Numerical Calculation and Analysis of Temperature Rise in Power Transformers with Different Insulating Liquids

Natural and synthetic esters have been increasingly used in fluid-filled transformers to address fire safety and environment-friendly concerns. However, the relatively higher viscosity of esters may slow down the heat-dissipation process and potentially affect the hot-spot and winding-temperature distributions. In this study, the different temperature rises of mineral oil, natural ester, and synthetic ester used in a 110 kV/50 MVA transformer were investigated by the computational fluid (CFD) dynamics method. Temperature rises in the hot-spot, average winding, and top-oil of different insulating liquids at an inlet flow rate of 0.018-0.5 m/s were investigated to identify the difference among the insulating fluids, including both oil-natural (ON) power transformer and oil-direct (OD) power transformers. Moreover, the hot-spot location at different flow rates was studied, which showed differences in the uniformity of the flow-field distribution between the mineral oil and ester under relatively lower flow rates. The numerical calculation and analysis results of this work shall be leveraged to optimize transformer design.