Disclosed is a device and method for reducing network feedback during operation of an electric-arc furnace (10). The electric-arc furnace (10) has three lines (7) with one electrode (4) each. A sensor (15) for measuring the currently flowing current and a sensor (16) for measuring the currently applied voltage are provided in each line. A control and regulating unit (30) calculates an electrical actual value (E.sub.ist1, E.sub.ist2, E.sub.ist3). A semiconductor tap changer (20) is assigned to the furnace transformer (6) such that, by suitably selecting three target winding taps (T.sub.SOLL1, T.sub.SOLL2, T.sub.SOLL3) of a primary side (P) of the furnace transformer (6), a target current (I.sub.S1, I.sub.S2, I.sub.S3) is adjustable in each line (7).

Disclosed is a device and method for reducing network feedback during operation of an electric-arc furnace (10). The electric-arc furnace (10) has three lines (7) with one electrode (4) each. A sensor (15) for measuring the currently flowing current and a sensor (16) for measuring the currently applied voltage are provided in each line. A control and regulating unit (30) calculates an electrical actual value (E.sub.ist1, E.sub.ist2, E.sub.ist3). A semiconductor tap changer (20) is assigned to the furnace transformer (6) such that, by suitably selecting three target winding taps (T.sub.SOLL1, T.sub.SOLL2, T.sub.SOLL3) of a primary side (P) of the furnace transformer (6), a target current (I.sub.S1, I.sub.S2, I.sub.S3) is adjustable in each line (7).

A non-linear load in the form of an arc furnace with an upstream furnace transformer is supplied with electric power from a power supply device with a plurality of converter units. The converter units have a plurality of main modules with inputs connected to a respective phase of a three-phase grid. The converter units have a common star point between the main modules and the primary side of the furnace transformer. Each main module has a series circuit with a coupling inductance and a plurality of submodules. The submodules have a bridge circuit with four self-commutated semiconductor switches and a bridge path with a storage capacitor between input and output. The semiconductor switches of the submodules can each be switched independently of the semiconductor switches of the other submodules of the same main module and of the other main modules.

Disclosed is a control system for a melting process in an electric arc furnace for melting a metallic material that minimizes desired process properties such as the melting time or the total power consumption of the melting process. The system includes a processing unit adapted for receiving or collecting measured data of at least one process variable, determining the current state of the process, performing an optimization of the melting process, determining a process input based on the result of the optimization, and controlling the melting process with the process input. A method is also presented herein.

Disclosed is a control system for a melting process in an electric arc furnace for melting a metallic material that minimizes desired process properties such as the melting time or the total power consumption of the melting process. The system includes a processing unit adapted for receiving or collecting measured data of at least one process variable, determining the current state of the process, performing an optimization of the melting process, determining a process input based on the result of the optimization, and controlling the melting process with the process input. A method is also presented herein.

An electric power apparatus for an electric arc furnace comprises at least one electrode and is connectable to a power network to supply to the electrode the electric energy to generate an electric arc to melt a metal mass. The apparatus comprises an electric regulation unit interposed and connected to the power network and to the electrode and configured to regulate at least one electric quantity for powering the electrode. The apparatus comprises at least one detection device to detect the electric quantity, interposed between the electrode and the electric regulation unit, a positioning device to move the at least one electrode nearer to/away from the metal mass to be melted and a control and command unit.

The invention concerns a method to supply electric power to furnaces (100) for melting and/or heating metal materials (M), which provides the supply of a mains voltage (Ur) and a mains current (Ir), both having a predefined mains frequency (fr); the transformation of said mains voltage (Ur) and mains current (Ir) into selectively settable alternating secondary voltage (Us) and secondary current (Is); the rectifying of said secondary voltage (Us) and secondary current (Is) and the conversion of the direct intermediate voltage (Ui) and intermediate current (Ii) into selectively settable alternating supply voltage (Ua) and supply current (Ia); the feeding of said supply voltage (Ua) and supply current (Ia) to a plurality of electrodes (102) of the furnace (100). The invention also concerns an apparatus (10) for supplying electric power to furnaces (100) for melting and/or heating metal materials (M).

The invention concerns a method to supply electric power to furnaces (100) for melting and/or heating metal materials (M), which provides the supply of a mains voltage (Ur) and a mains current (Ir), both having a predefined mains frequency (fr); the transformation of said mains voltage (Ur) and mains current (Ir) into selectively settable alternating secondary voltage (Us) and secondary current (Is); the rectifying of said secondary voltage (Us) and secondary current (Is) and the conversion of the direct intermediate voltage (Ui) and intermediate current (Ii) into selectively settable alternating supply voltage (Ua) and supply current (Ia); the feeding of said supply voltage (Ua) and supply current (Ia) to a plurality of electrodes (102) of the furnace (100). The invention also concerns an apparatus (10) for supplying electric power to furnaces (100) for melting and/or heating metal materials (M).