Research On Power Transformer Thermal-hydraulic Coupling Based On Hydraulic Network Pressure Balance

With the rapid development of my country's power industry,as an important device in the power system,the capacity and load of transformers are also increasing.Whether the operating state of the transformer is stable is the basic element that determines the safe operation of the power grid.If the transformer is improperly designed,causing excessive losses,excessive internal temperature rise or excessive pressure,it will directly affect the insulation performance,the service life of the transformer and the safe operation of the power grid.Therefore,it is very important to analyze the loss,temperature rise and oil flow of large power transformers.Based on the thermal circuit method and fluid network method,this paper takes a 240000 k VA,330 k V strong oil-cooled oil-immersed power transformer as an example to study the heat transfer and flow characteristics of the oil-immersed transformer.According to the heating situation and heat transfer relationship of each part of the oil-immersed transformer,a modified equivalent thermal circuit model for calculating the temperature of bottom oil,top oil and hot spot and an equivalent thermal circuit model for calculating the temperature rise of winding and core are established.According to the structural characteristics and oil flow characteristics,a global fluid network model is established for them.The relevant thermal parameters in the thermal circuit model are solved according to the relevant knowledge of heat transfer.The electromagnetic calculation model of the prototype transformer is established,and it is calculated by the finite element method as the heat source condition of the thermal circuit model.The relevant pressure parameters in the fluid network are solved according to the relevant knowledge of fluid mechanics and fluid network theory.The temperature obtained by the thermal circuit model is brought into the fluid network,and the pressure equilibrium of each branch of the fluid network is used as the constraint condition.Through the iterative calculation of the loop,the two are effectively combined.When each branch of the fluid network reaches the pressure balance,the temperature,oil flow and pressure of each part when the transformer is thermally stable are obtained.A two-dimensional fluid-solid coupling calculation model was established,and the temperature and fluid fields were calculated and analyzed to verify the method described in this paper.The results prove the effectiveness of this method.This method provides a new idea for the calculation of the temperature of power transformers and fluid pressure in other structures.Finally,the three-dimensional modeling of the high-voltage winding,considering the number of line cakes between the oil baffles,the height of the horizontal oil passage and the position of the oil baffle on the hot spot temperature of the high-voltage winding,analyze the results for optimization.