Stranded Wire With Uninsulated Strands as a Low-Cost Alternative to Litz Wire

High-frequency loss in transformer windings using stranded wire is analyzed. A complete loss prediction method is presented. The interstrand resistivity, which is an important parameter to determine the power loss, is measured experimentally. The analytical model is solved to get an optimal pitch, which specifies the degree of twisting that results in minimum loss. A transformer using a stranded wire winding is built and measured. The model prediction is verified to have high accuracy in the frequency range up to 100 kHz. Compared with the same transformer using a solid wire winding, about 67 percent less power loss at 100 kHz is achieved using stranded wire. Using the loss-prediction model provided in this paper, engineers will be able to control eddy-current losses in high-frequency transformer and inductor windings using stranded wire at a relatively low cost compared to using litz wire.