Abstract: A current-limiting device for an alternating current system has at least two iron-cored saturable reactors for each phase, each reactor core being of double-window configuration with an alternating current winding on the central limb, and a superconducting bias winding screened alternating magnetic flux is in the form of a loop with two parallel sides which pass through the two windows of at least two of the reactor cores. For a three phase system the three pairs of reactors may be on a single bias winding loop or each pair may have its own bias winding. In a preferred construction two bias winding loops each link three reactor cores and each phase includes one reactor from each of the bias windings.