A device for limiting current with variable coil impedance includes a choke coil and a cooling device. An additional coil is made of a high-temperature superconducting material and is disposed in the choke coil such that the current is limited by the device without using an iron core.

A fault current limiter is provided that comprises a fault current limiter comprising first, second and third magnetically saturable cores. The fault current limiter comprises a magnetic biasing arrangement arranged to produce a first magnetic circuit in the first magnetically saturable core, a second magnetic circuit in the second magnetically saturable core, and a third magnetic circuit in the third magnetically saturable core; first and second AC coils connected in series and connected to a first phase AC source, wherein the first AC coil is wound on a portion of the first magnetically saturable core and the second AC coil is wound on a portion of the third magnetically saturable core; third and fourth AC coils connected in series and connected to a second phase AC source, wherein the third AC coil is wound on a portion of the first magnetically saturable core and the fourth AC coil is wound on a portion of the second magnetically saturable core; and fifth and sixth AC coils connected in series and connected to a third phase AC source, wherein the fifth AC coil is wound on a portion of the second magnetically saturable core and the sixth AC coil is wound on a portion of the third magnetically saturable core.

The invention relates to a superconducting electrical switch. The switch comprises two parallel branches of superconducting material in a loop, and a magnetic field generator which generates a time-varying magnetic field through the loop in a direction generally parallel to the axis of the loop. The magnetic field generator is selectively activated and de-activated to switch the electrical switch between a low-resistance state and a higher-resistance state. In the low-resistance state, there is no magnetic field through the loop and transport current flows through the loop. In the higher-resistance state, a magnetic field through the loop induces a screening current such that the sum of the transport current and the screening current is substantially equal to the critical current or is greater than the critical current of the superconducting material. The switch may be used in, for example, a rectifier or fault current limiter.