Zhaoliang Gu

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.

Using a sensitive optical system to analyze gases dissolved in samples extracted from transformer oil

A sensitive optical system which can be used to measure accurately the concentrations of fault gases dissolved in samples extracted from transformer oil is described, and some test results are presented.

In situ detection of trace furfural in aqueous solution based on Au nanoparticle/Au film surface-enhanced Raman spectroscopy

Furfural is an important chemical solvent and intermediate. Sensitive detection of this compound has attracted great interest in various fields. Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive method for material detection because of its optical enhancement effect of plasmonic nanostructures. This study presents a simple and versatile method to synthesize a SERS substrate, where polyaminothiophenol (PATP) was used to realize the stable combination of Au nanoparticles (AuNPs) and Au film via self-assembly. The near-field electric field distribution was calculated using the finite difference time domain (FDTD) simulation to determine the parameters responsible for electric field enhancement. The simulation results show that SERS enhanced factors are sensitive to interparticle spacing and materials for solid support but insensitive to particle size. Moreover, the experimental results show that the optimized substrates with the highest Raman activity were formed by six layers of 60 nm AuNPs decorated on a 30 nm thick Au film, thereby validating the simulation results. The SERS factor of the optimal substrates is approximately 5.57 × 103, and the in situ detection limit is 4.8 ppm. The 3D Raman spectra, relative standard deviation values for major peaks, and changes in signal intensity with time show the good reproducibility and stability of the substrates.

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.

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.

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.