An improved model of hot-spot temperature for oil-immersed transformers based on multi-parameter fusion

For large power transformers, the hot-spot temperature (HST) of windings has a significant effect on its thermal aging rate and operation reliability. However, the computation of HST is a sophisticated engineering problem all the time because of varied external environment, multi-heat source and the sensitivity of heat transfer coefficients. This paper proposes an improved model of HST for oil-immersed transformers based on the heat transfer theory, which could analyze the heat dissipation process of transformers. In order to enhance the applicability of this model, the ambient wind velocity, which affects the cooling efficiency and the form of thermal convection between the tank walls and ambience of transformer, is regarded as a vital factor leading into the calculation formula of thermal resistance. On the other hand, the sunshine radiation power absorbed by transformer is also introduced as one of the heat sources. Besides, the changes of load loss and oil viscosity with temperature is considered to guarantee the accuracy of this model, too. Lastly, the proposed model has been verified by utilizing experimental data, which was collected by a 220kV transformer operating under different load conditions. Compared with the measured values of HST and the calculated results by the IEC guide, it is found that this method can improve the calculation accuracy of HST by 2.64% and has more real-time performance and faster dynamic response capacity.