Fu Wan

Analysis of furfural dissolved in transformer oil based on confocal laser Raman spectroscopy

Furfural (Furan-2-carbaldehyde) dissolved in transformer oil is regarded as an important mark of the thermal and mechanical degradation in oil-paper insulation. Confocal laser Raman spectroscopy (CLRS) is an effective means of detecting trace liquid and has been widely applied in many fields. Using CLRS to detect furfural concentration can overcome many disadvantages of traditional detection methods and accelerate testing. Thus, the application of CLRS in the detection of furfural concentration was investigated in this research. A structure model of a furfural molecule was constructed with Gaussian 09W software. Then, the Raman spectrum of this molecule was analyzed theoretically. Meanwhile, a set of liquid test platforms was set up based on basic CLRS principles. Subsequently, standard transformer oil samples were tested by utilizing extraction technology together with the CLRS liquid test platform. As a result, the peak at 1677 cm-1 was selected as the Raman characteristic peak. The detection limit reached 0.10 mg/L. In addition, a quantitative analysis model was constructed between the concentrations and the Raman characteristic peak areas by applying external standard method and least square method. Finally, six types of oil samples with different furfural concentrations were detected; the test results were compared with those obtained through high-performance liquid chromatography. Comparison results showed that CLRS with extraction can quantitatively and effectively detect the furfural concentration in transformer oil (with a maximum error less than 11.7%). Therefore, a new detection tool is presented for assessing the degradation of insulating papers in power transformers.

Heterodimer nanostructures induced energy focusing on metal film

As an interesting surface plasmon phenomenon discovered several years ago, electromagnetic field redistribution in nanoparticle dimer on film system provides a novel thought to enhance the light power on a plain film which could been widely used in surface enhanced Raman scattering (SERS), solar cells, photo-catalysis, etc. Homodimers on film are mainly investigated in past years, while the properties of heterodimers on film are still unclear. In this work, size difference induced electromagnetic field redistribution in Ag nanoparticle dimer on Au film system is investigated first. The results obtained from finite element method indicate that the smaller nanoparticle has much greater ability to focus light energy on Au film, which even reached more than 5 time compared to the larger one. Further researches indicate that this energy focusing ability has a strong relationship to the wavelength and diameter ration in dimer. Similar focusing phenomenon is found in the system of thick wire-smaller particle on film. Later, the SERS spectra collected in the small nanoparticle-large nanowire system provide an experimental evidence for this theoretic predication. Our results strengthen the understanding of surface plasmon on plane film and have potential application prospects in the surface plasmon related fields.

Study on the gas pressure characteristics of photoacoustic spectroscopy detection for dissolved gases in transformer oil

Photoacoustic spectroscopy (PAS) is a highly sensitive gas analyzing method without the shortcoming of gas consumption, which can be well applied in online monitoring of dissolved gas-in-oil. The effect of gas pressure on the photoacoustic spectroscopy detection is significant. Functional relations between gas pressure and gas absorption coefficient as well as PAV signal were derived theoretically. The experimental results of the acetylene , methane and carbon dioxide dissolved in transformer oil show the correctness of the functional relations above and that Photoacoustic spectroscopy voltage signal has a good linear dependence on the 1.5th root of P (0KPa<;P<;75KPa ) and the square root of P(75KPa<;P<;100KPa)when without gas absorption saturation effect. The theoretical and experimental results supply reference and technical support for further improvements in oil gas photoacoustic spectroscopy of on-line monitoring system.

Substrate influence on the polarization dependence of SERS in crossed metal nanowires

The influence of polarization dependence is an unavoidable problem in surface-enhanced Raman spectroscopy (SERS) applications, especially for anisotropically-enhanced structures with strong surface plasmon coupling. In this work, the polarization dependence of SERS in crossed nanowires (NWs) on metal or dielectric films was investigated both experimentally and theoretically. The measured SERS spectra indicated that the strong polarization dependence of the crossed NWs was greatly influenced by the substrate, which was determined by only the direction of the bottom NWs for a metal film or the top NWs for a dielectric film. The studies further demonstrated that this polarization dependence was not related to the diameter ratio or intersecting angle of the NWs. The present work not only improves the applications of SERS but also increases our understanding of surface plasmon excitation in complicated metal nanostructures.

Laser Raman spectroscopy applied in detecting dissolved gas in transformer oil

Dissolved Gas Analysis (DGA) is regarded as one of the key technologies to diagnose the internal insulation condition of oil-immersed power transformers, since the concentrations and the generation rates of the fault characteristic gases dissolved in transformer oil can reflect the internal insulation defects and their developments. It is the precondition of DGA to find an accurate way to detect the composition and the content of the mixed gas. Comparing with the traditional on-line monitoring technologies, Laser Raman spectroscopy (LRS) has incomparable advantages, such as no carrier gas consumption, no sample gas separation, using single-frequency laser, which is easy to achieve online monitoring. Based on the basic principle of LRS, we elaborate the mechanism using LRS for quantitative and qualitative analysis and the relevant experimental methods. The Raman characteristic spectral lines of the seven fault characteristic gases in transformer are determined by calculating. Based on confocal Raman technology and high sensitivity gas sample cell, a LRS test device for gas detection is established. By using this device, a mixed gas sample containing the seven fault characteristic gases (H2, CH4, C2H6, C2H4, C2H2, CO, CO2) is tested. The results show that the qualitative and quantitative analysis of LRS for dissolved gas in transformer oil is feasible.

Application of surface enhanced Raman scattering and competitive adaptive reweighted sampling on detecting furfural dissolved in transformer oil

Detecting the dissolving furfural in mineral oil is an essential technical method to evaluate the ageing condition of oil-paper insulation and the degradation of mechanical properties. Compared with the traditional detection method, Raman spectroscopy is obviously convenient and timesaving in operation. This study explored the method of applying surface enhanced Raman scattering (SERS) on quantitative analysis of the furfural dissolved in oil. Oil solution with different concentration of furfural were prepared and calibrated by high-performance liquid chromatography. Confocal laser Raman spectroscopy (CLRS) and SERS technology were employed to acquire Raman spectral data. Monte Carlo cross validation (MCCV) was used to eliminate the outliers in sample set, then competitive adaptive reweighted sampling (CARS) was developed to select an optimal combination of informative variables that most reflect the chemical properties of concern. Based on selected Raman spectral features, support vector machine (SVM) co...

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.

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.

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.