Since resistive superconducting fault current limiters (SFCLs) are inserted to a power system directly, it is necessary to recover instantly after the clearance of a fault. Most resistive SFCLs using BSCCO bulk or thick film have a recovery time of tens of seconds. An SFCL using YBCO coated conductor (CC) has a large surface area contacted to liquid nitrogen. Joule heat flux of the SFCL is smaller than that of other types when a fault occurs. Therefore, it is important for the SFCL employing CC to investigate a recovery time. In this paper, the recovery characteristics of SFCL with respect to applied voltage were analysed in a power system. All tests were performed in liquid nitrogen and sub-cooled nitrogen. From this result, the parameters for recovery time were obtained.

This paper deals with the fabrication and performance testing of a prototype machine for the world’s first implementation of a new type high-temperature superconducting rotating machine (HTSRM), which is charged and operated by the application of a contactless superconducting excitation technique with a rotary-type HTS flux pump based on a permanent magnet. Although this type of flux pump has been actively applied in stationary superconducting applications, its practical demonstration on rotary superconducting applications, namely, rotating machines, has not yet been conducted or reported. Therefore, laboratory-scale hardware implementation was conducted to investigate the feasibility of using an HTS contactless field exciter (CFE) as the field exciter of an HTSRM. Firstly, the various core components were manufactured, assembled, and tested to configure the 1-kW-class high-temperature superconducting generator (HTSG) system. Then, the assembled machine was connected with a conventional induction motor and three-phase resistive load. In non-load tests, the characteristics of the induced voltage of the HTSG, which was generated and affected by contactless field excitation and the operating speed, respectively, were tested and measured. In particular, the charge and discharge behaviors of the field current excited by the HTS CFE were experimentally analyzed based on the induced voltage profiles of the HTSG. Then, the HTSG output characteristics were tested and measured by performing experiments on the characteristics of constant load and constant speed, respectively. The generator test results were satisfactory in terms of output, voltage regulation, and the total harmonic distortion in the voltage and current.Our developed HTS CFE can excite an HTS field coil with 101 A in a noncontact manner, resulting in an operating field current margin of approximately 79% and a decrease of approximately 91.5% in the field excitation loss. In addition, the results demonstrated the possibility of designing HTS magnets with self-protecting features.

A superconducting fault current limiter (SFCL) using high temperature superconducting (HTS) wire has been developed in Korea. While the first-generation wire has difficulty in adopting various matrices because it is made by PIT process, the second-generation wire has flexibility in the design of its stabilizer. In general, coated conductor (CC) tape is clad with a thick metal layer as a stabilizer on the superconducting layer such as YBCO. In addition, the metal layer has good electrical conductivity. However, resistive SFCL, when a fault occurs, limits fault current using high resistance of the stabilizer. Therefore, the design of stabilizer is one of the most important parts in the design of SFCL. In this paper, over-current characteristics of CC tapes clad with stabilizers having various specifications were experimentally investigated. It was possible to design the stabilizer of CC based on calculation. An SFCL rated on 13.2 kV/630 A was designed using the optimal design of the stabilizer.

Quench protection is one of the most important issues for magnet applications using 2 G HTS tapes because of their non-self-protecting properties. Although many researchers have examined the quench/recovery characteristics of HTS magnets to establish the required stability, new information on the quench/recovery characteristics of the recently commercialized HTS magnet with GdBCO CC is needed. In this study, the quench/recovery characteristics of Zr-doped (Gd,Y)BCO CC pancake coils that were insulated with various materials, such as copper and Kapton tapes, were examined in a liquid nitrogen (LN2) bath. The minimum quench energy (MQE) and normal zone propagation (NZP) velocity of the Zr-doped (Gd,Y)BCO CC pancake coils are discussed in terms of the quench/recovery test results.

Here we suggest stable maximum temperature criteria of YBCO coated conductors (CCs) considering degradation of YBCO by repetitive exposure to excessive temperature rise. Stable maximum permissible temperature was experimentally determined as the maximum temperature at which CC does not suffer from critical current degradation or burnout. By comparing various over-current characteristics with short-circuit characteristics in regards to the pattern of generated resistance and joule heating flux, maximum permissible temperature rise of YBCO CC in superconducting fault current limiter (SFCL) can be determined as 400 K. Our research is expected to provide rudimental basis for the temperature design of various superconducting power applications including SFCL.