AC Arc Furnace

Abstract

To provide an AC arc furnace capable of dissolving unevenness of a temperature distribution in a furnace and melting scrap in a short time.SOLUTION: An AC arc furnace comprises: plural power fixed electrodes disposed according to respective phases of a three-phase AC; first power supply means that generates arcs between the plural power fixed electrodes and scrap in the furnace so as to supply predetermined power to the scrap; plural power variable electrodes disposed so as to supply power to a low temperature area of molten steel of the scrap; second power supply means that supplies power to the plural power variable electrodes; an image pickup device disposed so as to be able to acquire image data showing a temperature distribution of the molten steel; and a control unit that estimates unevenness of the temperature distribution of the molten steel based on the image data, calculates power to be supplied to the plural power variable electrodes so as to dissolve the unevenness of the temperature distribution of the molten steel and controls the second power supply means so as to output the calculated power.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an AC arc furnace. [Background technology]

[0002] In a typical AC arc furnace, an arc is generated between the scrap inside the furnace and three graphite electrodes connected to the secondary side of the furnace transformer to melt the scrap, and the voltage and current between the graphite electrodes and the scrap are controlled by raising and lowering each of the three electrodes to change the arc length.

[0003] In recent years, AC arc furnaces using inverter devices have been developed and have begun to be used in order to improve the power consumption rate and suppress flicker generation.

[0004] In an AC arc furnace utilizing such an inverter device, the number and arrangement of electrodes are similar to that of a typical AC arc furnace, with three electrodes arranged in a triangle when viewed from the top of the furnace. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 114320 / 1983 [Patent Document 2] Japanese Patent Application Publication No. 8-78156 [Patent Document 3] JP 2014-40965 A [Patent Document 4] JP 2021-139582 A Summary of the Invention [Problem to be solved by the invention]

[0006] In this way, whether it is a general AC arc furnace or an inverter type AC arc furnace, three electrodes are arranged in a triangle when viewed from the top of the furnace, and depending on the arrangement of the electrodes, the temperature distribution of the molten steel in the furnace may become uneven. If the power supply is continued in a state where the temperature distribution of the molten steel in the furnace is uneven, a problem may occur in which the temperature near and around the electrodes becomes high, while the temperature does not rise sufficiently in the area between the electrodes. In an area of ​​the furnace where the temperature becomes high, if a furnace wall is located close to the area, the high temperature may cause deterioration of the furnace wall, which may affect the operation. In an area of ​​the furnace where the temperature is low, the scrap does not melt, and the operation continues for a long time, making it difficult to meet the demand for reducing the power consumption rate.

[0007] Advantageous Effects of Invention An embodiment of the present invention provides an AC arc furnace that reduces unevenness in temperature distribution within the furnace and enables scrap to be melted in a short period of time. [Means for solving the problem]

[0008] An embodiment of the present invention includes a plurality of power fixed electrodes provided for each phase of a three-phase AC, a first power supply means for generating an arc between the plurality of power fixed electrodes and scrap inserted in a furnace to supply a predetermined power to the plurality of power fixed electrodes, a plurality of power variable electrodes arranged to supply power to a region of molten steel formed by melting the scrap, the region having a lower temperature than other regions, a second power supply means for supplying power to the plurality of power variable electrodes, an imaging device provided to acquire image data representing a temperature distribution of the molten steel, and a control device for estimating a bias in the temperature distribution of the molten steel based on the image data, calculating powers to be supplied to the plurality of power variable electrodes so as to eliminate the bias in the temperature distribution of the molten steel, and controlling the second power supply means to output the calculated power. Effect of the Invention

[0009] According to the embodiment, an AC arc furnace is provided that reduces unevenness in temperature distribution within the furnace and enables scrap to be melted in a short period of time. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic block diagram illustrating an AC arc furnace according to a first embodiment. [Diagram 2] FIG. 2 is a schematic block diagram illustrating a converter that is part of an AC arc furnace according to a first embodiment. [Diagram 3] 3(a) and 3(b) are schematic diagrams for explaining the operation of the AC arc furnace according to the first embodiment. [Figure 4] 4(a) and 4(b) are schematic diagrams for explaining the operation of the AC arc furnace according to the first embodiment. [Diagram 5] FIG. 2 is a schematic block diagram illustrating a control device that is a part of the AC arc furnace according to the first embodiment. [Figure 6] FIG. 2 is a schematic graph for explaining the operation of the AC arc furnace according to the first embodiment. [Figure 7] FIG. 6 is a schematic block diagram illustrating an AC arc furnace according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0012] (First embodiment) FIG. 1 is a schematic block diagram illustrating an AC arc furnace according to a first embodiment. As shown in FIG. 1, the AC arc furnace 10 according to this embodiment includes a furnace transformer 14a, a fixed power electrode 16a, a furnace transformer 14b, a converter 20, a variable power electrode 16b, an imaging device 30, and a control device 40.

[0013] The furnace transformer (first power supply means) 14a is connected to the AC bus 1 via a circuit breaker 12a. The furnace transformer 14b is connected to the AC bus 1 via a circuit breaker 12b. The AC bus 1 is a three-phase AC. The furnace transformer 14a supplies the power supplied from the AC bus 1 to three fixed power electrodes 16a. A plurality of taps are provided on the secondary side of the furnace transformer 14a, and a desired voltage is output by switching the taps. The furnace transformer 14a and the fixed power electrodes 16a can be existing arc furnace equipment.

[0014] A converter (second power supply means, first inverter device) 20 including an inverter circuit is connected to the secondary side of the furnace transformer 14b connected to the AC bus 1, and the power supplied from the AC bus 1 is converted to appropriate power by the converter 20 and supplied to the three power variable electrodes 16b. In this example, the furnace transformer 14b adopts a side-extended delta connection for the secondary winding to set the phase of the AC voltage output from the furnace transformer 14b.

[0015] The circuit breakers 12a and 12b are turned on at the same time when melting of scrap is started. The circuit breakers 12a and 12b are turned off when the operation of the AC arc furnace 10 is stopped or when an abnormality or the like occurs in the operation of the AC arc furnace 10.

[0016] The imaging device 30 is disposed so as to acquire image data representing the temperature distribution of the molten steel in which the scrap is melted. The imaging device 30 is disposed, for example, above the furnace 2 and captures an image of the molten steel from above. For example, the imaging device 30 is a camera that measures the temperature of an object to be imaged by infrared rays. The imaging device 30 acquires image data representing the temperature distribution of the molten steel and transmits it to the control device 40.

[0017] The control device 40 is connected to the converter 20 and the imaging device 30. The control device 40 calculates data representing the bias in the temperature distribution of the molten steel in the furnace 2 based on the image data acquired by the imaging device 30. The control device 40 controls the converter 20 based on the calculated data of the bias in the temperature distribution of the molten steel.

[0018] The calculation of the data representing the deviation of the temperature distribution in the control device 40 is performed, for example, by using an existing image processing technique. In one specific example, the calculation is performed as follows.

[0019] The control device 40 processes the acquired image data to generate two-dimensional mesh-like temperature data. The control device 40 calculates an average temperature T0 of a preset area of ​​the two-dimensional mesh temperature data. The preset area is an area that may become hot when power is applied, and does not become a cold spot, which will be described later. The control device 40 calculates an area Scs of an area of ​​the two-dimensional mesh-like temperature data that has a temperature T1 that is α times the average temperature T0 (α is a preset fixed value, 0<α<1). At this time, the temperature T1 may have a certain range, such as T1±ΔT. The control device 40 sets the area Scs at this time as the deviation Tdeb of the temperature distribution of the molten steel (FIGS. 5 and 6). The calculation of the data representing the deviation of the temperature distribution of the molten steel is not limited to this specific example, and other appropriate methods may be used.

[0020] FIG. 2 is a schematic block diagram illustrating a converter that is part of an AC arc furnace according to an embodiment of the present invention. As shown in Fig. 2, the converter 20 has rectifier circuits 22a to 22c and inverter circuits 24a to 24c. The rectifier circuits 22a to 22c are connected to the secondary winding of the furnace transformer 14b. Smoothing capacitors 26a to 26c are connected to the outputs of the rectifier circuits 22a to 22c. The rectifier circuits 22a to 22c and the smoothing capacitors 26a to 26c convert the three-phase AC output from the secondary side of the furnace transformer 14a into DC and output it.

[0021] The inverter circuits 24a to 24c convert the direct currents output from the rectifier circuits 22a to 22c and the smoothing capacitors 26a to 26c into three-phase alternating currents and output the three-phase alternating currents. In this example, for example, three power variable electrodes 16b are connected to the output of the inverter circuit 24a, the output of the inverter circuit 24b, and the output of the inverter circuit 24c, respectively.

[0022] Preferably, as in this example, the inverter circuits 24a to 24c are self-excited conversion circuits. The inverter circuits 24a to 24c are not limited to self-excited conversion circuits, and may be externally excited conversion circuits. By using self-excited conversion circuits, it becomes possible to output a continuously set power according to the deviation of the temperature distribution of the molten steel.

[0023] The distance between the fixed power electrodes 16a and the variable power electrodes 16b and the molten steel is controlled by an electrode lifting device (not shown). The electrode lifting device lifts and lowers the six fixed power electrodes 16a and the six variable power electrodes 16b, for example, based on a speed reference generated by the control device 40, and controls the arc length of each electrode, for example, to achieve a desired impedance.

[0024] The operation of the AC arc furnace 10 according to this embodiment will be described. 3(a) and 3(b) are schematic diagrams for explaining the operation of the AC arc furnace according to the first embodiment. 3(a) and 3(b) show the arrangement of the fixed power electrode 16a and the variable power electrode 16b when the furnace 2 is viewed from above. As shown in Figures 3(a) and 3(b), the power fixed electrodes 16a are disposed at the vertices of an approximately equilateral triangle. The power variable electrodes 16b are disposed between the power fixed electrodes 16a. More specifically, the R'-phase power variable electrode 16b is disposed between the R-phase power fixed electrode 16a and the S-phase power fixed electrode 16a. The S'-phase power variable electrode 16b is disposed between the S-phase power fixed electrode 16a and the T-phase power fixed electrode 16a. The T'-phase power variable electrode 16b is disposed between the T-phase power fixed electrode 16a and the R-phase power fixed electrode 16a.

[0025] The phase voltages of the three-phase AC supplied to the three power fixed electrodes 16a are shifted in phase by 120°. The phase voltages of the three-phase AC rotate from the R phase to the S phase to the T phase, as shown in FIG. 3(a). The phase voltages supplied to the three power variable electrodes 16b are shifted in phase by 120°. In this example, the phase voltages supplied to the three power variable electrodes 16b are shifted in phase by 60° from the phase voltages of the three power fixed electrodes 16a. For example, the phase of the R'-phase voltage and the line current lags behind the phase of the R-phase voltage by 60°, the phase of the S'-phase voltage lags behind the phase of the S-phase voltage by 60°, and the phase of the T'-phase voltage lags behind the phase of the T-phase voltage by 60°. In this example, the phase voltages and the line currents supplied to the three power variable electrodes 16b rotate in phase from the R'-phase to the S'-phase to the T'-phase, as shown in FIG. 3(b).

[0026] The three power variable electrodes 16b are not limited to being arranged in a substantially equilateral triangle between the three fixed power electrodes 16a arranged in a substantially equilateral triangle as described above. The fixed power electrodes 16a and the power variable electrodes 16b are arranged in appropriate positions according to the temperature distribution of the molten steel. The power variable electrodes 16b can be arranged in any appropriate position where they can effectively heat the cold spot of the molten steel, for example.

[0027] 3(a) and 3(b), the directions of phase rotation of the three-phase AC supplied to the three fixed power electrodes 16a and the three variable power electrodes 16b are the same, but this is not limited thereto and the directions of phase rotation may be different. In addition, the arrangement of each phase is not limited to this example, and an appropriate arrangement is selected depending on the configuration of the furnace 2 and the amount and type of scrap charged into the furnace 2.

[0028] FIG. 3(a) shows a schematic state in which no power is supplied to the molten steel by the variable power electrode 16b, and power is supplied to the molten steel from the fixed power electrode 16a. As shown by the dashed circle in FIG. 3(a), heat is transmitted to the molten steel around the fixed power electrode 16a. The further away from the dashed line area in FIG. 3(a), the less heat is transmitted to the molten steel. Heat is less transmitted from either of the fixed power electrodes 16a to the molten steel between the adjacent fixed power electrodes 16a, and the temperature is lower in the area marked "SPOT" in FIG. 3(a) than in other areas. The area marked "SPOT" is an area where the temperature rise due to the power supply of the fixed power electrode 16a is insufficient, and is called a "cold spot." In this example, when there are three fixed power electrodes 16a, three main "cold spots" are formed.

[0029] That is, the three power variable electrodes 16b are disposed at three cold spots formed by the fixed power electrodes 16a. In Fig. 3(b), the transfer of heat to the molten steel when power is supplied to the three power variable electrodes 16b is shown by a broken circle around the power variable electrodes 16b. In the AC arc furnace 10 according to this embodiment, the power variable electrodes 16b supply power to the cold spots, thereby eliminating the cold spots and eliminating the uneven temperature distribution of the molten steel, thereby shortening the melting time of the scrap.

[0030] 4(a) and 4(b) are schematic diagrams for explaining the operation of the AC arc furnace according to the first embodiment. 4(a) and 4(b) show a schematic diagram of the molten steel to which power is supplied by the fixed power electrode 16a and a cold spot (indicated as SPOT in the figure) formed in the molten steel. The imaging device 30 is disposed above the furnace 2 so as to be able to measure the temperature distribution of the molten steel. As shown in Fig. 4(a) and Fig. 4(b), the imaging device 30 acquires data showing the temperature distribution of the molten steel. The imaging device 30 captures an image of the molten steel so as to include an area including the size of the cold spot in the molten steel and an area other than the cold spot that is at a high temperature, and generates image data of the molten steel. In the case of Fig. 4(a), the size of the cold spot in the molten steel is large, and in the case of Fig. 4(b), the size of the cold spot is small. In this example, the larger the cold spot, the greater the deviation in the temperature distribution of the molten steel. In the furnace 2, a furnace lid is installed after the scrap is charged into the furnace body, so that the imaging device 30 that detects infrared rays acquires data on the temperature distribution of the molten steel via the furnace lid.

[0031] The imaging device 30 sequentially captures images of the molten steel and transmits image data representing the temperature distribution of the molten steel to the control device 40. The control device 40 performs image processing on the received image data to calculate the size of the cold spot. The control device 40 supplies power to the cold spot from the power variable electrode 16b so that the deviation Tdeb of the temperature distribution of the molten steel, represented by the size of the cold spot, follows a preset temperature distribution command value Tdeb*. That is, in the AC arc furnace 10 according to this embodiment, when the cold spot is large, the control device 40 determines that the deviation of the temperature distribution of the molten steel is large, and inputs a larger amount of power to the molten steel via the power variable electrode 16b. As a result, in the AC arc furnace 10, the cold spot is reduced or eliminated, and the deviation of the temperature distribution of the molten steel is reduced or eliminated, so that the scrap melting time relative to the input amount of power is shortened.

[0032] FIG. 5 is a schematic block diagram illustrating a control device that is a part of the AC arc furnace according to the present embodiment. 5, the control device 40 has a controller 42. As in this example, the control device 40 may have a limiter 44. The difference between the deviation Tdeb of the temperature distribution of the molten steel calculated based on the image data acquired by the imaging device 30 and a preset temperature distribution command value Tdeb* of the molten steel is input to the controller 42, and the controller 42 outputs the power Pin to be supplied to the molten steel from the power variable electrode 16b. The controller 42 is, for example, a PI controller.

[0033] The limiter 44 sets a maximum power Pmax determined based on the power ratings of equipment such as the furnace transformer 14b and the converter 20. When the controller 42 outputs a power value greater than the set maximum power Pmax, the limiter 44 limits the output of the controller 42 to the maximum power Pmax.

[0034] FIG. 6 is a schematic graph for explaining the operation of the AC arc furnace according to the first embodiment. FIG. 6 shows a schematic example of the relationship between the deviation Tdeb of the temperature distribution of the molten steel and the supplied power Pin. In the graph of FIG. 6, the horizontal axis represents the temperature deviation Tdeb of the molten steel, and the vertical axis represents the power Pin supplied by the power variable electrode 16b.

[0035] As shown in the graph of Fig. 6, the larger the deviation Tdeb of the temperature distribution of the molten steel, the larger the supply power Pin is supplied to the power variable electrode 16b. In this example, when the deviation Tdeb of the temperature distribution of the molten steel exceeds a value Tdeb1, the controller 42 shown in Fig. 5 outputs more than the maximum power Pmax, so that the supply power Pin is limited to the maximum power Pmax.

[0036] When the value of the deviation Tdeb of the temperature distribution of molten steel is in the range of 0 to Tdeb1, the value of the supply power Pin is determined according to a coefficient set in the controller 42. Parameters including the coefficient of the controller 42 are set for each AC arc furnace according to the characteristics of the AC arc furnace.

[0037] The control system shown in Fig. 5 and Fig. 6 is an example, and is not limited thereto. For example, the relationship between the deviation Tdeb of the temperature distribution of the molten steel acquired in advance and the supply power Pin may be made into a table, and the control device 40 may refer to the table and determine the supply power Pin every time it calculates the deviation Tdeb of the temperature distribution. Also, a combination of a plurality of methods may be implemented in the control device 40.

[0038] The effects of the AC arc furnace 10 according to this embodiment will be described. The AC arc furnace 10 according to this embodiment includes a furnace transformer 14b, a converter 20, and a power variable electrode 16b in addition to the furnace transformer 14a and the power fixed electrode 16a. The power variable electrode 16b is placed at the position of a cold spot that occurs when the power fixed electrode 16a is placed in the furnace 2. The presence or absence of a cold spot and its size are determined by image processing of image data acquired by the imaging device 30 by the control device 40. When the cold spot is large, the control device 40 can instruct the converter 20 to supply power from the power variable electrode 16b according to the size of the cold spot. Therefore, the cold spot in the furnace 2 can be made small, and the temperature distribution of the molten steel can be made closer to a desired temperature distribution.

[0039] In the AC arc furnace 10 according to this embodiment, as described above, the cold spots in the furnace 2 can be reduced to bring the molten steel closer to a desired temperature distribution, so that the amount of power input to the molten steel per unit time can be increased sufficiently. Therefore, the scrap can be melted in a short time, and the input energy intensity can be reduced.

[0040] When the fixed power electrodes 16a are arranged in a triangular shape in top view, if power supply to the molten steel is continued by the fixed power electrodes 16a in a state where a cold spot is formed, the temperature of the wall surface of the furnace 2 close to the fixed power electrodes 16a increases, and deterioration is likely to progress. In the AC arc furnace 10 according to this embodiment, the variable power electrodes 16b can be arranged at the position where the cold spot is formed, and power can be supplied to the molten steel so that the cold spot does not become larger. Therefore, it is possible to suppress the temperature rise of the furnace wall, and the life of the furnace 2 can be improved.

[0041] When the converter 20 is a self-excited converter, the power supplied from the power variable electrode 16b to the molten steel can be set continuously according to the size of the cold spot, which makes it possible to finely adjust the power supply to the cold spot, thereby enabling more effective reduction in the energy consumption rate.

[0042] In the AC arc furnace 10 according to this embodiment, power is supplied to the fixed power electrode 16a by the furnace transformer 14a. In other words, this configuration is the configuration of an existing AC arc furnace, and the AC arc furnace 10 according to this embodiment can be obtained by adding the furnace transformer 14b, the converter 20, the variable power electrode 16b, and the imaging device 30 to an existing AC arc furnace. Therefore, it is possible to reuse existing equipment, and it is possible to realize a low-cost, high-performance AC arc furnace 10 in a short installation period.

[0043] In the above description, the number of power variable electrodes 16b is three, and each of the three power variable electrodes 16b is disposed between adjacent power fixed electrodes 16a, but this is not limited thereto. The number of power variable electrodes may be more than three, and may preferably be 3×n (n is an integer greater than 1). For example, the number of power variable electrodes 16b may be six, with two of them disposed between adjacent power fixed electrodes 16a. By providing a large number of power variable electrodes 16b in this manner, the power input to the cold spot can be set more precisely, and the power consumption rate can be further reduced.

[0044] Second Embodiment FIG. 7 is a schematic block diagram illustrating an AC arc furnace according to the second embodiment. The AC arc furnace 210 according to this embodiment includes a furnace transformer 214a and a converter 220 instead of the furnace transformer 14a in the first embodiment. Also, the AC arc furnace 210 according to this embodiment includes a control device 240 instead of the control device 40 in the first embodiment. Other points are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and detailed descriptions thereof are omitted as appropriate.

[0045] As shown in FIG. 7, the AC arc furnace 210 according to this embodiment includes a furnace transformer 214a, a converter 220, a fixed power electrode 16a, a furnace transformer 14b, a converter 20, a variable power electrode 16b, an imaging device 30, and a control device 240.

[0046] The furnace transformer 214a is connected to the AC bus 1 via the circuit breaker 12a. The furnace transformer 214a supplies the power supplied from the AC bus 1 to the three fixed power electrodes 16a. A converter (second inverter device) 220 including an inverter circuit is connected to the secondary side of the furnace transformer 214a, and the power supplied from the AC bus 1 is converted to appropriate power by the converter 220 and supplied to the three fixed power electrodes 16a.

[0047] The converter 220 may have the same configuration as the converter 20. The converter 220 may include, for example, a self-excited inverter circuit as shown in Fig. 2, thereby continuously varying the power supplied to the power fixed electrode 16a. In the case of the converter 220 including a self-excited inverter circuit, the power supplied to the scrap can be finely set, which can contribute to reducing the power consumption rate.

[0048] The control device 240 is connected to the converters 220 and 20 and the imaging device 30. As in the first embodiment, the control device 240 acquires data on the temperature distribution of the furnace 2 based on the image data acquired by the imaging device 30, and controls the converter 20 so as to eliminate bias in the temperature distribution. In addition, the control device 240 sets the power to be supplied to the power fixing electrode 16a for the converter 220, and controls the output of the converter 220.

[0049] In the AC arc furnace 210 according to this embodiment, the power supplied to the fixed power electrode 16a can be driven by a converter 220 using an inverter circuit. This makes it possible to reduce the power consumption rate throughout the entire scrap melting process.

[0050] In this way, it is possible to realize an AC arc furnace that reduces the unevenness of the temperature distribution inside the furnace and enables scrap to be melted in a short period of time.

[0051] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0052] 1 AC busbar, 10,210 AC arc furnace, 12a,12b circuit breaker, 14a,14b,214a furnace transformer, 16a power fixed electrode, 16b power variable electrode, 20,220 converter, 22a-22c rectifier circuit, 24a-24c inverter circuit, 30 imaging device, 40,240 control device

Claims

1. A plurality of power fixing electrodes provided for each phase of a three-phase AC; a first power supply means for generating an arc between the plurality of fixed power electrodes and scrap inserted in a furnace to supply a predetermined power to the plurality of fixed power electrodes; a plurality of power variable electrodes arranged to supply power to a region of the molten steel formed by melting the scrap, the region having a lower temperature than other regions; a second power supply means for supplying power to the plurality of power variable electrodes; an imaging device provided to acquire image data representing a temperature distribution of the molten steel; a control device that estimates a bias in a temperature distribution of the molten steel based on the image data, calculates powers to be supplied to the plurality of power variable electrodes so as to eliminate the bias in the temperature distribution of the molten steel, and controls the second power supply means to output the calculated power; An AC arc furnace equipped with

2. 2. The AC arc furnace according to claim 1, wherein the plurality of variable power electrodes are disposed between adjacent ones of the plurality of fixed power electrodes.

3. 2. An AC arc furnace as claimed in claim 1, wherein said second power supply means includes a first inverter device.

4. 4. An AC arc furnace as claimed in claim 3, wherein said first power supply means includes a second inverter device.

Images