硅脂对硅橡胶电树枝劣化特性的影响机制研究
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摘要
电树枝劣化是硅橡胶电缆附件绝缘性能下降甚至击穿的主要原因,但电缆附件安装时在电缆本体与附件界面处涂覆的硅脂对硅橡胶电树枝劣化性能的影响目前尚缺乏研究。该文研究硅脂对硅橡胶电树枝劣化特性的影响,发现硅脂导致硅橡胶的起树电压由13.5kV下降至10.8kV,电树枝形貌由枝状向丛状转变。进一步的表面电位衰减特性、热分解过程和交联密度的测试结果表明,硅脂导致硅橡胶主链断裂,硅橡胶与白炭黑的物理交联结构被破坏、交联密度下降,硅橡胶中的自由体积增大,电荷迁移率上升。因此,注入的电荷在电场作用下获得更高的能量,撞击分子链段使其破坏程度加剧,最终导致硅橡胶绝缘起树电压降低。同时,自由体积的增大使得在较低的径向电场下,电荷也能加速获得足够的能量打断分子链。因此,电树枝形貌逐渐由树枝状向丛林状转变。
Electrical tree degradation is one of the main reasons for the decline of insulation performance or even failure of silicone rubber based cable accessories. During the installation of cable accessory, the interface between cable accessory insulation and cable insulation is usually coated by silicone grease. However, the influence of silicone grease on electrical tree degradation is not fully understood. The effect of silicone grease on the electrical tree degradation characteristics of SR was studied in the paper. The results showed that, due to the silicone grease, the electrical tree initiation voltage decreased from 13.5kV to 10.8kV, while the pattern of the electrical tree changed from branch type to bush type. Further analysis were carried out by trap charge characteristic, thermal decomposition analysis and crosslinking density measurement. It was suggested that the break of physical crosslinking and molecular chain caused by silicone grease led to the decline of crosslinking density as well as the increase of free volume and charge mobility. Therefore, due to increased free volume, higher energy of injected charges can be achieved, which consequently led to more broken chains in silicon rubber and eventually a lower electrical tree initiation voltage. At the same time, the charges can also be accelerated to break the molecular chains under weak radial electric field in a larger free volume. Therefore, the pattern of electrical tree was changed from branch type to bush type.
Electrical tree degradation is one of the main reasons for the decline of insulation performance or even failure of silicone rubber based cable accessories. During the installation of cable accessory, the interface between cable accessory insulation and cable insulation is usually coated by silicone grease. However, the influence of silicone grease on electrical tree degradation is not fully understood. The effect of silicone grease on the electrical tree degradation characteristics of SR was studied in the paper. The results showed that, due to the silicone grease, the electrical tree initiation voltage decreased from 13.5kV to 10.8kV, while the pattern of the electrical tree changed from branch type to bush type. Further analysis were carried out by trap charge characteristic, thermal decomposition analysis and crosslinking density measurement. It was suggested that the break of physical crosslinking and molecular chain caused by silicone grease led to the decline of crosslinking density as well as the increase of free volume and charge mobility. Therefore, due to increased free volume, higher energy of injected charges can be achieved, which consequently led to more broken chains in silicon rubber and eventually a lower electrical tree initiation voltage. At the same time, the charges can also be accelerated to break the molecular chains under weak radial electric field in a larger free volume. Therefore, the pattern of electrical tree was changed from branch type to bush type.
引文
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[23]付秋兰,吴向荣,温茂添.缩合型室温硫化硅橡胶耐热性的研究进展[J].有机硅材料,2003,17(1):28-31.Fu Qiulan,Wu Xiangrong,Wen Maotian.Study progress on thermal stability of condensed type RTV silicone rubber[J].Silicone Material,2003,17(1):28-31(in Chinese).
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[2]Kamiya Y,Muramoto Y,Shimizu N.Influence of vacuum evacuation on electrical tree initiation in silicone rubber[C]//Proceedings of IEEE Conference on Electrical Insulation and Dielectric Phenomena.Cansas,USA:IEEE,2006.
[3]Kamiya Y,Muramoto Y and Shimizu.Effect of gas impregnation in silicone rubber on electrical tree initiation[C]//Proceedings of IEEE Conference on Electrical Insulation and Dielectric Phenomena.Vancouver,Canada,2007.
[4]Tanabe K,Muramoto Y,Shimizu N.Effect of H2Omolecule on electrical tree initiation voltage of silicone rubber[C]//IEEE International Conference on Solid Dielectrics.Bologna,Italy,2013.
[5]周远翔,刘睿,张云霄,等.硅橡胶电树枝的引发与生长过程[J].高电压技术,2014,40(12):3656-3664.Zhou Yuanxiang,Liu Rui,Zhang Yunxiao,et al.Initiation and propagation processes of electrical tree in silicone rubber[J].High Voltage Engineering,2014,40(12):3656-3664(in Chinese).
[6]周远翔,侯非,聂琼,等.温度对硅橡胶电树枝老化特性的影响[J].高电压技术,2012,38(10):2640-2646.Zhou Yuanxiang,Hou Fei,Nie Qiong,et al.Temperature effects on electrical tree aging characteristics of silicone rubber[J].High Voltage Engineering,2012,38(10):2640-2646(in Chinese).
[7]周远翔,张云霄,张旭,等.热老化时间对硅橡胶电树枝起始特性的影响[J].高电压技术,2014,40(4):979-986.Zhou Yuanxiang,Zhang Yunxiao,Zhang Xu,et al.Influence of thermal aging time on electrical tree initiation of silicone rubber[J].High Voltage Engineering,2014,40(4):979-986(in Chinese).
[8]聂琼,周远翔,陈铮铮,等.频率对硅橡胶起树电压及电树枝形态的影响[J].高电压技术,2009,35(1):141-145.Nie Qiong,Zhou Yuanxiang,Chen Zhengzheng,et al.Influence of frequency on tree initiation voltage and electrical tree shape in silicone rubber[J].High Voltage Engineering,2009,35(1):141-145(in Chinese).
[9]苏金刚.多场耦合作用硅橡胶电树枝产生机理研究[D].天津:天津大学,2014.Su Jingang.Research on the Treeing mechanism of silicone rubber under several coupling fields[D].Tianjin:Tianjin University,2014(in Chinese).
[10]杜伯学,苏金刚,徐航,等.机械应力下高温硫化硅橡胶电树枝生长特性[J].中国电机工程学报,2016,36(24):6627-6634.Du Boxue,Su Jingang,Xu Hang,et al.Treeing growth characteristics in HTV silicone rubber considering mechanical stress[J].Proceedings of the CSEE,2016,36(24):6627-6634(in Chinese).
[11]古亮.交联聚乙烯-硅橡胶界面电痕破坏现象研究[D].天津:天津大学,2010.Gu Liang.Tracking Failure at Interface between XLPEand Silicon-rubber[D].Tianjin:Tianjin University,2010(in Chinese).
[12]陈果.XLPE-SIR接头界面电场分布及其电痕破坏特征研究[D].重庆:重庆理工大学,2015.Chen Guo.Study on the electric field distribution of XLPE-silicon rubber and tracking failure[D].Chongqing:Chongqing University of Technology,2015(in Chinese).
[13]Normand A,Daniel F.Influence of thermal cycling on the cable joint interfacial pressure[C]//IEEE International Conference on Solid Dielectrics.Eindhoven,Netherlands,2001.
[14]巫松桢,谢大荣,陈寿田,等.电气绝缘材料科学与工程[M].西安:西安交通大学出版社,1996:63-65.Wu Songzhen,Xie Darong,Chen Shoutian,et al.Electrical insulating material science and engineering[M].Xi’an:Xi’an Jiaotong University Press,1996:63-65(in Chinese).
[15]王霞,姚航,吴锴,等.交联聚乙烯与硅橡胶界面涂抹不同硅脂对其电荷特性的影响[J].高电压技术,2014,40(1):74-79.Wang Xia,Yao Hang,Wu Kai,et al.Effect of different coating silicone grease on space charge characteristics at XLPE/SR interface[J].High Voltage Engineering,2014,40(1):74-79(in Chinese).
[16]王霞,朱有玉,张宇巍,等.界面涂敷料对XLPE和SIR复合绝缘界面空间电荷特性的影响[J].高电压技术,2016,42(8):2382-2387.Wang Xia,Zhu Youyu,Zhang Yuwei,et al.Influence of interfacial coating on charge property of XLPE and SIRcomposite insulation[J].High Voltage Engineering,2016,42(8):2382-2387(in Chinese).
[17]Li J,Zhou F,Min D,et al.The energy distribution of trapped charges in polymers based on isothermal surface potential decay model[J].IEEE Transactions on Dielectrics and Electrical Insulation,2015,22(3):1723-1732.
[18]Flory P J,Rehner J.Statistical mechanics of cross-linked polymer networks I rubberlike elasticity[J].Journal of Chemical Physics,1943,11(11):512-520.
[19]Flory P J,Rehner J.Statistical mechanics of cross-linked polymer networks II swelling[J].Journal of Chemical Physics,1943,11(11):521-526.
[20]Zhou F,Li J,Yan Z,et al.Investigation of charge trapping and detrapping dynamics in LDPE,HDPE and XLPE[J].IEEE Transactions on Dielectrics and Electrical Insulation,2017,23(6):3742-3751.
[21]朱利明.有关相似相溶规律的讨论[J].大学化学,2003,18(1):45-45.Zhu Liming.Discussion about the Law of Similar Mutual Solubility[J].University Chemistry,2003,18(1):45-45(in Chinese).
[22]韩黎刚.纳米碳材料复配氢氧化铝阻燃HDPE的研究[D].杭州:浙江大学,2015.Han Ligang.Study on flame retardant HDPE with aluminium hydroxide/nano carbon material complex[D].Hangzhou:Zhejiang University,2015(in Chinese).
[23]付秋兰,吴向荣,温茂添.缩合型室温硫化硅橡胶耐热性的研究进展[J].有机硅材料,2003,17(1):28-31.Fu Qiulan,Wu Xiangrong,Wen Maotian.Study progress on thermal stability of condensed type RTV silicone rubber[J].Silicone Material,2003,17(1):28-31(in Chinese).
[24]Dissado L A,Fothergill J C.Electrical degradation and breakdown in polymers[M].London:Peter Peregrinus Ltd.,1992:125-131.
[25]李盛涛,郑晓泉.聚合物电树枝化[M].北京:机械工业出版社,2006:133-134.Li Shengtao,Zheng Xiaoquan.Electrical trees in polymers[M].Beijing:China Machine Press,2006:133-134(in Chinese).