The Nexans SFCL controls potentially damaging current peaks caused by short circuits in the electricity supply system. The device relies on the particular physical properties of an oxide ceramic superconductor: In regular operation, the superconducting material acts as a near-perfect electrical conductor without ohmic resistance. Unlike a conventional fault current limiting reactor, a SFCL is practically invisible in the grid. A fault current, however, will be limited within the first half cycle as it exceeds the ampacity of the oxide ceramic. The material temporarily loses its superconducting property and builds up a high ohmic resistance that keeps the fault current to a pre-defined maximum. Stress on downstream circuit breakers is diminished further, since the device reduces phase differences between fault current and voltage as well.
The fault current is limited for a pre-defined time interval to enable fault-identification, before the SFCL is temporarily disconnected from the grid. The oxide ceramic components heat up briefly during current-limiting and regain their superconducting property after automatic re-cooling to operating temperature. The device then resumes its rated current operation in the grid. Disruption-free grid operation during the system recovery interval can be provided, according to customer requirements, by inductive or resistive shunts.