The aim of asymmetrical dynamic melting control for A.C. arc furnaces is to optimise the melting rate while limiting the heat load on the wall cooling elements.

The control system monitors and evaluates the electrical variables as well as the heat load on the water-cooled wall elements. If the heat load is heavy, the arc radiation onto the area concerned is suitably reduced, for which purpose the furnace is operated asymmetrically for a time, if possible solely through asymmetrical adjustment of the arc lengths via the automatic electrode control impedance set-points, or otherwise in conjunction with asymmetrical reduction of the voltage levels.

In melting phases in which the heat load on the wall is non-critical, the control system adjusts the currents for a power-optimal operating point through selection of impedance set-points.

The system is realised on an industrial PC and provides coordinating control of the set-points for the automatic electrode control system and the furnace transformer. It visualises the heat load on the wall, including the arc radiation and the operator interventions with regard to the electrical set-points.

In the course of a ten-month trial period in which the melting control system was tested at an electric arc furnace in the melt shop of ThyssenKrupp Nirosta GmbH in Bochum, the melting rate was improved by as much as 8 % by increasing the mean electric power input and by shortening the power-off times. The economical mode of operation reduced the consumption of refractory gunning mixes by around 10 %.

Literature:
Stahl u. Eisen 117 (1997) No.2, pp 91-96