Numerical and experimental thermo-fluid dynamic analysis of a power transformer working in ONAN mode

Abstract

This paper presents semi-analytical calculations, computational fluid dynamic simulations and experimental measurements accomplished on a typical 30 MVA power transformer. An ad hoc workbench was devised to carry out the experimental measurements. This facility allowed to estimate the values of different key variables involved in heat dissipation within the radiator, like convective heat transfer coefficients, oil-flow rate, air-flow speed between radiator fins and overall dissipated heat, among others. The main objectives of the study are to analyze the cooling capacity of the current radiator design working in ONAN mode and to validate the numerical simulation and calculation procedures for further design optimizations. The coupled thermo-hydraulic numerical simulations were performed on a computer cluster due to the high computational cost of the resulting models. The results of the simulations show good agreement with the experimentally measured values and with those obtained with the semi-analytical model, thus confirming that this model together with the CFD simulations are an accurate analysis tool. The heat transfer coefficients in the oil, the radiator panel and the air are computed. It is found that convective heat transfer from the panel to the air is approximately 10 times lower than heat transfer in the oil. Possible improvements on the current radiator design are briefly mentioned.