Analytical approach for the calculation of the stray field of large power transformers

The paper discusses a novel analytic method for determining the stray field of the windings of large power transformers. Taking into account the detailed arrangements of low and high voltage windings as well as tapping windings, the algorithm utilizes series expansions of orthonormal eigenfunctions for the Laplacian equation of a gauged 3D magnetic vector potential. In order to fulfill the appropriate boundary conditions at the boundaries of the high permeable laminated iron core, fictious surface currents at these boundaries are introduced. Thus, a very fast evaluation of the stray field suitable for an inclusion with the initial design of large power transformers within an industrial environment is achieved.