摘要
硅橡胶复合绝缘子老化后易引入乙烯基、羰基、羟基等强极性基团,形成化学性陷阱,进而加剧绝缘子老化甚至引发绝缘事故。为探究硅橡胶老化后不同化学基团的陷阱特性,以聚二甲基硅氧烷(PDMS)为基体,运用分子模拟软件分别构建含羰基、羟基和乙烯基的PDMS缺陷模型,针对稳定构型后的缺陷模型,利用第一性原理,对含不同结构的PDMS在电场作用下的键长、键角、原子布局及偶极矩变化进行了计算,获得了对应的陷阱能级和态密度分布变化。通过分析不同缺陷模型的微观分子结构与陷阱特性之间的内在联系,探究了不同化学陷阱在电场作用下的变化规律。结果表明,含羟基的PDMS引入了浅陷阱,而含乙烯基和羰基的PDMS引入了深陷阱;三种缺陷的陷阱深度均随着电场的增大而增加,且变化率由大到小依次为羰基、乙烯基和羟基;随着电场的增大,含乙烯基的PDMS结构中出现了空穴陷阱,含羰基的PDMS中的电子陷阱出现了消散,而含羟基PDMS的陷阱分布变化不大。由此可见,硅橡胶老化后形成的羰基基团在其老化进程中的作用不容忽视。老化后的硅橡胶陷阱态和基团含量有望作为硅橡胶老化评估的新的参考标准,可为硅橡胶老化实验提供理论依据。
Some strong polar groups such as vinyl,carbonyl and hydroxyl can be produced or elevated after the composite insulators’aging.These groups may further aggravate insulators’aging and cause insulation accidents in the field.So,this paper discusses the effects of different chemical groups on the trap characteristics of aged silicone rubber.The polydimethylsiloxane(PDMS)chain was used as the matrix.The defect models containing carbonyl group,hydroxyl group and vinyl group were constructed with molecular simulation technology.Then,the stable models were obtained after the dynamic simulation to the defect models.Firstly,based on the density functional theory,the microscopic structure parameters of stable defect models were calculated with first principles.The changes of bond length,bond angle,atomic layout and dipole moment under the action of electric field were obtained.Also,the corresponding trap energy levels and density distribution of states were derived.The internal relationships between the micro-structure of defect models and the trap characteristics were analyzed.The trap characteristics variety of defect models with the electric field was explored from three aspects.They are the trap depths,the variety rate of trap depth and density with the electric field and the trap types.The results show that the bond lengths and bond angles of PDMS containing vinyl and carbonyl groups decrease with the electric field.The PDMS containing carbonyl groups exhibits the greatest changes.This results in a greater degree of molecular chain curling and contraction,providing favorable conditions for charging accumulation.However,the PDMS containing hydroxyl groups presents the opposite trends.This is not conducive to the accumulation of charges and the formation of deeper traps.On the other hand,the PDMS containing carbonyl groups has the maximum molecular dipole moment and the smallest molecular energy gap.This brings stronger molecular chemical activity.So the charges were easy to be captured and the traps are deeper.Therefore,the trap depth of PDMS containing carbonyl groups is the largest.The variation of trap depths with the electric field indicates the trap depth of the defect models all increases with the electric field.The change rates in descending order was carbonyl,vinyl,and hydroxyl.A possible explanation is that the molecular activity is more related to its corresponding energy gap.The PDMS containing carbonyl groups has a stronger ability to capture charges under the electric field,and the corresponding trap depth changes is the most.As for the trap density,the results show it is linearly corresponding to the trend of trap depth variation.The highest energy level corresponds to the highest density,which is consistent with relevant experimental results.The trap types could transform with the electric field.However,the three defect models take different change trends.The electron and hole traps of PDMS containing hydroxyl groups do not change significantly,which were all shallow traps.The hole traps appeared in the structure of PDMS containing vinyl group.And the number of electron traps was much greater than that of hole traps.The electron traps of PDMS containing carbonyl groups dissipated with the electric field.The following conclusions can be drawn from the simulation analysis:(1)The trap deepening of PDMS containing carbonyl groups’may mainly be attributed to the hole traps.(2)The dissipation and recombination of charges in electron traps are important factors causing aging and surface discharge.(3)The role of PDMS containing carbonyl groups in the aging process of silicone rubber cannot be ignored.It is expected to be a new reference standard for silicone rubber aging evaluation.
作者
沈瑶
刘兴杰
梁英
薄天利
赵涛
Shen Yao;Liu Xingjie;Liang Ying;Bo Tianli;Zhao Tao(School of Electronic and Electrical Engineering Ningxia University,Yinchuan 750021 China;Department of Electric Power Engineering North China Electric Power University,Baoding 071003 China)
出处
《电工技术学报》
EI
CSCD
北大核心
2024年第17期5545-5554,共10页
Transactions of China Electrotechnical Society
基金
国家自然科学基金地区项目(12062023)
自治区重点研发计划社发领域项目(2021BEG03029)资助。
关键词
硅橡胶
复合绝缘子
老化
化学陷阱
陷阱分布
Silicone rubber
composite insulator
aging
chemical trap
trap distribution
