The influence of the leg cutting on the core losses in the amorphous modular transformers Bronislaw Tomczuk, Dariusz Koteras and Andrzej Waindok Department of Electrical Engineering, Automatic Control and Computer Science, Opole University of Technology, Opole, Poland Abstract Purpose – In a modular transformer with a wounded amorphous core, the authors should make some cutting to limit the eddy currents in its magnetic ribbon. The purpose of this paper is to deal with 3D magnetic field analysis, including the eddy currents induced by varying frequency of power. The influence of the core leg cutting on the power losses values, in the three variants of a one-phase modular transformer structure, has been presented. Design/methodology/approach – 3D field problems including eddy currents of various frequency were analysed using the electrodynamic potentials and V within the finite element method. The wave method and iterative one of the laminated core homogenization, have been employed. The values of the calculated losses have been verified experimentally. Findings – The reduction of the core losses by axial cutting of the transformer legs is an efficient approach for the loss limitation. The wave method is not acceptable for homogenization of the amorphous core for its operation above 1 kHz. The iterative method is the better way to perform the homogenization. Research limitations/implications – Due to very thin (less than 50 μm) amorphous ribbon, the unhomogenization of the laminated magnetic core should be performed. Thus, the solid core with equivalent parameters has been assumed for the computer simulations. For the frequencies above 1 kHz, the iterative method should be used to determine the equivalent electrical conductivity of the solid substitute core. Originality/value – Using the wave method with the electrodynamic similarity laws and assuming the wave penetration depth, the equivalent electrical conductivity of the homogenized core, has been determined. This approach is valid for supply frequencies below 1 kHz. For the higher frequencies the authors had to use the iterative method. It seems to be valid for another cores with amorphous and nanocrystalic ribbons. For the modular amorphous core it is only way to calculate the losses in the solid geometry of the homogenized laminated magnetic circuit. Keywords 3D magnetic field modelling, Amorphous modular transformer, Core equivalent electrical conductivity, Core with amorphous ribbon, Eddy currents losses, Homogenization method Paper type Research paper I. Introduction Soft ferromagnetic materials are widely used in industrial applications. They are characterized by various nonlinear B/H curves. One of the most important characteristic is the core loss value. They affect the efficiency and temperature of the magnetic cores of electromagnetic (EM) devices. Thus, there is a need for minimization of the losses in ferromagnetic materials (Tomczuk et al., 2013). The classic way to reduce these losses lies in the lamination structure of these materials, where the metal sheets are as thin as possible. COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering Vol. 34 No. 3, 2015 pp. 840-850 © Emerald Group Publishing Limited 0332-1649 DOI 10.1108/COMPEL-10-2014-0258 Received 10 October 2014 Revised 12 January 2015 Accepted 13 January 2015 The current issue and full text archive of this journal is available on Emerald Insight at: www.emeraldinsight.com/0332-1649.htm 840 COMPEL 34,3