Quenching Characteristics of YBCO Bulk Contacts

A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of Y-Ba-Cu-O (YBCO) bulk as a mechanical PCS. In previous study, in order to investigate the contact characteristics of the switch, 50A current tests were performed and the contact resistance between two YBCO contacts was measured by four terminal method. As a result, it became clear that polishing and metal depositing on contact surfaces was effective to reduce the residual resistance, and the authors achieved to reduce this resistance to 0.27 muOmega, which was less than our target value of 1 muOmega. This paper focused on the transfer from superconductive to normal conductive state in the YBCO contacts (quenching characteristics), which was not obtained by former 50 A current test. In order to perform this experiment, 150 A DC power supply and two kinds of curvature silver contacts (R15 and R7.5) as an anode were introduced. The authors investigated that the relationship between the quench current and the layer thickness of deposited silver on the YBCO surface. And it was also observed whether the curvature radius for silver contact affected the value of quench current. Additionally, the contact area of the sample was analyzed with FEM. The analytical results may lead to the elucidation of a contact mechanism and a quench mechanism.