First-order Longitudinal Photoacoustic Cell And Multi-component Gas Detection Characteristics Based On Photoacoustic Spectroscopy

Gas dissolved in transformer oil is one of the important characteristic quantities which reflect the early discharge faults of transformers. Timely detection of gases dissolved in insulating oils is an effective method to predict the potential inner faults and the development of electrical equipment for early diagnosis, and so it is important for safe operation of transformers. Laser based photoacoustic spectroscopy technique of high sensitivity can be well applied to detect gas dissolved in transformer oil, due to its good selectivity, large dynamic range, without gas separation and consumption and etc.Research statuses of multi-component gas detection using photoacoustic spectroscopy technology and structure characteristics of the photoacoustic cell are analyzed firstly. Then the paper starts from the theory of gas molecular spectroscopy, the heat generation and excitation of photoacoustic signals are analyzed in-depth. The amplitude of the photoacoustic signal which is proportional to the incident laser power and gas absorption coefficient in resonant acoustic cell are described, and the theoretical analysis results laid the foundation for gas photoacoustic spectroscopy detection and optimal design of photoacoustic cell.According to the characteristics of radiation source and the selection principle of gas absorption spectral lines, the characteristic absorption lines of three important feature gases C₂H₂, CH₄, and CO are choosed, and an experimental-setup for gas photoacoustic spectroscopy based on the array light source which is composed of three DFB lasers is established. Analysis on the influence factors of photoacoustic cell performance which include materials, working mode, geometric size, anti-noise measures and so on, the first-order longitudinal resonant photoacoustic cell is designed. Besides, the DFB laser wavelength modulation, the response characteristics of photoacoustic cell and the noise of detection system are analyzed theoretically and experimentally.The influence that the pressure and temperature on the gas infrared absorption properties of C₂H₂, CO and CH₄ are discussed, indicating that the gas peak absorption coefficient and the line width are related with the pressure and temperature closely. Photoacoustic spectroscopy detection characteristics of the gas C₂H₂, CH₄, and CO are studied experimentally, mainly from the relationship between the gas photoacoustic signals and gas concentration, laser power analyzed. Photoacoustic signals linearly increase with the gas concentration and the laser power in the absence of absorption saturation. The high resolution photoacoustic spectroscopys around 1520.09nm, 1653.72nm, 1567.32nm in the near infrared band of C₂H₂, CH₄, and CO gas are given by narrow linewidth and wavelength tunable characteristics of DFB diode lasers Through the experimental analysis on the three-component gas in the selected absorption lines not exist cross-absorption interference, a model of photoacoustic quantitative analysis is proposed on the basis of partial least squares regression. To calculate multi-component gas concentration using this model, the model calculation results coincide with the analysis results by gas chromatography. The results confirm the effectiveness of the model for multi-component photoacoustic quantitative analysis based on the photoacoustic spectroscopy detection technique.