Thermal hydraulic network model for prediction of oil and temperature distribution in ester oil transformer under air natural and air forced cooling conditions

Recently, there is a growing interest in ester oil transformer for fire safety, eco-friendly and continuous over loading capability in comparison to conventionally used mineral oil transformer. The high interest on ester oil transformer has led to several analysis aimed at prediction of their dielectric analysis, thermal analysis and process development. In order to utilize the ester oil as an alternative to mineral oil, the internal and external cooling modes in thermal analysis of transformer needs to be evaluated to get a continuous overloading capability advantageous of ester oil. In this paper, Thermal Hydraulic Network Model (THNM) are effectively used to predict the oil flow distribution and the temperature distribution in 12.5/16MVA, 132/11kV transformer and compared with mineral oil in steady state conditions. The total oil flow rates of mineral oil and ester oil oils are compared with same winding geometry, power loss distribution (resistive losses in the winding conductors, winding eddy loss and stray loss) in a cooling mode. The power losses are calculated using finite element method (FEM) based simulation software and utilized for thermal analysis in THNM model. The oil flow rate within the winding, top oil rise, winding rise, gradient of the winding and hot-spot temperature rise are calculated for both natural ester oil and synthetic ester oil with respect to mineral oil under air natural and air forced cooling modes.