The Study Of Temperature Field Of No-Encapsulated-Winding Dry-Type Power Transformer And Its Structural Optimization

With small size, low loss, and high reliability, dry-type transformers (DT) are widely used in recent years, especially in places with high requirements for fire protection and safety, such as high buildings, petroleum and chemical industries. On the other hand, the technical demand for the capacity of DT is increasing as the society develops. So, the heating and cooling of DT have been paid much attention. The generated heat by the windings and iron core of DT can cause the temperature rise of both the body and the surrounding medium. If the local temperature of DT is overheated, the insulation will be destroyed, which can greatly reduce the service life of DT. It is of significance to the study of the temperature field and the temperature of the highest hot point of DT.In the present work, a two-dimensional axis-symmetric model of the DT winding is presented based on a proper structural simplification. The temperature and flow field inside the DT are simulated using the CFD software of Fluent. The effects of loads and cooling patterns on the temperature rise of the windings are discussed. The behavior of heat transfer between the surface of the windings and the air in the vertical and horizontal flow tunnels both inside and outside the high and low voltage coils are analyzed. Further, the heat-transfer empirical equations are obtained using the multi-variant regression, and then the formula of the temperature rise of air inside the flow tunnels are presented.An interface-friendly computer tool for the numerical calculation of the temperature field of the air-cooled DT windings is compiled using code of Visual C++ and MATLAB. With this tool, the temperature field of high and low voltage coils of DT can be obtained with ease. Besides, the calculated results can be shown in the graphical forms, and if necessary, the user can view the temperature field, the temperature rise and locations of hot point of expected windings.The comparison on the experimental and calculated results shows that, in spite of a certain relative error, both the methods appear a similar distribution of temperature field. Therefore, the computer tool in this paper is helpful for the design of DT and the prediction of its hot points.