摘要
基于Davidson-Cole模型提取极化响应的弛豫强度、弛豫时间及电导损耗等特征量,分析热氧老化过程中核级低压电缆绝缘各特征量的变化规律,阐明老化过程中微观与宏观性能下降的一致性。首先在165℃下对试样进行人工加速老化实验,获得不同劣化程度的试样,测试老化过程中试样理化特性、力学特性与介电响应的变化规律,发现老化过程中试样发生再交联反应,老化后期氧化反应加速进行;然后利用Davidson-Cole介电模型提取弛豫与电导特征参数,发现分子链段运动弛豫强度Δεα、热离子弛豫强度Δεδ与直流电导率σ_(dc)随老化时间增加呈逐渐下降趋势,老化504 h后,氧化反应的加速进行减缓了Δεα与σ_(dc)的下降,再交联反应对特征参数的变化起主导作用;最后对介电模型特征参数Δεα、Δεδ、σ_(dc)与断裂伸长率进行初步拟合,结果显示Δεα、Δεδ和σ_(dc)与断裂伸长率呈正相关,可见频域介电谱的定量分析可应用于低压电缆老化状态评估。
The low-voltage(LV)cables in nuclear power plants would be affected by heat and oxygen under actual operation,and the cable materials would gradually deteriorate with the increase of service time.The most common standard traditionally used to evaluate the insulation state of LV cables was the mechanical parameter,mainly elongation at break(EAB),however,the tensile experiments were destructive.Rencently,frequency domain spectroscopy(FDS),as one new non-destructive diagnostic technology,had the advantages of being non-destructive and simple,and was suitable for the characterization of the overall insulation state of the cables.However,the vast majority of studies focused on qualitatively analyzing the variation of the FDS with various influencing factors.Therefore,one scientific dielectric model was used to quantitatively analyze the dielectric response characteristics of LV cables,and the correlation between the dielectric parameters and the physical,chemical,mechanical properties of the materials was discussed.Firstly,the accelerated aging experiments were carried out on the cross-linked polyethylene(PE)/ethylene-vinyl acetate copolymer(EVA)specimens at 165℃ to obtain the samples with different degrees of deterioration.The changes in physical and chemical properties of PE/EVA specimens were tested through the Fourier transform infrared(FTIR)spectroscopy and the gel content.The deterioration of the mechanical property was investigated through the EAB experiment,and the dielectric properties were analyzed through the FDS at 100℃.The PE/EVA specimens had two relaxation processes form the analysis of FDS,and the DC conductance was considered at the same time.Therefore,the complex permittivity spectra of the PE/EVA samples with different aging degrees were fitted by the Davison-Cole dielectric model to extract the characteristic parameters of polarization and conductance.The results showed that the re-crosslinking reaction of the specimens occurs during the whole aging process,which increased the three-dimensional network structure.The carbonyl index of PE/EVA showed a trend of decreasing at the beginning and then increasing,which was caused by the degradation of vinyl acetate groups at the early stage and the oxidation reaction after 504 h.It was found that the relaxation strengthΔεαdue to the motion of segmental chains,the thermionic polarization strengthΔεδas well as the DC conductivityσdc gradually decreased with the increase of aging time through the Davidson-Cole dielectric model.The decrease ofΔεαandσdc slowed down due to the accelerated oxidation reaction after 504 h.The preliminary fitting of the characteristic parametersΔεα,Δεδ,σdc of the dielectric model and the traditional state evaluation criteria EAB showed a positive correlation.The following conclusions can be drawn from the analysis of experimental and fitting results:(1)The degree of cross-linking,as the key parameter during the aging process,is the most important determinant of the consistency between the dielectric parameters and the mechanical parameter.The increase in the degree of cross-linking of PE/EVA inhibits the migration of ions,so that the DC conductivityσdc and the relaxation strength of the samples decrease with the aging time.The free volume of PE/EVA specimens is reduced due to the augment of the macromolecular network structure,which weakens the movement of the molecular segments.At the same time,the increase of the degree of cross-linking reduces the flexibility of macromolecules of PE/EVA,and then the EAB decreases during the aging process.(2)It is found that the quantitative analysis of the frequency domain spectroscopy can not only characterize the dielectric response mechanism of the materials,but also has a strong correlation with the elongation at break,which can be better applied in the evaluation of the state and life of the LV cables.
作者
王镜然
王英杰
庄宏伟
纪民尊
刘文凤
Wang Jingran;Wang Yingjie;Zhuang Hongwei;Ji Minzun;Liu Wenfeng(State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong University,Xi’an 710049,China;Suzhou Nuclear Power Research Institute,Suzhou 215004,China;Guangxi Fangchenggang Nuclear Power Co.Ltd,Fangchenggang 538001,China)
出处
《电工技术学报》
EI
CSCD
北大核心
2023年第15期4030-4039,共10页
Transactions of China Electrotechnical Society
基金
陕西省重点研发计划资助项目(2020ZDLGY09-10)。
