THE CURRENT STATUS OF SUPERCONDUCTING FAULT CURRENT LIMITER DEVELOPMENT

Demand for electric power in Japan has been steadily increasing in rec ent years. To meet this demand, power networks have been more robustly connected with a view to improving their reliability. However, this h as been accompanied by a trend toward a greater incidence of fault cur rents in these power networks. If a fault current limiter is used to c onnect these systems, electric power utilities will be able to accommo date 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 o f faults in a system. The authors have developed a 6.6 kV/2.0 kA class superconducting fault current limiter used for power distribution sub stations, as the preliminary stage of development of current for trunk power systems. In order to reduce impedance under normal operating co nditions and quickly switch to high impedance in a fault condition, th e limiter consists of a pair of double-layer non-inductive superconduc ting windings connected in series. Each winding is wound with a 36-str anded AC superconducting wire having ultra-fine NbTi filaments in a hi gh-resistivity matrix. The device successfully limited a 6.9 kA short- circuit current to 3.4 kA and transmitted continuous power at 2.0 kArm s.