Abstract
Dissolved gas analysis (DGA) is widely used in monitoring and diagnosing of power transformer, since the insulation material in the power transformer decomposes gases under abnormal operation condition. Among the gases, acetylene, as a symbol of low energy spark discharge and high energy electrical faults (arc discharge) of power transformer, is an important monitoring parameter. The current gas detection method used by the online DGA equipment suffers from problems such as cross sensitivity, electromagnetic compatibility and reliability. In this paper, an optical gas detection system based on TDLAS technology is proposed to detect acetylene dissolved in transformer oil. We selected a 1530.370 nm laser in the near infrared wavelength range to correspond to the absorption peak of acetylene, while using the wavelength modulation strategy and Herriott cell to improve the detection precision. Results show that the limit of detection reaches 0.49 ppm. The detection system responds quickly to changes of gas concentration and is easily to maintenance while has no electromagnetic interference, cross-sensitivity, or carrier gas. In addition, a complete detection process of the system takes only 8 minutes, implying a practical prospect of online monitoring technology.
Highlights
When specific defects such as overheating, partial discharge, or arc discharge occurs in the transformer, the insulation oil or paper decomposes and produces gases, and the gases are dissolved in insulating oil[3,4,5,6]
Besides that, dissolved gas analysis and detection in transformer oil is a useful method for evaluating the transformer condition[9,10,11]
There are 7 fault gases produced by oxidation, insulation decomposition, and oil breakdown: H2, CH4, C2H2, C2H4, C2H6, CO, CO2
Summary
When specific defects such as overheating, partial discharge, or arc discharge occurs in the transformer, the insulation oil or paper decomposes and produces gases, and the gases are dissolved in insulating oil[3,4,5,6]. Dissolved gas analysis (DGA) is an oil-immersed transformer fault prediction and detection technique, based on the measurement of dissolved gases[12]. There are some methods to detect fault gases, such as: gas chromatography (GC)[13], thermal conductivity detector (TCD) and optical methods such as: spectral absorption method, photoacoustic spectroscopy[14,15]. These methods have following drawbacks: 1) GC is a widely used technique for quantitatively measuring fault gases concentration. 4) Laser calorimetry spectroscopy (LCS), an in-liquid detection technique, will be a promising technology if it can achieve a lower detection limit, but at present, the minimum detection limit for acetylene in transformer oil is 10 ppm[18] which does not meet the requirement of DGA
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