In-situ Detection Technology Of Dissolved Gas In Oil Based On Photoacoustic Sensor

At present,the content of dissolved gas in oil is often used as a common indicator to determine the type of transformer overheating or discharge failure.Generally,the detection of gas requires pumping transformer oil into the oil and gas separation chamber.During the process of oil-gas separation,oil contact with air are easily contaminated,and there are hidden safety hazards such as oil leakage.However,the photoacoustic spectroscopy?PAS?technology has the advantages of no gas consumption,no carrier gas,and high sensitivity compared with other gas detection technologies.The membrane separation technology has the advantages of continuous separation,no oil pumping,and no pollution of oil samples in oil-gas separation.This paper realized in-situ detection of C₂H₂ gas dissolved in oil based on the photoacoustic sensor and membrane separation technology.The main contents are listed below.This paper emphasis on the analysis of gas PAS theories and the excitation process of photoacoustic signals,in-depth study of the resonance and non-resonant photoacoustic signals and the distribution of the acoustic field generated in the PA cell,and the theories of MEMS microphone and fiber optical cantilever acoustic sensor in the detection of sound pressure.There is mainly introduced the separation process of characteristic gas in oil by non-porous membrane in membrane separation,and the affecting membrane separation internal and external factors are analyzed.An in-situ detection system for dissolved gas in oil based on MEMS microphone was designed for detecting dissolved C₂H₂ gas in oil.The experimental results show that when the oil temperature is 60?and the laser wavelength is 1531.6nm,the balance time for oil-gas separation is achieved to be 4.5 h.The peak value of the 2f-WMS signal with the different gas concentration of dissolved C₂H₂ gas in oil has a good linear response and the response degree is 0.86?V/(?L·L^-1),the detection limit of C₂H₂ gas is 1?L/L.This paper proposed a fiber optic cantilever acoustic sensor that is anti-electromagnetic interference,intrinsically safe and highly sensitive compared with traditional capacitive acoustic sensor.Using cantilever and high-resolution fiber Fabry-Perot interferometer,ultra-high sensitivity detection of photoacoustic signal is realized.The experimental results demonstrate that when the oil temperature is 50?and the laser wavelength is 1532.831nm,and the operating frequency of 640 Hz,the linear fit of the second harmonic peak value shows that the system responsivity of C₂H₂ gas is 17.4 pm/??L/L?.The result showed that as the temperature increased,the equilibrium time of oil-gas separation was shortened.The response time was¹.8 h at 50°C and the error of the measured value of 0.5?L/L dissolved C₂H₂ gas is within±30%.The detection sensitivity of the system has doubled compared with the detection system of MEMS microphone.