Power supply device and method for electric furnace

Abstract

A device (10) for powering a furnace (100) for melting and / or heating metal material provided with electrodes (102), comprising at least one power supply line (201, 201L, 201M) and connected at least one base module (20, 120, 220) configured to convert an alternating power grid voltage and current (Ur, Ir) having a power grid frequency (fr) into an alternating power supply voltage and current (Ua, Ia) having 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 DC 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 operation of the inverter devices (15) and adjust the supply frequency (fa). The invention also relates to a method for powering a furnace (100) for smelting and / or heating metallic material.

Description

Technical Field

[0001] This invention relates to a power supply device and method for an electric furnace suitable for steelmaking applications in iron and steel production, or for processing other metals, glass materials, or similar materials. The power supply device is particularly suitable for electric furnaces operating using alternating current and voltage. Background Technology

[0002] As is well known, electric furnaces used in steelmaking applications to melt metals require efficient power supply systems capable of providing high power.

[0003] It is also well known that the smelting process involves several steps, which typically include drilling the metal material, smelting the material, and refining.

[0004] The power and electrical energy required by the electric furnace during the smelting process can vary significantly from one step to another, so it is necessary to adjust the electrical energy supplied each time appropriately.

[0005] In particular, during the drilling of metal materials or even the smelting process, the power absorbed by the electric furnace is typically greater than that required for the refining process, and this varies considerably even within the same process step, depending on the type of material fed into the furnace. During the drilling process, the electric arc between the electrode and the metal material exhibits highly unstable behavior. This instability gradually improves as smelting progresses because undiluted scrap accumulating near the electrodes collapses, creating a short circuit. This results in a significant reduction in usable active power and a rapid increase in current drawn from the grid. The instability of the arc can cause unexpected and sudden changes in power absorption, which can negatively impact the power grid, for example, by causing so-called flickering phenomena that can damage the grid and connected infrastructure.

[0006] As melting progresses, and the arc is effectively covered by solid material or foamy liquid (slag), its behavior gradually becomes more stable, allowing the arc length to increase and consequently increasing the heat power transferred to the material being melted. The arc tension and length are adjusted according to the melting process, also to prevent excessive wear of the refractory material.

[0007] To prevent adverse effects on the power grid, it is known that the power supplied to the electric furnace can be rapidly adjusted by continuously adjusting at least the position of the electrodes and the voltage and current parameters applied to the electrodes.

[0008] In particular, the voltage and current parameters, as well as the position of the electrodes, are adjusted appropriately at each step of the process.

[0009] For electric arc furnaces, there are known power supply devices that connect to the power grid (typically a three-phase grid) and convert the voltage and current supplied by the grid into voltage and current suitable for powering the electrodes of the electric arc furnace. These known devices include rectifier devices that convert the alternating current supplied by the grid into direct current; and one or more inverter devices that convert the direct current into alternating current to power the electrodes, adjusting the electrical energy supplied to the electrodes by appropriately controlling the inverter devices.

[0010] These inverter devices include one or more switches that are frequently turned on and off, resulting in voltage fluctuations that can propagate in the reverse direction of the circuit and cause problems for the power grid.

[0011] In addition, these inverter devices generate current harmonics due to their current modulation methods, which may cause harm if fed into the power grid.

[0012] Therefore, it is necessary to improve a power supply device for DC user equipment to overcome at least one of the shortcomings of the prior art.

[0013] One object of the present invention is to provide an apparatus and method for supplying power to an electric arc furnace, which allows for efficient adjustment of the furnace's operation and power as required.

[0014] In particular, an object of the present invention is to provide an apparatus and to improve a method for supplying power to an electric furnace for melting and / or heating metallic materials, which improves the efficiency of the melting and / or heating process and reduces the power required therefrom.

[0015] Another object of the present invention is to provide an apparatus and a method for implementing a method that allows adjustment of the voltage and current characteristics supplied to an electric furnace (particularly an electric arc furnace) to ensure the stability of the electric arc at various steps of the melting process.

[0016] Another object of the present invention is to improve an apparatus and method for supplying power to an electric furnace for melting and / or heating metallic materials, allowing for a reduction in melting time or overall metal processing.

[0017] Another object of the present invention is to provide an apparatus for supplying power to an electric furnace for melting and / or heating metallic materials, which is simple, economical, reliable, and can reduce interference phenomena in the power grid, such as harmonics and flicker.

[0018] Another object of the present invention is to improve a power supply device having a modular structure, so that it can be adapted to the needs of the facility or the characteristics of the electric furnace used.

[0019] The applicant has designed, tested and implemented the present invention to overcome the shortcomings of the prior art and to achieve these and other objectives and advantages. Summary of the Invention

[0020] The invention is set forth and defined in the independent claims. The dependent claims describe other features of the invention or variations of the main inventive concept.

[0021] In accordance with the above objectives, a power supply device according to the present invention is provided, suitable for supplying power to smelting and / or heating electric furnaces in steelmaking applications for steel production, or for supplying power to other fields that process metals, glass materials, similar or analogous materials.

[0022] The device includes at least one power supply line and at least one base module connected to the power supply line and configured to convert AC voltage and current having a predetermined mains frequency into AC supply voltage and current having a desired supply frequency, wherein the base module includes:

[0023] - A transformer, connected to the power supply line, and configured to convert the mains voltage and mains current into AC secondary voltage and secondary current, respectively;

[0024] - Multiple rectifiers, connected to the transformer, are configured to convert AC secondary voltage and secondary current into DC voltage and current;

[0025] - One or more DC intermediate circuits configured to store electrical energy;

[0026] - Multiple inverter devices, connected to one or more intermediate circuits, and configured to convert DC voltage and current into AC supply voltage and supply current with the desired frequency, and

[0027] - A control and command unit, at least connected to the inverter equipment, and configured to control and command the operation of the inverter equipment and adjust the power supply frequency during each step of the electric furnace process.

[0028] The power supply device is suitable for supplying power to an electric melting furnace or heating furnace, which is selected from an electric arc furnace (with electrodes arranged through a furnace cover), a submerged arc furnace, a ladle furnace, a melting furnace, or a similar or analogous electric furnace, which is configured to generate an electric arc between the corresponding electrodes and the metal to be processed.

[0029] According to some embodiments, the device includes an adapter device connected between at least one base module and corresponding electrodes of the electric furnace, and configured to adapt parameters of the supply voltage and / or current supplied by the at least one base module to adapted voltage and current suitable for supplying power to the electrodes.

[0030] According to some embodiments, the adapter device may include one or more of an adapter transformer, a reactor, a filter, or a disconnecting switch.

[0031] According to some embodiments, the power supply line is connected to a three-phase power grid with grid frequency via at least one input transformer device.

[0032] According to some embodiments, the three-phase power grid is high voltage, in the 70-600kV range, and the input transformer equipment can be configured to convert high voltage to medium or low voltage.

[0033] Specifically, depending on the type and number of transformers present between the high-voltage grid and the power supply line, the latter (power supply line) can be configured to operate at medium voltage (approximately 1.5 to 35 kV) or low voltage (approximately 50 V to 1.5 kV).

[0034] According to some embodiments, the adapter device is an adapter transformer, including a primary coil connected to at least one base module or possibly multiple base modules, and a secondary coil connected to electrodes. This solution is particularly advantageous if the power grid is medium voltage. In fact, in this case, the power supply unit and its components can be configured to operate at medium voltage, and the adapter transformer can be configured to convert the voltage from medium voltage to low voltage.

[0035] According to this solution, the input transformer equipment can be of high voltage / medium voltage type. If the power grid segment connected to the primary coil of the transformer is already of medium voltage, or if there is an additional transformer equipment upstream configured to convert high voltage to medium voltage, then it can be of medium voltage / medium voltage type.

[0036] Depending on some variations, particularly where the power supply line itself is low voltage, or the input transformer is of medium / low voltage type, the adapter device may include at least one of the following: an inductor or capacitor, a filter, or a disconnecting switch adapted to allow the desired reactance value to be obtained by adjusting the power supply frequency.

[0037] In this case, in addition to properly adapting the voltage and current to be supplied to the electrodes, the adapter device can also eliminate any harmonics belonging to certain undesirable frequency bands, thereby helping to eliminate interference.

[0038] According to one aspect of the invention, the control and command unit is provided with an adjustment device configured to adjust the power supply frequency of the AC power supply voltage and current during each step of the electric furnace melting cycle, such that the power supply frequency is lower than or equal to the grid frequency, and that the power supply frequency is between 40% and 80% of the grid frequency during at least one step of the electric furnace working cycle.

[0039] Advantageously, the configuration of this device can protect the power supply components from interference caused by the working process (especially the melting process in an electric arc furnace or submerged arc furnace) (reducing flicker, harmonics, etc.), while ensuring the stability of the electric arc in all steps.

[0040] According to some embodiments, the device includes multiple basic modules connected in parallel between a three-phase power grid and a load to be powered, wherein each basic module is configured to convert electrical energy supplied by the grid and supply at least one pair of single-phase alternating current and voltage with desired strength and frequency at its output.

[0041] According to some embodiments, the base module or each base module includes at least two sub-modules, each sub-module being adapted to supply single-phase voltage and current.

[0042] Specifically, the basic power supply module or each basic power supply module includes multiple sub-modules, the number of which corresponds to the number of connectors or phases supplied at the output end.

[0043] Preferably, in at least one base module, a DC intermediate circuit (or DC link) is provided for each phase supplied at the output end of the base power supply module, and each DC link is connected to at least one inverter device. Therefore, the number of DC links and phases is preferably the same.

[0044] According to the present invention, the intermediate circuits of all sub-modules are short-circuited to each other, that is, they are all at the same potential, which can compensate for a set of harmonics and obtain a common average value, thereby reducing the degree of interference in one or more sub-modules.

[0045] Furthermore, if a DC intermediate circuit of a submodule fails, one or more other submodules can compensate for the failed submodule and may supply power to the inverter equipment connected to the non-functional DC intermediate circuit.

[0046] This solution benefits from the redundancy of the rectifier equipment and the short-circuit connections between different intermediate circuits, enabling it to power all required output phases under any circumstances (even with reduced power) and absorb any imbalance between at least two phases.

[0047] According to one aspect of the invention, a transformer includes a single primary winding having a three-phase input terminal connected to a phase of the power supply line during operation; and a plurality of secondary windings, each secondary winding being connected to a corresponding submodule via a corresponding three-phase output terminal. In this solution, the single primary winding is coupled to all secondary windings. This solution allows for reduction of any interference on the grid side, i.e., reducing harmonic content and reactive power exchange in the grid through the combination of transformer secondary windings and rectifier equipment.

[0048] According to some embodiments, the phases of the secondary coils of each transformer in the same basic power supply module are different from each other in order to achieve a balance between current and / or corresponding voltage within each basic power supply module.

[0049] According to another aspect of the invention, the device includes a plurality of basic modules connected in parallel between power supply lines and connection lines, wherein each basic module receives three three-phase connectors at its input and supplies two, three, four, six or more single-phase voltage and current connectors at its output.

[0050] The number of basic modules can be increased exponentially as needed. For example, the number of basic power supply modules can be between 2 and 60, such as 24, 30, 36, 48, or even intermediate values, including even or odd numbers. For instance, each conversion module can be configured to supply power from a minimum of 1MW to a maximum of 30MW. Typically, the preferred size of each of these basic modules ranges from 15 to 20MW, more preferably about 10MW.

[0051] This modular structure advantageously allows the power supply unit to adapt to the needs of the facility, whether during the design phase to determine the total number of basic modules according to the required scale and production needs, or during use, by keeping only a portion of the basic modules operational at a time, thereby enabling the supplied power to be optimally regulated according to demand.

[0052] Some embodiments described herein also relate to a method for supplying power to an electric furnace for melting and / or heating metallic materials, including:

[0053] -Supply AC grid voltage and current with a predetermined grid frequency through power supply devices;

[0054] - The grid voltage, current and frequency are converted into AC secondary voltage, current and frequency with selectable set values ​​by a transformer, wherein the secondary frequency is substantially the same as the grid frequency;

[0055] - Multiple rectifiers are used to rectify the secondary voltage and current to obtain the DC intermediate voltage and current;

[0056] - Using multiple inverter devices, intermediate voltage and current are converted into AC supply voltage and current, which have frequencies that can be selectively set by control and command units connected to the inverter devices;

[0057] - Adapt and / or filter the supply voltage and current in order to adjust its parameters and obtain a suitable supply voltage and current;

[0058] - Supply the appropriate power supply voltage and current to the electrodes of the electric furnace.

[0059] According to one aspect of the invention, the power supply method specifies that during each step of the electric furnace working cycle, the adjustment device of the control and command unit adjusts the power supply frequency of the power supply voltage and power supply current, such that in at least some steps of the working process, the power supply frequency is lower than or equal to the grid frequency, and in at least one step of the working cycle, the power supply frequency is between 40% and 80% of the grid frequency.

[0060] According to some embodiments, the method according to the invention specifies that the frequency is lower than the power grid frequency during at least 80% of the smelting process.

[0061] For electric arc furnaces or submerged arc furnaces, at least in open-hearth conditions (i.e., when refining occurs and the metal material is no longer being loaded), the frequency can be between 40% and 80% of the grid frequency.

[0062] For ladle furnaces, the frequency can be between 40% and 80% of the grid frequency throughout the entire process.

[0063] According to one aspect of the invention, the power supply method specifies that during each step of the electric furnace working cycle, the adjustment device of the control and command unit adjusts the power supply frequency of the power supply voltage and current, such that the power supply frequency is lower than the grid frequency for at least 80% of the duration of the working cycle.

[0064] According to some other embodiments, the power supply frequency is lower than the grid frequency for 100% of the entire duration of the duty cycle.

[0065] The feasibility of adjusting the frequency to a value lower than the grid frequency allows for a reduction in induced losses on the conductor, such as those caused by the skin effect, thereby improving the efficiency of current flow inside the copper conductor and allowing current to pass through a larger portion of the conductor's cross-sectional area.

[0066] Furthermore, using low-frequency current to power the electrodes allows for improved stirring within the molten pool, increased heat exchange, and improved temperature uniformity within the molten pool, thereby enhancing system efficiency. Attached Figure Description

[0067] These and other aspects, features, and advantages of the invention will become apparent from the following description of some embodiments and with reference to the accompanying drawings, which are described by way of non-limiting example only.

[0068] - Figure 1 This is a schematic diagram of a power supply device according to a first embodiment of the present invention;

[0069] - Figure 2 This is a schematic diagram of a power supply device according to a second embodiment of the present invention;

[0070] - Figure 3This is a schematic diagram of a power supply device according to the present invention. The device has a basic module including two sub-modules, and the device is applied to an electric arc furnace.

[0071] - Figure 4 This is a simplified circuit diagram of the two sub-modules;

[0072] - Figure 5 This is a schematic diagram of a power supply device according to a variant of the present invention, the device having a base module including three sub-modules, and the device being applied to an electric arc furnace;

[0073] - Figure 6 This is a schematic diagram of a power supply device based on another variant, in which each basic module includes six sub-modules, and the device is applied to a submerged arc furnace;

[0074] - Figure 7 and Figures 8-8b This is a graph showing the changes over time of electrical parameters applied to the electrodes of an electric arc furnace during a working cycle of a smelting furnace according to some embodiments of the present invention.

[0075] - Figure 9 This is a graph showing the changes over time of electrical parameters applied to the electrodes of the ladle furnace during a working cycle according to some embodiments of the present invention;

[0076] - Figure 10 This is a chart showing the power trend of the electric arc furnace during its working cycle;

[0077] - Figure 11 The chart shows the trend of power consumption of the ladle furnace as a function of frequency.

[0078] For ease of understanding, the same reference numerals are used as much as possible to identify the same common elements. It should be understood that elements and features of one embodiment can be readily combined with or incorporated into other embodiments without further explanation. Detailed Implementation

[0079] Possible embodiments of the invention will now be described in detail, with one or more examples illustrated in the accompanying drawings. The wording and terminology used herein are for illustrative purposes only and are not intended to be limiting.

[0080] refer to Figure 1 and Figure 2 Some embodiments of the present invention relate to a device 10 for supplying power to an electric furnace 100 for melting and / or heating metallic materials.

[0081] According to some embodiments, device 10 includes a power supply line 201 connected to a power supply device 200, which is particularly of a three-phase type.

[0082] exist Figures 1-5In this context, the letters R, S, and T represent the three phases of the three-phase voltage / current.

[0083] According to the reference Figure 1 In the described embodiment, the power supply line 201L is of low voltage (LV) type, so the device 10 can be configured to operate entirely at low voltage (e.g., between 50V and 1.5kV). According to this embodiment, a step-down transformer 202 can be installed upstream of the power supply line 201L, which is configured to reduce the voltage supplied by the main grid 203 (which can be high voltage or medium voltage) to obtain a low-voltage grid voltage Ur.

[0084] According to the reference Figure 2 In the described variant, the power supply line 201M is of medium voltage (MV) type, so the device 10 can be configured to operate at medium voltage (e.g., between 1.5 and 35 kV). According to this embodiment, a step-down transformer 204 can be provided upstream of the power supply line 201M, which is configured to reduce the voltage supplied by the main grid 203 (which can be high voltage or medium voltage) to obtain a medium voltage grid voltage Ur.

[0085] From this point onward, unless otherwise specified, reference numeral 201 will generally denote low-voltage and medium-voltage power supply lines 201L and 201M.

[0086] The grid voltage Ur and grid current Ir supplied by the power supply line 201 can have a predetermined grid frequency fr, for example, a value between 50Hz and 60Hz, i.e., according to the frequency of the grid in the country where the electric furnace 100 is installed.

[0087] According to some embodiments, device 10 can be configured to supply power to a three-phase load, particularly to supply power to a three-phase electric furnace 100.

[0088] The electric furnace 100 of the type discussed can typically be a melting furnace, refining furnace, heating furnace, or similar furnace, suitable for use in steelmaking facilities or metal processing facilities for producing steel. Preferably, the invention is applicable to electric arc furnaces (EAF), ladle furnaces (LF), submerged arc furnaces (SAF), and furnaces that use electrodes 102 to transfer heat energy to the material to be processed.

[0089] Figure 1 and Figure 2 An exemplary device 10 is shown connected to an electric arc furnace (EAF) and a ladle furnace (LF). If both an electric arc furnace (EAF) and a ladle furnace (LF) are present in a steelmaking facility, two devices 10 may be provided, each connected to one of the furnaces, or a single device 10 may be provided that is capable of supplying power to each of the two furnaces, the EAF and the LF, in a suitable manner.

[0090] For an electric arc furnace 100 of type EAF, it includes a container 101 or crucible for introducing the metal material M to be melted into it.

[0091] The EAF furnace is also provided with multiple electrodes 102, three electrodes in the case shown, labeled with the letters A, B, and C, which are configured to ignite an electric arc and melt the metal material M.

[0092] For a ladle furnace (LF), it typically includes a ladle 104 adapted to contain molten metal poured from an EAF furnace, a furnace cover 105 that seals the ladle 104 on top, and a plurality of electrodes 102 (represented by the letters A, B, and C) disposed through the furnace cover 105.

[0093] For example, for submerged arc furnace (SAF) Figure 6 As shown, it is equipped with a container 107 or crucible for introducing the metal material M to be melted into it; and a plurality of electrodes 102, in the example case six electrodes 102, denoted by the letters AF.

[0094] The following descriptions will primarily use examples to illustrate electric arc furnaces (EAF), ladle furnaces (LF), and submerged arc furnaces (SAF).

[0095] According to some embodiments of the invention, electrode 102 is mounted on mobile device 103, which is typically configured to selectively move electrode 102 toward or away from metallic material M or molten metal pool.

[0096] The mobile device 103 may be selected from at least one of the following: mechanical actuators, electric actuators, pneumatic actuators, hydraulic actuators, articulated mechanisms, mechanical kinematic devices, similar or related components, or possible combinations thereof.

[0097] According to a feasible solution of the present invention, if there are three electrodes 102, then each electrode is connected to the corresponding phase voltage and three-phase current of the device 10.

[0098] If there are more than three electrodes 102, then each power supply phase can be connected to two or more of them.

[0099] According to some embodiments, the device 10 is able to receive energy supplied by the power supply line 201 and convert it into a supply voltage and current with specific electrical parameters Ua*, Ia*, fa, which are suitable for supplying power to the electrodes 102 of the electric furnace 100.

[0100] According to some embodiments, the device 10 includes at least one base module 20 configured to convert an AC voltage and current having a mains frequency fr into an AC voltage or current having a desired power supply frequency fa.

[0101] According to some embodiments, the device 10 may include a plurality of basic modules 20 connected in parallel between the power supply line 201 and the electric furnace 100 (i.e., the electrode 102).

[0102] Each basic module 20 includes a transformer 11 connected to a power supply line 201 and configured to convert a primary AC voltage Up and current Ip into a secondary AC voltage Us and current Is.

[0103] According to feasible solutions, transformer 11 may include transformer primary coil 12 that is magnetically coupled to at least one transformer secondary coil 13.

[0104] This solution can reduce the impact of grid-side interference, namely, reduce the harmonic content and reactive power exchanged with the main grid 203.

[0105] The secondary electrical energy supplied by transformer 11 has secondary voltage Us, secondary current Is, and secondary frequency fs, which are predefined and set by the design characteristics of transformer 11 itself.

[0106] According to some embodiments, the secondary frequency fs can be substantially equal to or lower than the grid frequency fr, or in general, equal to or lower than the primary frequency fp of the current flowing in the primary coil 12.

[0107] The secondary voltage and current Us and Is can be related to the grid voltage and current Ur and Ir, respectively, or in general, to the primary voltage and current Up and Ip of the primary coil 12. This relationship is determined by the transformer ratio of the transformer 11 itself.

[0108] The transformer 11 may be equipped with an adjustment device (not shown) configured to selectively adjust its transformer ratio according to specific requirements.

[0109] The device 10 according to the invention also includes a plurality of rectifiers 14 for each base module 20, which are connected to the transformer 11 and configured to convert AC secondary voltages and currents Us, Is into DC intermediate voltages and currents Ui, Ii.

[0110] According to some embodiments, the device 10 includes a plurality of inverter devices 15 for each base module 20, which are connected to the rectifier 14 and configured to convert DC intermediate voltage and current Ui, Ii into AC supply voltage Ua and current Ia.

[0111] According to feasible solutions, rectifier 14 can be connected to inverter device 15 via at least one intermediate circuit 16 or DC link, which operates in DC mode.

[0112] Intermediate circuit 16 can be configured to form isolation between rectifier 14 and inverter device 15, thus isolating the power supply device 200 connected upstream of intermediate circuit 16 from the electric furnace 100. In particular, the rapid power fluctuations caused by this process are partially filtered by intermediate circuit 16, thereby reducing their impact on the power supply device 200 side.

[0113] The intermediate circuit 16 can also be configured to continuously store electrical energy. According to some embodiments, the intermediate circuit 16 includes at least one capacitor.

[0114] According to some embodiments, the base module 20 includes a separate rectifier 14, intermediate circuit 16 and inverter 15 for two or more sub-modules 21, each sub-module being associated with phase R, S, T of the power supply line 201.

[0115] According to some embodiments, each submodule 21 includes multiple inverter devices 15 connected in parallel to each other to an intermediate circuit 16, all of which power the same output phase, such as phases R, S, and T of the connection line 24.

[0116] For example, two to eight inverter devices 15 can be provided, preferably four to six.

[0117] According to some embodiments, the transformer 11 is preferably physically separated from the corresponding sub-module 21 and kept at a certain distance, and can also be built in different buildings or different factory areas.

[0118] For example, device 10 may include adjustment unit G1 and transformer unit G2. Adjustment unit G1 includes rectifier 14, inverter 15, intermediate circuit 16 and adapter device 19, and is located near electric furnace 100. Transformer unit G2 includes transformer 11, which is separated from adjustment unit G1 and kept at a certain distance, even up to tens of meters or more.

[0119] Depending on possible variations and considerations of available space, the two units G1 and G2 could also be built in the same building.

[0120] exist Figures 3-6 The diagram shows the transformer secondary coil 13 (for illustrative purposes only), which is represented by the letters R, S or T, depending on the phase provided by the associated submodule 21.

[0121] According to this solution, transformer 11 may include: a single transformer primary coil 12, having a three-phase input terminal connected to power supply line 201; and multiple transformer secondary coils 13, each phase R, S, T corresponding to one transformer secondary coil, wherein each transformer secondary coil 13 is connected to rectifier 14.

[0122] According to some embodiments, the transformer device 11 includes a single transformer primary coil 12, which is coupled to all transformer secondary coils 13.

[0123] According to some embodiments, the phases R, S, T of the primary coil 12 and the secondary coil 13 of the transformer are connected in a star or delta configuration.

[0124] According to a preferred embodiment, the phases R, S, and T of the primary coil 12 and the secondary coil 13 of the transformer are connected in a delta configuration.

[0125] According to some embodiments, the phases of the secondary coils 13 of each transformer in the same basic power supply module 20, 120, 220 are different phases relative to each other, thereby achieving a balance between current and / or respective voltage in each basic power supply module 20, 120, 220.

[0126] According to feasible embodiments, the connection methods between each phase of the transformer secondary coil 26 associated with the same basic module 20, 120, 220 are different.

[0127] According to some embodiments, all intermediate circuits 16 of the base module 20 are short-circuited to each other.

[0128] In other words, there are corresponding electrical connectors 22 and 23 among the intermediate circuits 16 belonging to the same basic module 20, whose impedance is basically zero or at least negligible, so that the intermediate circuits 16 of the basic module 20 are basically at the same potential.

[0129] According to feasible variations, the intermediate circuits 16 are independent of each other, that is, there is no electrical connection between them.

[0130] According to some embodiments, each base module 20 is configured to supply at least one pair of single-phase alternating current and voltage with desired strength and frequency at the output.

[0131] Each phase provided by the base module 20 can be connected to the electrode 102 of the electric furnace 100 via the connecting line 24.

[0132] According to some embodiments, the device 10 includes a control and command unit 17 configured to control at least the inverter 15 to selectively set parameters of the supply voltage Ua and supply current Ia generated by the inverter 15 and supplied to the electrode 102.

[0133] Specifically, the supply voltage Ua and supply current Ia can be selectively adjusted according to the required operating power. For example, in the case of an EAF furnace, they can be adjusted according to the smelting power involved.

[0134] Furthermore, some solutions of the present invention specify that the control and command unit 17 is also connected to the mobile device 103 to allow adjustment of the position of the electrode 102 according to different steps of the melting process. In particular, the electrode 102 is moved by the mobile device 103 to follow the position of the material, thereby changing the arc length.

[0135] In fact, during the smelting step, the electrical power supplied to electrode 102 can be increased compared to the drilling step, because the arc is covered and kept at a certain distance from the furnace top, thus avoiding the risk of damaging the furnace top.

[0136] The reference values ​​of the supply voltage Ua and supply current Ia can be changed by the control and command unit 17 to increase the effective power. In this step, the electric arc is more stable due to the protection provided by the waste or slag.

[0137] In addition, the process is more stable and requires less power during the refining step.

[0138] In this way, the control and command unit 17 can manage and command at least the following parameters for specific steps of the process: supply voltage Ua, supply current Ia, supply frequency fa, and the position of electrode 102. The possibility of effectively controlling different parameters is high, which enables optimization of energy transfer to the process while reducing the impact on the power grid 201 due to rapid changes in power on the furnace side.

[0139] The electrical topology used for inverter 15 also protects grid 203 from interference caused by the smelting process (such as flicker reduction, harmonics, power factor, etc.), while ensuring the stability of the electric arc in all operating steps of electric furnace 100, whether in EAF furnace, ladle furnace LF or submerged arc furnace SAF.

[0140] According to one aspect of the invention, the apparatus 10 includes at least one adapter device 19 connected between at least one base module 20 and an electrode 102, and configured to adapt the parameters of the supply voltage and / or current Ua, Ia supplied by the at least one base module to an adapted current and voltage Ua*, Ia* suitable for supplying power to the electrode 102.

[0141] According to some embodiments, adapter device 19 may include one or more of adapter transformer 25, reactor 26, filter 27 and disconnect switch 28.

[0142] According to some embodiments, in the case of a low-voltage power supply line 201L, for example... Figure 1As shown, the adapter device 19 can be selected from the reactor 26 (e.g., an inductor or capacitor), a filter, or a disconnecting switch, because the supply voltage Ua at the output of at least one base module 20 is already in a low-voltage state, and therefore does not need to be further reduced before it is suitable to be directly fed to the electrode 102.

[0143] According to one feasible solution, reactor 26 may be or include an inductor whose size is designed to obtain a specific equivalent reactance, which is determined by the contribution of the inductor and the reactance introduced by the conductor connecting device 10 to electrode 102 (e.g., the conductor of connecting line 24).

[0144] By changing the supply frequency fa relative to the mains frequency fr, the reactance of the component in the circuit can be changed while keeping the inductor constant, thereby achieving the desired total equivalent reactance value.

[0145] According to some embodiments, in the case of a 201M medium-voltage power supply line, for example... Figure 2 As shown, the adapter device 19 is or includes an adapter transformer 25, which includes a transformer primary coil 29 connected to at least one or more base modules 20 and a transformer secondary coil 30 connected to the electrode 102.

[0146] In this configuration, adapter transformer 25 is configured to at least reduce the medium-voltage MV supply voltage Ua to the low-voltage LV adapted supply voltage Ua*. The supply frequencies fa upstream and downstream of adapter transformer 25 can be substantially the same.

[0147] The primary coil 29 and secondary coil 30 of the transformer may include a corresponding number of input terminals and output terminals, respectively corresponding to the number of base modules 20 or the number of current / voltage phases supplied on one side, and corresponding to the number of electrodes 102 on the other side. Alternatively, multiple adapter transformers 25 may be provided that are connected in parallel or cascaded with each other.

[0148] In the case of multiple adapter transformers 25, these adapter transformers are preferably partially star-connected, partially delta-connected, and more preferably have a phase difference between each other or relative to a common reference point.

[0149] The control and command unit 17 may include adjustment device 18.

[0150] According to a feasible solution of the present invention, by way of example only, the adjustment device 18 may include a hysteresis modulator or a pulse width modulation (PWM) modulator or a similar device.

[0151] These types of modulators can be used to command the semiconductor devices of rectifier 14 and inverter 15: with proper control, they generate voltage or current values ​​that need to be supplied to furnace 100 (in this case, to electrode 102). Specifically, the modulator processes these voltage and current values ​​and generates commands to at least drive rectifier 14 and inverter 15, resulting in the required voltage and current amounts at the terminals connected to electrode 102. The required driving voltage and current are the result of the control and command unit 17 operating based on quantities read from the process and based on a process model.

[0152] According to the present invention, the adjusting device 18 is configured to adjust the supply frequency fa of the supply voltage Ua and the supply current Ia during each step of the melting cycle of the electric furnace 100.

[0153] The adjustment device 18 is commanded by the control and command unit 17.

[0154] Specifically, the adjusting device 18 is commanded by the control and command unit 17 to ensure that the power supply frequency fa is lower than or equal to the grid frequency fr for at least 80% of the total working cycle duration.

[0155] According to some embodiments, in at least one step of the duty cycle, the power supply frequency fa is between 0.5% and 200% of the grid frequency fr.

[0156] According to some embodiments, the power supply frequency fa is always lower than or equal to the grid frequency fr from the start of the operating cycle, and at least in one step of the operating cycle of the electric furnace 100, the power supply frequency fa is lower than the grid frequency fr of the power supply device 200, particularly between 40% and 80% of the grid frequency fr.

[0157] According to some embodiments, typically in at least one step of the working cycle of the electric furnace 100, the power supply frequency fa can be lower than the grid frequency fr.

[0158] According to a feasible solution, the control and command unit 17 is connected to all the base modules 20 to control at least their respective inverters 15, such that each module 20 supplies the same supply voltage Ua, supply current Ia, and supply frequency fa to the electrode 102. This prevents the entire system from failing.

[0159] According to other variations, the base module 20 can also be controlled to supply different values ​​of supply voltage Ua, supply current Ia and supply frequency fa to each electrode 102, for example, to change the power distribution within the molten metal pool.

[0160] Figure 3An example is used to describe a device 100 having multiple basic modules 20, each of which includes two sub-modules 21, denoted by the letters A and B for ease of identification only.

[0161] In this case, the transformer device 11 includes a primary transformer coil 12 and two secondary transformer coils 13, denoted by the letters R and S.

[0162] In this case, the phases of the two transformer secondary coils 13 can be connected in a delta configuration and have their own symmetrical positive and negative phase shift angles α relative to a common reference, for example, between 15° and 25°.

[0163] Each submodule 21 includes rectifier devices 14 arranged sequentially to each other, an intermediate circuit 16 or DC link shared by all phases, and at least one inverter device 15 connected to the intermediate circuit 16.

[0164] The intermediate circuits 16 of the two sub-modules 21 are interconnected by electrical connectors 22 and 23 with negligible impedance.

[0165] exist Figure 3 In the example, device 100 is configured to operate at medium voltage and includes an adapter transformer 25 connected between base module 20 and electrode 102.

[0166] According to feasible embodiments (which may be combined with other embodiments described herein), an inductor 33 may also be provided between the base module 20 and the adapter transformer 25, which has the function of filtering the output voltage and current.

[0167] According to the feasible variants, Figure 3 The device 10 can be configured to operate at low voltage; in this case, the adapter transformer 25 can even be omitted.

[0168] According to some embodiments, such as reference Figure 4 As described, each rectifier device 14 may include a corresponding rectifier circuit 14R, 14S, 14T for each phase.

[0169] The rectifier 14 can be selected from the group including diode bridges, thyristor bridges or other devices.

[0170] According to one possible solution, the rectifier 14 includes, for example, a device selected from the group consisting of diodes, silicon controlled rectifiers (SCRs), gate turn-off thyristors (GTOs), integrated gate commutated thyristors (IGCTs), metal-oxide-semiconductor controlled thyristors (MCTs), bipolar junction transistors (BJTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), and insulated-gate bipolar transistors (IGBTs).

[0171] Each submodule 21 has its own DC intermediate circuit 16. The rectifier devices, namely each rectifier circuit 14R, 14S, 14T, are connected to the intermediate circuit 16 on one side and to one or more inverter devices 15 on the other side.

[0172] The intermediate circuit 16 may include one or more capacitors 31, such as a capacitor bank, which is suitable for storing energy and provides isolation between the rectifier device 14 and one or more inverter devices 15, and thus also provides isolation between the grid 201 and the electrode 102 (i.e. the connection line 24).

[0173] According to some embodiments, the inverter device 15 may include one or more switches 32, which are selected, for example, from the following types of thyristors or transistors: gate turn-off thyristors (GTOs), integrated gate commutated thyristors (IGCTs), metal-oxide-semiconductor controlled thyristors (MCTs), bipolar junction transistors (BJTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), or similar devices. Switches 32 may typically be associated with respective diodes (not shown).

[0174] Figure 5 A second exemplary embodiment of the device 10 is shown, which includes a base module 120 having three sub-modules 21, each sub-module including a rectifier device 14, a DC intermediate circuit 16, and five inverter devices 15. In this case, the base module 120 is configured to provide three different current and voltage phases R, S, and T at its output. The three intermediate circuits 16 are interconnected via short-circuit connectors 22 and 23.

[0175] exist Figure 5 In the example case, the transformer secondary coil 13S has a zero phase shift angle, while the other transformer secondary coils 13R and 13T are offset by the corresponding positive and negative phase shift angles α, respectively.

[0176] exist Figure 5 In an exemplary embodiment, device 10 may be configured to operate at low voltage, and adapter device 19 may be filter 27, but depending on feasible variations, the latter may be replaced by reactor 26 or disconnect switch 28.

[0177] Variations may also be provided in which module 120 is configured to operate at medium voltage; in this case, adapter device 19 may include adapter transformer 25.

[0178] Figure 6Another embodiment of the device 10 is shown, in which it is exemplarily connected to an electric furnace 100 of the submerged arc furnace (SAF) type. In this example case, the electric furnace includes six electrodes 102A-102F, although the number may vary.

[0179] The apparatus 10 according to this embodiment includes one or more basic modules 220, each module having six sub-modules 21, the intermediate circuits 16 of these sub-modules being interconnected via short-circuit connectors 22, 23. In this example, there are five inverter devices 15, but as mentioned above, this number can be fewer or more.

[0180] In this configuration, the six sub-modules 21 of the base module 220 are connected in pairs to phases R, S, and T of the connection line 24, and each electrode 102 is connected to one of said phases R, S, and T. In this example configuration, each phase R, S, and T is connected to two different electrodes 102.

[0181] In this embodiment, the primary coil 11 of the transformer is coupled to the six secondary coils 13 of the transformer.

[0182] According to some embodiments, the phase offset of the transformer secondary coil 13 can be specified, such as... Figure 3 As shown in the example, different phase shift angles can also be provided. For example, transformer secondary coils 13A and 13C can be offset by a first phase shift angle α1 relative to transformer secondary coil 13B, while transformer secondary coils 13D and 13F can be offset by a second phase shift angle α2 relative to transformer secondary coil 13E, which is different from the first angle α1.

[0183] However, it is clear that there are other possible connection combinations and / or corresponding phase shift angles.

[0184] exist Figure 6 In an example embodiment, device 10 may be configured to operate at low voltage, and adapter device 19 may be disconnect switch 28, but depending on feasible variations, the latter may be replaced by reactor 26 or filter 27.

[0185] Variations may also be provided in which module 220 is configured to operate at medium voltage; in this case, adapter device 19 may include adapter transformer 25.

[0186] According to one aspect of the invention, the device 10 may include N basic modules 20, 120, 220, which are connected in parallel between the power grid 201 and the electric furnace 100. The number N of basic modules can be selected according to requirements or parameters (e.g., the power required by the electric furnace 100, the required productivity, the total number of electrodes 102 to be powered).

[0187] For example, the value of the quantity N can be between 2 and 60, such as 3, 4, 5, 6, 8, 10, 12, 18, 24, 36, 48, or an even or odd number between these numbers.

[0188] Preferably, the number N of the basic modules 20, 120, and 220 is such that the total number of sub-modules 21 is a multiple of 3, so as to evenly supply power to the three phases R, S, and T of the connecting line 24.

[0189] According to feasible variations, in the case of multiple base modules 20, 120, 220, it can be specified that the connection type between each phase R, S, T of the primary coil 12 and / or secondary coil 13 of at least one transformer 11 is different from that of at least another transformer device 11.

[0190] "Different types of connections" refers to the following two situations: First, at least one phase R, S, T of the primary winding 12 or secondary winding 13 of one transformer device 11 is connected in a star configuration, while the other phase R, S, T is connected in a delta configuration; second, both use the same type of connection (e.g., delta connection), but there is a certain angular phase shift between the corresponding phases R, S, T. This is done to achieve current and voltage balance within a single basic module 20, and also to achieve current and voltage balance throughout the entire device 10.

[0191] Some embodiments described herein also relate to a facility 50, including a power supply device 10 according to the invention and an electric furnace 100 having two or more electrodes 102, each electrode being connected to at least one phase R, S, T of a base module 20, 120, 220 via at least one adapter device 19.

[0192] The operation of the apparatus 10 described above for supplying power to the electric furnace 100 equipped with electrodes 102 for melting and / or heating metal materials (corresponding to the method of the present invention) is specified as follows:

[0193] - Supply AC grid voltage and current Ur and Ir with a predetermined grid frequency fr to at least one basic module 20, 120, 220 via three-phase power supply lines 201, 201L, 201M;

[0194] - Transformer 11 converts the grid voltage and current Ur and Ir into selectively set AC secondary voltage and current Us and Ir;

[0195] - Multiple rectifiers 14 are used to rectify the secondary voltage and current Us and Is in order to obtain the DC intermediate voltage and current Ui and Ii;

[0196] - Using multiple inverter devices 15, the DC intermediate voltage and current Ui, Ii are converted into AC supply voltage Ua and supply current Ia. The AC supply voltage Ua and supply current Ia can be selectively set by the control and command unit 17 connected to the inverter device 15 and have the required supply frequency fa.

[0197] - The supply voltage and current Ua, Ia are adapted and / or filtered downstream of inverter device 15 in order to adjust their parameters and obtain the adapted supply voltage and current U*, I* to be fed to electrode 102.

[0198] According to some embodiments, the method specifies the use of a base module 20, 120, 220 comprising at least two sub-modules 21, each sub-module being adapted to supply power to a single phase R, S, T of a three-phase power grid. In each sub-module 21, the voltage and current of each phase are rectified and energy is temporarily stored. The power supply line 201 and the electrode 102 are isolated by a DC intermediate circuit 16, and the DC voltage and current Ui, Ii are inverted by at least one inverter device 15 to obtain the corresponding single-phase AC power supply voltage and current.

[0199] According to another aspect of the invention, the method specifies that all DC intermediate circuits 16 of at least one basic module 20, 120, 220 are short-circuited to each other so that they have the same potential.

[0200] In this way, the inverter devices 15 of each submodule 21 belonging to the same basic module 20, 120, 220 will operate with the same DC voltage and current, which can be considered as the average of the voltage and current supplied by the corresponding rectifier device 14 in each submodule 21.

[0201] According to another aspect of the invention, the method specifies that during each step of the working cycle of the electric furnace 100, the adjustment device 18 of the control and command unit 17 adjusts the power supply frequency fa of the power supply voltage Ua and the power supply current Ia, such that for at least 80% of the duration of the working cycle, the power supply frequency fa is lower than or equal to the grid frequency fr, and in at least one step of the working cycle of the electric furnace 100, the frequency is lower than the grid frequency fr, preferably between 40% and 80% of the grid frequency fr.

[0202] According to a preferred embodiment, the power supply frequency fa is lower than or equal to the grid frequency fr for at least 90% of the duration of the entire operating cycle.

[0203] According to a further embodiment, for at least 95% of the duration of the entire operating cycle, the power supply frequency fa is lower than or equal to the grid frequency fr.

[0204] According to some embodiments, for at least 90% of the duration of the entire operating cycle, preferably for at least 95% of the duration, the power supply frequency fa is lower than the grid frequency fr.

[0205] According to some embodiments, the method specifies that, in at least one step of the operating cycle, the power supply frequency fa is between 10% and 80% of the grid frequency fr.

[0206] According to some embodiments, the method specifies that, in at least one step of the duty cycle, the power supply frequency is adjusted to a value in the range of 1 to 48 Hz.

[0207] According to some embodiments, the method specifies that, in at least one step of the operating cycle, the power supply frequency fa is between 45% and 75% of the grid frequency fr.

[0208] According to a further embodiment, the method specifies that, in at least one step of the operating cycle, the power supply frequency fa is adjusted to a frequency approximately half that of the grid frequency fr.

[0209] According to some embodiments, the method specifies that, in at least one step of the operating cycle, the power supply frequency fa is between 101% and 200% of the grid frequency fr.

[0210] Adjusting the power supply frequency fa to a value higher than the grid frequency fr can improve the stability of the electric arc, thereby shortening the time for melting metal materials.

[0211] According to some embodiments, in cases where the absorbed power is unstable, i.e., when the power supplied to the electric furnace fluctuates rapidly, such as during the drilling step, the power supply frequency fa is kept above the grid frequency fr to counteract such fluctuations and improve the smelting process.

[0212] According to some embodiments, the method specifies that, in at least one step of the operating cycle, the power supply frequency fa is adjusted to a value in the range of 55 to 120 Hz.

[0213] During the working cycle, the power supply frequency fa can be dynamically adjusted. The operator can adjust it manually or automatically according to the instructions and programs executed by the control and command unit 17.

[0214] In this description, a work cycle refers to a series of work steps set for a particular electric furnace 100.

[0215] For example, such as Figure 7 and Figure 8 , Figure 8a (A) and Figure 8b As shown in (B), for an EAF furnace, the working cycle may include at least the drilling of the metal material M step, the smelting step, and possibly the refining of the smelted material step.

[0216] Specifically, during the drilling step, electrode 102 gradually approaches the discharged solid metal material M to trigger an electric arc and begin melting the metal material M. As the metal material M melts, electrode 102 gradually penetrates into the still solid portion of the metal material M, thus gradually melting it. When electrode 102 reaches a position inside container 101, the actual melting of the remaining metal material M surrounding electrode 102 begins.

[0217] Based on a feasible solution ( Figure 7 Before the refining step, the drilling step and the smelting step can be repeated multiple times, and there is also a step between the two steps to load more metal material M into the electric furnace 100.

[0218] For example, refer to Figure 3 The procedure stipulates that metal material M is loaded, holes are drilled in the metal charge using electrode 102, and then it is melted. This operation can be repeated three times each time metal material M is loaded.

[0219] according to Figure 8 , Figure 8a (A) and Figure 8b The solution shown in (B) provides a substantially continuous loading method that begins before the drilling step and continues until the electric furnace is completely filled, and also continues during the smelting step of the metal material.

[0220] According to this embodiment, the power supply frequency fa is lower than or equal to the grid frequency fr throughout the entire operating cycle (i.e., 100% of the duration).

[0221] According to some embodiments, the method can specify that the power supply frequency fa decreases as the working cycle of the electric furnace 100 progresses.

[0222] The power supply frequency fa can be reduced starting from a preset value, such as the value of the mains frequency fr or the value of the primary frequency fp on the primary coil 12 of the transformer 11, preferably starting from the value of the mains frequency fr.

[0223] The power supply frequency fa can decrease continuously over time, for example, in a linear or exponential manner, such as... Figure 4 (B) shows the dotted line.

[0224] The power supply frequency fa can decrease over time in a discontinuous manner, for example, decreasing in a stepwise manner, such as... Figure 4 As shown by the double-dotted line in (B). Therefore, the power supply frequency fa exhibits multiple values ​​f1 that are lower than the grid frequency fr.

[0225] The method can also stipulate that the power supply frequency fa remains essentially constant at least during the time corresponding to each working step of the electric furnace 100.

[0226] The method can specify that at the end of the working cycle of the electric furnace 100, the power supply frequency fa reaches a value that is at least 20% lower than the grid frequency fr, preferably at least 40%, and more preferably, essentially half of the grid frequency fr.

[0227] The method can specify that, in at least one or more steps of the working cycle of the electric furnace 100, the power supply frequency fa presents a value that is substantially between 30 and 40 Hz.

[0228] For example, referring to the EAF furnace, in the drilling step, the power supply frequency fa can be basically equal to the grid frequency fr, while in the refining step, it can be between 0.45 and 0.55 times the grid frequency fr.

[0229] This method can specify that, in the EAF furnace, during the drilling step, the power supply frequency fa is essentially equal to the grid frequency fr, and gradually decreases in subsequent working steps until it reaches a value f1, for example, essentially half the value of the grid frequency fr. Figure 3 ).

[0230] According to another example, such as Figure 4 As shown in (A), the method can specify that, in the EAF furnace, during the drilling and smelting steps, the power supply frequency fa is essentially equal to the grid frequency fr, and decreases in a stepwise manner in subsequent working steps.

[0231] According to other embodiments not shown, it may also be specified that the power supply frequency fa is lower than the grid frequency fr in all operating steps.

[0232] According to some variations, the method specifies that, in at least one step of the duty cycle, the power supply frequency fa is higher than the grid frequency fr, for example, between 101% and 200% of the grid frequency fr.

[0233] According to some embodiments, the method specifies that, in at least one step of the duty cycle, the power supply frequency is adjusted to a value between 51 and 100 Hz or 61 and 120 Hz, depending on the value of the grid frequency.

[0234] According to some embodiments, the power supply frequency fa is adjusted to be higher than the grid frequency fr, at least when the power absorbed by the EAF furnace fluctuates rapidly, for example, when loading metallic materials.

[0235] For example, Figure 10There is a chart showing the trend of electrical power absorbed by the furnace charge during the working cycle at the top and how the power supply frequency fa can be adjusted relative to the grid frequency fr at the bottom.

[0236] The parts highlighted with solid lines represent situations where power fluctuations and rapid changes occur: it can be seen that in these cases, the supply frequency fa is higher than the grid frequency fr, while for the remainder of the duty cycle, the frequency is lower than or equal to the grid frequency fr.

[0237] Therefore, by means of the present invention, once the operating points of the electric furnace 100 are determined (at least in terms of power, voltage, current and frequency), the method can stipulate that the control and command unit 17 should also follow these operating points as closely as possible by continuously adjusting the power supply frequency fa.

[0238] The working point can be determined by the operator or automatically by the control and command unit 17, for example, based on a mathematical model of the electric furnace 100 and / or a given melting and / or heating process, or even calculated based on data received from the input (regarding the type of material to be melted, the final product to be obtained, the characteristics of the electric furnace 100, the required hourly productivity, or other factors).

[0239] Therefore, the present invention allows for the optimization of electrical parameters in each step of a process by adjusting the frequency at different stages.

[0240] As another example, see reference Figure 9 As described, in a ladle furnace LF, a work cycle includes at least one step of refining molten metal material M.

[0241] According to feasible embodiments, the method may specify that in a ladle furnace LF, the power supply frequency fa remains constant throughout the entire working cycle, or the power supply frequency fa decreases linearly, stepwise, exponentially, or according to other mathematical curves over time, and may also decrease in a combination of these.

[0242] In any case, in a ladle furnace LF, the power supply frequency fa is preferably kept below the grid frequency fr throughout the entire operating cycle.

[0243] For example, according to the reference Figure 9 In the described embodiment, the method may specify that in the ladle furnace LF, the power supply frequency fa remains constant throughout the entire working cycle and adopts a value lower than the grid frequency fr, preferably a value between 0.4 and 0.6 times the grid frequency fr.

[0244] Preferably, in the ladle furnace LF, the power supply frequency fa is basically equal to half the value of the grid frequency fr until the refining step is completed.

[0245] Advantages, such asFigure 11 As shown, in the example case of the LF furnace, although the same temperature gradient is obtained, the present invention is able to reduce the power consumption required by the electric furnace 100: for example, under the same operating conditions, for an LF furnace with an operating frequency of 40 Hz, it is possible to achieve a 12% reduction in power consumption compared to the power required at a frequency of 50 Hz.

[0246] As another advantage, for example, in a 40Hz operating cycle, under all other operating conditions being equal, the power factor can increase from 0.90 to 0.96.

[0247] Another advantage is that the melting time can be shortened because the arc power can be increased by reducing the operating frequency.

[0248] For example, in an EAF furnace, melting time can be reduced by about 20% at a frequency of 25Hz, and by about 35% at a frequency of 10Hz. Similarly, in an LF furnace, energizing time can be reduced by an average of about 20-22 minutes at an operating frequency of 40Hz.

[0249] Advantageously, the consumption of electrodes 102 and 106 can also be reduced: for example, at an operating frequency of 40 Hz, the consumption of electrodes 102 and 106 can be reduced by about 10%.

[0250] Obviously, modifications and / or additions can be made to the aforementioned apparatus 10 and method without departing from the scope and range of the invention as defined in the claims.

[0251] It is equally apparent that, although the invention has been described with reference to some specific examples, those skilled in the art will be able to implement other equivalent forms of the method and apparatus 10 for powering an electric furnace for melting and / or heating metallic materials, having the features described in the claims, and thus all falling within the scope of protection defined by the claims.

[0252] In the following claims, the references in parentheses are for ease of reading only and should not be considered as limiting factors of the scope of protection defined by the claims.

Claims

1. A device (10) for supplying power to a furnace (100) provided with electrodes (102) for melting and / or heating metallic materials, comprising: At least one power supply line (201, 201L, 201M) and at least one connected base module (20, 120, 220), said at least one base module being configured to convert AC grid voltage and current (Ur, Ir) having a grid frequency (fr) to AC supply voltage and current (Ua, Ia) having a desired supply frequency (fa), wherein said at least one base module (20, 120, 220) includes: - A transformer (11) is connected to the power supply lines (201, 201L, 201M) and configured to convert the AC mains voltage and current (Ur, Ir) into AC secondary voltage and current (Us, Is); - Multiple rectifiers (14) are connected to the transformer (11) and configured to convert the AC secondary voltage and current (Us, Is) into DC intermediate voltage and current (Ui, Ii); - One or more DC intermediate circuits (16) configured to store electrical energy; - Multiple inverter devices (15) are connected to the one or more DC intermediate circuits (16) and configured to convert the intermediate voltage and current (Ui, Ii) into AC supply voltage and current (Ua, Ia) having the desired supply frequency (fa); - A control and command unit (17), configured to control and command the operation of the inverter device (15) and adjust the power supply frequency (fa) during each step of the process of the furnace (100), characterized in that the device (10) includes an adapter device (19) connected to the at least one base module (20, 120, 220) and capable of being connected to the electrode (102), and configured to adapt the parameters of the power supply voltage and current (Ua, Ia) to adapted voltage and current (Ua*, Ia*) for the electrode (102).

2. The apparatus (10) as claimed in claim 1, characterized in that, The power supply lines (201, 201L) are configured to operate at low voltage (LV), and the adapter device (19) includes one or more of a reactor (26), a filter (27), or a disconnecting switch (28).

3. The apparatus (10) as claimed in claim 1, characterized in that, It includes a step-down transformer device (202) connected upstream of the power supply lines (201, 201L) and configured to reduce the voltage supplied by the high-voltage or medium-voltage main grid (203) to the low-voltage grid voltage (Ur).

4. The apparatus (10) as claimed in claim 1, characterized in that, The power supply lines (201, 201M) are configured to operate at medium voltage (MV), and the adapter device (19) includes at least one adapter transformer (25) having a primary coil (29) connected to the at least one base module (20) and a secondary coil (30) that can be connected to the electrode (102) during use.

5. The apparatus (10) as claimed in claim 4, characterized in that, It includes: A step-down transformer device (202) is connected upstream of the power supply lines (201, 201M) and configured to reduce the voltage supplied by the high-voltage or medium-voltage main grid (203) to the medium-voltage grid voltage (Ur).

6. The apparatus as claimed in any of the preceding claims, characterized in that, The control and command unit (17) is provided with an adjustment device (18) configured to adjust the power supply frequency (fa) to be lower than or equal to the grid frequency (fr) during each step of the working cycle of the furnace (100), and in at least one step of the working cycle, the power supply frequency (fa) is between 40% and 80% of the grid frequency (fr).

7. The apparatus as claimed in any of the preceding claims, characterized in that, The at least one basic module (20, 120, 220) includes at least two sub-modules (21, 21A-21F), each sub-module including at least one rectifier (14), intermediate circuit (16) and inverter device (15), and each sub-module is configured to supply single-phase voltage and current of multiple interconnected wires (24) at the output.

8. The apparatus as claimed in claim 7, characterized in that, All intermediate circuits (16) of the at least one basic power supply module (20, 120, 220) are short-circuited to each other through short-circuit connectors (22, 23).

9. The apparatus (10) as claimed in claim 7 or 8, characterized in that, The transformer (11) includes a single transformer primary coil (12) provided with three-phase input terminals, which are connected to phases (R, S, T) of the power supply lines (201, 201L, 201M) during use. The transformer primary coil (12) is coupled to a plurality of transformer secondary coils (13), each of the sub-modules (21, 21A-21F) corresponding to one transformer secondary coil. The transformer is characterized in that the phases of at least two of the transformer secondary coils (13) of the at least one basic module (20, 120, 220) are different phases relative to each other.

10. A facility (50) for smelting metallic materials, comprising a power supply device (10) as claimed in any one of claims 1 to 9 and an electric furnace (100), the electric furnace being provided with two or more electrodes (102), the electrodes being connected via at least one adapter device (19) to the corresponding phases (R, S, T) of the power supply voltage and current (Ua, Ia) supplied by the at least one base module (20, 120, 220).

11. A method for supplying power to an electric furnace (11) having two or more electrodes (102), comprising: - Supply AC grid voltage and current (Ur, Ir) to at least one basic module (20, 120, 220) via three-phase power supply lines (201, 201L, 201M) with a predetermined grid frequency (fr); - The grid voltage and current (Ur, Ir) are converted into selectively configurable AC secondary voltage and current (Us, Ir) by a transformer (11); - The secondary voltage and current (Us, Is) are rectified using multiple rectifiers (14) to obtain a DC intermediate voltage and current (Ui, Ii); - The DC intermediate voltage and current (Ui, Ii) are converted into AC supply voltage (Ua) and supply current (Ia) that can be selectively set by the control and command unit (17) connected to the inverter device (15) and have the desired supply frequency (fa). - The supply voltage and current (Ua, Ia) are adapted and / or filtered downstream of the inverter device (15) to adjust its parameters and obtain an adapted supply voltage and current (U*, I*) and supply it to the electrode (102).

12. The method as described in claim 11, characterized in that, It provides that, during each step of the working cycle of the electric furnace (100), the adjustment device (18) of the control and command unit (17) adjusts the inverter device (15) such that, for at least some steps of the working process, the power supply frequency (fa) is lower than or equal to the grid frequency (fr), and in at least one step of the working cycle, the power supply frequency (fa) is between 40% and 80% of the grid frequency (fr).

13. The method as described in claim 12, characterized in that, It provides that the inverter device (15) is adjusted such that for at least 80% of the operation, preferably at least 90%, and more preferably at least 95%, the power supply frequency (fa) is lower than the grid frequency (fr).

14. The method according to any one of claims 11 to 13, characterized in that, It provides a medium-voltage (MV) AC grid voltage and current (Ur, Ir) and adapts the supply voltage and current (Ua, Ia) downstream of the inverter device (15) via at least one adapter transformer (25), which is connected to the inverter device (15) via a transformer primary coil (29) and to the electrode (102) via a transformer secondary coil (30) to obtain a low-voltage (LV) adapted supply voltage and current (Ua*, Ia*).

15. The method according to any one of claims 11 to 13, characterized in that, It provides a low-voltage (LV) AC grid voltage and current (Ur, Ir) and adapts the supply voltage and current (Ua, Ia) downstream of the inverter device (15) via an adapter device (19) connected between the inverter device (15) and the electrode (102), the adapter device (19) including one or more of a reactor (26), a filter (27) or a disconnecting switch (28).

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