Multigas Analysis by Cavity-Enhanced Raman Spectroscopy for Power Transformer Diagnosis.

We demonstrate the utility of cavity-enhanced Raman spectroscopy (CERS) as a unique multigas analysis tool for power transformer diagnosis. For this purpose, improvements have been added to our recently introduced CERS apparatus. Based on optical feedback frequency-locking, laser radiation is coupled into a high-finesse optical cavity, thus resulting in huge intracavity laser power. With 20 s exposure time, ppm-level gas sensing at 1 bar total pressure is achieved, including carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2), methane (CH4), ethane (C2H6), ethylene (C2H4), acetylene (C2H2), nitrogen (N2), and oxygen (O2). By using the internal standard gas (sulfur hexafluoride, SF6), the quantification of multigas with high accuracy is also realized, which is confirmed by the measurement of calibration gases. For fault diagnosis, transformer oil is sampled from a 110 kV power transformer in service. Dissolved gases are extracted and analyzed by the CERS apparatus. Then the transformer is diagnosed according to the measurement results. CERS has the ability to analyze multigas with high selectivity, sensitivity, and accuracy, it has great potential in gas sensing fields.