| As one of the central components of the power supply system,the safety of the transformer is of great significance to the stable operation of the power grid.Monitoring the operating status of the transformer is one of the important means to effectively prevent power system failures.At present,transformers usually use insulating oil as the insulating arc extinguishing medium.Faults such as overheating and discharge of the transformer will cause the insulating oil to crack and deteriorate,and a trace amount of gas is generated to dissolve in the oil.Analysis of the concentration and type of gas dissolved in the transformer oil can determine the current operating status of the transformer,in order to corresponding measures can be taken in time to avoid major losses.Therefore,it is of great significance to detect ultra-low concentration gases dissolved in transformer oil.Compared with other detection methods,photoacoustic spectroscopy（PAS）has the advantages of high sensitivity,no carrier gas,and good repeatability.By studying the principle of gas photoacoustic spectroscopy,the conversion of light energy into heat energy by molecules and the generation process of sound waves in the photoacoustic cell,different types of oil and gas separation technologies have been studied,and the theoretical model of the headspace oil and gas separation method has been established.In-depth analysis of the influence of degassing time and other influencing factors on degassing is carried out.Through simulation verification,it is concluded that the equilibrium time of the headspace degassing model established in the experiment is much smaller than that of the membrane separation vacuum degassing method,which can realize the working condition of the transformer.Perform real-time monitoring.Based on the advantages of small size and easy integration of non-resonant photoacoustic cells,combined with headspace oil and gas separation technology and optical fiber photoacoustic gas sensing technology,a detection system for dissolved acetylene in oil based on optical fiber acoustic wave sensing was built.The light source,photoacoustic cell and degassing module used in the system were optimized and analyzed,and the near-infrared absorption spectrum of the gas was analyzed,and 1532.8 nm was selected as the center wavelength of the laser used in the experiment.The modulation current,modulation frequency,degassing time,etc.of the experiment were optimized.The results show that the response of the system to the acetylene oil sample is 7.7 pm/(μL·L-1),and it can actually detect the oil sample of 1μL/L.In order to improve the detection limit of the system,a detection system for dissolved acetylene in oil based on a resonant photoacoustic cell was designed to enhance the photoacoustic signal.The resonant photoacoustic cell is combined with the optical fiber cantilever acoustic wave sensor to realize the detection of ultra-low concentration acetylene dissolved in oil.By optimizing the laser modulation parameters,the interference of carbon dioxide and water vapor in the air to the ultra-low concentration acetylene gas in the near-infrared band is reduced.The feasibility of the system is verified by detecting oil samples containing different concentrations of acetylene.The response of the system to acetylene is 86 pm/(μL·L-1),and the acetylene oil sample with a concentration of 0.05μL/L can be detected,and the error value is within 20%.Compared with the non-resonant system,the system can detect gas.The limit has been increased by an order of magnitude,and the ultra-low concentration detection of dissolved acetylene in oil can be realized,which provides a new idea for the application of optical fiber acoustic wave sensing technology in the field of dissolved gas in transformer oil. |
