Dynamic Thermal Modeling of Power Transformers: Further Development—Part II

This paper presents new temperature calculation methods based on heat-transfer theory, the application of the lumped capacitance method, the thermal-electrical analogy, and a new definition of nonlinear thermal resistances at different locations within a power transformer. The methods presented in this paper take into account oil viscosity changes and loss variation with temperature. The changes in transformer time constants due to changes in the oil viscosity are also accounted for in the thermal models. The models are validated using experimental results, which have been obtained from a series of thermal tests performed on a range of power transformers. The results are also compared with the IEEE-Loading guide (1995) Annex G method