Optimization of stranded-wire windings and comparison with litz wire on the basis of cost and loss

Stranded wire with uninsulated strands has been proposed as a low-cost alternative to litz wire. In this paper, we develop a method to optimize stranded-wire designs on the basis of cost and loss, and compare the results to optimized litz-wire designs. A simply calculated parameter is shown to be useful to predict when each type of wire is preferred. A method to extend both loss prediction and optimization for arbitrary geometries and waveforms is also introduced. Deliberate oxidation of strands is proposed as a method to improve performance of stranded wire, and to increase its range of applicability. Experimental measurements with approximately 0.15 μm oxide show dramatic increases in interstrand resistivity, indicating that this approach could be very effective.