A switching apparatus for varying an impedance of a phase line of a segment of an electrical power line, the phase line including n conductors electrically insulated from each other, n being equal to or greater than 2, the n conductors being short-circuited together at two ends of the segment; the apparatus comprising: for each conductor, a controllable interrupter connected in series, said interrupter having command terminals for receiving first command signals for selectively switching said interrupter into a closed or an opened position; a parameter detector for detecting a parameter representative of an actual operating condition of the phase line; a first controller for controlling the interrupters via their command terminals, according to the parameter detected by the detector; characterized in that the apparatus further comprises a disabling unit for disabling the interrupters, said disabling unit comprising: n controllable switches associated respectively to the n controllable interrupters for respectively disabling the n controllable interrupters; position detectors for detecting which of the n interrupters is closed; and a second controller having first inputs (11, 13) for receiving position signals from the position detectors, a second input for receiving second command signals for commanding the disabling unit, and command outputs to command the n controllable switches in view of said second command signals and said position signals so that, at all operating times, at least one of the n interrupters is closed and disabled. for each conductor, a controllable interrupter connected in series, said interrupter having command terminals for receiving first command signals for selectively switching said interrupter into a closed or an opened position; a parameter detector for detecting a parameter representative of an actual operating condition of the phase line; a first controller for controlling the interrupters via their command terminals, according to the parameter detected by the detector; characterized in that the apparatus further comprises a disabling unit for disabling the interrupters, said disabling unit comprising: n controllable switches associated respectively to the n controllable interrupters for respectively disabling the n controllable interrupters; position detectors for detecting which of the n interrupters is closed; and a second controller having first inputs (11, 13) for receiving position signals from the position detectors, a second input for receiving second command signals for commanding the disabling unit, and command outputs to command the n controllable switches in view of said second command signals and said position signals so that, at all operating times, at least one of the n interrupters is closed and disabled. n controllable switches associated respectively to the n controllable interrupters for respectively disabling the n controllable interrupters; position detectors for detecting which of the n interrupters is closed; and a second controller having first inputs (11, 13) for receiving position signals from the position detectors, a second input for receiving second command signals for commanding the disabling unit, and command outputs to command the n controllable switches in view of said second command signals and said position signals so that, at all operating times, at least one of the n interrupters is closed and disabled.