光谱学与光谱分析, 2019, 39 (6): 1929, 网络出版: 2019-07-10  

表面粗糙度对激光诱导击穿光谱信号的影响

Influence of Sample Surface Roughness on Signal of Laser-Induced Breakdown Spectroscopy
作者单位
1 深圳复杂滨海环境电力装备可靠性工程实验室, 清华大学深圳研究生院, 广东 深圳 518055
2 南方电网科学院有限责任公司, 广东 广州 510080
3 国网南京供电公司, 江苏 南京 210019
4 深圳森日有机硅材料有限公司, 广东 深圳 518000
摘要
硅橡胶复合绝缘子是高压输电线路的关键设备, 长期在复杂外界环境条件下带电运行后会发生表面老化, 表现为粉化、 褪色、 粗糙度和硬度上升等现象。 粗糙度作为复合绝缘子的老化特征量之一, 其测量是复合绝缘子在线带电检测的难题。 激光诱导击穿光谱技术(laser-induced breakdown spectroscopy, LIBS)适用于开展输电线路复合材料的远程在线检测, 但粗糙度对LIBS信号的影响还没有得到系统的研究, 利用这种基体效应进行绝缘子表面粗糙度的测量尚无报道。 制备了不同粗糙度的硅橡胶新样品, 与500 kV线路退运的复合绝缘子样品进行对比分析, 研究了硅橡胶材料的粗糙度对LIBS信号的影响, 结果表明, 对于新制备硅橡胶材料随着粗糙度的增加, 各主体元素特征谱线强度会随之增强, 不同主体元素之间的原子谱线强度比(Si 288.2 nm/C 247.9 nm和Al 394.4 nm/Si 288.2 nm)随之下降, 说明样品粗糙度对LIBS测量结果影响显著。 但特征谱线强度及不同主体元素原子谱线强度比与粗糙度之间的函数关系不明显, 难以用于粗糙度测量。 硅橡胶的主体元素为Si, Al, C和O等, 考虑元素含量及特征谱线的选取方便选择Si为主要分析元素。 对于Si原子谱线强度比, 选取了两条上能级相近(Eki=40 991.88, 39 955.05 cm-1)的原子谱线(SiⅠ288.2 nm, SiⅠ250.7 nm)作为分析线, 在满足局部热力学平衡与光学薄的条件下两条谱线的强度比应为定值, 但样品粗糙度的改变会影响脉冲激光烧蚀材料表面的过程, 从而改变等离子体的状态, 使得谱线强度比值也随之变化。 上述两条硅原子谱线强度比和粗糙度建立的定标关系, 线性相关系数为0.88。 对于500 kV输电线路退运的老化硅橡胶材料, 其表面由于老化有部分氢氧化铝填料析出, 使得基体成分不均匀性更为显著, 其表面也变得更为粗糙, 这导致一对谱线强度比值作为定标函数, 实用性降低。 因此针对老化硅橡胶材料, 除了选择Si元素谱线(SiⅠ250.7 nm, SiⅠ251.4 nm, SiⅠ251.9 nm)以外, 还引入了Al元素谱线(AlⅠ305.7 nm, AlⅠ305.9 nm), 利用三组谱线强度比进行多元回归分析, 对于两个实测粗糙度为2.659和2.523 μm老化硅橡胶样品, LIBS测量的相对误差分别为0.218和0.189。 结果表明对同样成分的复合材料, 表面粗糙度对LIBS信号的影响是必须考虑的, 而利用这种基体效应, 开展远程在线测试复合绝缘子表面粗糙度, 对于高压输电线路检测运维具有重要的应用价值。
Abstract
Silicone rubber composite insulators are key equipment of HV transmission lines. Their surfaces will gradually deteriorate after running under a harsh environmental condition for a long time, and become chalked, faded, more rough and tough. As one of the characteristics of aging, surface roughness measuring is always difficult in power transmission line condition monitoring. Laser induced breakdown spectroscopy(LIBS) is suitable for remote condition monitoring in power system, but the influence of roughness on LIBS signal hasn't been systematically studied, and taking advantage of this matrix effect for insulator surface roughness testing hasn't been reported yet. New silicone rubber samples with different surface roughness were made, compared with those retired from a 500 kV power transmission line. The influence of roughness of new silicone rubber material on LIBS signal was studied and the results showed that when roughness increases, the spectral line intensity increases, while the ratio of different element line intensity(Si 288.2 nm/C 247 nm and Al 394 nm/Si 288.2 nm) decreases. It showed that roughness has a significant effect on LIBS signal. However, since there had been no obvious linear relationship between intensity and roughness or intensity ratio and roughness, it was hard to measure roughness by these relationships.The major elements of silicone rubber material were Si, Al, C, O and so on. Si was selected as the analytical element considering element content and spectral line selection convenience. Two atomic line of Si(SiⅠ288.2 nm, SiⅠ250.7 nm) was selected as the analytical line whose upper energy levels were nearly the same (Eki=40 991.88 and 39 955.05 cm-1). When the laser induced plasma satisfies LTE and optically thin condition, the ratio of line intensity should be constant, but the ablation process is affected by material surface roughness, and then the plasma state and intensity ratio will be changed. A calibration line of roughness and the above ratio was established and the linear correlation coefficient was 0.88. As for the aged silicone rubber material retired from the 500kV transmission line, the surface was precipitated by some ATH fillers because of the aging process, leading to a more inhomogeneous content in the matrix and a rougher surface. So it is not practical to measure roughness by only one couple of spectral lines. Therefor it is necessary to introduce Al atomic lines (Al Ⅰ 305.7 nm, Al Ⅰ 305.9 nm) in the calculation model besides Si atomic lines for the aged silicone rubber material. Multivariate regression was carried on with 3 sets of spectral intensity ratios, and then 2 agedsilicone rubber material were measured by LIBS whose actual roughness were 2.659 and 2.523 μm. The relative error was 0.218 and 0.189, respectively. The results show that roughness cannot be ignored in LIBS measurement for material with the same constitution, and the exploitation of this matrix effect for the remote measuring of composite insulators is meaningful for the checking and operation of HV transmission lines.

陈凭, 王希林, 洪骁, 王晗, 赵晨龙, 贾志东, 邹林, 李彦民, 范建华. 表面粗糙度对激光诱导击穿光谱信号的影响[J]. 光谱学与光谱分析, 2019, 39(6): 1929. CHEN Ping, WANG Xi-lin, HONG Xiao, WANG Han, ZHAO Chen-long, JIA Zhi-dong, ZOU Lin, LI Yan-min, FAN Jian-hua. Influence of Sample Surface Roughness on Signal of Laser-Induced Breakdown Spectroscopy[J]. Spectroscopy and Spectral Analysis, 2019, 39(6): 1929.

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