Parallel switching occurs when two or more circuit-breakers are tripped to interrupt a shared fault current. This is typically the case for such bus arrangements as a double breaker, breaker-and-a-half, breaker-and-a-third, and ring buses. Ideally, all of the circuit-breakers should... Read more

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Fault Current Limiters (FCL) provide protection for upstream and/or downstream devices in electric power grids. Conventional FCL require the use of expensive conductors and liquid or gas cryogen handling. Disclosed embodiments describe FCL systems and devices that use lower cost superconductors, require no liquid cryogen, and are fast cycling. These improved FCL can sustain many sequential faults and require less time to clear faults while avoiding the use of liquid cryogen. Disclosed embodiments describe a FCL with a superconductor and cladding cooled to cryogenic temperatures; these are connected in parallel with a second resistor across two nodes in a circuit. According to disclosed embodiments, the resistance of the superconducting components and its sheath in the fault mode are sufficiently high to minimize energy deposition within the cryogenic system, minimizing recovery time. A scheme for intermediate heat storage also is described which allows a useful compromise between conductor length enabled energy minimization and allowable number of sequential faults to enable an overall system design which is affordable, and yet allows conduction cooled (cryogen free) systems which have fast recovery and allows for multiple sequential faults.

An inductive fault current limiter (1), has a normally conducting primary coil assembly (2) with a multiplicity of turns (3), and a superconducting, short-circuited secondary coil assembly (4). The primary coil assembly (2) and the secondary coil assembly (4) are disposed at least substantially coaxially with respect to each other and at least partially interleaved in each other. The secondary coil assembly (4) has a first coil section (4a) disposed radially inside the turns (3) of the primary coil assembly (2) and a second coil section (4b) disposed radially outside the turns (3) of the primary coil assembly (2). The fault current limiter has an increased inductance ratio.