Current Limiting Performance of Three-Phase Concentric Transformer Type SFCL at Unbalanced Fault Conditions

We have proposed a transformer type SFCL whose primary and secondary superconducting coils have rewound structure. The primary coil is connected to a power line. The secondary one is short-circuited and has fewer turns than the primary coil. For small fault current, only the secondary coil turns to normal state. Inductive component of impedance at the primary terminal mainly appears. For larger fault current, the primary coil also turns to normal state, resistive component additively appears. A three-phase concentric model of the proposed SFCL was designed and fabricated. Each phase SFCL must work independently without large interference among phases. Fundamental current limiting characteristics of the proposed SFCL were reported at a three-line-to-ground fault using a lab scale power transmission system. In this paper, current limiting performance of the SFCL at unbalanced fault conditions was investigated and discussed. Influence of operations of the fault phase SFCL to the nonfault phase ones was discussed. It was confirmed that fault current limiting operation was successfully performed in single-line-to-ground fault, double-line-short fault, and double-line-ground fault.