Analysis for Oil Thermosyphon Circulation and Winding Temperature in ON Transformers

An analysis of oil thermosyphon circulation and winding hot-spot temperature in Oil Naturally Cooled (ON) transformer system has been conducted in this study. The oil circulation is analyzed as a flow network of multiple thermosyphon loops, through winding columns, iron cores, oil tank, radiators and other transformer units. A network-based non-isothermal hydraulic model has been developed to predict oil flow, pressure, and temperature distribution over the entire oil circulation loops, in which, the hydraulic and thermal fields at each of transformer components are simulated with individual sub-models. The secant numerical method is employed to guarantee a convergent solution. The predicted oil temperatures have a good agreement with actual heat-run testing data. With the determination of the global oil distribution, winding temperature can be obtained from winding sub-model developed by authors in previous studies. Taking oil pump as a pressure source, the global model can also be applied in the analysis and optimization of forced oil transformer, as well as ON transformer.