Coolant flow distribution and pressure loss in ONAN transformer windings $Part I: Theory and model development

A comprehensive resistance network-based hydraulic model for mass flow distribution and pressure loss in disk-type oil-cooled transformer windings with zigzag cooling flow passages is presented. The number, size, and location of the horizontal ducts and fluid properties are considered variable, and the distribution of mass flow rates is determined by associated pressure losses, including the so-called "minor losses". Axisymmetry of the winding geometry is taken into consideration, and the pressure loss calculation is based on the discretization of flow domains in order to tackle the nonuniformity of the cross-sectional area in the horizontal ducts and to provide easy coupling with thermal analysis for the cooling of winding disks. Successive under relaxation method is used for numerical convergence.