Analysis of Inlet Conditions in a CFD Application on Ester Immersed Power Transformers

Resumo

This work presents a study of the cooling performance of a natural ester in a power transformer winding
by using CFD analysis. Thus, the study is performed under heat-run test conditions and considers two different
dielectric fluids, a mineral oil which is the original cooling fluid and a natural ester as an alternative fluid. The
inlet boundary conditions are calculated by considering the thermal and hydraulic balance of the transformer
cooling system. When considering natural ester, the inlet mass flow rate and temperature obtained are lower than
the mineral oil case. For the CFD analysis, a portion of the low voltage winding in a 3D model is selected, using
the Conjugate Heat Transfer model for the fluid-solid thermal interaction and the Boussinessq approach for the
buoyancy terms. The results from transformer balance and thermal model obtained for mineral oil are compared
to the heat run test results to validate the model. Regarding the CFD results, natural ester leads to higher hot-spot
temperature in the winding and higher oil temperature rise than mineral oil.