Nonlinear dynamic thermal modeling of oil-immersed distribution transformers

Transformers are the largest part of the investments of transmission and distribution systems and have a considerable economic impact on the operation of an electrical network. It is advisable to know the insulation condition, operating life, and loading capacitance of transformer to ensure its economical operation and secured service. The most important parameter in transformers life expectancy is the insulation temperature level which accelerates the rate of aging of the insulation. The variation of the temperature is described by an exponential equation based on the time constant of the system. In the thermal equivalent circuit model the time constant is equal to multiplication of thermal capacitance and thermal resistance. The aim of this study is to present a nonlinear dynamic thermal model for top oil temperature of oil immersed transformers. The presented model has considered assorted materials as conductor in their windings and the nonlinear parameter of transformer oil. Calculated model is verified by experimental works on oil immersed transformers.