Temperature Distribution Evolution of Transformer Windings Thermal Defect and Its Identification Method
In recent years, transformers have been occasionally burnt down due to thermal failure of windings, which has seriously threatened the safety of power grid. In order to ensure the safe and stable operation of transformer, this paper studies the temperature evolution law and identification method of thermal defects in transformer windings. First, based on the finite element method, a coupling simulation model of electromagnetic-temperature-fluid multi-physical field in transformer windings was constructed, and the validity of the simulation model was verified by the temperature rise tests. Then, the influences of different overheating positions, the severity of thermal defects and transformer operating condi-tions on local temperature of winding were simulated and analyzed. Finally, a method to identify the location and severity of winding thermal defects is proposed by using multi-point temperature mutation analysis of winding axial oil passage. The research results show that the error between the calculated temperature value based on the multi-field coupling simu-lation model and the measured temperature rise test is less than 6％. When thermal defects occur in different regions of the winding, the heat in the overheating area will be transferred rapidly along the oil flow guide path, and the multi-point temperature appreciation in the winding oil passage will linearly increase with the increase of the overheating temperature in the region below it. The accuracy of thermal defect identification model proposed in this paper is 100％, and the rela-tive root-mean-square error of thermal defect temperature estimation is 6.1％. By using the research achievement of this paper, the thermal defects on the winding can be found early in the transformer operation process, so as to avoid the de-velopment from defects to more serious faults and ensure the safe operation of the transformer.
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