A power supply system for an arc furnace, suitable for converting voltage of a three-phase electric power network into power supply voltage for the arc furnace, has an indirect AC/AC converter having a converter input and a converter output, and a matching apparatus having a matching transformer having a secondary side connectable to the arc furnace and a primary side operatively connected to the converter output. An input transformer group, inserted between the indirect AC/AC converter and the three-phase electric power network, has an input transformer primary side connectable to the three-phase electric power system, an input transformer secondary side connected to the converter input, a first input transformer and a second input transformer. Each of the first and second input transformers has three mutually displaced groups of secondary windings, each of which has a winding for each phase corresponding to a phase of the three-phase electric power network.

A rectifier arrangement includes at least one input alternating voltage terminal to which an alternating current can be supplied, at least two output direct voltage terminals at which direct current can be tapped and at least one series circuit with at least two sub-modules connected in series. Each sub-module of the series circuit includes at least one converter module, an inverter module and a transformer module. Each sub-module of the series circuit additionally includes a rectifier module. The outputs of the rectifier modules are connected in parallel and form the output direct voltage terminals of the rectifier arrangement.

Apparatus for melting metal material comprising a container for metal material, by way of example, but not limited to, metal scrap, DRI, cast iron, supplied in an electric arc-type melting furnace, and a plurality of electrodes to melt the metal material, which can be inserted in said container.

An electric arc furnace (1) operated with alternating current has a converter (2) which converts mains voltage (U), into primary voltage (U′) having a furnace frequency (f′). A furnace transformer (4) transforms the primary voltage (U′) into a secondary voltage (U″), supplied to electrodes (6) in a furnace vessel (8) (1). They apply electric arcs (10) to a melt material (9) in the vessel (8). The secondary voltage (U″) is also supplied to a capacitor assembly (7) on the output side of the furnace transformer (4) and the furnace transformer (4) is connected on the output side. A control device (5) controls the converter (2) such that a primary voltage (U′) output from the converter (2) to the furnace transformer (4) has a furnace frequency (f) of least ten times the mains frequency (f) and/or greater than 1 kHz.

Apparatus for melting metal material comprising a container for metal material, by way of example, but not limited to, metal scrap, DRI, cast iron, supplied in an electric arc-type melting furnace, and a plurality of electrodes to melt the metal material, which can be inserted in said container.

An electrical arrangement for an electric arc furnace (1) operated with alternating current has a converter (2) which converts mains voltage (U), having a mains frequency (f), of a supply grid (3) into primary voltage (U) having a furnace frequency (f). A furnace transformer (4) of the electrical arrangement transforms the primary voltage (U) into a secondary voltage (U). The secondary voltage (U) is supplied to a number of electrodes (6) of the electric arc furnace (1). The electrodes (6) are arranged in a furnace vessel (8) of the electric arc furnace (1). They apply electric arcs (10) to a melt material (9) in the furnace vessel (8). The secondary voltage (U) is also supplied to a capacitor assembly (7) which is on the output side of the furnace transformer (4) and to which the furnace transformer (4) is connected on the output side. The converter (2) is controlled by a control device (5) such that a primary voltage (U) output from the converter (2) to the furnace transformer (4) has a furnace frequency (f) which is at least ten times the mains frequency (f) and/or is greater than 1 kHz.

Provided is an AC-DC-AC converter for delivering power to a load from a power source that includes a front-end converter, a load-end converter, and a DC link. The front-end converter being a hybrid modular multilevel rectifier, and the load-end converter being either a modular multilevel converter or a hybrid modular multilevel converter.

An electric arc furnace has a safety device (3) connected to an earthed peripheral device. An earth cable (4) is provided to the peripheral device of the arc furnace (2). An ammeter (6) measures the current across the earth cable (4). A circuit breaker (8) in the earth cable (4) has a tripping time of less than 100 ms.