Abstract: In a method for stabilizing a power supply network against fluctuations of the reactive power of an electrical system, in particular of an arc furnace (5), having at least one transformer (3), the at least one transformer (3) is switched on and off on the supply network side in switching sequences which result in a fundamental-frequency power factor with a value at least approximately equal to 1. The fundamental-frequency reactive power is thus at least approximately equal to zero.

Abstract: When operating, DC arc furnaces generate undesired reactive load fluctuations which are compensated without special compensation reactance by a reactive power controller. As compensation reactance, use is made of inductors, which are always present and via which the arc furnace is fed by rectifiers. A current controller is connected to the rectifiers via a first summer. On the input side, the first summer is further operationally connected to the output of the reactive power controller and, as the case may be, to an AC--AC converter which supplies a signal proportional to the power supply voltage (U.sub.xN). In addition, it is possible to provide an inverter which is connected in parallel with the arc furnace on the DC side and which is operationally connected on the AC side to a feeding AC power supply network (N) via a stabilization transformer or via auxiliary windings of a furnace transformer, and to the output of the reactive power controller on the control side.