Study On On-line Monitoring System For Moisture Content In SF₆ Circuit Breaker Gas

SF6 Gas-insulator switchgear was used widely because of its excellent insulation performance. When moisture content in SF6 Gas-insulator switchgear reaches to a certain extent, It could be compounded with product of SF6's decompose under arc action and then produces poison which results in chemical corrupt. At the same time, it also arouses the drop of insulated performance and bring on flashover of insulated surface. The electrical and mechanical characteristic is influenced by moisture content, as well as the badness would happen.The paper studies the source, change rule and quantitatively harm of moisture content in SF6 Gas, and also analyses the actual testing methods and it's disadvantages of moisture content in SF6 Gas, then the author bring forward the necessary of testing moisture content on-line. Author brings forward the scheme of using relative humidity, temperature and pressure as character values and gives the conversion formulae of humidity. Using the formulae with character values, it can get other express methods of humidity: dew point temperature, absolute humidity, volume ratio and weight ratio. The measure results can display to user by computer.The paper studies the present situation and characteristic of humidity sensor and brings forward using macromolecule polyimide-based capacitive humidity sensor in the moisture monitoring system which has physical adsorption and can continuously measure between 0 to 100% in RH. By adopting the method of saturated aqueous salt solution, the paper designs the equipment to produce the humidity source and scale sensors. The paper also selects a thermo- sensitive resistance and a piezoresistive pressure sensor to measure temperature and measure of SF6 Gas.Author designed all the hardware circuits, sensor sealed chamber and spot box. Frequency sending circuit, signal isolation circuit and control circuit work well. Sensor sealed chamber performs a good condition, and sensors fixed in it can do their job excellently. The on-line monitoring system has almost completed.