A device (8), for adjusting the impedance of a high voltage line (9), supplying an alternating current, has at least one control coil (2), which may be inserted in series in the high voltage line (9) and at least one switching device (3,10), provided for each control coil (2). The device is compact and economical. A control unit (4) for controlling each switching device (3,10) is also provided, such that the reactance of the control coil (2), acting in the device may be adjusted by the switching of the switching device (3,10), whereby each switching device (3,10) is arranged parallel to the corresponding control coil (2) in a parallel branch (5).