Assessment of Effect of Winding Geometry on Thermal Performance of Retrofilled Transformers

The increasing fire safety and environmental concerns have significantly increased the retrofilling of large number of indoor distribution transformers. However, the effects of the winding geometric parameters on the hot spot temperature of the retrofilled transformer have not been explored thoroughly. In this paper, a parametric sweep analysis is performed to investigate the effects of the winding geometric parameters on the hot spot temperature of a layered winding distribution transformer. The investigation is carried out using the same winding geometry filled with mineral oil and natural ester liquid. Firstly, the hot spot temperatures are determined using computational fluid dynamics (CFD) simulations. The simulation results are then validated with fibre optic sensors measurement. Secondly, the effects of winding geometric parameters on the hot spot temperature are analyzed using CFD simulations for mineral oil filled and natural ester filled cases. The oil flow rate is estimated to thoroughly investigate the influence of the winding geometric parameters on the hot spot temperature. Also, a relationship is developed showing the effects of the winding geometric parameters on the hot spot temperature. The simulation results indicate that the hot spot temperature is likely to be influenced more by the space between the LV winding layers as compared to the width of cooling ducts and the space between the HV winding layers.