AC arc furnace system

Abstract

This invention provides an AC arc furnace system that can shorten the scrap melting time as an AC arc furnace system without increasing energy consumption, even when there is variation in the height of the scrap to be melted located directly below the three electrodes. [Solution] The AC arc furnace system comprises a furnace body into which metal scrap is loaded, and three electrodes inserted into the furnace body. Three-phase alternating current is supplied to the three electrodes to generate an arc discharge between each electrode and the scrap, thereby melting the scrap. The AC arc furnace system is equipped with a lifting device that allows each electrode to be raised and lowered independently in the vertical direction. During the melting of the scrap, the AC arc furnace system is further equipped with a control device that acquires the height of the scrap to be melted located directly below each of the three electrodes, and changes the distribution of the total current supplied to the three electrodes to each electrode according to the acquired height of the scrap to be melted.

Description

Technical Field

[0002]

[0001] The present disclosure relates to an alternating current arc furnace system that generates an arc discharge between three electrodes inserted into a furnace body and scrap to melt the scrap, and more particularly to an alternating current arc furnace system provided with a lifting device capable of independently lifting and lowering each electrode.

Background Art

[0002] This type of alternating current arc furnace system is disclosed, for example, in Patent Document 1 below. In this system, the arc voltage is determined by the tap voltage set by the tap changer of the furnace transformer. From the arc voltage and the arc current, the impedance value between the scrap and each electrode is calculated, and the lifting device is used to lift and lower each electrode in the vertical direction so that the impedance value becomes a constant value with respect to the accumulated height of the scrap that changes as the melting of the scrap progresses, that is, so that the distance between each electrode and the scrap located directly below each electrode (hereinafter also referred to as "scrap to be melted") becomes constant.

[0003] The arc current used for calculating the impedance value is set by an operator. Here, since the specifications of the three electrodes (mechanical specifications including the drive device and electrical specifications) are common, it is common to set a common (identical) arc current for the three electrodes. In other words, there is no reason to individually set different arc currents for the three electrodes of the same specification.

[0004] Although Patent Document 1 discloses that the progress of melting of the scrap to be melted is determined for each of a plurality of electrodes and the change from the parameter for the variable state to the parameter for the stable state is independently performed, it does not disclose setting different arc currents for each electrode.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] By the way, the point at which scrap melting is complete in an AC arc furnace system is when the melting of all the scrap directly beneath the three electrodes is complete.

[0007] Here, scrap is randomly fed into the furnace body, and since the size and shape of the scrap itself are not uniform and vary, variations in the height of the scrap charged into the furnace body are unavoidable. When a common arc current is set for the three electrodes, the variation in the height of the scrap to be melted located directly below each electrode affects the melting completion time of the AC arc furnace system. That is, the height of the scrap to be melted located directly below one of the electrodes will inevitably be higher, so the melting completion time of the scrap directly below that electrode will be later than the melting completion time of the scrap directly below the other electrodes, and as a result, the melting time of the AC arc furnace system will be longer. On the other hand, it is conceivable to increase the arc current supplied to each electrode in order to shorten the melting time of the AC arc furnace system, but this is undesirable from an energy conservation standpoint because it increases the energy consumption required to melt the scrap.

[0008] Therefore, the present disclosure aims to provide an AC arc furnace system that can shorten the scrap melting time as an AC arc furnace system without increasing energy consumption, even when there is variation in the height of the scrap to be melted located directly below the three electrodes. [Means for solving the problem]

[0009] The first aspect of this disclosure relates to an AC arc furnace system comprising a furnace body into which metal scrap is charged, and three electrodes inserted into the furnace body, wherein three-phase alternating current is supplied to the three electrodes to generate an arc discharge between each electrode and the scrap, thereby melting the scrap. The AC arc furnace system includes a lifting device that allows each electrode to be raised and lowered independently in the vertical direction. The AC arc furnace system further includes a control device that, during the melting of the scrap, obtains the height of the scrap to be melted located directly below each of the three electrodes, and changes the distribution of the total current supplied to the three electrodes to each electrode according to the obtained height of the scrap to be melted.

[0010] The second aspect, in addition to the first aspect, has the following further characteristics: The electrode with the highest height of the scrap to be dissolved is designated as the first electrode, the electrode with the lowest height of the scrap to be dissolved is designated as the second electrode, and the electrode with the intermediate height of the scrap to be dissolved is designated as the third electrode. The control device is configured to supply a reference arc current obtained by dividing the total current value into three equal parts to the third electrode, to supply an arc current obtained by adding a predetermined correction current to the reference arc current to the first electrode, and to supply an arc current obtained by subtracting the above correction current from the reference arc current to the third electrode.

[0011] The third perspective, in addition to the second perspective, further includes the following features: The AC arc furnace system is further equipped with a learning device that acquires operational data of the AC arc furnace system and uses machine learning to calculate the correction current based on the acquired operational data.

[0012] The fourth perspective, in addition to the third perspective, has the following further characteristics: The correction current is expressed as the product of the height of the scrap to be dissolved and a coefficient, the coefficient being expressed as a function of the height of the scrap to be dissolved. The learning device is configured to machine-learn the coefficient based on operational data. [Effects of the Invention]

[0013] According to this disclosure, instead of applying a common arc current to the three electrodes, a configuration is adopted in which the distribution of the total current value to each electrode is changed according to the height of the scrap to be melted located directly beneath each electrode. The first electrode, where the height of the scrap to be melted is highest, is supplied with an arc current obtained by adding a correction current to a reference arc current obtained by dividing the total current value into three equal parts, thereby increasing the melting rate of the scrap located directly beneath the first electrode. On the other hand, the second electrode, where the height of the scrap to be melted is lowest, is supplied with an arc current obtained by subtracting the above correction current from the reference arc current, thereby slowing down the melting rate of the scrap located directly beneath the second electrode. In this way, by dynamically changing the arc current applied to the three electrodes according to the height of the scrap to be melted during the melting of the scrap, it is possible to proceed with melting while reducing variations in the height of the scrap, and as a result, the melting time of the scrap can be shortened. Moreover, since only the distribution of the total current value is changed and the total current value itself does not increase, the amount of energy required for melting the scrap does not increase. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing an example configuration of an AC arc furnace system according to Embodiment 1. [Figure 2] This is a phase diagram showing the variation in the height of the scrap located directly beneath the three electrodes. [Figure 3] This is a phase diagram showing the abrupt change in the distance between the electrode and the scrap due to scrap decay. [Figure 4] This is a schematic diagram showing an example configuration of an AC arc furnace system with added machine learning capabilities. [Modes for carrying out the invention]

[0015] The AC arc furnace system according to the embodiments of this disclosure will be described below with reference to the drawings. Common or corresponding elements in each drawing are denoted by the same reference numerals, and their descriptions are simplified or omitted. Furthermore, since each drawing is schematic or conceptual, the relationship between the thickness and width of each part, the ratio of the sizes of the parts, etc., are not necessarily the same as those of actual structures.

[0016] Figure 1 is a schematic diagram showing an example of the configuration of an AC arc furnace system 1 according to an embodiment. The AC arc furnace system 1 is one of the electric furnaces used as a metal melting apparatus. The AC arc furnace system 1 comprises a furnace body 2 into which metal (e.g., iron) scrap Sc is charged, three electrodes 31, 32, and 33 charged inside the furnace body 2, a furnace transformer (also called a "higher-level transformer") 4, a current transformer 5, a secondary transformer 6, a control device 7 having a programmable logic controller (hereinafter referred to as "PLC") 70, AC motors 81, 82, and 83, motor drive units 91, 92, and 93, and an operator's room 20 where an operator resides.

[0017] The PLC 70 implemented in the control device 7 includes an impedance calculation unit 71, a main control unit 72, and an electrode position measurement unit 73.

[0018] The three electrodes 31, 32, and 33 are positioned at the vertices of a triangle in a plan view. Each electrode 31, 32, and 33 has the same shape and is made of, for example, carbon. Three-phase alternating current is supplied to each electrode 31, 32, and 33 from a furnace transformer 4, which serves as an AC power source. An AC voltage (tap voltage) set by a tap changer (not shown) of the furnace transformer 4 is applied to each electrode 31, 32, and 33.

[0019] The current transformer 5 is installed on the secondary side of the furnace transformer 4, measures the arc current Iarc, and outputs the measured arc current value Iarc to the impedance calculation unit 71 and the main control unit 72.

[0020] The secondary transformer 6 is provided on the secondary side of the furnace transformer 4, measures the arc voltage Varc, and outputs the measured arc voltage Varc to the impedance calculation unit 71 and the main control unit 72.

[0021] The impedance calculation unit 71 calculates the impedance values between each of the electrodes 31, 32, 33 and the scrap Sc from the arc current Iarc and the arc voltage Varc, and outputs the impedance values to the main control unit 72.

[0022] The main control unit 72 generates operation commands and speed commands so that the calculated impedance values become constant values, and outputs the generated operation commands and speed commands to the motor drive devices 91, 92, 93. The speed commands are for controlling the vertical positions of the electrodes 31, 32, 33, and are generated individually for each of the electrodes 31, 32, 33.

[0023] The motor drive devices 91, 92, 93 control the rotational speed and rotational direction of the AC motors 81, 82, 83 based on the operation commands and speed commands from the drive conversion device operation control unit 73. As a result, each of the electrodes 31, 32, 33 is moved up and down in the vertical direction, and the distance between each of the electrodes 31, 32, 33 and the scrap Sc is maintained at a constant distance appropriate for arc discharge generation. The AC motors 81, 82, 83 and the motor drive devices 91, 92, 93 correspond to the "lifting device" in the claims.

[0024] Speed sensors (not shown) for measuring the rotational speed are respectively attached to the AC motors 81, 82, 83, and the rotational speeds FBK1, FBK2, FBK3 of the AC motors 81, 82, 83 measured by each speed sensor are input to the electrode position measuring unit 73 via the motor drive devices 91, 92, 93. The rotational speeds FBK1, FBK2, FBK3 are, for example, pulse signals.

[0025] The electrode position measuring unit 73 calculates the payout length of the wire rope connected to each electrode 31, 32, and 33 by integrating the rotation speeds FBK1, FBK2, and FBK3. From the calculated payout lengths, it calculates the height of each electrode 31, 32, and 33 and outputs it to the main control unit 72. Here, as described above, the distance between each electrode 31, 32, and 33 and the scrap Sc is kept constant based on the impedance value. Therefore, the main control unit 72 can calculate the height of the scrap Sc located directly below each electrode 31, 32, and 33 from the height of each electrode 31, 32, and 33.

[0026] Here, the arc current setting device 21 in the operator's cab 20 sets the target value of the arc current (hereinafter also called the "arc current setting value") Icom by the operator's operation and outputs the arc current setting value Icom to the main control unit 72. The arc current setting value Icom is a value obtained by dividing the total current value Itotal, which will be described later, into three equal parts. Conventionally, the arc current setting value Icom was set for each of the three electrodes 31, 32, and 33. The arc current setting value Icom is set as a static target value and does not change during operation unless manually changed by the operator, and the arc current flowing through each electrode 31, 32, and 33 is controlled so that there are no individual differences.

[0027] Figure 2 is a phase diagram showing the variation in the height of scrap located directly below the three electrodes 31, 32, and 33. As mentioned above, the scrap Sc is randomly fed into the furnace body 2, and the size of the scrap Sc itself is not uniform. Therefore, as shown in Figure 2, there is variation in the stacking height (hereinafter simply referred to as "height") of the scrap Sc charged into the furnace body 2. In the example shown in Figure 2, with respect to the height H0 of the furnace bottom 2a of the furnace body 2, the height H1 of the scrap Sc located directly below electrode 31 is the highest, the height H2 of the scrap Sc located directly below electrode 32 is the lowest, and the height H3 of the scrap Sc located directly below electrode 33 is somewhere in between.

[0028] When current is applied to each electrode 31, 32, and 33 in the state shown in Figure 2, an arc discharge occurs between each electrode 31, 32, and 33 and the scrap Sc, and the melting of the scrap Sc begins due to the heat of the arc. Here, when a common power is applied to each electrode 31, 32, and 33, it is assumed that the melting capacity of each electrode 31, 32, and 33 is the same. Therefore, it is predicted that the time required for melting to be completed will be longest for electrode 31, which has the highest height of the strap located directly below each electrode 31, 32, and 33 (hereinafter also referred to as the "strap to be melted"). The voltage value, which is one of the factors that determine the power, is a constant value uniquely determined by the tap position of the upper transformer 4. On the other hand, the current value, which is another factor, is arbitrarily set by the arc current setting device (external device) 21 by manual operation by the operator in the control room 20, but normally, rather than setting different values ​​individually for each electrode 31, 32, and 33, it is common to set a common value for all three electrodes 31, 32, and 33. Therefore, the time at which dissolution is completed will differ depending on the amount of scrap Sc that is directly dissolved by each electrode 31, 32, and 33.

[0029] When scrap Sc is piled up in a mound and the melting process proceeds with large differences in the height of the scrap Sc, the area of ​​unmelted scrap in contact with the melted and liquefied scrap Sc decreases. As a result, the heat conduction efficiency due to residual heat decreases, and the time required for the AC arc furnace system 1 to complete the melting process increases.

[0030] Furthermore, as shown in Figure 3, if there is a large step in the stacked scrap Sc, continuing the melting process makes it easier for the unmelted scrap Sca to collapse to a lower position, a phenomenon known as scrap collapse. When scrap collapse occurs, in the example shown in Figure 3, the distance H2 between the electrode 32 and the scrap Sc changes rapidly, overcurrent is detected, and consequently, operational losses such as a rapid rise in the electrode 32 are likely to occur.

[0031] Therefore, in order to ensure stable melting progress throughout the AC arc furnace system 1 and shorten the melting time, reducing variations in the height of the piled-up scrap Sc and averaging the pile height as much as possible will improve the heat transfer efficiency from the melted and liquefied scrap Sc, which will help to suppress the number of scrap collapses.

[0032] Since the method of charging scrap Sc into the furnace body 2 cannot be changed due to the machine's mechanism, variations in the stacking height of scrap Sc at the start of melting are unavoidable. Therefore, by controlling the process so that the difference in the height of the scrap to be melted at each electrode 31, 32, and 33 decreases as melting progresses, it is possible to equalize the height of the scrap Sc, thereby shortening the melting time of the scrap Sc and improving the melting efficiency.

[0033] In this embodiment, the main control unit 72 dynamically changes the setting of the arc current flowing through the three electrodes 31, 32, and 33 according to the height of the scrap to be melted. In the state shown in Figure 2, the arc current flowing through electrode 31, where the scrap to be melted is highest, is set to be greater than the arc currents flowing through the other electrodes 32 and 33. This allows the power supplied to electrode 31 to be greater than the power supplied to electrodes 32 and 33, thereby increasing the melting capacity per unit time of the scrap directly below electrode 31.

[0034] In this case, if a large current is passed only to a specific electrode 31, the power consumption of the furnace transformer 4 increases, leading to increased energy consumption, which is undesirable from an energy conservation standpoint. Furthermore, there is a risk of overloading the furnace transformer 4.

[0035] If the arc current setting value set by the arc current setting device 21 in the operator's cab 20 is denoted as Icom, then the sum of the arc currents flowing through the three electrodes 31, 32, and 33 (hereinafter also referred to as the "total current value") Itotal is expressed as shown in equation (1) below when a common arc current flows through each electrode 31, 32, and 33. That is, the arc current setting value Icom is obtained by dividing the total current value Itotal into three equal parts. The arc current setting value Icom corresponds to the "reference arc current" in the claims. Total = 3 × Icom (1)

[0036] The total current value Itotal, expressed in equation (1) above, represents the upper limit of the current that can be supplied from the furnace transformer 4, according to the setting in the arc current setting device 21.

[0037] In this embodiment, in order to reduce the variation (difference) in the height of the scrap Sc without increasing the total current value Itotal supplied from the furnace transformer 4, the arc current of the other electrodes 32 is reduced by the amount by which the arc current of a specific electrode 31 is increased. In the state shown in Figure 2, the relative heights H1, H2, and H3 of the scrap to be melted below electrodes 31, 32, and 33 are expressed as shown in (2) below. H1 > H3 > H2...(2)

[0038] If the arc currents flowing through electrodes 31, 32, and 33 are Iarc1, Iarc2, and Iarc3 respectively, then equation (3) below can be obtained from the conditions in equation (1) above. Itotal=Iarc1+Iarc2+Iarc3=3×Icom...(3)

[0039] Since the largest current needs to be applied to electrode 31, which has the highest height of scrap to be melted, the relationship between arc currents Iarc1, Iarc2, and Iarc3 can be expressed as shown in (4) below, similar to the relationship (2) above. Iarc1 > Iarc3 > Iarc2 ... (4)

[0040] The arc currents Iarc1, Iarc2, and Iarc3 flowing through electrodes 31, 32, and 33 are determined by adding a correction current Icor, which is determined by the height of the scrap to be melted, to a common arc current setting value Icom set by the arc current setting device 21. The current setting for each electrode 31, 32, and 33 is expressed by the following equation (5). In the following equation (5), i is the electrode number. For example, the electrode number of electrode 31 is 1, the electrode number of electrode 32 is 2, and the electrode number of electrode 33 is 3. Iarc(i) = Icom + Icor(i) ... (5)

[0041] The correction current Icor in equation (5) above changes depending on the height of the scrap to be dissolved, and is expressed as shown in equation (6) below. Icor(i) = K × DH···(6)

[0042] In equation (6) above, K is a positive coefficient. Also, DH is the height from the reference position Hbase and is expressed by equation (7) below. Note that the reference position Hbase is not limited to this and may be set as appropriate. Hbase=(Hmax-Hmin) / 2+Hmin...(7)

[0043] In equation (7) above, Hmax is the maximum height of the strap to be dissolved, and Hmin is the minimum height of the strap to be dissolved. Applying equation (7) above to the state shown in Figure 2, it is expressed as equation (8) below.

[0044] Hbase = (H1 - H2) / 2 + H2 ... (8)

[0045] Furthermore, from equation (7) above, DH(i) in equation (6) above can be expressed as in equation (9) below.

[0046] DH(i) = H(i) - Hbase···(9)

[0047] From equation (9) above, if the amount of scrap to be melted at each electrode 31, 32, and 33 is high relative to the reference position Hbase, DH(i) > 0, and the correction current Icor is added to the arc current setting value Icom. Conversely, if the stacking position of the scrap to be melted at each electrode is low, DH(i) < 0, and the correction current Icor is reduced from the arc current setting value Icom. As a result, the sum of the arc currents of the three electrodes 31, 32, and 33 does not increase compared to the conventional case where the sum is the same and fixed value, and it is possible to dynamically set the current according to the stacking state of the scrap Sc.

[0048] Furthermore, as shown in Figure 3, if clap collapse occurs and a rapid increase in the measured arc current is detected, the polarity of the coefficient K is changed from a positive value to a negative value, thereby rapidly decreasing the arc current reference value of electrode 32 from the common current setting value. This makes it possible to quickly raise electrode 32 to prevent overcurrent detection due to a rapid shortening of the distance between electrode 32 and scrap Sc.

[0049] The coefficient K in equation (6) above is the weighting coefficient of the correction current Icor, which corresponds to the height of the scrap to be dissolved. Therefore, the coefficient K can be expressed as a function of the height H of the scrap to be dissolved, as shown in equation (10) below.

[0050] K=f(H)···(10)

[0051] The coefficient K is a setting value used to compensate for the difference in dissolution progress between electrodes 31, 32, and 33. A larger value for coefficient K shortens the time required to reduce the difference in dissolution progress between electrodes 31, 32, and 33, but also increases the likelihood of arc current fluctuations. Conversely, a smaller value for coefficient K reduces the likelihood of arc current fluctuations, but lengthens the time required to reduce the difference in dissolution progress between electrodes 31, 32, and 33, making the effect of the correction current Icor less pronounced.

[0052] The coefficient K can be set by approximating a linear relationship where the amount of scrap Sc dissolved per unit time is proportional to the arc current flowing from electrodes 31, 32, and 33. By continuing to collect actual data (operational data) while operating the AC arc furnace system 1, it becomes possible to obtain the optimal correction current Icor and coefficient K value according to the trends in the actual data that have been identified.

[0053] Figure 4 is a schematic diagram showing an example of the configuration of an AC arc furnace system 1 with added machine learning capabilities. As shown in Figure 4, the AC arc furnace system 1 is further equipped with a data storage and learning device 22 in the operator's chamber 20.

[0054] The data storage and learning device 22 collects time-series data from the aforementioned performance data, including the coefficient K, the positions of each electrode 31, 32, and 33 as they dissolve, the arc voltage Varc, and the arc currents Iarc1, Iarc2, and Iarc3.

[0055] When the coefficient K in equation (6) above is linearly approximated as a function of the height H of the scrap to be melted, the data storage and learning device 22 performs machine learning on the collected time-series data and applies a simple perceptron algorithm to store data on the relationship between the set value and the melting time, thereby further refining the condition judgment and enabling the calculation of the optimal value of K. The set value includes not only the coefficient K but also the arc currents Iarc1, Iarc2, and Iarc3.

[0056] As explained above, according to this embodiment, instead of applying a common (identical) arc current setting value Icom to the three electrodes 31, 32, and 33, the distribution of the total current value Itotal to each electrode 31, 32, and 33 is changed according to the height of the scrap to be melted located directly below each electrode 31, 32, and 33. For the first electrode 31, where the height of the scrap to be melted is highest, an arc current is applied that is obtained by adding a correction current Icor to the arc current setting value Icom, which is obtained by dividing the total current value Itotal into three equal parts, thereby accelerating the melting rate of the scrap to be melted located directly below the first electrode 31 (promoting melting). On the other hand, for the second electrode 32, where the height of the scrap to be melted is lowest, an arc current is applied that is obtained by subtracting the above correction current Icor from the arc current setting value Icom, thereby slowing down the melting of the scrap to be melted located directly below the second electrode 32. In this way, by dynamically changing the arc current flowing through the three electrodes according to the height of the scrap being melted during the melting process, variations in scrap height can be reduced while the melting process progresses, and as a result, the melting time of the scrap can be shortened. Moreover, since the total current value itself does not increase as long as the distribution of the total current value is changed, the energy consumption required for melting the scrap does not increase.

[0057] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and can be implemented in various modified forms without departing from the spirit of the present disclosure. In the above embodiments, the data storage and learning device 22 is provided outside the control device 7 (for example, in the driver's cab 20), but it may also be provided in the control device 7. However, considering the computational load of the control device 7, it is preferable to provide it outside the control device 7.

[0058] Furthermore, although the above embodiment was described using the case where the coefficient K is linearly approximated as an example, it is not limited to this. While it is thought that a certain degree of accuracy of the coefficient K can be achieved by linear approximation, the types of scrap Sc charged into the furnace body 2 (material, size, etc.) vary, and strictly speaking, the coefficient K is affected by various combinations of factors such as the type of scrap Sc, the arc voltage Varc, and the arc current setting value Icom set by the operator, leaving the possibility that it cannot be uniquely determined by a simple linear coefficient (constant) K.

[0059] Therefore, in order to further improve the accuracy of machine learning by the data storage and learning device 22, a multilayer perceptron algorithm may be applied to generate a function f from multiple condition factors, thereby enhancing the data storage and learning device 22 to be able to handle more complex nonlinear problems. Furthermore, instead of keeping the coefficient K constant during operation, the input power applied to electrodes 31, 32, and 33 and the height of the scrap to be melted as the progress of the melting of the scrap Sc are constantly observed, and the power allocated to each electrode 31, 32, and 33, i.e., the arc current ratio (the ratio of arc currents Iarc1, Iarc2, and Iarc3), is dynamically changed, thereby further improving energy efficiency.

[0060] Furthermore, when the number of elements, quantities, amounts, ranges, etc., are mentioned in the embodiments described above, the invention is not limited to the number mentioned unless it is specifically stated or clearly defined in principle. Also, the structures, etc., described in the embodiments described above are not necessarily essential to the invention unless they are specifically stated or clearly defined in principle. [Explanation of Symbols]

[0061] 1…AC arc furnace system, 2…furnace body, 31,32,33…electrodes, 4…furnace transformer (AC power supply), 5…current transformer, 6…secondary transformer, 7…control device, 70…PLC, 71…impedance calculation unit, 72…main control unit, 73…electrode position measurement unit, 81,82,83…AC motor (lifting device), 91,92,93…motor drive device (lifting device), Sc…scrap

Claims

1. An AC arc furnace system comprising a furnace body into which metal scrap is loaded, and three electrodes inserted inside the furnace body, wherein three-phase alternating current is supplied to the three electrodes to generate an arc discharge between each electrode and the scrap, thereby melting the scrap, In a device equipped with a lifting mechanism that allows each electrode to be raised and lowered independently in the vertical direction, An AC arc furnace system further comprising a control device that, during the melting of the scrap, acquires the height of the scrap to be melted located directly below each of the three electrodes, and changes the distribution of the total current supplied to each of the three electrodes according to the acquired height of the scrap to be melted.

2. In the AC arc furnace system according to claim 1, The electrode with the highest height of the scrap to be dissolved is designated as the first electrode, the electrode with the lowest height of the scrap to be dissolved is designated as the second electrode, and the electrode with an intermediate height of the scrap to be dissolved is designated as the third electrode. The control device is A reference arc current obtained by dividing the aforementioned total current value into three equal parts is supplied to the third electrode, The first electrode is supplied with an arc current obtained by adding a predetermined correction current to the reference arc current. The arc current obtained by subtracting the correction current from the reference arc current is supplied to the third electrode, An AC arc furnace system configured to perform the following.

3. In the AC arc furnace system according to claim 2, An AC arc furnace system further comprising a learning device that acquires operational data of the AC arc furnace system and performs machine learning on the acquired operational data to determine the correction current.

4. In the AC arc furnace system according to claim 3, The correction current is expressed as the product of the height of the scrap to be dissolved and a coefficient, and the coefficient is expressed as a function of the height of the scrap to be dissolved. The learning device is an AC arc furnace system configured to learn the coefficients based on the operational data.

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