An apparatus and a method are for varying an impedance of a phase line of a segment of a first electrical power line, the phase line including n conductors electrically insulated from each other and short-circuited together at two ends of the segment. The apparatus includes at least one controllable switching device for connection with at least one of the conductors. The apparatus also includes a controller for performing control of the at least one controllable switching device, the controller having at least one optical port for receiving first optical signals on which the control is based, and for sending second optical signals to adjacent switching apparatuses, the second optical signals including status information of the one switching apparatus, upon which control of adjacent switching apparatuses is based.