外电场下交联聚乙烯电介质材料分子结构变化及其电老化微观机理研究
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摘要
为了从微观角度分析交联聚乙烯(XLPE)材料的电树枝老化,本文采用分子模拟方法计算并优化得到了XLPE分子结构.沿着聚乙烯链施加不同大小电场强度,分析交联聚乙烯分子的几何结构、偶极矩、极化率、电荷分布、前线轨道能量和红外光谱变化规律.计算结果表明,随着外电场的增大,交联聚乙烯分子红外光谱发生较大变化;当外施电场达到0.026a.u.后,红外光谱图中出现虚频,表明分子空间结构不再稳定,易发生断键;另外从前线轨道图的变化可以看出断键现象最先发生在交联聚乙烯链端部;沿着电场方向,原子所带电荷量由交联处向端部转移,当外施电场达到0.029a.u.后,链端部的C-H和C-C键断裂产生H·和CH_3·自由基.游离的自由基会形成空间电荷并发生积聚,产生局部较大场强,从而进一步影响交联聚乙烯链的空间结构.而电介质内部微观特性的变化必定会导致交联聚乙烯材料绝缘性能的下降,这些变化对揭示交联聚乙烯电缆电树枝形成的微观规律具有重要研究意义.
In order to analyze the electrical tree aging of cross-linked polyethylene(XLPE) material from the micro views, this paper adopts molecular simulation method to calculate and optimize the XLPE molecular structure. Exerting different grades electric field intensities along the polyethylene chain, the geometrical structure, dipole moment, polarizability, charge distribution, frontier orbital energy and infrared spectrum of the cross-linked polyethylene molecule were analyzed. The calculation results show that infrared spectrum of cross-linked polyethylene molecular changes greatly with the increase of the external electric fields. When the external electric field intensity reaches 0.026 a.u., virtual frequency appears in infrared spectrum. This indicates that the molecular spatial structure is no longer stable and prone to bond breaking. In addition, from the change of frontier orbital diagram, it is found that the bond breaking occurs firstly at the ends of polyethylene chains. Along the direction of the electric field, the atomic charge amount is transferred from the junction to the end. When the exerted electric field reaches 0.029 a.u., the C-H and C-C bonds at the end of the chain break to produce H· and CH_3· radicals. The free radicals form the space charge and accumulate, resulting in a larger local electric field, which further influences the spatial structure of the cross-linked polyethylene chain. The change of dielectric micro characteristics will lead to the decrease of insulation property of XLPE material. These changes have important significance for revealing the microscopic rules of electrical tree formation.
In order to analyze the electrical tree aging of cross-linked polyethylene(XLPE) material from the micro views, this paper adopts molecular simulation method to calculate and optimize the XLPE molecular structure. Exerting different grades electric field intensities along the polyethylene chain, the geometrical structure, dipole moment, polarizability, charge distribution, frontier orbital energy and infrared spectrum of the cross-linked polyethylene molecule were analyzed. The calculation results show that infrared spectrum of cross-linked polyethylene molecular changes greatly with the increase of the external electric fields. When the external electric field intensity reaches 0.026 a.u., virtual frequency appears in infrared spectrum. This indicates that the molecular spatial structure is no longer stable and prone to bond breaking. In addition, from the change of frontier orbital diagram, it is found that the bond breaking occurs firstly at the ends of polyethylene chains. Along the direction of the electric field, the atomic charge amount is transferred from the junction to the end. When the exerted electric field reaches 0.029 a.u., the C-H and C-C bonds at the end of the chain break to produce H· and CH_3· radicals. The free radicals form the space charge and accumulate, resulting in a larger local electric field, which further influences the spatial structure of the cross-linked polyethylene chain. The change of dielectric micro characteristics will lead to the decrease of insulation property of XLPE material. These changes have important significance for revealing the microscopic rules of electrical tree formation.
引文
[1] Zhou Y X,Zhao J K,Liu R,et al.Key technical analysis and prospect of high voltage and extra-high voltage power cable[J].High Voltage Eng.,2014,40:2593 (in Chinese) [周远翔,赵健康,刘睿,等.高压/超高压电力电缆关键技术分析及展望[J].高电压技术,2014,40:2593]
[2] Ouyang B H,Zhao J K,Chen Z Z,et al.Influence of aging mode on space charge distribution of AC XLPE cables[J].High Voltage Eng.,2012,38:2123 (in Chinese) [欧阳本红,赵健康,陈铮铮,等.老化方式对交流交联聚乙烯电缆空间电荷分布的影响[J].高电压技术,2012,38:2123]
[3] Li W,Wu L L,Zhang X,et al.Research progress in ageing and evaluation of XLPE cable[J/OL].Insulating Mater.,2016,49:36 (in Chinese) [李伟,吴麟琳,张幸,等.交联聚乙烯电缆的老化及其诊断方法研究进展[J/OL].绝缘材料,2016,49:36]
[4] Zhou K,Yang M L,Huang M,et al.Changes of electrical properties and micro structures of water-tree cables rejuvenated by siloxane during the process of electrical-thermal aging[J/OL].High Voltage Eng.,2017,43:1656 (in Chinese) [周凯,杨明亮,黄明,等.有机硅修复后水树电缆在电热老化下的电气性能和微观结构变化[J/OL].高电压技术,2017,43:1656]
[5] Zhou K,Tao X T,Wang X J,et al.Insight into the new role of titanium isopropoxide catalyst on rejuvenation for water tree aged cables[J].IEEE Transactions on Dielectrics and Electrical Insulation,2015,22:611.
[6] Wang X,Sun X T,Liu Q Y,et al.Research development of aging models of insulation materials based on space charge effect[J] High Voltage Eng.,2016,42:861 (in Chinese)[王霞,孙晓彤,刘全宇,等.基于空间电荷效应的绝缘老化寿命模型的研究进展[J].高电压技术,2016,42:861]
[7] Yang L J,Huang J J,Xu Z M,et al.Investigation on thermal aging characteristics and lifetime model of oil-Paper insulation for HV AC bushing[J].Transact.China Electrotechn.Soc.,2016,31:144 (in Chinese) [杨丽君,黄加佳,许佐明,等.高压交流套管的油纸绝缘热老化特性及寿命模型研究[J].电工技术学报,2016,31:144]
[8] Zhang A P,Wang R J.Cable fault on-line monitoring and fire pre-warning system based on digital temperature[J].Electric Power Automation Equipment,2003,23:57.(in Chinese) [张艾萍,万瑞军.基于数字温度传感器的电缆故障在线监测及火灾预警系统[J].电力自动化设备,2003,23:57]
[9] Liao R J,Hao J,Liang S W,et al.Influence of water and acid on the thermal aging of mineral oil mixed with natural ester oil-Paper insulation[J].Transact.China Electrotech.Soc.,2010,25:31 (in Chinese) [廖瑞金,郝建,梁帅伟,等.水分和酸对矿物油与天然酯混合油-纸绝缘热老化的影响[J].电工技术学报,2010,25:31]
[10] Younker J M,Sunkara H B,Bendler H V,et al.Prediction of flex modulus and solubility parameters for environmentally friendly nylon plasticizers by molecular dynamics simulations[C]//248th National Meeting of the American-Chemical-Society,the united states,2014:248.
[11] Wang X L,Li Q M,Zhang Y,et al.Simulation of reactive molecular dynamics of transformer oil pyrolysis at high temperature and the influence mechanism of acid in oil[J].High Voltage Eng.,2017,43:247 (in Chinese) [王学磊,李庆民,张颖,等.变压器油高温裂解及油中酸影响机理的反应分子动力学模拟[J].高电压技术,2017,43:247]
[12] Liao R J,Hu J,Yang L J,et al.Molecular simulation for thermal degradative micromechanism of power transformer insulation paper[J].High Voltage Eng.,2009,35:1565 (in Chinese) [廖瑞金,胡舰,杨丽君,等.变压器绝缘纸热老化降解微观机理的分子模拟研究[J].高电压技术,2009,35:1565]
[13] Liu Y F,He M,Luo Z,et al.Quantitative research on structure evolution of silane natural cross-linked polyethylene by Infrared spectrum[J].Eng.Plastics Appl.,2015,43:97 (in Chinese) [刘玉飞,何敏,罗筑,等.红外光谱法定量研究硅烷自然交联聚乙烯的结构演变[J].工程塑料应用,2015,43:97]
[14] Yang D,Zhou K,Tao X T,et al.Microstructure changes of XLPE cable in water tree area before and after injection rejuvenation[J].Transact.China Electrotech.Soc.,2015,30:228 (in Chinese) [杨滴,周凯,陶霰韬,等.交联聚乙烯电缆水树修复前后电缆微观结构的变化[J].电工技术学报,2015,30:228]
[15] Liu X D,Zheng X Q,Tu D M,et al.The influence of cross-linking process on space charge in XLPE[J].Insulating Mater.,2005:23 (in Chinese) [刘晓东,郑晓泉,屠德民,等.交联工艺对交联聚乙烯中空间电荷的影响[J].绝缘材料,2005:23]
[16] Wu X K,Tang Y L,et al.Molecular structure and infrared spectrum for SF6 under external electric fields[J].J.At.Mol Phys.,2016,33:385 (in Chinese) [吴学科,唐延林,等.外电场作用下SF6分子结构与红外光谱[J].原子与分子物理学报,2016,33:385]
[17] Yin W Y,Liu Y Z,Zhang X Y,et al.Molecular structure and spectrum of SiC under the radiation fields[J].J.At.Mol Phys.,2018,35:1 (in Chinese) [尹文怡,刘玉柱,张翔云,等.SiC在辐射场中的物理特性和光谱研究[J].原子与分子物理学报,2018,35:1]
[18] YinY H,Wang L.Structure and properties of AgBr under an external electric field[J].J.At.Mol Phys.,2017,34:9 (in Chinese) [尹跃洪,王莉.外电场下AgBr分子的结构及性质[J].原子与分子物理学报,2017,34:9]
[19] Wu Y G,Luo Y,Ling H R F.Molecular character and potential energy function of CO under external electric field[J].J.Sichuan Univ.:Nat.Sci.Ed.,2017,54:1007 (in Chinese)[吴永刚,罗娅,令狐荣锋.CO在外电场下的分子特性和势能函数研究[J].四川大学学报:自然科学版,2017,54:1007]
[20] Wu D L,Wu A J,Wen Y F,et al.External field effect on the molecular characteristics and potential energy of SiH[J].J.At.Mol Phys.,2017,54:79 (in Chinese) [伍冬兰,吴爱金,温玉锋,等.SiH分子特性和势能函数的外场效应[J].四川大学学报:自然科学版,2017,54:79]
[21] Chen Z Z.Theoretical study on the polarizability properties of liquid crystal in the THz range[J].Acta Phys.Sin.,2016,65:85 (in Chinese) [陈泽章.太赫兹波段液晶分子极化率的理论研究[J].物理学报,2016,65:85]
[22] Li L,Wang X,Sun W F,et al.Molecular dynamics simulation of polyethylene/silver-nanoparticle composites[J].Acta Phys.Sin.,2013,62:317 (in Chinese) [李琳,王暄,孙伟峰,等.聚乙烯/银纳米颗粒复合物的分子动力学模拟研究[J].物理学报,2013,62:317]
[2] Ouyang B H,Zhao J K,Chen Z Z,et al.Influence of aging mode on space charge distribution of AC XLPE cables[J].High Voltage Eng.,2012,38:2123 (in Chinese) [欧阳本红,赵健康,陈铮铮,等.老化方式对交流交联聚乙烯电缆空间电荷分布的影响[J].高电压技术,2012,38:2123]
[3] Li W,Wu L L,Zhang X,et al.Research progress in ageing and evaluation of XLPE cable[J/OL].Insulating Mater.,2016,49:36 (in Chinese) [李伟,吴麟琳,张幸,等.交联聚乙烯电缆的老化及其诊断方法研究进展[J/OL].绝缘材料,2016,49:36]
[4] Zhou K,Yang M L,Huang M,et al.Changes of electrical properties and micro structures of water-tree cables rejuvenated by siloxane during the process of electrical-thermal aging[J/OL].High Voltage Eng.,2017,43:1656 (in Chinese) [周凯,杨明亮,黄明,等.有机硅修复后水树电缆在电热老化下的电气性能和微观结构变化[J/OL].高电压技术,2017,43:1656]
[5] Zhou K,Tao X T,Wang X J,et al.Insight into the new role of titanium isopropoxide catalyst on rejuvenation for water tree aged cables[J].IEEE Transactions on Dielectrics and Electrical Insulation,2015,22:611.
[6] Wang X,Sun X T,Liu Q Y,et al.Research development of aging models of insulation materials based on space charge effect[J] High Voltage Eng.,2016,42:861 (in Chinese)[王霞,孙晓彤,刘全宇,等.基于空间电荷效应的绝缘老化寿命模型的研究进展[J].高电压技术,2016,42:861]
[7] Yang L J,Huang J J,Xu Z M,et al.Investigation on thermal aging characteristics and lifetime model of oil-Paper insulation for HV AC bushing[J].Transact.China Electrotechn.Soc.,2016,31:144 (in Chinese) [杨丽君,黄加佳,许佐明,等.高压交流套管的油纸绝缘热老化特性及寿命模型研究[J].电工技术学报,2016,31:144]
[8] Zhang A P,Wang R J.Cable fault on-line monitoring and fire pre-warning system based on digital temperature[J].Electric Power Automation Equipment,2003,23:57.(in Chinese) [张艾萍,万瑞军.基于数字温度传感器的电缆故障在线监测及火灾预警系统[J].电力自动化设备,2003,23:57]
[9] Liao R J,Hao J,Liang S W,et al.Influence of water and acid on the thermal aging of mineral oil mixed with natural ester oil-Paper insulation[J].Transact.China Electrotech.Soc.,2010,25:31 (in Chinese) [廖瑞金,郝建,梁帅伟,等.水分和酸对矿物油与天然酯混合油-纸绝缘热老化的影响[J].电工技术学报,2010,25:31]
[10] Younker J M,Sunkara H B,Bendler H V,et al.Prediction of flex modulus and solubility parameters for environmentally friendly nylon plasticizers by molecular dynamics simulations[C]//248th National Meeting of the American-Chemical-Society,the united states,2014:248.
[11] Wang X L,Li Q M,Zhang Y,et al.Simulation of reactive molecular dynamics of transformer oil pyrolysis at high temperature and the influence mechanism of acid in oil[J].High Voltage Eng.,2017,43:247 (in Chinese) [王学磊,李庆民,张颖,等.变压器油高温裂解及油中酸影响机理的反应分子动力学模拟[J].高电压技术,2017,43:247]
[12] Liao R J,Hu J,Yang L J,et al.Molecular simulation for thermal degradative micromechanism of power transformer insulation paper[J].High Voltage Eng.,2009,35:1565 (in Chinese) [廖瑞金,胡舰,杨丽君,等.变压器绝缘纸热老化降解微观机理的分子模拟研究[J].高电压技术,2009,35:1565]
[13] Liu Y F,He M,Luo Z,et al.Quantitative research on structure evolution of silane natural cross-linked polyethylene by Infrared spectrum[J].Eng.Plastics Appl.,2015,43:97 (in Chinese) [刘玉飞,何敏,罗筑,等.红外光谱法定量研究硅烷自然交联聚乙烯的结构演变[J].工程塑料应用,2015,43:97]
[14] Yang D,Zhou K,Tao X T,et al.Microstructure changes of XLPE cable in water tree area before and after injection rejuvenation[J].Transact.China Electrotech.Soc.,2015,30:228 (in Chinese) [杨滴,周凯,陶霰韬,等.交联聚乙烯电缆水树修复前后电缆微观结构的变化[J].电工技术学报,2015,30:228]
[15] Liu X D,Zheng X Q,Tu D M,et al.The influence of cross-linking process on space charge in XLPE[J].Insulating Mater.,2005:23 (in Chinese) [刘晓东,郑晓泉,屠德民,等.交联工艺对交联聚乙烯中空间电荷的影响[J].绝缘材料,2005:23]
[16] Wu X K,Tang Y L,et al.Molecular structure and infrared spectrum for SF6 under external electric fields[J].J.At.Mol Phys.,2016,33:385 (in Chinese) [吴学科,唐延林,等.外电场作用下SF6分子结构与红外光谱[J].原子与分子物理学报,2016,33:385]
[17] Yin W Y,Liu Y Z,Zhang X Y,et al.Molecular structure and spectrum of SiC under the radiation fields[J].J.At.Mol Phys.,2018,35:1 (in Chinese) [尹文怡,刘玉柱,张翔云,等.SiC在辐射场中的物理特性和光谱研究[J].原子与分子物理学报,2018,35:1]
[18] YinY H,Wang L.Structure and properties of AgBr under an external electric field[J].J.At.Mol Phys.,2017,34:9 (in Chinese) [尹跃洪,王莉.外电场下AgBr分子的结构及性质[J].原子与分子物理学报,2017,34:9]
[19] Wu Y G,Luo Y,Ling H R F.Molecular character and potential energy function of CO under external electric field[J].J.Sichuan Univ.:Nat.Sci.Ed.,2017,54:1007 (in Chinese)[吴永刚,罗娅,令狐荣锋.CO在外电场下的分子特性和势能函数研究[J].四川大学学报:自然科学版,2017,54:1007]
[20] Wu D L,Wu A J,Wen Y F,et al.External field effect on the molecular characteristics and potential energy of SiH[J].J.At.Mol Phys.,2017,54:79 (in Chinese) [伍冬兰,吴爱金,温玉锋,等.SiH分子特性和势能函数的外场效应[J].四川大学学报:自然科学版,2017,54:79]
[21] Chen Z Z.Theoretical study on the polarizability properties of liquid crystal in the THz range[J].Acta Phys.Sin.,2016,65:85 (in Chinese) [陈泽章.太赫兹波段液晶分子极化率的理论研究[J].物理学报,2016,65:85]
[22] Li L,Wang X,Sun W F,et al.Molecular dynamics simulation of polyethylene/silver-nanoparticle composites[J].Acta Phys.Sin.,2013,62:317 (in Chinese) [李琳,王暄,孙伟峰,等.聚乙烯/银纳米颗粒复合物的分子动力学模拟研究[J].物理学报,2013,62:317]