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Natural Cooling Oil Flow in Disk-Type Transformer Windings with Zigzag Flow Passages
Jiahui Zhang and Xianguo Li

An experimental study has been conducted to investigate cooling dielectric oil flow in ON transformer windings. Static pressure in winding ducts has been measured at various strategic locations. Experimental results have been used for the validation of an existing hydraulic network simulation model developed earlier by the authors. It is found that minor losses in ON transformer windings are on the same order of magnitude as frictional loss. Since empirical correlations in literature overestimate the minor losses in low Reynolds number laminar flow regime, an implicit nonlinear optimization model has been used to calibrate the existing hydraulic model. Consequently, an accurate correlation for minor loss coefficients has been developed, and is valid for Reynolds numbers ranging from 1.1 to 20.9 in horizontal cooling ducts and up to 102.0 in vertical ducts. It is shown that the improved hydraulic network model is in good agreement with the present experimental results and previous results in the literature.

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