Shield Current of 3-in-One High-Temperature Superconducting Cables

This paper discusses the shield current of 3-in-One high-temperature superconducting (HTS) cables. The cable core consists of the HTS conductor and the HTS shield, which is coaxially wound around the former. By short-circuiting the three-phase shields at both ends, electromagnetic induction makes it possible to pass a current through the shield that is nearly identical to the conductor current and opposite in phase. In the case of 3-in-One cables, in which the three cores are tightly wound, the inductivity of the shield current is heavily influenced by the winding direction and the spiral pitch of the shield. Reversing the winding direction of the multi-layer shield or designing the shield layer with long spiral pitch are both effective ways to keep inductivity high. The shield current of a 240 meter cable was measured, and the measured inductivity was comparable to the numerically simulated value.