변압기를 이용한 고온 초전도 한류기의 사고전류제한 특성에 관한 연구

Abstract

The fault current levels has gradually increased to exceed breaker interruption ratings due to the variation of the power demands. The mechanical impacts of protective equipments on the power system have been increased by the increase of these fault current levels. Therefore, it is demanded to suppress the fault currents with reliability and rapidity. Under these situations, the appearance of the superconducting fault current limiter (SFCL) suggests a positive alternative for reduction of the fault current. SFCLs can limit the fault currents within very short response time (less than 6 msec). There are various kinds of SFCLs : resistive, inductive, flux-lock, and so on. Resistive-type SFCL using intrinsic zero-impedance characteristic of the superconductor has a simple structure. It could be made small-sized and compact by using thin films. The simultaneous quenching between the superconducting elements is important for the capacity increase in serial and parallel connections. The unbalanced quenching of the resistive-type SFCL at the serial and parallel connections between superconduc- ting elements occurs by slight difference in their critical current density. The slight difference is unavoidable because of inhomogeneity generated in their manufacturing process. To connect the superconducting elements in series and parallel without unbalanced quench is necessary for the increase of capacity in SFCLs. As other types of SFCLs, we have tested the characteristics of the SFCLs using a transformer with a primary winding and several secondary windings. In this paper, we investigated the three structures as follows : 1. The SFCL consisted of a transformer with a primary winding and three secondary windings. 2. The SFCL consisted of a transformer with a primary winding and the serial or the parallel connections of three secondary windings from the parallel connection of three superconducting elements. 3. The SFCL consist of a transformer with closed or open-loop iron core. From the analysis for the results obtained by the experiments of the SFCL using a transformer, the conclusions were found as follows : 1. The SFCL using a transformer with a primary winding and three secondary windings achieved the simultaneous quenching due to the electrical isolation and the mutual flux linkage among the secondary windings by using the transformer. The SFCL also has the easiness of capacity increase by simultaneous quenching between each superconducting element and by almost same resistance compared to resistive-type SFCL. 2. The SFCL with parallel connection of secondary windings and three superconducting elements was more effective in the limitation of the fault current, the consumption power and the quenching time of the superconducting elements when it compared to both the resistive-type SFCL and a SFCL with the serial connection of secondary windings. 3. The consumption power of the SFCL with the closed-loop iron core was lower than in the open-loop iron core because of the reduction of mutual inductance between primary and secondary windings from the increase of the leakage flux.