Feasibility Study of Closed-Loop No-Insulation Coil to Shield Alternating Magnetic Field

No-insulation (NI) coil made of 2G high-temperature superconductor tape is widely used in a dc magnet due to its excellent performance of engineering current density, thermal stability, and mechanical strength. While the charging/discharging delay of the NI coil has become the biggest obstacle to applying it into an ac power device. In this paper, as a preliminary study, we test the capability of the NI coil to shield alternating magnetic field (AMF). When shielding AMF, the NI coil works in inductive mode such that each turn in the NI coil is induced at the same time and there might no longer exist any delay caused by turn-to-turn current path. To verify this hypothesis, three closed-loop coils, two NI coils, and an insulated (INS) coil are fabricated. The result of the contrast experiments shows that the NI coil could shield all the alternating magnetic flux through it, independent of turn-to-turn resistance and frequency of the background AMF. This capability is promising for the NI coil to be applied in the inductive superconducting fault current limiter (iSFCL) as the secondary winding, which can shield all the magnetic flux generated by the primary winding to keep the impedance of the iSFCL at a very low level during normal the operation of the power system.