Study Of On-line Monitoring Of Dissolved Gases In Transformer Oil Based On Photoacoustic Spectroscopy

The reliability and security of power grid has got more and more widespread concern from the society. Faults in Electrical equipment, especially in large power transformers, has always been the most important factor that Influence the regular operation of entire grid. However, The comprehensive early prevention and diagnosis of the faults in transformers mainly relies on the analysis of dissolved gases in transformer oil. Currently, there are many techniques for on-line monitoring of such gases, but compared with traditional methods, more novel technique called photoacoustic spectroscopy has many advantages including high sensitivity, good selectivity and wide detection range, and has huge application potential in on-line monitoring of dissolved gases in transformer oil. Therefore, the study of gas monitoring technique based on photoacoustic spectroscopy is very meaningful.This thesis starts from studying the theory of infrared absorption spectrum and photoacoustic spectroscopy, then achieves the setup of gas monitoring system, and analyzes the photoacoustic spectroscopy gas detection technique systematically. The main content of the thesis includes:(1) The mechanism of infrared absorption spectrum and photoacoustic effect is described. The field distribution of sound in photoacoustic cell is researched. The proportional relationship between photoacoustic voltage signal, gas concentration and optical power is deduced. Meanwhile, the basic principles and methods of photoacoustic spectroscopy gas detection is analyzed.(2) According to the design principles of on-line monitoring system, components of photoacoustic spectroscopy detection system are analyzed and selected, and a testing platform is build. In addition, the noise source and its control method is discussed.(3) The distribution model of photoacoustic signal in photoacoustic cell is built, and the theoretical formulas of photoacoustic cell parameters are derived. The simulation of these formulas describes the relationship between photoacoustic cell parameters and photoacoustic cell dimensions. COMSOL Multiphysics 5.0 is used to simulate the distribution of photoacoustic signals and the characteristics of resonance. Furthermore, photoacoustic cell is designed and manufactured.(4) Through experimental analysis, the relationship between the C2H4 absorption characteristics and CO2 laser line is determined, and the C2H4 detection characteristics of photoacoustic spectroscopy is studied. Besides,The minimum detection limit 20.1ppb of the system is calculated by measuring different kinds of noise in photoacoustic cell. At last, the C2H4 concentration is quantitatively analyzed and signal reproducibility is researched.Through the use of photoacoustic spectroscopy technique, the system achieves low concentration monitoring of C2H4. Accurate detection of gas concentration of the system is proved by experiments, and the system can achieve a long-term stable operation.