Computational fluid dynamics calibration for network modelling of transformer cooling flows - Part II: pressure loss at junction nodes

Two important factors affecting the characteristics of 'hot-spot' inside an oil cooled transformer winding are the total amount of oil being supplied into the winding and its flow distribution across the discs arrangement. The latter is unavoidably related to the hydraulic network of winding ducts where oil flow is combining or dividing at duct junctions. The expressions describing junction pressure loss often contain a significant number of empirical parameters obtained by limited experimental tests. Applicability of these parameters should therefore be carefully verified for the use in network modelling; this is the objective of this study. Computational fluid dynamics simulations have been performed upon a large set of two-dimensional junction models, based on which new values of the empirical parameters were then obtained specifically for winding oil ducts. A validation test showed that the newly proposed parameter values give better performance than the currently used 'off-the-shelf' values.