Contact resistance characteristics of high temperature superconducting bulk

A Persistent Current Switch (PCS) is a key component for Superconducting Magnetic Energy Storage (SMES) system because it is used to change a superconducting coil from storage mode to transfer mode. In a previous paper, YBa₂Cu₃O_6+δ (YBCO) bulk of High-temperature superconductor (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. The threshold current is called a transfer current. In this paper, the relation between surface treatment and transfer current is investigated and the transfer current is found to be larger in a finely finished surface. Also instability of contact voltage is observed in the low resistance range. Further, a numerical analysis of the current and temperature distributions is attempted to clarify the transition between high and low contact resistance ranges.