Heat transfer in power transformer windings with oil-forced cooling

Power transformer outages have a considerable economic impact on the operation of an electrical network. One of the most important parameters governing a transformer´s life expectancy is the hot-spot temperature (HST) value. The classical approach has been to consider the HST as the sum of the ambient temperature, the top-oil temperature rise and the hot-spot-to-top-oil temperature gradient. Temperature distribution is solved using the heat conduction equation. Finite element method is used in the numerical solution. The transformer selected for simulation is 32 MVA transformer with non-directed oil-forced cooling and directed oil-forced cooling. Comparing the results with those obtained from finite integral transform and experimental test checks the validity and accuracy of the proposed method.