Influence of winding geometrical deviations on the hot spot temperature in a disc type power transformer

Summary

Loss distribution and oil flow distribution within a transformer winding influence the location and value of the hot spot temperature. Oil flow distribution is affected by the winding geometries, and deviations in the cooling duct dimensions influence the hot spot temperature. Deviations can be created during transformer assembly by discs protruding into axial cooling duct or by insulating paper purging and so narrowing the radial cooling duct. In this work, an experimental investigation was carried out to highlight the influence of geometrical deviations on the hot spot temperature near the diverting washers which could adversely affect the hot spot temperature. A disc type winding model was used to create three cases of geometrical deviations. The temperature within the winding model was measured using thermocouples while oil flow rate in cooling ducts was measured using particle image velocimetry. Case 1 highlights the influence of geometrical deviations on oil flow and temperature distributions in a 15 disc segments per pass arrangement in which protrusions of winding discs into the axial cooling duct influenced the oil flow distribution and hence affected the hot spot temperature. Case 2 shows a 5-pass arrangement, 6-disc segments per pass, in which the influence of geometrical deviations on the temperature profiles of pass 3 and pass 4 is highlighted which caused the hot spot temperature in pass 4 to be around 5 oC higher than that in pass 3. Finally, case 3 shows a comparison between two winding model assemblies which have the same winding geometries but different geometrical deviations. Overall it is shown that geometrical deviations of discs, or washers, into axial cooling ducts may increase the hot spot temperature by several degrees. Such geometrical deviations should be minimised during the transformer manufacturing process.

Additional informations

Authors

BRAMBILLA, Fijalkowski, KANEKO, AGURO, D'ADAMO

Keywords

Power Transformer, Disc Type Winding, Hot Spot Temperature, Thermal Performance, transformer ageing