Arrangement for controlling the electrodes of an arc furnace

In an arrangement for controlling arc furnace electrode means comprising at least one melting electrode fed from an output winding of a transformer, and including an impedance controller for each electrode, associated positioning means to adjust the height of each electrode, measuring means to furnish a first measured quantity proportional to the electrode voltage between the output winding of the transformer and the furnace jacket and a second measured quantity proportional to the electrode current, the invention comprising:

• a divider connected to the measuring means to produce an actual impedance value proportional to the ratio of the first measured quantity to the second measured quality;
• means to form a control deviation as the difference between a preset desired impedance value and the actual impedance value;
• a lowpass filter connected to the output of the divider;
• a first switching element connected in parallel to the filter, the output of the filter being connected to drive the impedance controller to the full in the event of a short circuit;
• and
• a second switching element connected to the output of the impedance controller to cut off signals therefrom at the instant the sum of the first and second measured quantities becomes zero.