Error Analysis of Transformer Hot Spot Temperature Measurement

According to the national standard GB/T 1094.7-2008, the method of hotspot measurement of oil-immersed transformer is used to place several tem-perature sensors inside the gasket within the predicted hot spot position tomeasure the temperature of winding transformer. The highest temperaturemeasured is regarded as the hot spot temperature of transformer. Sincethe winding and gasket are bad conductors of heat, there exists certaintemperature difference between the gasket and the hot spot temperature ofthe winding. This temperature difference is not mentioned in the nationalstandard GB/T 1094.7-2008, which is bound to affect the accuracy of thetransformer hot spot temperature measurement.In order to ensure safe oper-ation of transformer, the thermal environment of temperature measuringpoint is analyzed and the discrete equation of boundary node is estab-lished. The parameters are set according to the heat transfer mode of theoil-immersed transformer and the temperature characteristics of each heat transfer node is analyzed. Gauss-Seidel Iteration method is used to calculatethe theoretical value of the measuring point of the oil-immersed transformerand the heat transfer model of the measuring point is established for fur-ther analysis. The experimental platform of the oil-immersed transformersimulator is established according to the method described in the nationalstandard and used to measure the hot spot temperature and winding sur-face temperature. The results show that when the winding temperature is77◦C, the heat transfer model of the temperature measuring point is 74.7◦Cand the experimental temperature of the temperature measuring point is74.9◦C. The relative error between theoretical calculation temperature andexperimental temperature is 0.27%. As the temperature of the experimentincreases, the temperature difference between the temperature point andthe winding temperature gradually increases, and the maximum absoluteerror is 2.1◦C.