| 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 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. 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 developed the moisture content on-line monitoring system for SF6 Gas switchgear by designing all the hardware circuits, sensor sealed chamber and the control software. The on-line monitoring system has verified very well in Wudang 220kV substation, Guizhou province.
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