Modeling of Transformer Core Joints via a Subproblem FEM and a Homogenization Technique

A subproblem finite element method is developed for modeling the transformer core joints. It applies magnetostatic and magnetodynamic models on progressive geometries and different components of the solution, supported by different meshes. It allows an efficient and robust analysis of magnetic circuits in any frequency range, with an accurate calculation of flux density, losses, reluctance, and impedance in transformer core joint zone. The models of the study properly account for the effects of core design parameters such as length of air gaps and overlap length in stacked-lamination cores. The proposed models, which include saturation, are applied to grain-oriented silicon steel and two types of step-lap joints are considered: single-step-lap (SSL) joints and multistep-lap (MSL) joints. The values of magnetic reluctance, impedance, and Joule losses obtained with SSL joint are bigger than with MSL joint.