Analytical calculation of the frequency-dependent litz wire resistance considering the wire connectors

Eddy-current effects have an impact on the resistance of litz wire. They reduce the utilization of the wire cross section. In a certain parameter range, the dominant influencing factor is the current distribution in the wire connectors. The connector itself does not significantly contribute to the wire resistance but it results in an inhomogeneous current distribution among the strands. We quantify the resistance increase by introducing a connector skin-effect factor and give a mathematical derivation. Taking the twisting of the strands into account requires a probabilistic model of the radial strand position. Resistance measurement results validate the calculation approach. We discuss the assumptions and derive the parameter range where the model is valid.