[en] Highlights: • We propose the 3-dimensional temperature analysis method during a quench, considering a heat flow between a magnet surface and liquid helium. • The proposed method can calculate temperature, resistance and current of a LTS magnet during a quench with high accuracy. • The electrical equation coupled with the governing thermal equation was applied to calculate the change of the current decay, which is related with joule heat. And the cooling effect of liquid helium on the quenched magnet is considered to improve the calculation accuracy. • The calculated results (magnet temperature, current and so on.) were compared with experimental results and the simulated results were in good agreement with the real experimental results. • These calculation results demonstrated that the proposed analysis method should be an effective simulation model for a quench analysis and LTS magnet design. - Abstract: This paper represents a numerical calculation method that enables highly-accurate simulations on temperature analysis of superconducting magnets considering the heat flow between the magnet and liquid helium during a quench. A three-dimensional (3D) superconducting magnet space was divided into many cells and the finite-difference method (FDM) was adopted to calculate the superconducting magnet temperatures governed by the heat transfer and joule heating of the each cell during a quench. To enhance the accuracy of the temperature calculations during a quench, the heat flow between the superconducting magnet surface and liquid helium, which lowers the magnet temperatures, was considered in this work. The electrical equation coupled with the governing thermal equation was also applied to calculate the change of the decay of the magnet current related to the joule heating. The proposed FDM method for temperatures calculation of a superconducting magnet during a quench process achieved results that were in good agreement with those obtained from an experiment.

[en] Recent development of CC, usually called second generation (2G) HTS, is actively in progress. Because of its higher critical current density as well as higher n-value, 2G HTS is feasible for the applications such as superconducting fault current limiter and superconducting cable. For operating the HTS equipment stably, it needs to investigate the characteristics of normal zone propagation occurred by quench. Investigations on the fundamental characteristics can be one of the indispensable foundations for research and development of power equipments. In this paper, normal zone propagation (NZP) characteristics according to various insulation materials are researched. By heating with NiCr heater and insulating with epoxy, we applied the operating current with respect to the critical current for calculation of minimum quench energy (MQE) and measurement of NZP

[en] Based on active developing of YBCO coated conductor (CC), various applications of the conductor have been developed recently. HTS systems offer tremendous advantages. Of them, since YBCO material has a high index number and specifications such as thickness and material of the stabilizer of the conductor can be controlled, CC has many advantages for applying to superconducting fault current limiter (SFCL). In general, coated conductor has a thick metal layer as a stabilizer above superconducting layer such as YBCO. Since SFCL plays a role of limiting fault current using high resistivity when a fault occurs, it is important for the design of SFCL to choose and design the stabilizer. In this paper, the design parameters for SFCL have been found. For optimal design, specifications of CC and reached temperature during the fault as well as winding structure are investigated by experiments. From this investigation, safe electric field intensity was 40-56 V/m under the condition of temperature limit of 300-400 K. Considering the electric field intensity and the number of stacks, total required length of coated conductor was estimated. Consequently, required length of YBCO CC already commercialized with stainless steel stabilizer is between 5.66 and 7.92 km for three-phase distribution class SFCL rated on 22.9 kV/630 A. In addition, a possible design using expected wire was also conducted

[en] We studied the development of spatial pulse diagnostic apparatus with magnetic sensor array using giant magnetoresistance (GMR)/spin valves (SV). Magnetic field distributions for the permanent magnet of 10 arrays using the finite element method (FEM) in a sensing surface were simulated. The characteristics of GMR/SV sensor array consisted of the boundary limit of the sensing magnetic fields and the sensitivity of ΔMR/ΔH below 20 Oe and 1%/Oe, respectively

[en] Superconducting fault current limiters (SFCLs) have been developed in many countries, and they are expected to be used in the recent electric power systems, because of their great efficiency for operating these power system stably. It is necessary for resistive FCLs to generate resistance immediately and to have a fast recovery characteristic after the fault clearance, because of re-closing operation. Short-circuit tests are performed to obtained current limiting operational and recovery characteristics of the FCL by a fault controller using a power switching device. The power switching device consists of anti-parallel connected thyristors. The fault occurs at the desired angle by controlling the firing angle of thyristors. Resistive SFCLs have different current limiting characteristics with respect to the fault angle in the first swing during the fault. This study deals with the short-circuit characteristic of FCL coils using two different YBCO coated conductors (CCs), 344 and 344s, by controlling the fault angle and experimental studies on the recovery characteristic by a small current flowing through the SFCL after the fault clearance. Tests are performed at various voltages applied to the SFCL in a saturated liquid nitrogen cooling system

[en] This paper deals with the short-circuit characteristics, including current limiting and current distribution characteristics of non-inductive superconducting coil wound with stainless steel-stabilized coated conductor (CC). From the tests of current limiting characteristics, we concluded that: (1)stainless steel-stabilized CC is efficient in the reduction of the wires required and volume of bobbin. However, its current limitation was not as efficient due to its high resistivity; (2)proper thickness and intermediate resistivity between copper and stainless steel can be an optimal specification of stabilizer for resistive SFCLs. From current distribution measurement tests, we concluded that contact resistance, impedance and cooling condition plays a dominant role in the current distribution characteristics before the fault, during the fault and during the recovery, respectively

[en] In general, the current leads of high voltage superconducting apparatuses cooled by liquid nitrogen are exposed to gaseous insulation media. Therefore, the investigation on the electrical breakdown characteristics of gaseous insulation media should be performed to develop electrically reliable high voltage superconducting power apparatuses. In this study, the lightning impulse breakdown tests on gaseous insulation media are conducted by using sphere-to-plane electrode systems made of stainless steel. Also, the lightning impulse breakdown voltage tests on gaseous insulation media according to various pressures are performed. The experimental results show that the electrical breakdown characteristics under lightning impulse voltage are affected by the gap length between electrode systems, the size of electrodes, and the field utilization factors. From these results, the electrical insulation design criteria to estimate the electrical breakdown voltage are established. The results are expected to be applicable to the design of current leads for high voltage superconducting apparatuses.