3D Finite Element Simulation of Litz Wires with Multilevel Bundle Structure

Litz wires with large number of strands are usually manufactured by twisting several bundles of a moderate number of strands. Apart from manufacturing advantages, this technique also provides extra characteristics as current balancing between strands and, consequently, power loss balancing and optimal use of cross sectional copper area. However, complex twisting configurations carry analysis, modeling and design problems which make choosing the parameters of a particular arrangement difficult. A complete 3D finite element model that explicitly includes the effect of twisting at several bundle levels is introduced. This model captures the twisting details and allows observing the actual current density in the strands at the different positions in the wire for both net driven current and induced current by an external field. The model is implemented by using the rigourous mathematical description of trajectories of strands and it is used to analyze the effect of several parameters as bundle levels, pitch and isolation between strands.