AC Current limiting reactor - Mostly three phase devices with three electrically separate coils, i.e. not connected in a delta or wye configuration. Each coil is connected in series with each ac line to limit the current which can flow in the event of a fault condition in the circuit. Usually air cored.

Current limiting reactors are used to limit the fault current in a system, to a value which is within the withstand capability of the switchgear. In a three phase system, the three coils of the reactor are electrically separate, i.e. not connected in a delta or wye configuration and are each connected in series in the system, for example, between the switchgear and a transformer.
Current limiting reactors are inductance coils and do not have an iron core, hence the name, air-core inductor. Since no iron core is present, the reactor will not saturate and the inductance is therefore constant, irrespective of the current flowing through the reactor.
The use of a current limiting reactor can reduce the cost of the associated switchgear, since  a lower fault withstand rating is required of the switchgear./Current limiting reactors must be designed to withstand the mechanical and thermal effects of short circuits and overcurrents.