EP-4736578-A1 - ELECTRIC POWER SUPPLY APPARATUS AND METHOD FOR AN ELECTRIC FURNACE

Abstract

An apparatus (10) for the electric power supply of furnaces (100) for melting and/or heating metal materials provided with electrodes (102) comprises at least one power supply line (201, 20 IL, 20 IM) and at least one connected base module (20, 120, 220) which is configured to convert an alternating mains voltage and current (Ur, Ir) having a mains frequency (ft) into alternating supply voltage and current (Ua, la) with a desired power supply frequency (fa), wherein the at least one base module (20, 120, 220) comprises a transformer (11), a plurality of rectifiers (14) connected to the transformer (11), one or more direct current intermediate circuits (16) configured to store electrical energy, a plurality of inverter devices (15) and a control and command unit (17) configured to control and command the operation of the inverter devices (15) and adjust the power supply frequency (fa). The invention also concerns a method for the electric power supply of furnaces (100) for melting and/or heating metal materials.

Inventors

• MORDEGLIA, Antonello

Assignees

• Danieli Automation S.P.A.

Dates

Publication Date

20260506

Application Date

20240621

Claims (1)

1. CLAIMS 1. Apparatus (10) for the electric power supply of furnaces (100) for melting and/or heating metal materials provided with electrodes (102), comprising at least one power supply line (201, 20 IL, 20 IM) and at least one connected base module (20, 120, 220) which is configured to convert an alternating mains voltage and current (Ur, Ir) having a mains frequency (fr) into alternating supply voltage and current (Ua, la) with a desired power supply frequency (fa), wherein said at least one base module (20, 120, 220) comprises: - a transformer (11) connected to said power supply line (201, 20 IL, 20 IM) and configured to transform said alternating mains voltage and current (Ur, Ir) into alternating secondary voltage and current (Us, Is); - a plurality of rectifiers (14) connected to said transformer (11) and configured to transform said alternating secondary voltage and current (Us, Is) into direct current intermediate electric voltage and current (Ui, li); - one or more direct current intermediate circuits (16) configured to store electrical energy; - a plurality of inverter devices (15) connected to said one or more direct current intermediate circuits (16) and configured to convert said intermediate electric voltage and current (Ui, li) into alternating supply voltage and current (Ua, la) having said desired power supply frequency (fa); - a control and command unit (17) configured to control and command the operation of said inverter devices (15) and regulate, during each step of a process of said furnace (100), said power supply frequency (fa), characterized in that said apparatus (10) comprises an adapter device (19) connected to said at least one base module (20, 120, 220) and connectable to said electrodes (102) and configured to adapt the parameters of said supply voltage and current (Ua, la) into adapted electric voltage and current (Ua*, la*) for said electrodes (102). 2. Apparatus (10) as in claim 1 , characterized in that said power supply line (201 , 201 L) is configured to operate at low voltage (LV) and said adapter device (19) comprises one or more of either a reactance (26), a filter (27) or a disconnector switch (28). 3. Apparatus (10) as in claim 1, characterized in that it comprises a reducer transformer device (202) connected upstream of said power supply line (201, 20 IL) and configured to lower an electric voltage supplied by a high or medium voltage main network (203) into a low voltage mains voltage (Ur). 4. Apparatus (10) as in claim 1 , characterized in that said power supply line (201 , 20 IM) is configured to operate at medium voltage (MV) and said adapter device (19) comprises at least one adapter transformer (25) provided with a transformer primary (29) connected to said at least one base module (20) and a transformer secondary (30) connectable, during use, to said electrodes (102). 5. Apparatus (10) as in claim 4, characterized in that it comprises a reducer transformer device (202) connected upstream of said power supply line (201, 20 IM) and configured to lower an electric voltage supplied by a high or medium voltage main network (203) into a medium voltage mains voltage (Ur). 6. Apparatus as in any claim hereinbefore, characterized in that said control and command unit (17) is provided with regulating devices (18) configured to regulate, during each step of a work cycle of said furnace (100), said power supply frequency (fa) in such a way that it is lower than or equal to said mains frequency (fr) and, in at least one of the steps of said work cycle, said power supply frequency (fa) is comprised between 40% and 80% of said mains frequency (fr). 7. Apparatus as in any claim hereinbefore, characterized in that said at least one base module (20, 120, 220) comprises at least two sub-modules (21, 21A-21F), each comprising at least one rectifier (14), an intermediate circuit (16) and an inverter device (15) and each configured to supply at output a single-phase voltage and current of a multi-phase connection line (24). 8. Apparatus as in claim 7, characterized in that all the intermediate circuits (16) of the at least one base power supply module (20, 120, 220) are short-circuited to each other by means of short-circuit connections (22, 23). 9. Apparatus (10) as in claim 7 or 8, characterized in that said transformer (11) comprises a single transformer primary (12) provided with three-phase inputs which are connected, during use, to the phases (R, S, T) of said power supply line (201, 201L, 201M), coupled to a plurality of transformer secondaries (13), one for each of said sub-modules (21, 21 A-21F), and in that the phases of at least two of said transformer secondaries (13) of said at least one base module (20, 120, 220) are out of phase with respect to each other. 10. Plant (50) for melting a metal material comprising a power supply apparatus (10) as in any claim from 1 to 9 and an electric furnace (100) provided with two or more electrodes (102) connected to respective phases (R, S, T) of supply voltage and current (Ua, la) which are supplied by said at least one base module (20, 120, 220) by means of at least one adapter device (19). 11. Method for powering an electric furnace (11) having two or more electrodes (102), comprising: - supplying an alternating mains voltage and current (Ur, Ir) of a three-phase power supply line (201, 20 IL, 20 IM) having a predefined mains frequency (fr) to at least one base module (20, 120, 220); - transforming, by means of a transformer (11), said mains voltage and current (Ur, Ir) into alternating secondary voltage and current (Us, Ir) which can be selectively set; - rectifying said secondary voltage and current (Us, Is) with a plurality of rectifiers (14) to obtain a direct current intermediate voltage and current (Ui, li); - converting, with a plurality of inverter devices (15), said direct current intermediate voltage and current (Ui, li) into an alternating supply voltage (Ua) and supply current (la) which can be selectively set and have a desired power supply frequency (fa) by means of a control and command unit (17) connected to said inverter devices (15); - adapting and/or filtering said supply voltage and current (Ua, la) downstream of said inverter devices (15) in order to regulate their parameters and obtain an adapted supply voltage and current (U*, I*) and supply them to said electrodes (102). 12. Method as in claim 11, characterized in that it provides that, during each step of a work cycle of said furnace (100), regulating devices (18) of said control and command unit (17) regulate said inverter devices (15) in such a way that at least for some steps of the work process said power supply frequency (fa) is lower than or equal to said mains frequency (fr) and, in at least one step of said work cycle, said power supply frequency (fa) is comprised between 40% and 80% of said mains frequency (fr). 13. Method as in claim 12, characterized in that it provides to regulate said inverter devices (15) in such a way that said power supply frequency (fa) is lower than said mains frequency (fr) at least for 80% of the work process, preferably at least for 90% and even more preferably at least for 95%. 14. Method as in any claim from 11 to 13, characterized in that it provides to supply an alternating mains voltage and current (Ur, Ir) in medium voltage (MV) and to adapt said supply voltage and current (Ua, la) downstream of said inverter devices (15) by means of at least one adapter transformer (25) connected with a transformer primary (29) to said inverter devices (15) and with a transformer secondary (30) to said electrodes (102), in order to obtain an adapted supply voltage and current (Ua*, la*) in low voltage (LV). 15. Method as in any claim from 11 to 13, characterized in that it provides to supply an alternating mains voltage and current (Ur, Ir) in low voltage (LV) and to adapt said supply voltage and current (Ua, la) downstream of said inverter devices (15) by means of an adapter device (19) connected between said inverter devices (15) and said electrodes (102), said adapter device (19) comprising one or more of either a reactance (26), a filter (27) or a disconnector switch (28).

Description

“ELECTRIC POWER SUPPLY APPARATUS AND METHOD FOR AN ELECTRIC FURNACE” FIELD OF THE INVENTION The present invention concerns an electric power supply apparatus and method for an electric furnace for steelmaking applications for the production of steel, or for other sectors in which metals or glassy materials, or similar or comparable materials, are worked. The electric power supply apparatus is applicable, in particular, to electric furnaces that operate with alternating electric currents and voltages. BACKGROUND OF THE INVENTION As is known, the electric furnaces used to melt metal in steelmaking applications require an efficient electric power supply system that supplies high powers. It is also known that a melting process comprises several steps, which generally comprise a step of boring the metal material, a step of melting the material and a refining step. The power and electrical energy required by the electric furnace during the melting process vary even significantly from one step to another, therefore it is necessary to suitably adapt the amount of electrical energy supplied on each occasion. In particular, the power absorbed by the electric furnace during the step of boring the metal material, or even during the melting step, is generally greater than the one required during the refining step and, depending on the type of material that is fed into the furnace, can vary even considerably within the same process step. During the boring step, the electric arc between the electrodes and the metal material has a very unstable behavior, which progressively improves as the melting progresses, since the accumulated and not yet melted scrap can collapse near the electrodes, generating short circuit conditions that correspond to a considerable reduction in the useful active power and a rapid increase in the current absorbed from the electric network. The instability of the arc causes unexpected and sudden changes in the absorbed power that also negatively affect the power supply electric network, causing for example the so-called flicker phenomenon, with possible damage to the electric network and to the connected utilities. As the melting progresses, that is, when the arc is suitably shielded by the solid material or by the foamy liquid (slag), the behavior of the electric arc gradually becomes more stable, thus allowing its length to be increased, thus also increasing the thermal power transferred to the material to be melted. The tension and length of the arc are adjusted according to the melting process, also to prevent excessive wear of the refractory. In order to limit unwanted effects on the power supply network, it is known to make a rapid adjustment of the power supplied to the furnace by means of a continuous adjustment at least of the position of the electrodes and of the voltage and current parameters impressed on the electrodes. In particular, the voltage and current parameters, as well as the position of the electrodes, are appropriately adjusted at each step of the process. There are known power supply apparatuses for electric arc furnaces that connect to a power supply network, generally three-phase, and convert the electric voltage and current supplied by the power supply network into electric voltage and current suitable to power the electrodes of the electric arc furnace. Known apparatuses comprise a rectifier device, which transforms the alternating current supplied by an electric network into direct current, and one or more inverter devices which transform the direct current into alternating current to power the electrodes, and the amount of electrical energy supplied to the electrodes is adjusted by appropriately commanding the inverter devices. These inverter devices comprise one or more switches that are opened and closed with a high frequency, whereby fluctuations in the electric voltage can be generated that can also have an effect back along the circuit, creating problems for the electric network. Furthermore, these inverter devices, because of the modulation of the current that is performed, generate current harmonics that can be harmful if fed into the electric power supply network. There is therefore the need to perfect an electric power supply apparatus for a direct current user device that can overcome at least one of the disadvantages of the state of the art. One purpose of the present invention is to provide an apparatus and a method for the power supply of an electric arc furnace which allow to regulate the operation and power of an electric furnace effectively, according to requirements. In particular, one purpose of the present invention is to provide an apparatus and perfect a method for the electric power supply of furnaces for melting and/or heating metal materials, which increase the efficiency of the melting and/or heating process and reduce the power required thereby. Another purpose of the present invention is to provide an apparatus and implement a method whic