Device and method of power supply for an electric furnace

Claims

1. A device (10) for supplying electric power to furnaces (100) for melting and / or heating metallic materials provided with electrodes (102), comprising at least one electric power supply line (201, 201L, 201M) and at least one basic module (20, 120, 220) connected thereto, configured to convert alternating network voltage and current (Ur, Ir) with a network frequency (fr) into alternating voltage and supply current (Ua, Ia) with a required supply frequency (fa), wherein said at least one basic module (20, 120, 220) comprises: a transformer (11) connected to said power supply line (201, 201L, 201M) and configured to convert said alternating network voltage and current (Ur, Ir) into alternating secondary voltage and current (Us, Is); rectifiers (14) connected to said transformer (11) and configured to convert said alternating secondary voltage and current (Us, Is) into intermediate voltage and direct current (Ui, Ii); one or more intermediate direct current circuits (16) designed with the possibility of accumulating electrical energy; inverter devices (15) connected to said one or more intermediate direct current circuits (16) and configured to convert said intermediate voltage and current (Ui, Ii) into alternating voltage and supply current (Ua, Ia) with said required supply frequency (fa); a control and command unit (17) configured to control the operation of said inverter devices (15) and regulate the power supply frequency (fa) at each stage of the technological process of said furnace (100), characterized in that said device (10) contains an adapter device (19) connected to said at least one base module (20, 120, 220) and configured to be connected to said electrodes (102) and adapt the parameters of said supply voltage and current (Ua, Ia) to an adapted voltage and current (Ua*, Ia*) suitable for supplying said electrodes (102).

2. The device (10) according to claim 1, characterized in that said power supply line (201, 201L) is designed to operate at low voltage (LV), and said adapter device (19) contains one or more of the following devices: a reactor (26), a filter (27), or a disconnecting switch (28).

3. The device (10) according to claim 1, characterized in that it contains a step-down transformer device (202) connected upstream of said power supply line (201, 201L) and configured to reduce the voltage supplied by the high-voltage or medium-voltage main network (203) to a low-level mains voltage (Ur).

4. The device (10) according to claim 1, characterized in that said power supply line (201, 201M) is designed with the possibility of operation at medium voltage (MV), and said adapter device (19) contains at least one adapter transformer (25) having a primary winding (29) connected to said at least one base module (20), and a secondary winding (30) designed with the possibility of connection in operating mode to said electrodes (102).

5. The device (10) according to claim 4, characterized in that it contains a step-down transformer device (202) connected upstream of said power supply line (201, 201M) and configured to reduce the voltage supplied by the high-voltage or medium-voltage main network (203) to a medium-level network voltage (Ur).

6. A device according to any of the preceding claims, characterized in that said control and command unit (17) is provided with control devices (18) configured to regulate the power supply frequency (fa) at each stage of the operating cycle of said furnace (100) in such a way that it is lower than or equal to the network frequency (fr), and at least at one of the stages of said operating cycle the power supply frequency (fa) is from 40% to 80% of the network frequency (fr).

7. A device according to any of the preceding claims, characterized in that said at least one base module (20, 120, 220) contains at least two sub-modules (21, 21A-21F), each of which contains at least one rectifier (14), an intermediate circuit (16) and an inverter device (15) and is designed with the possibility of outputting single-phase voltage and current of a multi-pole connection line (24).

8. The device according to item 7, characterized in that all intermediate circuits (16) of at least one basic power supply module (20, 120, 220) are connected to each other by means of short-circuiting connections (22, 23).

9. The device (10) according to claim 7 or 8, characterized in that said transformer (11) contains a single primary winding (12) with three-phase inputs which, in the operating mode, are connected to the phases (R, S, T) of said power supply line (201, 201L, 201M), and is connected to secondary windings (13), one for each of said submodules (21, 21A-21F), wherein the phases of at least two of said secondary windings (13) of at least one base module (20, 120, 220) are phase-shifted relative to each other.

10. An installation (50) for melting a metallic material, comprising a power supply device (10) according to any one of paragraphs 1-9 and an electric furnace (100) equipped with two or more electrodes (102) connected to the corresponding phases (R, S, T) of the supply voltage and current (Ua, Ia) supplied by said at least one base module (20, 120, 220) via at least one adapter device (19).

11. A method for feeding an electric furnace (100) having two or more electrodes (102), comprising: supplying alternating network voltage and current (Ur, Ir) from a three-phase power supply line (201, 201L, 201M) with a given network frequency (fr) to at least one base module (20, 120, 220); conversion by means of a transformer (11) of the specified mains voltage and current (Ur, Ir) into an alternating secondary voltage and current (Us, Is) with a value that can be selectively set; rectification of the specified secondary voltage and current (Us, Is) using rectifiers (14) to obtain intermediate voltage and direct current (Ui, Ii); conversion, using inverter devices (15), of said intermediate direct current voltage and current (Ui, Ii) into alternating voltage (Ua) and current (Ia) of supply with a value that can be selectively set and with the required supply frequency (fa) by means of a control and command unit (17) connected to said inverter devices (15); adaptation and / or filtering of the specified supply voltage and current (Ua, Ia) after the specified inverter devices (15) to regulate their parameters and obtain an adapted supply voltage and current (U*, I*) supplied to the specified electrodes (102).

12. The method according to claim 11, characterized in that it provides that during each stage of the working cycle of said furnace (100), the control devices (18) of said control and command unit (17) control said inverter devices (15) in such a way that at least at some stages of the technological process the power supply frequency (fa) is lower than or equal to the network frequency (fr), and at least at one stage of said working cycle the power supply frequency (fa) is from 40% to 80% of the network frequency (fr).

13. The method according to claim 12, characterized in that it provides for controlling said inverter devices (15) in such a way that the supply frequency (fa) is lower than the network frequency (fr) for at least 80% of the duration of the technological process, preferably at least 90%, and even more preferably at least 95%.

14. The method according to any one of paragraphs 11-13, characterized in that it provides for the supply of alternating network voltage and current (Ur, Ir) at medium voltage (MV) and the adaptation of said supply voltage and current (Ua, Ia) after said inverter devices (15) by means of at least one adapter transformer (25), connected by the primary winding (29) to said inverter devices (15), and by the secondary winding (30) to said electrodes (102), in order to obtain an adapted supply voltage and current (Ua*, Ia*) at low voltage (LV).

15. The method according to any one of paragraphs 11-13, characterized in that it provides for the supply of alternating mains voltage and current (Ur, Ir) at low voltage (LV) and the adaptation of said supply voltage and current (Ua, Ia) after said inverter devices (15) by means of an adapter device (19) connected between said inverter devices (15) and said electrodes (102), wherein said adapter device (19) contains one or more of the following devices: a reactor (26), a filter (27) or a disconnecting switch (28).