The switching apparatus and the method are for varying the impedance of a phase line of a segment of an electrical power line. The phase line includes n conductors electrically insulated from each other and short-circuited together at two ends of the segment. The apparatus comprises at least one first vacuum interrupter connected in series with at least one of the conductors; at least one first controllable motor for selectively opening and closing the at least one first vacuum interrupter; a detector for detecting a parameter representative of current operating conditions of the phase line; and a controller for controlling the at least one first controllable motor according to the parameter detected by the detector.