A method and an apparatus for symmetrically modulating a controlled series compensation system (2) in electrical networks (6). Impedance manipulated variables determined from a current control for the series compensators (14) of the system (2) are limited by determining an upper or lower limiting value (Z.sub.OO,Z.sub.OU). The upper and lower limiting values are respectively determined by adding a positive or negative deviation (.DELTA.Z.sub.+,.DELTA.Z.sub.-) to and subtracting it from a reference manipulated variable (Z.sub.O) for impedance. The reference manipulated variable (Z.sub.O) for impedance is selected from the impedance manipulated variables (Z.sub.y1,Z.sub.y2,Z.sub.y3). Thus, small asymmetries can be corrected and, given network faults of generally only a brief duration, unnecessary control deviations can be avoided.