Calculation Of Hot Spot Temperature Of Oil-immersed Power Transformer Winding

Excessive hot spot temperature of power transformer windings will affect the service life of its insulation materials,and then determine whether the power system can operate safely and stably.Therefore,it is of great significance to study the hot spot temperature of the power transformer winding and reduce the temperature rise of the hot spot.This dissertation takes a 220 k V/180000 k VA oil-immersed power transformer as an example to study the influencing factors of hot spot temperature and top oil temperature.The main research work is as follows:Firstly,according to the generation of power transformer losses and the way of heat transfer,considering the influence of external environmental factors on the top oil temperature and hot spot temperature of transformer,the traditional hot path model is modified.Combining the characteristics of oil viscosity changing with oil temperature and the compound heat exchange process between the oil tank and the surrounding medium,the transformer oil viscosity correction factor is defined,and the revised mathematical model is derived,which is solved by the fourth order Runge-Kutta method.Secondly,based on the solution results of the thermal circuit model,the influence of ambient temperature and solar radiation on the hot spot temperature and top oil temperature is analyzed,and its dynamic temperature distribution is given.Considering environmental factors,the hot spot temperature and top oil temperature are 11 K higher than the calculation results of the uncorrected heat circuit model.According to the specific requirements of GB/T 1094.7-2008 "Guidelines for the Load of Oil-immersed Power Transformers",the influence of environmental factors on temperature during load change was further.The results show that the revised thermal circuit model can effectively reflect the influence of transformer load conditions and environmental factors on the internal temperature of the transformer.Finally,based on the heat transfer principle,structure type and oil flow characteristics,the calculation model of transformer temperature field is established.When setting the boundary conditions,environmental factors are fully considered to obtain the internal temperature and oil flow distribution of the transformer.On this basis,the influence of the position of the oil baffle plate,the number of line cakes between the oil baffle plates and the height of the horizontal oil passage on the hot spot temperature is further studied.In order to verify the accuracy of the solution results of the two models,a temperature measurement experiment was carried out on the prototype winding under the same environment setting,and the calculation results of hot spot temperature and top oil temperature obtained by the two methods were compared with the experimental data.The results show that the relative errors of hot spot temperature and top oil temperature calculated by hot path method are 3.62% and3.67% respectively,and the relative errors of hot spot temperature and top oil temperature calculated by temperature field are 1.19% and 2.20% respectively,which are within the allowable range of errors.