Design and Test Results of 66 kV High-Tc Superconducting Fault Current Limiter Magnet

This paper describes the design of a 66 kV high-Tc superconducting fault current limiter (FCL) magnet and the test results obtained. The magnet mainly consists of a vacuum vessel, a nitrogen bath, a pair of current leads, cryocoolers, and six sets of coils wound with Bi2223 tape. The rated current is 750 A. The insulation voltage of the magnet is of the 66 kV class. In the final year of the project, all six sets of the coils are set connected in the cryostat and evaluation tests have been implemented. In the cooling test, sub-cooled nitrogen of 65 K was obtained, with homogenous temperature distribution in the cryogen. The rated current of 750 A was successfully obtained for both direct and alternating current tests. In addition, the magnet passed the simultaneous current and voltage application test. The dielectric test results showed that the magnet satisfied the insulation for 66 kV apparatus in the Japanese Electrotechnical Committee Standard. Finally, the magnet was combined with a rectifier bridge circuit to form an FCL. In a fault current limiting test with a short-circuit generator, the FCL successfully limited short circuit current up to 20 kV applied voltage. The obtained result was in good agreement with the design and the Electro-Magnetic Transients Program (EMTP) analysis

I. Introduction

ASUPERCONDUCTING fault current limiter (FCL) is electrical equipment strongly expected in electric power systems where fault currents are serious problems. An FCL is a unique application of superconductors, which restricts a fault current arising in transmission or distribution lines with rapid response time as a quarter wave after the fault. While some developments of superconducting FCLs have progressed in recent years [1]–[4], no FCLs are practical as commercial switchgears. Among the various FCL applications proposed and requested, such as self-limiting interconnection and on-line limitation of transmission lines, a voltage level of several tens of kilo-volts would be a required milestone. Large current capacity is an attractive characteristic in superconductors, and moreover, a superconducting FCL needs to withstand high voltage in many applications. This background has been a strong motivation for this work to aim for a superconducting FCL at the several tens of kilo-volts level.