Study on the Influence of the Dynamic Film Resistance of Scale Layer on the Dynamic Deposition Characteristics of Grading Electrodes in Inner Cooling System of Converter Calve
Li Tong1, Liu Penglong2, Li Ningrui1, Kang Chao1, Lu Binxian2
1. State Grid Gansu Electric Power Company Extra High Voltage Company Lanzhou 730000 China; 2. School of Electrical and Electronic Engineering North China Electric Power University Beijing 102206 China
Abstract：The failures of the cooling system in the converter valve is directly or indirectly caused by the problem of thegrading electrode deposition which accounts for more than 70% and has become an important factor that affects the safe and stable operation of the HVDC transmission system. The cooling medium boundary and the electrode reaction kineticsareaffectedby dynamic deposition of the scale layer on the surface of the grading electrode. The deposition reaction involves ohmic polarization, concentration polarization and electrochemical polarization process. The deposition reaction is complex one. However, most of the existing studies on the grading electrode deposition ignore the influence of turbulent field, mass transfer field and dynamic deposition of scaling ion in scale layer in the internal cooling system. A three-dimensional simulation model of the cooling system in a single valve segment is established, in which electric field, turbulence fluid field and mass transfer field are coupled. Not only is the dynamic growth mechanism of the grading electrode scale layer analyzed and predicted, but also are the corresponding fitting formulas obtained. They provide the basis for the maintenance and scale removal of the grading electrode in the converter valves. Firstly, the potential difference of scale layer is introduced into the electrode kinetic equation, and the traditional Butler-Volmer equation is corrected. A dynamic film resistance model of scale layer is constructed to study the influence of dynamic scale layer deposition on the deposition reaction. The results show that the growth of scale layer can inhibit the deposition reaction. Secondly, the equivalent conductivity of the scale layer is determined by weighting conductivities of Al(OH)3 and deionized water. The maximum thickness of the grading electrode scale layer with the running time of 3 and a half years is 0.716 mm, which is 0.85% deviation from the statistical data of the scale layer in the actual converter station. It is 11.35% lower compared with the existing research. The simulation model is verified. Thirdly, not only are the growth rules of scale layer within 5 years predicted, including the change curves of scale layer thickness, deposition quality and deposition rate, but also are these curves fitted with a formula. The results show that the variation law of the scale layer average thickness and deposition mass are approximated with the zero-state response of the first-order RC circuit. Both forms are linear, and have the same time constant, their time constantsare 1 111 days. When the time reaches 3~5 τ, the deposition mass deposited on the grading electrode and the average thickness of the scale layer approximately reach the steady state. The deposition reaction on the grading electrode surface almost stops. The ultimate deposition mass is 377 mg, and the ultimate average thickness of the scale layer is 1.03 mm. However, the deposition rate decreased in a piecewise single-exponential pattern, with the decay time constant τ=36 d between 0~150 days and τ =406 d after 150 days. Finally, the electrolyte potential of the scale layer surface isonly decreased by 2.5%. The total leakage current in the branchpipe is only increased by 1.53% with the running time of 5 years,indicating that the increase of the scale layer thickness on the surface of the grading electrode hasa weak impact on the voltage equalization effect of the grading electrode.
李通, 刘鹏龙, 李宁瑞, 康超, 卢斌先. 垢层动态膜阻对换流阀冷却系统内均压电极动态沉积特性影响机理研究[J]. 电工技术学报, 2023, 38(7): 1695-1704.
Li Tong, Liu Penglong, Li Ningrui, Kang Chao, Lu Binxian. Study on the Influence of the Dynamic Film Resistance of Scale Layer on the Dynamic Deposition Characteristics of Grading Electrodes in Inner Cooling System of Converter Calve. Transactions of China Electrotechnical Society, 2023, 38(7): 1695-1704.
[1] 刘振亚, 舒印彪, 张文亮, 等. 直流输电系统电压等级序列研究[J]. 中国电机工程学报, 2008, 28(10): 1-8. Liu Zhenya, Shu Yinbiao, Zhang Wenliang, et al.Study on voltage class series for HVDC transmission system[J]. Proceedings of the CSEE, 2008, 28(10): 1-8. [2] 刘国友, 黄建伟, 舒丽辉, 等. 6英寸晶闸管的研究开发与特性控制[J]. 变流技术与电力牵引, 2007(6): 32-35. Liu Guoyou, Huang Jianwei, Shu Lihui, et al.R & D and characteristic control of 6-inch thyristors[J]. Converter Technology & Electric Traction, 2007(6): 32-35. [3] 赵畹君. 高压直流输电工程技术[M]. 2版. 北京: 中国电力出版社, 2011. [4] Jackson P O, Abrahamsson B, Gustavsson D, et al.Corrosion in HVDC valve cooling systems[J]. IEEE Transactions on Power Delivery, 1997, 12(2): 1049-1052. [5] 王远游, 郝志杰, 林睿. 天广直流工程换流阀冷却系统腐蚀与沉积[J]. 高电压技术, 2006, 32(9): 80-83. Wang Yuanyou, Hao Zhijie, Lin Rui.Primary analysis on corrosion and deposit in valve cooling system of Tian-Guang HVDC project[J]. High Voltage Engineering, 2006, 32(9): 80-83. [6] Siemens. Valve cooling system maintenance manual[M]. Power Transmission and Distribution, 1999. [7] Karady G G, Amarh F.Signature analysis for leakage current waveforms of polluted insulators[C]//1999 IEEE Transmission and Distribution Conference (Cat. No. 99CH36333), New Orleans, LA, USA, 1999: 806-811. [8] 卢斌先, 葛东阳, 周建辉, 等. 换流阀水路冷却系统电极反应的等效电路建模[J]. 高电压技术, 2016, 42(7): 2199-2206. Lu Binxian, Ge Dongyang, Zhou Jianhui, et al.Equivalent electric circuit modeling for electrode reaction in valve cooling water system[J]. High Voltage Engineering, 2016, 42(7): 2199-2206. [9] 贺婷婷, 高兵, 杨帆, 等. 电-流-传质场作用下的换流阀冷却系统均压电极垢层动态沉积特性研究[J]. 电工技术学报, 2019, 34(14): 2863-2873. He Tingting, Gao Bing, Yang Fan, et al.The dynamic deposition behavior of grading electrode in converter valve cooling system considering electro-velocity-mass transfer field[J]. Transactions of China Electrotechnical Society, 2019, 34(14): 2863-2873. [10] Tian Yingfu, Li Huixi, Wang Shengping, et al.Erosion-corrosion behavior of aluminum in a 50 ℃ ethylene glycol aqueous solution simulating cooling water in HVDC transmission[J]. Materials and Corrosion, 2021, 72(12): 1899-1907. [11] 李道豫, 邱志远, 李学武, 等. 铝在高压直流输电系统中高电压高温下的腐蚀行为研究[J]. 化工进展, 2016, 35(增刊2): 92-98. Li Daoyu, Qiu Zhiyuan, Li Xuewu, et al.Corrosion behavior of aluminum at high potential and high temperature in HVDC systems[J]. Chemical Industry and Engineering Progress, 2016, 35(S2): 92-98. [12] 段涛, 杨斌, 李贤庆, 等. ±500 kV换流站阀水冷系统隐患分析治理[J]. 电力系统保护与控制, 2014, 42(18): 132-138. Duan Tao, Yang Bin, Li Xianqing, et al.Analysis of potential dangers in ±500 kV converter station valve water cooling system[J]. Power System Protection and Control, 2014, 42(18): 132-138. [13] 葛东阳. 换流阀冷却系统腐蚀与沉积分析模型与影响因素研究[D]. 北京: 华北电力大学, 2016. [14] 张望平, 郑丰, 郝良收, 等. 基于恒电位法的阀冷却系统铝散热器腐蚀特性研究[J]. 高压电器, 2019, 55(5): 175-181. Zhang Wangping, Zheng Feng, Hao Liangshou, et al.Corrosion characteristics of aluminum radiator for valve cooling system based on constant potential method[J]. High Voltage Apparatus, 2019, 55(5): 175-181. [15] Zahraei M, Saidi M S, Sani M.Numerical simulation of electro-deposition process influenced by force convection and migration of ions[J]. Journal of Electroanalytical Chemistry, 2016, 782: 117-124. [16] Weber I, Mallick B, Schild M, et al.Behavior of highly diluted electrolytes in strong electric fields-prevention of alumina deposition on grading electrodes in HVDC transmission modules by CO2-induced pH-control[J]. Chemistry (Weinheim an Der Bergstrasse, Germany), 2014, 20(38): 12091-12103. [17] Yin Litao, Jin Y, Leygraf C, et al.A FEM model for investigation of micro-galvanic corrosion of Al alloys and effects of deposition of corrosion products[J]. Electrochimica Acta, 2016, 192: 310-318. [18] Sun Wen, Liu Guicheng, Wang Lida.A mathematical model for modeling the formation of calcareous deposits on cathodically protected steel in seawater[J]. Electrochimica Acta, 2012, 78: 597-608.
2023, Vol. 38 
