The rated power of a transformer is determined by the maximum power it can deliver in continuous operation without the operating temperature exceeding the permissible limit. The operating temperature determines the load and lifetime limits of the transformer. In this work, Quick Field software was used to model and simulate the operation of single-phase distribution transformers immersed in cooling oil using the finite elements method and to determine the temperature distribution inside the transformer. From catalog data, the parameters of the mathematical model of the transformer are determined, as well as the constructive characteristics of the transformers, while the load modeling is based on the information obtained from the different load graphs of the transformers. The research results are obtained as temperature gradients, multicolor maps and point values of temperatures in the modeled transformers.