3-D computation of transformers overheating under nonlinear loads

This paper deals with a mixed analytical and numerical method to study the electromagnetic and thermal behavior of a dry type transformer under nonlinear loads. First a three-dimensional finite element method (FEM) using a magnetic scalar potential formulation is applied to compute the magnetic field in the free and iron spaces. This nonlinear FEM calculation is then combined with a mixed analytical and numerical form of the electrical circuit equation to take into account the skin and proximity effects in the rectangular windings. Then a steady state thermal FEM using the previous resultant current densities allows to characterize the temperature distribution of the transformer with nonsinusoidal currents. Finally this coupling model is applied to a 10-kVA distribution transformer to validate the effectiveness of the proposed method.