Numerical Study Of The Winding Temperature Rise And Oil Flow Distribution For A ODFS Transformer

Transformer is one of the core equipment in the power system, reliability and stability of its operation directly concerns the security of the entire grid. With the growing demand for electricity, the transformer voltage levels and capacity also/continue to be improved, so that the problem of the winding temperature rise is getting increasingly serious, especially in recent years with the rapid development of large-capacity natural oil circulation transformer, high average winding temperature and local concentration of heat and other issues become more prominent. Therefore, to research the principle of heat and temperature distribution inside the transformer has important practical significance to find effective methods to reduce the transformer hot spot temperature for the safe operation and development of the power system.For oil immersed transformer, the winding temperature rise not only depends on the loss of transformer, but also relates to the size of oil flow rate. Firstly in this paper, a 3-D simplified calculation model has been established respectively for HP, MP and LP windings, radiator and pipelines connecting windings and radiator according to the symmetry geometry of transformer studied, then the resistance characteristics of all components were simulated by using the commercial CFD software CFX. The results show that the oil flow resistance loss mainly distributes in the winding and radiator, and less distribution in pipelines, which accounts for less than 1/20 of the total loss and can be neglected in some engineering calculation.Then a porous medium-pure fluid coupling calculation model was set up to simulate the oil flow rate and distribution among different windings. Besides, the network model was also utilized to theoretically calculate the oil flow rate. Through comparison, it was found that there was a good agreement between theoretical calculation results and numerical simulation ones, thus proving the feasibility and accuracy of the porous medium model.Finally, on the basis of the simulation and analysis mentioned above, the improved model for windings was built by setting additional oil guide baffle in vertical oil flow path, and the best one was obtained by comparing different improvement schemes. Furthermore, the resistance and flow rate changes for improved model were also studied. The results indicate that, after winding structure being improved, the flow resistance of windings is increased, and the oil flow rate is decreased, but the magnitude of change is small. The decreasing effect on the winding temperature rise is still obvious after the flow rate reduction being considered.