This work presents a methodology for estimating the maximum power that can be extracted from distribution substation transformers based on (i) estimated values of future load, (ii) current temperature values measured at various locations within the transformer, and (iii) transformer reliability requirements. The final goal of the methodology is to provide a sensible means of controlling transformer overloads, especially at peak times during the daily load curve. The methodology has been implemented as a software tool running on computers in the Distribution System Control Center. The software makes use of real-time data acquired directly from the local loading control subsystem installed in two major distribution substations within the CPFL (Companhia Paulistra de Forca e Luz) system.