Fault current limiters (fcl) with the cores saturated by superconducting coils

A method for reducing mass of a current limiting device for an AC supply, said current limiting device comprising for each phase of the AC supply a magnetic circuit that offers low impedance under non-fault conditions and high impedance under fault conditions, said method comprising:

• constructing the magnetic circuit so as to form an open magnetic core for at least one AC coil and forming a closed magnetic circuit for at least one superconducting DC bias coil that is adapted under non-fault conditions to bias the magnetic core into saturation so that each of the opposing limbs is saturated in opposite directions by the bias coil;
• whereby under fault conditions some of the cross-sectional area of the magnetic core always exhibits high permeability and serves, thereby, to resist the fault and allow the cross-sectional area of the at least one AC coil and magnetic core to be reduced.