Effects of oil leakage on thermal hydraulic characteristics and performance of a disc-type transformer winding

Abstract Conjugate heat transfer problem of a disc winding in a power transformer is studied using commercial CFD software. The study is done for oil flow, temperature distribution, hot spot location and temperature of the winding, for three different cases: first, no oil leakage past the top washer; second, partial leakage due to a 2 mm gap between the top oil guiding washer and cylindrical pressboard; third, full leakage, i.e., no oil guiding washer. The effect of leakage is studied for both uniform and non-uniform heat loss distributions in the winding. The leakage is found to lead to an onset of a reversal in flow direction: in the horizontal channels of the last pass of the winding. Under the effect of leakage, the variation in thermal performance of the winding is substantial for uniform and negligible for more practically encountered non-uniform heat loss distribution. However, for non-uniform heat loss distribution, the leakage leads to two local hotpots as compared to one for the non-leakage case. The partial as compared to complete leakage is found to give almost same thermal performance. This study will be useful – for transformer manufacturers – to realize the importance of leakage free washer design of a disc-type transformer winding.