Working Principle

FunctionThe 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.