Research And Development Of Online Monitoring System Of Oil For Oil-immersed Transformer

500kV and above three-phases integrated transformer which is an important equipment and its operating states relates to the security of the entire modern power system, is the future direction of development of large transformers. Moisture content and dissolved gases in transformer oil (DGA) are important indicators for monitoring transformers by power sectors, which reflect the operating conditions of the transformer. The paper describes the development of online monitoring technologies for transformer oil, analysis the key technologies of moisture content and DGA, the main works are:(1) The mechanism of moisture and its hazards are introduced;based on the relationship between moisture content in oil and the dielectric constant of the polyimide film,derived of the relations about moisture content,relative humidity and temperature;design an online monitoring method which based on relative humidity,and realize the online monitoring system of moisture content combined with temperature and humidity sensor MMT162,high-performance ARM7,high-precision AD chip-AD7710.The experimental results show that the drift of moisture content is±1ppm,and±0.2℃for temperature within half an hour.(2) Demonstrate the importance of a stable working temperature for chromatographic column and SOFC sensor. A temperature control system contains two control objectives, according to the characteristics of the objects, based on the time-optimal incremental PID, is designed and used in online monitoring of DGA, and get the baseline voltage fluctuation is less than200μV,meanwhile the temperature accuracy of column is±0.1℃when the target temperature is70℃, and SOFC sensor±0.5℃when the target temperature is700℃.(3) Study the mechanism of transformer oil and relationship between gas and transformer faulty. According to the permeable mechanism of polymer films, through experiments, choose Teflon PTFE to separate the oil and gas, together with micro-magnetic pump, vacuum pump and micro air chamber, making the separation just under an hour. Based on the principal of gas chromatography, using12-way valve associated with dual-column makes the separation of mixture gases reach1.2. Research the principal of the solid oxide fuel cell (SOFC), then use SOFC sensor to detect the gas, the detection accuracy of C2H2is0.1μL/L. After considering the safety measures and process control, an integration work is done to complete online monitoring system of dissolved gases in transformer oil, which contains four units, separation of oil and gases, separation of mixture gases, detection of gases and control unit.(4) From the aspects of software features, the overall framework, database, system processes, online monitoring software platform is designed and developed, which realizes real-time monitoring and diagnosing operating conditions of the transformer. The measures are proposed to solve the problems encountered in the system on-site construction and the installation process of equipment. Compared to laboratory offline testing data, the validity of the system is verified.