This paper proposes algorithm, defining the dynamic transformer rating (DTR) for maximization of energy transfer through oil-immersed transformer. Algorithm ensures that windings temperature and loss of insulation life do not exceed their permissible limits. To achieve this goal, we use receding horizon control. Receding horizon control considers load and ambient temperature at past and future intervals to update the DTR. Proposed algorithm is intended for application in real-time economic dispatch at balancing market where it could allow the decreasing of energy generation cost. We consider a two-machine power system as case study, where cheap generation is constrained by transformer rating. The expensive generation does not have any network constraints. The algorithm application increased the cheap generation by 12% in comparison with static thermal limit and by 3% in comparison with static thermal limit corrected to ambient temperature. The generation rescheduling, allowed by DTR, decreased the energy generation cost by 27.9% and 9.8% correspondingly.