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) system because it is used to switch a superconducting coil from storage mode to transfer mode. In previous research on a mechanical PCS for SMES, a metallic superconductor made of Nb and NbTi is used as a switching material. However, recently the research of SMES coil of a high-temperature superconductor (HTS) is widely carried out, in which a PCS is also expected to work in liquid nitrogen temperature. In this paper, yttrium barium copper oxide (YBCO) bulk of HTS was proposed as a switch material, and the test on 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. It means a possibility of a superconducting mechanical switch using YBCO bulks. Furthermore, the tests indicate that a certain amount of current needs to flow before the switching phenomenon is obtained.