An innovative fiber-enhanced Raman gas sensing system with a hollow-core anti-resonant fiber is introduced. Two iris diaphragms are implemented for spatial filtering, and a reflecting mirror is attached to one fiber end that provides a highly improved Raman signal enhancement over 2.9 times than the typical bare fiber system. The analytical performance for multigas compositions is thoroughly demonstrated by recording the Raman spectra of carbon dioxide (CO2), oxygen (O2), nitrogen (N2), hydrogen (H2), and sulfur dioxide (SO2) with limits of detection down to low-ppm levels as well as a long-term instability < 1.05%. The excellent linear relationship between Raman signal intensity (peak height) and gas concentrations indicates a promising potential for accurate quantification.
In order to overcome the shortcomings of traditional methods for corrosive sulfur detection in transformer oil, Raman spectroscopy based detection is proposed in this paper. The widely concerned corrosive sulfur, Dibenzyl Disulfide (DBDS), was chosen as the characteristic molecule to be detected. A series of oil samples with different DBDS concentrations was prepared. And these samples were extracted by 1-methyl-2pyrrolidinone for DBDS enrichment to improve the sensitivity of detection. Then Raman spectra of samples were obtained, and a linear model was established by analysing the relationship between the characteristic peak and the DBDS concentration. The limit of detection reached 7.98 mg/kg. For determining the DBDS concentrations causing sulfur corrosion, the sulfur weight content on the copper conductor surface was measured by Scanning Electron Microscope-Energy Dispersive Spectrometer after a corrosion test. The results show that the corrosion limitation highly depends on the type of transformer oil, and the Raman spectroscopy detection can meet the limit of detection requirement in practical condition. Finally, an on-site oil sample and five Lab-made samples were detected via our new method and the current Gas Chromatography-Mass Spectrometry based method. It is found that there is no significant divergence between the measurement results. And good applicability was also demonstrated in onsite sample test.
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