Petersen coils regulated by steps (with off voltage tap changer)
Single phase reactors with or without magnetic core, connected between a neutral point and ground in MV distribution network.
They are designed to be resonant with network capacitance, limiting earth fault current.
In this type the value of the reactance and the compensation current are the main factor for design.
They can be designed also for a range min/max fault current, selected by a tap changer.