Solutions of three-dimensional multiply connected and open boundary problems by BEM in three-phase combination transformers

A boundary element method (BEM) in terms of magnetic vector potential and electric scalar potential is successfully applied to three-dimensional, multiply connected, and open boundary problems caused by the heavy current of leads in a three-phase combination transformer. The quasi-frontal method is employed for the solution of the set of equations with asymmetric and full coefficient matrix. At most a quarter of the whole matrix needs to be stored. The numerical results are compared with experimental values and show very good agreement. Corrective measures for reducing the losses and preventing the box from locally overheating are presented