Numerical study of 8.5 MVA disk-type ONAN transformer cooled by biodegradable esters with coupled CFD-CFD and CFD-EMAG modelling

STEBEL, MICHAL; PALACZ, MICHAL; MELKA, BARTLOMIEJ; BODYS, JAKUB; GARELLI, L.; GUSTAVO A. RÍOS RODRIGUEZ; KUBICZEK, K.; LASEK, P.; STEPIEN, M.; HAIDA, MICHAL; PESSOLANI, F.; AMADEI, M.; GRANATA, DANIEL; STORTI M.

Krakow

Congreso; 6th International Conference on Contemporary Problems of Thermal Engineering. CPOTE 2020; 2020

Silesian University of Technology and AGH University of Science and Technology

Nowadays, the constant growth of the population leads to increased energy consumption and higher generation of electricity. Power transformers are the very first devices used to transfer huge amounts of electricity produced in power plants to the grid. During their operation, the heat resulting from the device power losses in the energy conversion process has to be effectively dissipated. Currently, active elements of the large-power power transformers are cooled in mineral oil. It performs well in such devices due to its very good thermal and dielectric properties. However, many companies, governments and the global society require more environmental-friendly alternatives in the industry. Therefore, the aim of this study is to present the numerical results of disk-type power transformer working in ONAN cooling mode. This device, manufactured by Tadeo Czerweny, has the nominal power of 8.5 MVA. The cooling is realised by eight external radiators. Due to the complexity of the whole unit, three coupled CFD models have been developed to investigate the fluid flow and the heat transfer for the assessment of the transformer cooling with different oil types. One model performs a detailed simulation of the oil flow within the windings of the transformers. The volume of each low and high voltage disk has been homogenised in order to reduce the computational effort. However, effective values of anisotropic thermal conductivity have been defined for the winding wires with the insulation and the core. The domain of this model has been simplified to include 1/16th of the winding domain. The second model includes the power transformer interior and computes the natural convective flow of the oil within the analysed transformer. The third thermal model has been developed to simulate the oil cooling is the external radiator. The distribution of the power loss within the magnetic core and windings was evaluated by performing electromagnetic simulations. The coupling strategy between all these three models allows for the temperature distribution determination within the power transformer. The result discussion includes the thermal performance assessment of the power transformer using well-known mineral oils and natural esters for warm (Argentinian) and moderate (Polish) climate zones.