Patent EA-004169-B1 (EA)
Title: Method and device for supplying an electric arc melting furnace with current
Inventor: BREKER DIRK
IPC: H05B7/11
Filed: 2000-04-20
Abstract: 1. Process for supplying current to an electric-arc melting unit for melting and heating metal, which unit is operated with at least two electrodes, characterized by the following steps: (a) the electric current from mains to a three-phase a.c. source is divided over at least two parallel power supply modules, containing uncontrolled three-phase bridge, connected in series, to produce direct current; direct-current intermediate circuits to store rectified direct-current, and transistor unit to produce the current as a direct or alternating current and a value, corresponding to the power required for the running of electric-arc melting unit, and (b) brought together via current-carrying line to an electrode of the melting unit. 2. Process according to claim 1, characterized in that the primary power factor of the power supply module is kept at a constant high level by the three-phase bridge connected to the input side. 3. Process according to claim 1, characterized in that, relative to a predetermined capacitance, each direct current intermediate circuit is supplied with an amount of current at which the arc will not exert any negative feedback on circuit. 4. Process according to claim 1, characterized in that the phase shift of the three-phase a.c. source is divided in n-fold phase-shifted windings in such a way that its characteristic corresponds to an n x 6-pulse circuit design. 5. Process according to claim 1-4, characterized in that the rectified partial currents are controlled by the transistor units in such a way that the current conducted to the first current-carrying line is a direct current, which is sent to at least two electrodes of melting unit.. 6. Process according to claim 1-4, characterized in that the rectified partial currents are controlled by the transistor units in such a way that produced single-phase alternating current is conducted to the current-carrying line. 7. Process according to claim 1-4, characterized in that three of the rectified partial currents, which are electrically phase-shifted by 120 degree by the transistor units, form a three-phase a.c. unit, which is sent over three current-carrying lines as three-phase alternating current to at least three electrodes assigned to the melting. 8. Apparatus for supplying current to an electric-arc melting unit for melting and heating metal of method of claim 1, with a three-phase a.c. source, which sends the current via devices for producing direct or alternating current to at least one electrode projecting into the vessel of the melting unit, characterized in that said devices for producing direct or alternating current are at least two power supply modules (41, 4n) connected in parallel to each other; in that each power supply module (41, 4n) has an uncontrolled three-phase bridge (51, 5n) for producing a direct current, a direct-current intermediate circuit (61, 6n)for storing the energy of rectified direct current, and a transistor unit (71, 7n) for production of current as a direct current or alternating current and a value, corresponding to the powers required for the running of electric-arc melting unit, the power supply modules (41, 4n) are connected with said electrodes (21, 22, 23, 24) via current-carrying lines (31, 34, 32, 33, 35). 9. The apparatus for supplying current according to claim 8, characterized in that the transistor units (71, 7n) contain components (82) by means of which the level of the current can be controlled in correspondence with the power required during the melting and heating while keeping the power factor constant. 10. The apparatus according to claims 8 or 9, characterized in that the transistor units (71, 7n) are connected to control devices (81), by means of which direct currents can be formed, power supply modules (41, 4n) via at least two current-carrying lines (31, 34) being connected with at least two electrodes (21, 24) at least one electrode (21) being introduced in the vessel (12) of the melting unit (11) and at least one of electrodes, which is a bottom electrode being connected with vessel (12) of melting unit (12). 11. The apparatus for supplying current according to claim 8 or 9, characterized in that the transistor units (71, 7n) are connected to control devices (81), by means of which single-phase alternating currents can be formed, power supply modules (41, 4n) via at least two current-carrying lines (31, 34) being connected with at least two electrodes (21, 24) introduced in the vessel (12) of melting unit (11). 12. The apparatus for supplying current according to claim 8 or 9, characterized in that the transistor units (71, 7n) are connected to control devices (81), by means of which alternating currents can be formed in each power supply module, said modules (41, 4n) forming three-phase alternating currents via three current-carrying lines (32, 33, 35) are connected with at least three electrodes (21, 22, 23) provided in the vessel (12) of melting unit. 13. The apparatus for supplying current according to claim 12, characterized in that the control devices (81) connected to the transistor units (71, 7n) form alternating currents, which are shifted electrically by 120 degree from each other.