Simulation and analysis of oil-immersed transformer based on thermal-fluid coupled field

Power transformer plays a pivotal role in the power transmission, whose failures have serious impact on reliability of power supply and operation stability of power system. Partial insulation aging caused by thermal effects in large-scale transformers is one of significant factors which have a negative effect on operation stability. Just because temperature change of in large power transformers is obvious before and after fault, Real time temperature monitoring have contributed to early warning for operation risks and potential faults In actual operation. Some operation experience indicated that temperature-monitoring aimed at main components of transformers is rather sensitive. Therefore, it makes a lot of sense to research and predict the hottest spot temperature and temperature distribution of transformers. Those traditional methods, such as the thermal circuit model, fail to meet the requirements of large transformer design and operation. In order to simulate temperature and flow velocity distribution in an oil-filled transformer under different conditions, mathematical simulation technology is adopted in this paper. Firstly, by analyzing the relation between heat and losses of transformer, a 720MVA/500kV oil-immersed transformer model is built and then the related losses are calculated in the FEA software ANSOFT. In view of thermal-fluid coupling relationship in heat transfer, the viscous fluid-flow model of the above transformer is set up in CFD software FLUENT. Using the above losses as heat sources, temperature and flow velocity distribution of the transformer is solved according to the basic principles of heat transfer and fluid mechanics. Moreover, the factors which affect the temperature field and oil flow field are analyzed and concluded based on the simulations under different conditions. The study in this paper analyzes the coupling relationship between temperature of transformer tanks and oil flow velocity and summarizes the factors which affect the temperature field and oil flow field, including load coefficient and cooling pattern. The simulation results is veritable accurate, which can provide the reference to transformer temperature measuring and lay the foundation for the further study on transformer non-electrical protection.