| It’s very important to detect water vapor concentration in many areas. The presence of water in the natural gas could result in natural gas pipeline water blocking and ice blocking which will corrode pipelines, equipment and instrumentation, Influence the measurement accuracy of natural gas, do great harm for the safety of the natural gas production and use. The more water content in transformer oil, the speed of the oil itself aging, equipment insulation aging and corrosion of metal parts faster. It’s necessary to monitor the water content of the oil. In electrical equipments such as the high-voltage switchgear and so on, SF6gas has been widely used because of its excellent insulation properties. However, when the moisture content is excessive in SF6, a chemical reaction will take place between SF6and water vapor and generate toxic substances which not only corrode the equipment, resulting in the equipment’s insulation performance’s decline, endangering the system’s safe operation, but also cause the environment’s pollution. Therefore, it’s very important to monitor water content in SF6precisely and timely.In this paper, a micro-water concentration monitoring method based on spectral scanning was proposed, which overcomes many shortcomings of traditional monitoring methods. This Fiber Optic Sensor also has plenty of advantages, such as fast response speed, high sensitivity and good security. First of all, the theory of water vapor’s absorption was researched and analyzed deeply, especially the situation in atmospheric pressure and under high pressures. Secondly, on the basis of theoretical analysis, the laser light source, detectors, collimators, and other devices were selected based on the specific requirements of the design. Then we designed the monitoring system including optical path, electric circuit and air chamber, etc. Finally, the water vapor absorption spectrum was verified through the experiments, which supplied a good technical foundation for the detection of micro-water.Main work and innovations of the paper is summarized as follows:1. The importance of detecting micro-water content in various fields were summarized; The traditional micro-water testing methods were summarized and their problems were analyzed; Domestic and overseas detection of micro-water situation at present were researched. And then the significance of this subject is proposed.2. The water vapor absorption theory was researched and analyzed deeply. Under different pressure, different absorption line-shape should be chosen to fit for water vapor absorption lines. The applicable pressure ranges for variety of absorption line-shape were given. Based on this conclusion, we do deep analysis and research on water vapor absorption when the pressure is higher than atmospheric pressure. Besides, three different methods for gas concentrations calibration were proposed, which were also simulated theoretically and verified experimentally.3. Monitoring system was proposed. Certain devices such as the DFB semiconductor lasers, transmission collimator device were selected to complete system’s design, including electrical circuit, the optical path and chamber design. The power:triangle wave was output by MCU to drive DFB-LD. The combination of temperature modulation and PID control were selected to operate the laser; Detection part:A sealing gas chamber embedded with a transmission collimator was selected as the signal detection part; Signal processing parts:amplifying and filtering hardware signal processing circuit and the method of moving average were used to process the experiment data.4. A series of experiments using the above system verifying the gas absorption theory were done which laid a good foundation for water vapor detection... |
PDF Full Text Request