Current-limiting unit for an AC device, and use of the unit in a power transmission system

In order to reduce the energy losses, at least two saturable inductor devices (12, 13) are provided in the current-limiting unit for each phase of the AC device. Each inductor device has an AC winding (10A, 10B, 10C; 11A, 11B, 11C) and a superconductive DC premagnetising winding (20, 36) which saturates the inductor core (12A; 12B; 12C; 13A; 13B; 13C) in such a manner that the latter remains saturated even when the AC device is on full load. The AC windings (10A, 10B, 10C; 11A, 11B, 11C) act per phase such that, at full load, a change in the saturation level in one of the inductor cores (12A; 12B; 12C; 13A; 13B; 13C) with respect to the saturation level produced just by the premagnetising winding (20, 36) is associated with an opposing change in the saturation level in the other inductor core (12A; 12B; 12C; 13A; 13B; 13C) of the same phase. The current limiting takes place when, in each half-cycle, one or other of the inductor cores (12A; 12B; 12C; 13A; 13B; 13C) is forced out of its saturation state. The unit is particularly suitable for power transmission between two power AC devices.