Comparisons of transformer thermal behaviours between conventional disc type and S disc type windings

Abstract

Controlling the highest temperature in the windings is the primary objective of transformer thermal design to guarantee designed transformer thermal life expectancy. Temperature rise test results of a transformer with computational fluid dynamics (CFD) modelling results are compared here to determine typical OD and ON flow rates in the transformer. It then presents CFD studies that compare the thermal behaviour of two types of disc-type windings. The S disc-type winding refers to one that has only axial cooling ducts and physically resembles a layer-type winding. The other type is of conventional disc-type winding. The S disc-type winding shows robust thermal performance due to its quasi-uniform flow distributions in the axial cooling ducts, irrespective of the total oil flow rates or the cooling modes. In contrast, the conventional disc-type windings converted from the S disc-type winding experience uneven flow distributions in the radial cooling ducts that can cause localised overheating. Control of oil flow distribution in conventional disc-type windings is found critical for its thermal design. Heat transfer for the S disc-type winding is further enhanced by axially partitioning the winding into multiple sections, which is optimized based on theoretical analyses and is then verified by CFD modelling.