Aging effect on oil cooling capacity of a non-guided disc windings power transformer

Many transformers around the world are serving close to or beyond their design life. In these important asset, cores and coils losses cause heating and energy losses within the core decreasing their efficiency and shortening their life expectancy. The aim of this contribution was to study the aging effect on mineral oil cooling capacity of power transformers. The oil aging effect on its viscosity and its physicochemical properties is also reported. A 2D axisymmetric thermo-fluid numerical model was developed with COMSOL Multiphysics to study the cooling capability of oil aged at different levels. The results show that the oil viscosity increase considerably with aging and its physicochemical properties are also affected. It was found that sludge as oil oxidation byproduct contributes to the widening of hot spots in the transformers with non-guided disc windings.