Investigation of Thermal Behavior of an Oil-Directed Cooled Transformer Winding

In this contribution, the oil speed in horizontal channels of an oil-directed cooled winding is investigated by experimental and numerical methods. The presented winding model offers insight into the horizontal cooling channels perpendicular to the main oil-flow direction. To visualize oil flow, tracing particles were added to the cooling oil and illuminated by high-power light-emitting diodes. The particle velocities were then determined by taking photographs with a defined exposure time. The design of the sophisticated winding model is described in the contribution. In addition to the experimental results, this contribution presents a comparison with respective numerical results from 2-D and 3-D computational fluid dynamics calculations. Finally, numerical results from the winding model concerning the oil-flow distribution inside the winding at various operating conditions are presented. The investigation indicated a strong nonuniform oil-flow distribution on the horizontal channels. The presented results give a deep insight into the oil flow and temperature behavior of windings, enabling the designer to optimize the cooling of the power transformer windings.