Effective helical-pitch adjustment in a high- Tc superconducting cable for reducing AC losses

Abstract

We have reported that AC losses in a high- T c superconducting transmission cable fabricated by Tokyo Electric Power Company and Sumitomo Electric Industries Ltd. are calculated correctly by using an electric-circuit model. According to the calculated results, the circumferential field losses are dominant in the total losses. The helical pitches of each layer in the cable are designed to obtain almost same layer currents, which gives the minimum self-field losses. We think that the optimum helical pitches giving the minimum total losses are different from the helical pitches designed by the companies and calculate the optimum ones in the condition of the same helical direction of each layer in the cable. As a result, for example, it is found that the AC loss of 2.1 W m −1 cm −3 at transporting 1 kA rms can be reduced to 1.8 W m −1 cm −3 (about 14% reductions) after redesigning the cable with the optimum helical pitches. The optimum helical pitches are obtained for each given transport current. After redesigning, the distribution of layer currents is not uniform and the circumferential fields are reduced.