The operation stability of a three-phase matrix-type SFCL against break-down of superconducting elements

When the fault occurred in the power system, the superconducting fault current limiter (SFCL) rapidly limited the fault current to protect the power devices with preventing power failure. Therefore, the application of the matrix-type SFCL in the power system could improve of its reliability and stability. To apply the SFCL into the real power system, many superconducting elements should be connected in series and parallel. If any superconducting element of the matrix-type SFCL breaks down, it cannot basically limit the fault current. In this paper, we analyzed operation stability of the matrix-type SFCL which was divided into trigger and current-limiting parts as follows: Case 1. Break-down of a superconducting element in the trigger part. Case 2. Break-down of a superconducting element in the current-limiting part. Case 3. Break-down of two superconducting elements in the current-limiting part. When any superconducting element was broken down, we confirmed that all fault current flowed into other normal superconducting element connected in parallel and its power burden was largely increased. At that time, the matrix-type SFCL was operated well to limit the fault, but the fault current was decreased a little bit because the resistance generated in the superconducting element was abruptly increased. If the excessive current of the superconducting element exceeds its capacity, it could cause the break-down of the other superconducting element, shunt resistors, or shunt reactors, and then the break-down could be extended to the whole matrix-type SFCL. Through these results, we found that the number of superconducting elements connected in series and parallel should be designed with enough margins against the break-down of superconducting elements and optimal conditions for shunt resistors and reactors should be determined.