A preliminary study of mechanical switch using high temperature superconducting material

A persistent current switch (PCS) is a key component for superconducting magnetic energy storage (SMES) systems because it is used to switch a superconducting coil from storage mode to transfer mode. In past research on a mechanical PCS for SMES, a metallic superconductor made of Nb and NbTi was used as switching material. However, recent research using SMES coils of high-temperature superconductor (HTS) has been widely carried out, in which a PCS is also expected to work at liquid nitrogen temperature. In this paper, YBCO (yttrium barium copper oxide) bulk HTS was proposed as a switch material, and testing of the fundamental characteristics of a mechanical contact between two YBCO bulks was carried out. As a result, a switching phenomenon between low and high resistance ranges is observed at a threshold current value in the V-I characteristics of the YBCO contact. This phenomenon is also observed after the break and make action is carried out in liquid nitrogen, which indicates the possibility of a superconducting mechanical switch using bulk YBCO. Furthermore, the tests indicate that a certain amount of current must flow before the switching phenomenon, since the discontinuous transition occurred after the surface-insulating layer formed by degradation of YBCO was destroyed in the contact area.