Superconductors are expected to be used in DC power cables because they have no DC electrical resistance and can carry a large current. Generally, when a current is applied to a superconductor, the critical current density decreases due to the self-magnetic field. Therefore, most of the superconducting cables are designed to suppress the effect of the magnetic field. On the other hand, we have proposed a superconducting cable based on the longitudinal magnetic field effect. As shown in Fig. 1, by changing the winding angle of the cable by a few degrees, a magnetic field is generated in parallel with the current and it can be expected to suppress of reduction of the critical current density. In this study, we compare the current values of a cable that generates a longitudinal magnetic field with those of a conventional cable and investigate the superiority of the longitudinal field cable in a 10 kA class superconducting cable.

In this study, we designed a DC cable based on the J_c-B characteristics of REBCO-coated wire. The critical current density, magnetic field, and angle of the magnetic field for each layer were calculated using parameters such as the inner diameter of the formers and the number of layers. Based on the results of these calculations, we numerically obtained the total current value for the entire cable by an iterative approximation. [1]

Fig. 2(a) shows the dependence of the total current flowing through the cable on the maximum winding angle at 30 mm inner diameter and three shield layers each. As the angle is increased, the number of wires decreases and the current value decreases. The current in the cable at 30° angle is about 15% higher than that in the conventional cable, which shows its superiority. Fig. 2(b) shows the results of the calculations for each of the four layers. The longitudinal field cable is about 20% higher than that of the cable, which satisfies the requirement of 10 kA at 30°. The increase of the current in the shielding layer is considered to be responsible for the increase of the longitudinal magnetic field and the increase of the critical current density.

[1] Vyatkin V S, Tanabe K, Wada J, Kiuchi M,Otabe E S and Matsushita T 2013 Physica C 494 135

 Fig. 1 Structure of superconducting DC cable using longitudinal magnetic field effect.
Fig. 2 Comparison of current value for (a) 6 layers and (b) 8 layers.

Keywords: longitudinal magnetic field effect, superconducting DC cable, iterative approximation