The Techniques On Dissolved Gas-in-Oil Separation And Photoacoustic Detection Of Transformers

Online monitoring of power transformer gases dissolved in insulation oil is one of the most valuable tools in preventing a catastrophic power failure. The unique technical advantages have made photoacoustic spectroscopy technology the preferred solution for next generation transformer monitoring equipment. Efficient separation of fault gases from insulation oil is an important part to achieve high sensitivity gas detection and analysis. In this paper, gas-oil separation method has been studied in depth by using near-infrared photoacoustic spectroscopy gas analysis system. On this basis, a gas and oil separation device for simulation experiment is built and the simultaneous measurement of C2H2and CO2dissolved in oil is achieved. The detection limit can reach12ppb and36ppm separately, and the calibration linearity is over0.999.At the aspects of photoacoustic spectroscopy technology, this paper focuses on how the optical power and temperature affect the monitoring results. The studies show that system’s repeatability and error can be effectively improved by normalizing the photoacoustic signal; temperature will have an significant influence on photoacoustic signal through affecting the gas absorption coefficient, the photoacoustic cell’s resonance frequency and the cell constant. Based on these, a method to eliminate the impact of temperature has been proposed.In addition, at the aspects of gas-oil separation method, the feasibility and advantages of headspace degassing device in online monitoring system is demonstrated by comparing with the membrane separation method. And a theoretical model of headspace degassing is established. Based on this model, a set of headspace degassing unit is designed. Test results show that the balance times for C2H2and CO2of this unit are around50minutes, which is far superior to membrane separation method. Furthermore, through optimization, this unit does not require carrier gas, and the operation is simple in practical application. Therefore it is a good choice for online monitoring equipments before the mature of membrane separation.Initial results obtained in this paper lay some theoretical foundations for photoacoustic spectroscopy technology to be actually used in transformer monitoring equipment.