Calculation Model Of Hot-spot Temperature In Oil-immersed Transformers Based On Thermal-electrical Analogy Theory

The hot spot temperature is an important factor of power transformer insulation life. Accurate estimation of hot spot temperature in power transformer is useful to improve its economic and security level. By analyzing the thermal process of oil-immersed power transformer, the author proposes an improved method of estimating transformer winding hot spot temperature. The method is based on thermal model of transformer and the transformer tank temperature is used to estimate the transformer hot spot temperature.in the method. Specific research performed by the author is mainly from the following aspects:â‘ The paper studys both the winding loss and the core loss of the transformer and analyses the impact of the two losses to the transformer temperature. By analyzing the heat transfer process of transformer, the paper discusses the relationship between the heat transfer process and the temperature distribution and obtains the heating and cooling characteristic equation of winding, iron core and transformer oil. The analysis shows that, it is the winding loss that plays a decisive part in the production of winding hot spot temperature.â‘¡The paper analyzes the thermal model based on the top oil temperature and the thermal model based on the bottom oil temperature and discusses the two models'deficiencies.By analyzing the transformer tank and the application conditions and methods of thermal-electrical analogy theory, the paper models to thermal process inside the transformer tank and concludes the hot spot temperature model based on the tank temperature.â‘¢Carry out short-circuit temperature rise tests in the transformer temperature rise test platform. Control the current to the transformer and the pump by the radiator to simulate the heating and the cooling process of transformer in different load conditions. The temperature distribution inside the transformer is mesured through the thermocouples and FBG installed in the transformer. The result shows that, the place where the transformer hot spot temperature appears in different loads and different cooling modes is essentially constant.â‘£The paper compares the measured hot spot temperature, model value of this paper and the calculated value by IEEE guidelines and analyzes the errors. The result shows that, the hot spot temperature model based on the tank temperature has a smaller estimation error.The model is proved to be correct.