Device for feeding one or a plurality of electrodes in an electrothermal furnace

Claim 1

Operation control system for an electrothermal furnace having at least one heating electrode, and transformer means for supplying heating current to the electrode, the transformer means for the electrode including a transformer unit having a primary winding connected to receive a mains voltage, a first secondary winding constituting a source of heating current for the electrode, and a second secondary winding, an additional transformer unit connected to derive an adjustable additional voltage from the second secondary winding, and means connected for deriving operating current for the electrode from the voltage across the first secondary winding and the adjustable additional voltage, said control system including a control assembly for the transformer means for the electrode, said control assembly conprising: (a) measuring means operatively connected to the first secondary winding for deriving a first current signal representing the magnitude of the current through the first secondary winding; (b) signal supply means including a microprocessor for supplying a second current signal representing the desired magnitude of the current through the first secondary winding, based on a predetermined furnace operation schedule which represents the active power to be supplied by the electrode as a function of time; (c) arithmetic means connected to said measuring means and said signal supply means for providing a difference signal representative of the difference between current magnitudes represented by the first and second current signals; (d) current flow control means including a thyristor unit connected in series with said second secondary winding and said additional transformer unit for controlling the flow of current from said second secondary winding to said additional transformer, and thus the value of the additional voltage; (e) regulating means connected between said first arithmetic means and said current flow control means for supplying to said thyristor unit firing pulses which are timed for causing the flow of current from said second secondary winding to be a function of the difference signal; and (f) switch means operatively associated with said second secondary winding and switchable between a first state in which the operating current for the electrode is derived from the algebraic sum of the voltage across said first secondary winding and the adjustable additional voltage and a second state in which the operating current for the electrode is derived from the difference between the voltage across said first secondary winding and the adjustable additional voltage.