Simulation of the behaviour of fluids in thermal analysis of the windings of power transformers

The temperature distribution in transformer windings is affected by the heat transfer factors operative at the ends of the cooling ducts as well as by the magnitude and distribution of losses. These factors are not independent of one another, nor of the thermal process in various parts of the transformer. The oil circulating within the transformer in a laminar mode should improve the heat transfer which is effected by natural or forced convection according to the mode of cooling. During its movement the viscosity and density of the coolant vary with temperature; consequently its rate of distribution undergoes significant changes under the action of the thermal field. In industry, the methods of thermal evaluation are quite standard and often lack precision. Today numerical analysis tends increasingly to validate the results and strives to show that the temperature distribution and location of the hottest spot can be predicted with precision. This work uses the finite element method combining heat transfer and fluid dynamics to explore the phenomena of natural and/or forced convection in a transformer winding, its results are based on winding geometries already used (see IEE Proc., vol. 127, Pt. C, no.6, 1980) and predict the distributions of temperature and flow consequent on the variations in properties and in boundary conditions as a function of temperature. Problems related to discretisation of the model and to natural and/or forced convection are given together with procedures for their solution