Magnetic flux distribution in power transformer core with mitred joints

Abstract

The magnetic flux distribution in the transformer core, and particularly at the joints, has a considerable influence on the efficiency of the core. This paper considers a more realistic scenario of magnetic flux transfer, combining the effects of air gaps and the anisotropic characteristics of transformer core laminations. Based on the anisotropic magnetization characteristics of modern graded grain-oriented electrical steels, the magnetic flux distribution in the core joint region as a function of the operating flux density and the joint configuration is investigated using the finite element method up to high flux densities. 2D results illustrate the benefits of using multi-step lapped joints versus single-step lapped (SSL) joints at various flux densities. Thin low-permeability gaps are introduced in the 3D model with SSL 45° mitred overlapped joint configuration, which successfully addresses computation challenges of the large number of mesh elements for the air.