高压电容器接地故障保护方案[J]. 中国电机工程学报, 2019, 39(22): 6617-6627. Lin Sheng, Mu Dalin, Liu Lei, et al.HVDC filter high-voltage capacitor ground fault protection scheme based on characteristic harmonic impedance ratio[J]. Proceedings of the CSEE, 2019, 39(22): 6617-6627. [8] 查鲲鹏, 曹均正, 郑媚媚, 等. 计及金属化膜电容器失效的MMC换流阀组件可靠性评估[J]. 电力系统自动化, 2019, 43(4): 86-96. Zha Kunpeng, Cao Junzheng, Zheng Meimei, et al.Reliability evaluation of MMC converter valve components taking into account the failure of metallized film capacitors[J]. Automation of Electric Power Systems, 2019, 43(4): 86-96. [9] Kahouli A, Gallotlavallée O, Rain P, et al.Relationship between structure and dielectric properties of bi-oriented isotactic polypropylene films for capacitors[C]// IEEE International Conference on Solid Dielectrics, Bologna, 2013: 1068-1071. [10] Kurimsky J, Kosterec M, Vargova B.Breakdown voltage of polypropylene film during DC and thermal ageing[C]//IEEE International Scientific Conference on Electric Power Engineering, Ostrava, 2017: 1-4. [11] Ran Zhaoyu, Du Boxue, Xiao Meng, et al.Effect of Crystallization regulation on the breakdown strength of metallized polypropylene film capacitors[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(1): 175-182. [12] 许然然. 柔性直流换流阀直流支撑电容器用聚丙烯薄膜绝缘失效及其抑制方法研究[D]. 天津: 天津大学, 2020. [13] Zhou Shuofan, Fan Mingsheng, Li Zhonglei, et al.Effect of β-Spherulite on electrical tree characteristics of isotactic polypropylene insulation[C]//IEEE International Conference on Electrical Materials and Power Equipment, Chongqing, 2021: 1-4. [14] Standaert A, Gromada J.Process for the production of a propylene polymer having a broad molecular weight distribution and a low ash content[P]. US: 2011/0034649A1, 2011. [15] Du Boxue, Xing Jiwen, Ran Zhaoyu, et al.Dielectric and energy storage properties of polypropylene by deashing method for DC polymer film capacitors[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(6): 1917-1924. [16] Imburgia A, Miceli R, Sanseverino E R, et al.Review of space charge measurement systems: acoustic, thermal and optical methods[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2016, 23(5): 3126-3142. [17] Xu Ranran, Du Boxue, Xiao Meng, et al.Dielectric properties dependent on crystalline morphology of PP film for HVDC capacitors[J]. Polymer, 2020, 213: 123204. [18] 司马文霞, 华杰方, 孙魄韬, 等. 冲击电压作用下冲击电容器用聚丙烯薄膜累积失效特性[J]. 高电压技术, 2018, 44(2): 358-365. Sima Wenxia, Hua Jiefang, Sun Potao, et al.Cumulative failure characteristics of polypropylene film for shock capacitors under impulse voltage[J]. High Voltage Engineering, 2018, 44(2): 358-365. [19] Ran Zhaoyu, Du Boxue, Xiao Meng, et al.Crystallization morphology-dependent breakdown strength of polypropylene films for converter valve capacitor[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(3): 964-971. [20] Cheng Lu, Liu Wenfeng, Liu Xiaowei, et al.Online degradation of biaxial-orientated polypropylene film from HVDC filter capacitors[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2019, 26(1): 26-33. [21] Du Buxue, Su Jingang, Li Jin, et al.Effects of mechanical stress on treeing growth characteristics in HTV silicone rubber[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2017, 24(3): 1547-1556. [22] 聂洪岩, 魏新劳, 姚远航, 等. 热老化对干式空心电力电抗器匝间绝缘操作过电压耐受特性的影响[J]. 电工技术学报, 2020, 35(24): 5096-5104. Nie Hongyan, Wei Xinlao, Yao Yuanhang, et al.The influence of thermal aging on the overvoltage withstand characteristics of the inter-turn insulation of dry-type air-core power reactors[J]. Transactions of China Electrotechnical Society, 2020, 35(24): 5096-5104. [23] 叶润峰, 裴家耀, 郑明胜, 等. 高介电聚丙烯基纳米复合薄膜介电及储能性能抗老化特性[J]. 电工技术学报, 2020, 35(16): 3529-3538. Ye Runfeng, Pei Jiayao, Zheng Mingsheng, et al.Anti-aging characteristics of dielectric and energy storage properties of high dielectric polypropylene-based nanocomposite films[J]. Transactions of China Electrotechnical Society, 2020, 35(16): 3529-3538. [24] 李化, 章妙, 林福昌, 等. 金属化膜电容器自愈理论及规律研究[J]. 电工技术学报, 2012, 27(9): 218-223. Li Hua, Zhang Miao, Lin Fuchang, et al.Research on the self-healing theory and law of metallized film capacitors[J]. Transactions of China Electrotechnical Society, 2012, 27(9): 218-223. [25] 彭倩, 吴广宁, 张星海, 等. 机械应力对聚丙烯薄膜局部放电性能的影响[J]. 高电压技术, 2008, 34(6): 1261-1266. Peng Qian, Wu Guangning, Zhang Xinghai, et al.The effect of mechanical stress on the partial discharge performance of polypropylene film[J]. High Voltage Engineering, 2008, 34(6): 1261-1266. [26] 邹林, 赵正涛. 应用于DC-link电容器的金属化膜自愈特性分析[J]. 电力电容器与无功补偿, 2014(2): 69-74. Zou Lin, Zhao Zhengtao.Analysis of self-healing characteristics of metallized film applied to DC-link capacitors[J]. Power Capacitor & Reactive Power Compensation, 2014(2): 69-74. [27] Lahti K, Rytluoto I, Niittymki M, et al.From laboratory to industrial scale: comparison of short-and long-term dielectric performance of silica-polypropylene capacitor films[C]//IEEE International Conference on Dielectrics, Valencia, 2020: 661-664. [28] Ran Zhaoyu, Du Boxue, Xiao Meng, et al.Dielectric property improvement of polypropylene films doped with POSS for HVDC polymer film capacitors[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(4): 1308-1316. [29] Ran Zhaoyu, Du Boxue, Xiao Meng, et al.High temperature breakdown performance improvement of polypropylene films based on micromorphology control[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(5): 1547-1554. [30] Zhang Chuyan, Shi Weichen, Wang Qiao, et al.Effect of nano-clay filler on the thermal breakdown mechanism and lifespan of polypropylene film under AC fields[J]. IEEE Access, 2020, 8: 36055-36060. [31] Dang Bin, He Jinliang, Zhou Yao, et al.Large improvement in trap level and space charge distribution of polypropylene by enhancing the crystalline-amorphous interface effect in blends[J]. Polymer International, 2016, 65(4): 371-379. [32] 韩颖. POE、INFUSE、SEBS、LLDPE对聚丙烯微观结构与性能影响及其透明化研究[D]. 北京: 北京化工大学, 2017. [33] Fan Benhui, Zhou Mingyu, Zhang Chong, et al.Improved dielectric properties in polypropylene/ poly(vinylidene fluoride) binary blends containing boron nitride nanosheets (BNNS): towards high voltage current application[J]. Journal of Physical Chemistry C, 2019, 123: 11993-12000. [34] Du Boxue, Liu Chang, Li Zhonglei, et al.Effects of hindered phenolic antioxidants on space charge and breakdown properties of polypropylene[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(1): 124-132. [35] Du Boxue, Xing Jiwen, Xiao Meng, et al.Improved dielectric properties of polypropylene films based on aromatic compounds[C]//IEEE International Conference on Electrical Materials and Power Equipment, Chongqing, 2021: 15-19. [36] Huang Xingyi, Fan Yanyan, Zhang Jun, et al.Polypropylene based thermoplastic polymers for potential recyclable HVDC cable insulation applications[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2017, 24(3): 1446-1456. [37] 张伟, 徐曼, 陈光辉, 等. 等规和嵌段聚丙烯的结构和性能[J]. 高电压技术, 2017, 43(11): 3634-3644. Zhang Wei, Xu Man, Chen Guanghui, et al.Structure and properties of isotactic and block polypropylene[J]. High Voltage Engineering, 2017, 43(11): 3634-3644. [38] Liu Wenfeng, Cheng Lu, Liu Xiaowei, et al.Correlation between morphology and electrical breakdown strength of the polypropylene/maleic anhydride grafted polypropylene/nano-ZrO2 ternary system[J]. Journal of Applied Polymer Science, 2018, 135(43): 46842. [39] Zhang Gang, Nam C, Chung T C M, et al. Polypropylene copolymer containing cross-linkable antioxidant moieties with long-term stability under elevated temperature conditions[J]. Macromolecules, 2017, 50(18): 7041-7051. [40] Guo Qiyang, Li Xiaotian, Li Wenfei, et al.The balanced insulating performance and mechanical property of PP by introducing PP-g-PS graft copolymer and SEBS elastomer[J]. Industrial & Engineering Chemistry Research, 2018, 57(19): 6696-6704. [41] Zhou Yao, Li Qi, Dang Bin, et al.A scalable, high‐throughput, and environmentally benign approach to polymer dielectrics exhibiting significantly improved capacitive performance at high temperatures[J]. Advanced Materials, 2018, 30(49): e1805672. [42] Du Boxue, Xu Ranran, Li Jin, et al.Improved carrier mobility dependent surface charge and flashover voltage of polypropylene film under DC and pulse voltages[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2018, 25(3): 1014-1021. [43] Liu Haoliang, Du Boxue, Xiao Meng, et al.High temperature performance of dielectric breakdown in BOPP capacitor film based on surface grafting[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(4): 1264-1272. [44] Liu Haoliang, Du Boxue, Xiao Meng.Improved energy density and charge discharge efficiency of polypropylene capacitor film based on surface grafting[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(5): 1539-1546.
2023, Vol. 38 
