During operation, DC arc furnaces (8) produce undesired reactive load fluctuations which are compensated by means of a power factor compensator (31). An AC power controller (28) of the power factor compensator (31) is controlled as a function of a stabilization striking angle signal (.alpha..sub.st) which is controlled in accordance with the reactive power of filter branches (4, 4') by a function generator (26) as a function of a desired reactive power signal (Q.sub.des8), of a reactive power actual value signal (Q.sub.8) of the arc furnace (8) and of a filter reactive power signal (Q.sub.F). The desired reactive power signal (Q.sub.des8) is formed by means of a phase-angle controller (35) as a function of a total current intensity (i.sub.33) which, in addition to the current actual value (i.sub.act) of the arc furnace (8) also comprises the current of the filter branches (4, 4') and that of any auxiliaries.