The current status of superconducting fault current limiter development

Abstract

Demand for electric power in Japan has been steadily increasing in recent years.To meet this demand, power networks have been more robustly connected with a view to improving their reliability. However, this has been accompanied by a trend toward a greater incidence of fault currents in these power networks. If a fault current limiter is used to connect these systems, electric power utilities will be able to accommodate electric power through the superconducting limiter from a system with excess capacity to another system in which the available power is insufficient, while the limiter protects systems from the influence of faults in a system. The authors have developed a 6.6 kV/2.0 kA class superconducting fault current limiter used for power distribution substations, as the preliminary stage of development of current for trunk power systems. In order to reduce impedance under normal operating conditions and quickly switch to high impedance in a fault condition, the limiter consists of a pair of double-layer non-inductive superconducting windings connected in series. Each winding is wound with a 36-stranded AC superconducting wire having ultra-fine NbTi filaments in a high-resistivity matrix. The device successfully limited a 6.9 kA short-circuit current to 3.4 kA and transmitted continuous power at 2.0 kArms.