AC loss reduction of coaxial multi-layer HTS cable

Reducing AC losses, cable size and cost of HTS tapes are required for the practical application of HTS power transmission line. We have theoretically investigated the relationship between AC losses and cable parameters such as layer radius and twisting pitch and direction in coaxial multi-layer HTS cable using our developed simulation method and revealed that the larger number of HTS tapes and twisting pitch are desirable for reduction of AC losses. In this paper we investigated influence of twisting pitch and direction on cable size and total amount of HTS tapes under a condition of constant AC losses. The diameter of each layer and total amount of HTS tapes in the cable with the same twisting direction are much smaller than those of alternate twisting direction. The cable with the same tape current would be better than that of the same layer current because of the smaller difference of the number of tapes per layer. In the cable with the same tape current, cable size decreases with the number of layers in spite of almost the same amount of total HTS tapes in the whole cable. In cable design, we cannot handle the restrictions of AC loss and load factor individually; it would be difficult to satisfy both the conditions of low AC loss and high load factor. AC losses could be reduced by increasing critical current of HTS tape without the restriction of load factor, while AC losses increases with the critical current with the restriction of load factor.