Study On Transformer DGA Technology Based On Photoacoustic Spectrpscopy Theory

DGA is important means of transformer maintenance. As summarizing advantages and disadvantages of current methods used in DGA system, this thesis analyzed main advantage of photoacoustic spectroscopy applied in DGA. Meanwhile, the paper introduces the historical developments of photoacoustic spectroscopy, the new achievements in recent years, and the main points of the technology.Based on the molecule's structure and the molecule's spectrum and infrared spectrum structure of fault gases, the theory of gas detection using photoacoustic effect is discussed, which included the equation of photons absorption, the generation of acoustic energy, prompting of acoustic wave, and the detection of acoustic wave. The relationship between gas concentration and voltage output of microphone is deduced. All this become the foundation of the design of transformer DGA system.A model of DGA system is constructed based on photoacoustic spectroscopy. The movement form and absorption spectrum of six kinds of fault gases molecule is analyzed in this paper in order to confirm work wavelength of the system, and then the lamp-house used in this system is confirmed. Aiming high sensitivity at fault gas detection requirement, after comparing advantages and disadvantages of non-resonant cell with resonant cell, a small volume, non-reasonable cell was constructed, which is adapt to transformer DGA system.After studying on the theory of weak signal detection and noise restraint methods, a lock-in amplify detecting circuit was designed, which utilized cross-correlation technology. The whole circuit contains analog multiplier which realized phase signal detection function, both integral and low pass filter are used to reduce fluctuation of signal. The simulation result shows this circuit can realize high SNIR.An experimental system was established at last. The experiment data proved the partial feasibility of DGA system, and the response curve was fit.