Lingling Du

Charge Transfer Effect on Raman and Surface Enhanced Raman Spectroscopy of Furfural Molecules

The detection of furfural in transformer oil through surface enhanced Raman spectroscopy (SERS) is one of the most promising online monitoring techniques in the process of transformer aging. In this work, the Raman of individual furfural molecules and SERS of furfural-Mx (M = Ag, Au, Cu) complexes are investigated through density functional theory (DFT). In the Raman spectrum of individual furfural molecules, the vibration mode of each Raman peak is figured out, and the deviation from experimental data is analyzed by surface charge distribution. In the SERS of furfural-Mx complexes, the influence of atom number and species on SERS chemical enhancement factors (EFs) are studied, and are further analyzed by charge transfer effect. Our studies strengthen the understanding of charge transfer effect in the SERS of furfural molecules, which is important in the online monitoring of the transformer aging process through SERS.

Analysis of methyl formate dissolved in transformer oil by laser Raman spectroscopy

As an aging product of insulating paper, methyl formate dissolved in transformer oil can reflect the progress of oxidization and affect the insulating property of transformer oil. And the concentration of methyl formate dissolved in transformer oil has been given more and more attention. Confocal Laser Raman spectroscopy (CLRS) can directly perform non-contact fast measurement to transformer oil samples, especially being suitable for online monitoring. Using CLRS to detect the concentration of methyl formate dissolved in transformer oil can overcome many disadvantages of traditional methods. In this paper, the application of CLRS in the detection of methyl formate dissolved in transformer oil was studied. Firstly, Gaussian 09W was applied to analyze the Raman spectrum of methyl formate. Based on the CLRS test platform set up in the lab, oil samples with different methyl formate concentrations were detected. And methyl formate was characterized by Raman signal at 903 cm-1, where can be used to quantitative analysis with the least squares method. The results show that LRS can be used in the analysis of methyl formate dissolved in transformer oil, which lays the foundation for the online monitoring of dissolved methyl formate in transformer oil with CLRS.

Detection of methanol dissolved in transformer oil by laser Raman spectroscopy

The analysis of methanol concentration is regard as a new means of evaluating the aging degree of insulating paper in power transformers. Using Laser Raman Spectroscopy (LRS) to detect the concentration of methanol in transformer oil can overcome many shortcomings of traditional detection techniques and realize fast test. In this paper, the application of LRS in detecting methanol concentration has been studied. First of all, Gaussian 09W was used to build the structure model of methanol molecule and analyze the Raman spectrum of methanol molecule. LRS liquid detection test platform was built based on confocal Raman technology. Standard samples of transformer oil were tested utilizing this test platform directly, and the Raman characteristic peak at 1030 cm−1 was selected for quantitative analyses. In order to further improve the detection sensitivity, extraction technology was applied. At last, applying the least squares method, the quantitative analysis method was built between the areas of Raman characteristic peak and methanol concentrations. The experimental results showed that LRS method can effectively detect the concentration of methanol in transformer oil, which proposes a new way to realizing the fast test of methanol in transformer oil.

Laser Raman spectroscopy applied in detecting dibenzyl disulfide(DBDS) in transformer oil

Recently, copper sulfide which was formed by corrosive sulfur in transformer oil reacting with copper windings caused many faults of high voltage electric equipments. Online detection of dibenzyl disulfide (DBDS) has become a new way of avoiding happening major accident. Comparing with the traditional monitoring technologies, Laser Raman spectroscopy (LRS) has incomparable advantages, such as non-contact detection, quickly integrated detection of multiple characteristic substances, using single-frequency laser, which are necessary to achieve online monitoring. Based on the basic principle of LRS, we build up a platform using LRS for quantitative and qualitative analysis and develop the relevant experimental methods. Thermal aging tests are done at 140 °C with an air atmosphere up to 48h with copper strip. The test results indicate that Laser Raman spectroscopy can be applied to identify corrosivity of mineral oil for a running power transformer.

Analysis of methyl ethyl ketone dissolved in transformer oil using laser Raman spectroscopy

Methyl ethyl ketone dissolved in transformer oil can be used as the mark of thermal insulation degradation. As an effective detecting method for trace liquid, Laser Raman Spectroscopy (LRS) is more suitable for in-situ detecting methyl ethyl ketone concentration than traditional detection methods. The application of LRS in detecting methyl ethyl ketone concentration has been studied. Firstly, the structure model of methyl ethyl ketone molecule was built by Gauss View 5.0. Then, the Raman spectrum of methyl ethyl ketone was analyzed by Gaussian 09W software theoretically. And the liquid test platform was built based on confocal Raman technology in the lab. The Raman characteristic peak of methyl ethyl ketone dissolved in oil was selected by testing standard samples of transformer oil directly. Moreover, applying the least square method, the quantitative analysis method was built between the areas of Raman characteristic peak and the concentrations. The experimental results showed that LRS can be used to effectively detect the concentration of methyl ethyl ketone dissolved in transformer oil. Therefore, a new detection tool is presented for transformer health diagnosis.

Analysis of acetic acid dissolved in transformer oil based on laser Raman spectroscopy

Acetic acid produced in oil-paper insulation aging process would greatly reduce the quality of insulation performance of a transformer, and seriously affect the healthy operation of the transformer. The monitoring of acetic acid content dissolved in the transformer oil is of great significance for ensuring the safe and reliable operation of the transformer. Laser Raman spectroscopy is a molecular analysis technology based on the Raman effect, which can directly perform non-contact measurement to acetic acid dissolved in the transformer oil by a laser with single frequency. Compared to the conventional methods, laser Raman spectroscopy method is more simple and time-saving. In this paper, the application of laser Raman spectroscopy in the detection of acetic acid dissolved in the transformer oil was studied. Firstly, Gaussian 09W simulation was applied to analyze the Raman spectrum of acetic acid. The spectral peaks and Raman vibration modes of acetic acid were analyzed and assigned. Acetic acid dissolved in the transformer oil was directly detected based on the laser Raman spectroscopy liquid detection test platform. Acetic acid was characterized by Raman signal at 618cm−1, where no spectral interferences caused by oil-derived Raman signals occur. And the qualitative and quantitative analysis methods for the acetic acid based on the characteristic spectra and the least squares method were established. The results show that laser Raman spectroscopy can be used in the analysis of acetic acid dissolved in the transformer oil with good detection stability, which lays a good foundation for quantitative detection and the online monitoring of acetic acid dissolved in the transformer oil with laser Raman spectroscopy.

Laser Raman spectroscopy applied in detecting dibenzyl disulfide in transformer oil

Recently, copper sulfide which was formed by corrosive sulfur in transformer oil reacting with copper windings caused many faults of high voltage electric equipments. Online detection of dibenzyl disulfide (DBDS) is the key to avoid happening major accident. Comparing with the traditional monitoring technologies, Laser Raman spectroscopy (LRS) has incomparable advantages, such as non-contact detection, quickly integrated detection of multiple characteristic substances, using single-frequency laser, which are necessary to achieve online monitoring. Based on the basic principle of LRS, we build up a platform using LRS for quantitative and qualitative analysis and develop the relevant experimental methods. Thermal aging tests are done at 140 °C with an air atmosphere up to 48h with copper strip. The test results indicate that Laser Raman spectroscopy can be applied to identify corrosivity of mineral oil for a running power transformer.