The aim of the article is to provide the reader with the basic concept of the transformer’s heat utilization where a proposed technical solution anticipates the installation of an additional oil-water heat exchanger (ODWF) in the transformer\u27s cooling system. An increase in the transformer’s cooling capacity lowers the oil temperature and reduces the transformer’s loss of life expectancy. In order to estimate the transformer’s oil temperature profile, as well as the heat power potential at the water side of the ODWF cooler, a numerical investigation was performed on the 150 MVA 220 / 115 kV transformer unit which operates in Podlog substation in Slovenia
