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.