Integrated Flicker Control For Arc Furnace

Abstract

A control device for an arc furnace includes an arc furnace control module for controlling the arc furnace and a flicker module for determining a flicker value in a grid supplying the arc furnace, wherein the arc furnace control module is adapted for controlling the arc furnace based on the flicker value and wherein the arc furnace control module and the flicker module are integrated into one structural component.

Claims

1. A control device for an arc furnace, the control device comprising: a flicker module for determining a flicker value in a grid supplying the arc furnace; an arc furnace control module for controlling the arc furnace based on the flicker value; wherein the arc furnace control module and the flicker module are integrated into one structural component; wherein the flicker module is adapted for providing a short-term flicker value to the arc furnace control module, the short-term flicker value being based on voltage measurements in the grid in an interval of 10 min; and/or wherein the flicker module is adapted for providing a long-term flicker value to the arc furnace control module, the long-term flicker value being based on voltage measurements in the grid in an interval of 2 h; wherein the flicker module is adapted for providing an instantaneous flicker value to the arc furnace control module, the instantaneous flicker value being based on voltage measurements in the grid in an interval of less than 10 s; wherein the arc furnace control module is adapted for controlling an arc voltage and/or an arc current of the arc furnace based on the instantaneous flicker value and is adapted for controlling a converter for generating the arc current for the arc furnace.

2. The control device of claim 1, wherein the arc furnace control module and the flicker module are software modules executable in the control device in the same computing device.

3. The control device of claim 1, wherein the arc furnace control module and the flicker module are implemented in a programmable logic controller.

4. The control device of claim 1, wherein the arc furnace control module is adapted for controlling an electrical power supplied to the arc furnace dependent on the flicker value; and/or wherein the arc furnace control module is adapted for reducing the electrical power supplied to the arc furnace, when the flicker value is higher than a threshold value.

5. An arc furnace system, comprising: an arc furnace with at least one electrode for generating an arc with electrical energy; a control device for controlling an arc voltage and/or an arc current of an arc furnace according to one of the previous claims; a transformer for transforming a voltage from the grid into a voltage to be supplied to the arc furnace; a converter for converting the voltage from the transformer or from the grid into a voltage to be supplied to the electrode of the arc furnace or to the transformer.

6. A method for controlling an arc furnace, the method comprising: receiving grid voltage measurements from a grid supplying the arc furnace with electrical energy; determining a short-term flicker value to the arc furnace control module, the short-term flicker value being based on voltage measurements in the grid in an interval of 10 min; determining a long-term flicker value to the arc furnace control module, the long-term flicker value being based on voltage measurements in the grid in an interval of 2 h; determining an instantaneous flicker value from the grid voltage measurements, the instantaneous flicker value being based on grid voltage measurements in an interval of less than 10 s; controlling an arc current and/or an arc voltage of the arc furnace based on the instantaneous flicker value and controlling a converter for generating the arc current for the arc furnace.

7. The method of claim 6, further comprising: controlling an electrical power supplied to the arc furnace dependent on the instantaneous flicker value.

8. The method of claim 6, reducing an electrical power supplied to the arc furnace, when the instantaneous flicker value is higher than a threshold value.

9. The method of claim 6, further comprising: wherein arc furnace voltage and current measurements for controlling the arc furnace are measured between a transformer, which is adapted for transforming a grid voltage into a voltage to be supplied to the arc furnace, and the arc furnace; wherein grid voltage measurements for determining the instantaneous flicker value are performed directly at the grid.

10. The control device of claim 2, wherein the arc furnace control module and the flicker module are implemented in a programmable logic controller.

11. The control device of claim 2, wherein the arc furnace control module is adapted for controlling an electrical power supplied to the arc furnace dependent on the flicker value; and/or wherein the arc furnace control module is adapted for reducing the electrical power supplied to the arc furnace, when the flicker value is higher than a threshold value.

12. The method of claim 7, reducing an electrical power supplied to the arc furnace, when the instantaneous flicker value is higher than a threshold value.

13. The method of claim 7, further comprising: wherein arc furnace voltage and current measurements for controlling the arc furnace are measured between a transformer, which is adapted for transforming a grid voltage into a voltage to be supplied to the arc furnace, and the arc furnace; wherein grid voltage measurements for determining the instantaneous flicker value are performed directly at the grid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

[0046] FIG. 1 schematically shows an arc furnace system according to an embodiment of the invention.

[0047] FIG. 2 shows a flow diagram for a method for controlling an arc furnace according to an embodiment of the invention.

[0048] The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION

[0049] FIG. 1 shows an arc furnace system 10, which may be used for melting scrap metal, and which comprises an arc furnace 12 and its control device 14.

[0050] The arc furnace 12 comprises a vessel 16, which, for example, may be cooled with a cooling device 18. Furthermore, the arc furnace 12 comprises one or more electrodes 20, which may be moved in the vessel 16 with a hydraulic device or electrical drive 22.

[0051] The electrical energy used for heating the interior of the vessel 16, for example for melting the scrap metal, is supplied from a transformer 24 interconnected with a converter 26. The transformer 24 is supplied from an electrical grid 28. In general, it may be that the converter 26 is on the primary or secondary side of the transformer 24.

[0052] For example, the converter 26 may be a rectifier and the arc furnace 12 may be seen as a DC arc furnace. It also may be that the converter 26 is a chopper, a step-down converter or other AC-to-AC converter. In the latter case, the arc furnace 12 may be seen as an AC arc furnace.

[0053] The voltage in the grid may be a medium voltage, such as 5 kV to 80 kV. The transformer 24 may transform this voltage into a low voltage, such as 300 V to 2000 V. The current supplied to the electrode 20 may be between 30 kA and 160 kA.

[0054] The control device 14 comprises a flicker module 30 and an arc furnace control module 32.

[0055] The arc furnace control module 32 is adapted for controlling the arc furnace 12, for example, by controlling the hydraulic device 22, with which the electrode 20 may be moved. By moving the electrode 20, the length of the arc and a resistance may be controlled, which results in a control of the voltage and/or current of the arc furnace 12. Furthermore, the furnace control module 32 may control the converter 26 and/or the cooling device 18.

[0056] The arc furnace control module 32 may comprise several submodules, such as a cooling control module, a converter control module, a communication module, a system monitoring module, an electrode control module, a current control module, etc.

[0057] The furnace control module 32 receives voltage and current measurements 34 from the arc furnace and different kind of flicker values 36a, 36b, 36c from the flicker module 30 and controls the converter 26 and the hydraulic device 22 based on this information. Furthermore, the furnace control module 32 control the cooling device 18 with a control signal 38.

[0058] The flicker module 30 is adapted for determining different kind of flicker values 36a, 36b, 36c based on a flicker in the grid 28 supplying the arc furnace 12. Flicker in the grid 28 may be based on load variations in the grid causing the brightness of the lamp to vary and thus to visible flicker.

[0059] In general, the flicker module 30 receives voltage measurements 40 from the grid 28, for example via the separate transformer 42, and determines the flicker values 36a, 36b, 36c based on these measurements 40.

[0060] The instantaneous flicker value 36c is based on voltage measurements 40 in the grid 28 in an interval of less than 10 s. The short-term flicker value 36a is based on voltage measurements 40 in the grid 28 in an interval of 10 min. The long-term flicker value is based on voltage measurements 40 in the grid 28 in an interval of 2 h. The flicker module 30 directly determines the instantaneous flicker value 36c from the measurements and determines the short-term flicker value 36a and the long-term flicker value by averaging the instantaneous flicker value 36c.

[0061] The arc furnace control module 32 is adapted for controlling the arc furnace 12 based on at least one of the flicker values 36a, 36b, 36c and on the further arc furnace current and voltage measurements 34. In particular, the arc furnace control module 32 is adapted for controlling the electrical power supplied to the arc furnace 12 dependent on at least one of the flicker values 36a, 36b, 36c.

[0062] The arc furnace control module 32 and the flicker module 30 are integrated into one structural component 14, i.e. the control device. For example, the modules 30, 32 may be provided on the same board and/or in the same housing. The arc furnace control module 32 and the flicker module 30 may be software modules executable in the control device. For example, the arc furnace control module 32 and the flicker module 30 may be implemented in one programmable logic controller.

[0063] In other words, a flicker-meter in the form of a flicker module 30 and the arc furnace control module 32 may be implemented within the same computing device 14. In such a way, no additional interface is needed. The instantaneous flicker values 36c may be used instead or additionally to the short-term flicker values 36a and/or the long-term flicker values 36b as control parameter for the arc furnace control module 32. There is no extra communication delay between a separate flicker-meter and the control device 14, which may improve the overall control performance and to reduce flicker generation to the grid 28.

[0064] FIG. 2 shows a flow diagram for a method for controlling an arc furnace 12, which may be performed by the control device 14.

[0065] In step S10, the control device 14 receives grid voltage measurements 40 from the grid 28 and digitizes these measurements, which are supplied to the flicker module 30. The grid voltage measurements 40 may be performed directly at the grid 28.

[0066] In step S12, the flicker module 30 determines the instantaneous flicker value 36c from the grid voltage measurements 40. For example, the flicker module 30 may determine the flicker caused by voltage variations in the grid based on comparing voltage variations with a norm curve. Alternatively or additionally, the flicker module 30 may determine load and voltage changes in the grid 28 and may evaluate these values as described in the standard IEC 61000-4-15.

[0067] From the instantaneous flicker value 36c, the flicker module determines the short-term flicker value 36a and the long-term flicker value 36b by averaging the instantaneous flicker value 36c.

[0068] In step S14, the control device 14 receives voltage and current measurements 34 from the arc furnace 12, and digitizes these measurements, which are supplied to the arc furnace control module 30. The arc furnace voltage and current measurements 34 for controlling the arc furnace 12 may be measured between the transformer 24 or the converter 26 and the arc furnace 12.

[0069] In step S16, the arc furnace control module 32 controls the arc furnace based on voltage and/or current measurements 34, the instantaneous flicker value 36c and/or optionally on the short-term flicker value 36a and/or the long-term flicker value 36b. In particular, an electrical power supplied to the arc furnace 12 may be controlled dependent on the instantaneous flicker value 36c. As already described above, when the instantaneous flicker value 36c is low (for example lower than a threshold value), this indicates a continuous operation of the arc furnace and the power supplied to the arc furnace may be increased. On the other, when the instantaneous flicker value 36c is higher than a threshold value, the electrical power supplied to the arc furnace 12 may be reduced.

[0070] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.