Arc furnace using more than three-phase feed

Abstract

An electric arc furnace (2) has a plurality of electrodes (3) arranged in a furnace vessel (4) of the electric arc furnace (2) in such a way that energy can be introduced into a metallic material (6) located in the furnace vessel (4) via the electrodes (3). Each of the electrodes (3) is connected with one of a plurality of phases (9) of a feed supply system (8). The phase currents (I1 to In) supplied to the electrodes (3) can be set independently of one another by the feed supply system (8) for the phases (9) other than one phase (9). Alternatively, the phase voltages (U1 to Un) present at the electrodes (3) can be set independently of one another by the feed supply system for the phases (9) other than one phase (9). The number of phases (9) of the feed supply system (8) is greater than three. Furthermore, the supply system (8) comprises a transformer assembly (10) which is connected directly or indirectly on the secondary side with the electrodes (3). Upstream of the transformer assembly (10) a converter assembly (11) is provided.

Description

Technical Field

[0001] This invention relates to an energy introduction device for an electric arc furnace. - The electric arc furnace has multiple electrodes that can be arranged in the furnace vessel, enabling energy to be introduced into the metallic material located in the furnace vessel via the electrodes. Each of the electrodes is connected to one of the multiple phases of the power supply system. - Wherein, the phase current supplied to the electrode can be set independently by the power supply system for each phase except one phase, or the phase voltage existing at the electrode can be set independently by the power supply system for each phase except one phase. - In this case, the number of phases in the power supply system is greater than three. - The supply system includes a transformer assembly that is directly or indirectly connected to the electrodes on the secondary side. Background Technology

[0002] Such electric arc furnaces and associated energy introduction devices are known, for example, from JP 2004 096 897 A. Similar disclosures can be found from CN217 483 230 U and EP 1 848 248 A1. Summary of the Invention

[0003] Waste is melted in an electric arc furnace. For this purpose, the waste is introduced into the furnace vessel. Three electrodes are then typically lowered into the furnace vessel, generating arcs between the waste and the electrodes. The arcs heat the waste until it melts, and further heat the melt if necessary. Three-phase current is typically supplied to the electric arc furnace via a staged transformer. Typical phase voltages of the electrodes range from several hundred V to slightly above 1 kV, with extreme cases reaching up to 2 kV. Typical power ratings for industrial electric arc furnaces range from 50 MW to 300 MW. The staged transformer is switchable, allowing the heating power of the electric arc furnace to be set by switching the staged transformer (and, if necessary, in conjunction with the electrode positioning above the waste or melt).

[0004] The continuous flickering of the electric arc furnace causes a reaction on the power supply network. These reactions, commonly referred to as flickering, can cause fluctuations in brightness in lighting fixtures connected to the power supply network, for example. Avoiding flickering is an important aspect of operating an electric arc furnace.

[0005] There are various schemes that attempt to balance the power drawn from the power grid as much as possible. However, existing schemes all have certain drawbacks.

[0006] The problem with energy introduction devices of the type described at the beginning is that when one of the arcs in a conventional electric arc furnace with three electrodes is interrupted, the currents through the remaining two electrodes must be reversed and therefore have the same value. However, these currents can only be maintained for an extremely short time (within milliseconds) via the typically present transformer assembly. A zero-crossing of the current inevitably occurs thereafter. Therefore, power fluctuations are taken up, or rather, significant fluctuations. Furthermore, arc interruptions typically have a considerable duration. Therefore, grid backlash cannot be avoided in the event of an interruption of one arc.

[0007] Furthermore, it is known that a converter is arranged on the secondary side of the transformer assembly. In this case, it is possible to allow direct current to flow through the remaining two electrodes when one arc in the electric arc is interrupted, until the interrupted arc is reignited. While the power of the electric arc furnace may have to be reduced, at least zero-crossing of the power can be avoided. However, a disadvantage of this solution is that the converter must be able to withstand high secondary-side currents that may be well above 100 kA.

[0008] The objective of this invention is to provide a feasible solution that avoids the drawbacks of the prior art.

[0009] This task is accomplished by an energy introduction device having the features of claim 1. Advantageous designs of the energy introduction device are the subject of dependent claims 2 to 12.

[0010] According to the present invention, the energy introduction device of the type described at the beginning is designed such that a converter assembly is provided upstream of the transformer assembly.

[0011] Because more than three phases are used, there is redundancy in at least one phase, so that even if the arc is interrupted on one electrode, there is still an arc on at least three electrodes, thus maintaining a three-phase AC system. Therefore, even if power is not drawn through the corresponding phase for a short time during the zero-crossing period of the AC current at one of the at least three electrodes, the power drawn can be maintained overall and even precisely or at least substantially constant through the current flow in the at least two remaining phases.

[0012] When the transformer assembly is positioned between the converter assembly and the electrodes, the converter assembly is connected before the transformer assembly. In this case, the converter assembly can be designed as a multilevel converter. This allows for current carrying using lines with significantly smaller cross-sections compared to the converter being connected after the transformer assembly. Furthermore, it is significantly easier to avoid or suppress back-reactions to the power grid. Additionally, smoothing the DC voltage used within the converter is significantly easier, as a significantly smaller capacitance is sufficient at higher voltages. When the converter is positioned after the transformer, a correspondingly larger capacitance is practically impossible. To compensate, the transformer must have multiple secondary windings. Since this is not necessary when the converter assembly is connected before the transformer assembly, the transformer assembly can be constructed significantly more simply. Furthermore, the available installation space between a conventional furnace transformer and the electrodes is typically very small. Positioning the converter assembly there presents considerable difficulties.

[0013] In many cases, the transformer assembly is designed as a stepped transformer. In this case, the electrical energy supplied to the electric arc furnace can be set by the corresponding switching stages.

[0014] In the prior art, the number of switching stages is typically much greater than two. However, within the scope of this invention, it is also possible for the transformer assembly to be switchable or non-switchable between only two switching stages. This can be achieved by using an upstream converter assembly to set the phase voltage and phase current over a wide range.

[0015] Furthermore, transformer assemblies can be constructed as needed. For example, a transformer assembly can include at least one multiphase transformer. This applies even when the transformer assembly is directly connected to the electrodes on the output side. In this case, for example, the multiphase transformer can be designed for the number of phases of the supply system on both the input and output sides. It is also possible that while the multiphase transformer is designed for only three phases, there is at least one additional multiphase transformer or a corresponding number of single-phase transformers for the remaining phases of the supply system. Alternatively, a single-phase transformer may be provided for each phase of the supply system separately.

[0016] On the input side, the converter assembly can have a conventional three-phase design. However, on the output side, the converter assembly must be able to supply the stated number of phases of the system. Both of these cases apply independently of whether the converter assembly is connected before or after a transformer assembly. Furthermore, the converter assembly can be constructed as needed. The converter assembly preferably has an input-side rectifier with multiple input-side phases (typically three input-side phases, as mentioned earlier) and an output-side converter with multiple output-side phases, i.e., it is designed as an intermediate circuit converter. The number of output-side phases corresponds to the number of phases in the system.

[0017] The input-side rectifier can be designed as either a non-controlled rectifier or an open-loop controlled rectifier, depending on the requirements. In both cases, the input-side rectifier and the output-side converter have separate phase arms for each input or output phase. When the rectifier is designed as an open-loop controlled rectifier, the phase arms can be identical, allowing any phase arm of the rectifier and any phase arm of the converter to be interchanged without affecting the performance of the converter components.

[0018] Therefore, phase arms are preferably interchangeable or compatible with each other in principle. This simplifies not only the electrical and mechanical construction of the phase arms but also the operation of the semiconductor switches arranged in the phase arms. Furthermore, spare parts are easier to stock because the same semiconductor switch can be installed in the phase arms of the input-side rectifier or the output-side converter as needed. Another advantage arising from this is that, despite the identical phase arm structure, it is still possible to consider situations where the supply system on the output side must be designed to be larger than that on the input side. This larger design arises in the case where the number of phases in the supply system can be greater than the number of phases on the input side.

[0019] Typically, the energy input device includes an open-loop control unit for open-loop control of the supply system. Preferably, a target value for the power supplied to the total electrodes is preset in the open-loop control unit. This allows the open-loop control unit to operate the supply system as consistently as possible so that the power supplied to the total electrodes (as defined by the instantaneous value of the phase current supplied to the electrodes and the phase voltage applied to the electrodes) is as close as possible to the target value.

[0020] The phrase "as close as possible" was chosen because too many arc interruptions can occur. When only two arcs remain, especially at the point of zero current crossing, constant power can no longer be maintained. Instead, it is entirely possible that even when one phase is not carrying current during an arc interruption, the open-loop control unit maintains control over the supply system to ensure that the power supplied to all electrodes is as close to the target value as possible. It is even possible that as long as at least three phases are carrying current, the open-loop control unit maintains control over the supply system to ensure that the power supplied to all electrodes is as close to the target value as possible.

[0021] The two cases described above are the same when the number of phases in the supply system is four. However, when the number of phases in the supply system is five or more, the two cases are different from each other because even if two arcs are interrupted, at least three phases still carry current.

[0022] In a conventional three-phase electric arc furnace, the electrodes are arranged such that they form the corners of an equilateral triangle. A similar design, in the case of more than three electrodes (as is the case here), involves arranging the electrodes in a regular polygonal configuration. However, in the case of more than three electrodes, it is also possible, for example, that one electrode forms a central electrode, with the remaining electrodes arranged in a regular polygonal configuration around this central electrode. Alternatively, the electrodes can also be arranged sequentially or adjacently in rows within the electric arc furnace. Attached Figure Description

[0023] The features, characteristics, and advantages of the present invention described above, as well as the ways and methods of achieving these features, characteristics, and advantages, will become clearer and more apparent from the following description in conjunction with the embodiments, which are illustrated in more detail with reference to the accompanying drawings. In the drawings: Figure 1 The energy introduction device and electric arc furnace are shown. Figure 2 The energy introduction device is shown. Figure 3 The converter components are shown. Figure 4 The supply system and open-loop control unit are shown. Figure 5 The flowchart is shown, and Figures 6 to 8 A feasible arrangement of electrodes is shown. Detailed Implementation

[0024] according to Figure 1 The energy introduction device 1 for the electric arc furnace 2 has multiple electrodes 3. Figure 1 In the figure, only one of the electrodes 3 is marked with its reference numeral. Electrode 3 can be arranged in the furnace vessel 4 of the electric arc furnace 2. In particular, the electrode can be... Figure 1 As schematically shown by double-headed arrow 5, it descends from above onto or lifts from the metal material 6 (e.g., scrap). Energy can be introduced into the material 6 via electrode 3—more precisely, via an electric arc 7 constructed between the material 6 and electrode 3. The material 6 is thus heated, causing it to melt. After melting, the temperature of the now molten material 6 can be further increased by the electric arc 7. Figure 1 In the figure, only one arc of arc 7 is shown.

[0025] Electrical energy is supplied to electrode 3 via supply system 8. Supply system 8 thus powers electrode 3. To power electrode 3, electrode 3 is connected to phase 9 of supply system 8. Typically, there is a 1:1 relationship between electrode 3 and phase 9, such that each phase 9 is connected to exactly one electrode 3. However, it is also possible to connect multiple electrodes 3 to one, multiple, or even all of phase 9. The number of phase 9 in power supply system 8 is greater than three. Figure 1 The diagram shows a configuration where the number of phases 9, n, is five. However, the number of phases 9, n, can also be four (minimum configuration) or greater than five. The supply system 8 generates phase voltages U1 to Un (here, n=5) for phases 9, such that (after ignition of arc 7, phase currents I1 to In (here, n=5) are supplied to electrode 3).

[0026] The condition that phase current I1 must satisfy is that the sum of phase currents I1 to In (with the correct sign) is zero at all given points in time. This might be the case, for example, when a neutral point exists within supply system 8 but is not grounded, or when no neutral point exists at all. However, in any case, the phase currents I1 to In supplied by feeder system 8 to electrode 3 can only be set independently for each phase except for one phase 9. This ability to set the phase currents independently is... Figure 1 The target value of phase current I1 to In can be expressed as follows: it can provide the supply system 8 with the target value of phase current I1 to In. to However, the target value for the phase current In It is shown in parentheses because this is a target value. It can no longer be provided independently.

[0027] Similarly, the phase voltages U1 to Un of phase 9 may need to satisfy the condition that the sum of phase voltages U1 to Un (with the correct sign) is zero at all given points in time. This might be the case, for example, when (in a generalization of delta connection) an n-delta voltage is applied. Similar to phase currents I1 to In, in this case, the phase voltages U1 to Un present at electrode 3 can also be set independently of each other by the power supply system 8 for all phases 9 except for one phase 9. This ability to set the phase voltages independently is... Figure 1 The target values ​​of phase voltages U1 to Un can be provided to the supply system 8 in the following way: to However, the target value for phase voltage Un It is shown in parentheses because this is a target value. It can no longer be preset independently.

[0028] according to Figure 2The supply system 8 includes a transformer assembly 10. The transformer assembly 10 is directly or indirectly connected to the electrode 3 on the secondary side. The transformer assembly 10 can be designed, for example, as a non-switchable transformer assembly. Furthermore, a converter assembly 11 is disposed upstream of the transformer assembly 10. The transformer assembly 10 can be designed as a non-switchable or switchable transformer assembly, i.e., a stepped transformer. It may be sufficient when the transformer assembly 10 is switchable only between a few switching stages, especially between two switching stages.

[0029] The specific design of the transformer assembly 10 can be selected as needed. For example, the transformer assembly 10 can include at least one multiphase transformer and / or at least one single-phase transformer.

[0030] according to Figure 2 The converter assembly 11 has multiple input-side phases 12. A typical number of input-side phases 12, namely three, can be provided. Conversely, the converter assembly 11 has more than three output-side phases 15. The number of output-side phases 15 of the converter assembly 11 corresponds to the number of phases 9 in the supply system 8. Further design options for the converter assembly 11 can be determined as needed. In particular, the converter assembly 11 can be adapted to... Figure 3 The diagram shows an input-side rectifier 13 and an output-side converter 14. In this case, the rectifier 13 has an input-side phase 12 and the converter 14 has an output-side phase 15.

[0031] The input-side rectifier 13 can be designed as a non-controlled rectifier. However, preferably, the rectifier is designed according to... Figure 3 The diagram in the image is designed as an open-loop controlled rectifier.

[0032] The input-side rectifier 13 has phase arms 16, more specifically, one phase arm 16 for each input-side phase 12. The phase arms 16 can be identical, allowing them to be interchanged without affecting the performance of the converter assembly 11. For example, the phase arms 16 can be designed for a rated voltage of 110 kV, a rated current of 3 kA, and a rated power of 100 MW (or typically the same rated voltage, the same rated current, and the same rated power). The interchangeability of the phase arms 16 is achieved in… Figure 3 The arrows connecting the rectifiers 13 via the dashed lines above them are shown schematically.

[0033] Similarly, the output-side converter 14 also has phase arms 17, more specifically, one phase arm 17 for each output-side phase 15. The phase arms 17 can be identical to each other, allowing them to be interchanged without affecting the performance of the converter assembly 11. For example, phase arms 17—similar to phase arms 16—can be designed for a rated voltage of 110 kV, a rated current of 3 kA, and a rated power of 100 MW (or typically the same rated voltage, the same rated current, and the same rated power). The interchangeability of phase arms 17 is achieved in… Figure 3 The arrows connected by the dashed lines above converter 14 are shown schematically.

[0034] Furthermore, not only are phase arms 16 identical to each other, but preferably, phase arms 16 and 17 are also identical to each other. Therefore, phase arms 16 of the rectifier 13 and phase arms 17 of the converter 14 can be interchanged without affecting the performance of the converter assembly 11. This is in Figure 3 The single phase arm 16 of rectifier 13 and the single phase arm 17 of converter 14 are shown as arrows connecting them to each other via two dashed lines below converter assembly 11.

[0035] according to Figure 3 The diagram shows that arms 16 and 17 each have only two switches 18. However, this diagram should be generalized. Switches 18 can represent arms of a multilevel converter.

[0036] Energy introduction device 1 according to Figure 4 An open-loop control unit 19 is included. The supply system 8 uses the open-loop control unit 19 for open-loop control. The converter assembly 11 is also controlled in an open-loop manner by the open-loop control unit 19. In a preferred embodiment of the invention, a target value is provided to the open-loop control unit 19. The target value This corresponds to the power to be supplied to all electrodes 3. In this case, the open-loop control unit 18 preferably operates according to the following formula:

[0037] The corresponding instantaneous active power P is determined based on the current instantaneous phase voltages U1 to Un and phase currents I1 to In, respectively. Furthermore, the open-loop control unit determines the control signal C for supplying the system 8 and controls the system 8 according to the control signal C. The control signal C is determined in such a manner that the open-loop control unit 19 continuously controls the supply system 8 so that the power P supplied to all electrodes 3 is as close as possible to the target value. Other types of closed-loop control, such as closed-loop control for quantities averaged over the entire cycle or at least half a cycle of the supply network, include active power (averaged over the entire cycle or at least half a cycle), reactive power, apparent power, or cosine per 100°C. Therefore, it can be disregarded.

[0038] The following is combined Figure 5 The operation of the open-loop control unit 19 will be described in more detail. It should be noted that the open-loop control unit 19 executes its open-loop control process periodically. The cycle time is typically in the range of less than 1 ms to a maximum of several milliseconds, mostly between 0.1 ms and 1.0 ms.

[0039] according to Figure 5 In step S1, the open-loop control unit 19 receives the target value for power P. In step S2, the open-loop control unit 19 learns the current instantaneous phase voltages U1 to Un and the current instantaneous phase currents I1 to In. For example, it can measure the phase voltages U1 to Un and the phase currents I1 to In and can receive the relevant measured values ​​by the open-loop control unit 19. In step S3, the open-loop control unit 19 determines the corresponding current instantaneous active power P according to the relationship (1).

[0040] In step S4, the open-loop control unit 19 checks whether one of the arcs in arc 7 has been extinguished or interrupted. The check in step S4 essentially involves checking whether the phase currents I1 to In have a value of 0. However, it must be taken into account that the phase currents I1 to In are alternating currents and therefore have a brief zero-crossing even when the associated arc 7 is burning. This zero-crossing must be distinguished from the extinguishing of arc 7. However, this fact is generally known to those skilled in the art, and it is entirely possible to distinguish between the zero-crossing of phase currents I1 to In and the extinguishing of arc 7. For example, when the associated phase currents I1 to In have a value of 0 for a sufficiently long time, it can be identified as an interruption of arc 7.

[0041] When all arcs 7 are burning, i.e., no arc 7 is extinguished, the open-loop control unit 19 proceeds to step S5. In step S5, the open-loop control unit 19 determines the phase voltages U1 to Un and / or phase currents I1 to In to be set for phase 9 in the next cycle. This determination is made in such a way that the power P supplied to all electrodes 3 is as close as possible to the target value. .

[0042] However, if the open-loop control unit 19 determines in step S4 that one of the arcs in arc 7 has been extinguished, the open-loop control unit proceeds to step S6. In step S6, the open-loop control unit 19 checks whether the other arc in arc 7 has been extinguished. The check in step S6 is substantially similar to the check in step S4.

[0043] When all the other arcs 7 have burned, i.e., only one arc 7 is extinguished, the open-loop control unit 19 proceeds to step S7. In step S7, the open-loop control unit 19 determines the phase voltages U1 to Un and / or phase currents I1 to In for phase 9 to be set in the next cycle. Step S7 substantially corresponds to step S5. However, as part of the determination in step S7, the open-loop control unit 19 takes into account that the currents I1 to In of the extinguished arc 7 have a value of 0. For example, if the arc 7 fed via the electrode 3 of the nth phase 9 has been extinguished, the open-loop control unit 19 determines the phase voltages U1 to Un-1 for the remaining phases 9, such that the desired power is set in conjunction with the associated phase currents I1 to In-1. The phase voltage Un of the extinguished arc 7 can be set arbitrarily in principle. In practice, the phase voltage is set in a manner that facilitates the ignition of the extinguished arc 7. This can be achieved, for example, by setting the corresponding phase voltage Un to its minimum or maximum possible value.

[0044] The check sequence can continue until the open-loop control unit 19 checks in step S8 whether the third-to-last arc 7 has also been extinguished. As long as three arcs 7 are still burning, the open-loop control unit 19 proceeds to step S9. In step S9, the open-loop control unit 19 determines the phase voltages U1 to Un and / or phase currents I1 to In for the phases 9 of the still-burning arcs 7 that should be set in the next cycle. This determination is made in such a way that the power P supplied to all electrodes 3 is as close as possible to the target value. For the extinguished arc 7, the phase voltages U1 to Un can be set arbitrarily in principle. In practice, these phase voltages are set in a manner that facilitates the ignition of the extinguished arc 7.

[0045] However, if the open-loop control unit 19 determines in step S8 that the third-to-last arc 7 has also been extinguished, then the open-loop control unit 19 proceeds to step S10. Now only two arcs 7 remain available, forcing the currents I1 to In of the two associated phases 9 to be equal in magnitude and opposite in sign. In this case, no further action can be taken on the associated target values. Closed-loop control of the current instantaneous active power P.

[0046] Step S9, the handling when exactly three arcs 7 are still burning (more precisely: exactly three phase currents I1 to In can have a non-zero value), can be designed, for example, as detailed in the applicant's two European patent applications 23218774.0 and 23218588.4 (both filed on December 20, 2023). These handling methods can also be extended to more than three phases (step S5, and if necessary, step S7, and if necessary, unpresented steps prior to the check in step S8). The following outlines the associated handling methods for the common case where the sum of phase currents I1 to In must always result in a value of 0.

[0047] Suppose there is a system with N phases. If the total number of phases 9 in supply system 8 is, for example, ... The following implementation scheme applies to step S5 (where... ) and for step S7 (where )efficient.

[0048] Always apply relational expressions

[0049] Furthermore, relational expressions are always applicable.

[0050] Now regarding the normal vector Define an orthonormal basis. Normal vector. Given from the following

[0051] for The associated basis vectors and For example, it can be passed

[0052] Or through

[0053] Provided.

[0054] It is possible to easily determine the associated orthonormal basis. Any possible vector in N-dimensional space that can be represented as a linear combination of basis vectors. Both are related to the normal vector Orthogonal. For Therefore, any vector It can be achieved by using relational expressions

[0055] The presentation is related to the normal vector. Orthogonal.

[0056] The following text uses Represents a spatial vector. Spatial vector Must be with vector The difference. Especially, spatial vectors. Having dimensions And vector Having dimensions .

[0057] Clearly, given an orthonormal basis, space vectors and vector They are interchangeable. For this, an associated orthonormal mapping matrix B, which can be easily computed, is needed. For an orthonormal basis according to the above equations, the mapping matrix B is, for example, obtained through...

[0058] Definition. For an orthonormal basis according to other equations, the mapping matrix B is, for example, obtained through...

[0059] definition.

[0060] For an orthogonal matrix and therefore also for a mapping matrix B according to equations (8) and (9), the relation applies.

[0061] For the mapping matrix B according to equation (9), the relation also clearly applies.

[0062] from Spatial vectors in 3D space Convert to a vector in N-dimensional space Based on the following relationship

[0063] Vectors in N-dimensional space Reverse conversion to Spatial vectors in 3D space Based on the following relationship

[0064] value This is referred to as the zero component in the following text.

[0065] The above equations also apply to phase currents I1 to IN and phase voltages U1 to UN. If using... Let the current vector in N-dimensional space be denoted as , then the current vector... With spatial vectors and zero components Corresponding. Due to the conditions of equation (3), the zero component It has a value of 0. Similarly, it can be used... This represents the voltage vector in N-dimensional space. With spatial vectors and zero components Correspondence. Zero component It can have a value of 0 or a value other than 0.

[0066] Equation (2) can also be written as a current vector. With voltage vector scalar product:

[0067] However, it can also be easily shown that space vectors and The scalar product yields the same value. Because it also applies...

[0068] because Zero component and The product disappears. Therefore, the relation also applies.

[0069] Therefore, it is possible to obtain the current vector. spatial vector Starting from, it consists of two components for voltage vector spatial vector One component is parallel to the current vector. spatial vector This is extended and referred to below as the parallel component. The length of the parallel component must be determined such that it is used for the current vector. spatial vector The scalar product with the parallel components yields the desired power. The other component is in the space vector. and Defined The dimensional space is defined within a subspace, which is arranged to correspond to the current vector. spatial vector Orthogonal. This component is orthogonal to the vector used for the current vector. spatial vector Extended and therefore referred to below as orthogonal components. Used for the current vector. spatial vector The scalar product with the orthogonal component always yields a value of 0 and therefore contributes nothing to the power P. The orthogonal components can therefore be determined as needed. As already explained, the zero component... Similarly, it does not contribute to the power P. Therefore, the zero component can also be determined as needed. For example, the orthogonal component and the zero component. This determination ensures that transformer assembly 10 does not enter the saturation region. However, there are also methods for determining the quadrature components and zero components. Other possibilities.

[0070] The arrangement of electrode 3 in electric arc furnace 2 can be determined according to needs. For example, electrode 3 can be arranged in electric arc furnace 2 as follows: Figure 6 The electrodes 3 are arranged in a regular polygonal form, as shown in the electric arc furnace 2; that is, for example, for a total of five electrodes 3, they are arranged in a regular pentagonal form. Alternatively, according to... Figure 7 The diagram shows that one of the electrodes 3 can be centrally positioned, forming the central electrode 3. The remaining electrodes 3 can then be arranged in a regular polygon around the central electrode 3. With a total of five electrodes 3, the remaining electrodes 3 can thus be positioned at the corners of a square, with the central electrode 3 located at the center of the square. As an alternative, according to... Figure 8 As shown in the diagram, electrodes 3 can be arranged in rows sequentially or adjacent to each other in the electric arc furnace 2.

[0071] This invention has many advantages. In particular, even in the event of a limited number of arc interruptions, it is still possible to reference a constant or only slowly varying rated power. Closed-loop control is implemented. This possibility exists as long as at least three electric arcs 7 are still burning. As a result, even if the electric arcs 7 are interrupted for a long time, a constant or at least slowly varying electrical power P can continue to be supplied to the electric arc furnace 2.

[0072] Although the invention has been shown and described in more detail by way of preferred embodiments, the invention is not limited to the disclosed examples and other variations can be derived by those skilled in the art without departing from the scope of protection of the invention.

[0073] List of reference numerals

[0074] 1. Energy introduction device

[0075] 2. Electric Arc Furnace

[0076] 3 electrodes

[0077] 4 Furnace Containers

[0078] 5. Double-headed arrow

[0079] 6. Metallic Materials

[0080] 7. Electric arc

[0081] 8. Supply System

[0082] 9 phases

[0083] 10 Transformer Assembly

[0084] 11 Converter Components

[0085] 12 Input phase

[0086] 13 Rectifier

[0087] 14 Output-side converter

[0088] 15 Output phase

[0089] 16, 17 phase arms

[0090] 18 switches

[0091] 19 Open-loop control unit

[0092] C control signal

[0093] I1 to In phase current to Target value of phase current P Current instantaneous active power The target value of the current instantaneous active power Steps S1 to S10 Phase voltages from U1 to Un to The target value of the phase voltage.

Claims

1. An energy introduction device for an electric arc furnace (2), - in, The electric arc furnace (2) has a plurality of electrodes (3) that can be arranged in the furnace container (4) of the electric arc furnace (2), so that energy can be introduced into the metal material (6) located in the furnace container (4) via the electrodes (3). - Each of the electrodes (3) is connected to one of the multiple phases (9) of the power supply system (8). - Wherein, the phase currents (I1 to In) supplied to the electrode (3) can be set independently by the power supply system (8) for each phase (9) except for one phase (9), or the phase voltages (U1 to Un) present at the electrode (3) can be set independently by the power supply system for each phase (9) except for one phase (9). - Wherein, the number of phases (9) in the power supply system (8) is greater than three. - Wherein, the supply system (8) includes a transformer assembly (10), which is directly or indirectly connected to the electrode (3) on the secondary side. Its features are, A converter assembly (11) is provided upstream of the transformer assembly (10).

2. The energy introduction device according to claim 1, Its features are, The transformer assembly (10) is designed as a graded transformer.

3. The energy introduction device according to claim 2, Its features are, The transformer assembly (10) can only switch between two switching stages.

4. The energy introduction device according to claim 1, 2 or 3, Its features are, The transformer assembly (10) includes at least one multiphase transformer.

5. The energy introduction device according to any one of the preceding claims, Its features are, The transformer assembly (10) includes at least one single-phase transformer.

6. The energy introduction device according to any one of the preceding claims, Its features are, The converter assembly (11) has an input-side rectifier (13) with multiple input-side phases (12) and an output-side converter (14) with multiple output-side phases (15), and the number of output-side phases (15) is the same as the number of phases (9) of the supply system (8).

7. The energy introduction device according to claim 6, Its features are, The input-side rectifier (13) is designed as an open-loop controlled rectifier.

8. The energy introduction device according to claim 7, Its features are, The input-side rectifier (13) and the output-side converter (14) have phase arms (16, 17) for each input-side or output-side phase (12, 15), and the phase arms (16, 17) are identical, such that any phase arm (16) of the rectifier (13) and any phase arm (17) of the converter (14) can be interchanged without affecting the performance of the converter assembly (11).

9. The energy introduction device according to any one of the preceding claims, Its features are, The energy introduction device has an open-loop control unit (19) for performing open-loop control of the supply system (8), thereby providing the open-loop control unit (19) with a target value of the power (P) to be supplied to all the electrodes (3). And the open-loop control unit (19) controls the supply system (8) as consistently as possible, so that the power (P) supplied to all the electrodes (3) is as close as possible to the target value. The power is defined by the instantaneous values ​​of the phase currents (I1 to In) supplied to the electrode (3) and the instantaneous values ​​of the phase voltages (U1 to Un) applied to the electrode (3).

10. The energy introduction device according to claim 9, Its features are, Even when one of the phases (9) is not carrying current during an arc interruption, the open-loop control unit (19) continues to control the supply system (8) so that the power (P) supplied to all the electrodes (3) is as close as possible to the target value. .

11. The energy introduction device according to claim 10, Its features are, As long as at least three of the phases (9) carry current, the open-loop control unit (19) continues to control the supply system (8) so that the power (P) supplied to all the electrodes (3) is as close as possible to the target value. .

12. The energy introduction device according to any one of the preceding claims, Its features are, The electrodes (3) are arranged in the electric arc furnace (2) in the form of regular polygons, or one of the electrodes (3) forms a central electrode and the remaining electrodes (3) are arranged in the form of regular polygons around the central electrode, or the electrodes (3) are arranged in a row in sequence or adjacent to each other.

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