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GIS is designed as an Enclosed SF6 Gas-Insulated Switchgear comprising device, including the breaker,isolating gear, bus, lightning arrester, voltage mutual inductor, current mutual inductor and bushing, insulated with SF6 gas. When the water content in SF6 gas reahes certain degree, it adversly effects the electrical and mechanical performace of the equipment, thus to the equipment failure.This dissertation analyzes the source and harm of moisture, describes the representation of the gas moisture and the critical criterion described in the relative standard codes. It also presents the visual representation of the equipment insulation conditions through adopting the characteristic quantities of the relative humidity. According to the effects of temperature and pressure on the gas moisture, and converting the characteristic quantities to conform to the standard, it reaches the conclusive judgments.Based on the comparison analysis on the performance of dew point transmitter, temperature sensor and pressure sensor, and according to the site specific technical requirements for the moisture on-line monitoring system, the dew point transmitter, temperature sensor and pressure sensor of high reliability and high sensitivity and high speed responsibility and strong chemical corrosion proof should be used.This dissertation presents the working principle of the moisture on-line monitoring system, the design of the whole hardware system structure. The server is set up in the main control room in the distribution substation, and the communications between the moisture on-line monitoring units on the GIS shell and the server are established. The moisture on-line monitoring system units collect the real-time values of pressure, temperature and dew point, and connect to the server with CAN bus. The system software includes monitoring unit software, the server software and customer software.This dissertation also studies the remote data transmission technique of on-line monitoring system, and the remote monitoring of SF6 GAS is fulfilled through electrical data network. In the remote monitoring station, the functions of data storage, data display, alarm and query, and the on-line monitoring and analysis on the GIS electrical device on site can be fulfilled. Now, the moisture on-line monitoring system is successfully applied on the 110kV Commercial Transformer in Taizhou Electric Power Bureau.
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