JP6910741B2 - Electrode lifting device for arc furnace - Google Patents

Description

An embodiment of the present invention relates to an arc furnace electrode elevating device for a rope-making arc furnace that melts scrap by generating an arc discharge between the electrode and scrap.

In a steelmaking arc furnace, the electrodes for performing arc discharge are automatically raised and lowered by the arc furnace electrode elevating device to control the distance between the electrodes and scrap to be constant, and stable arc discharge. (For example, Patent Document 1).

The electrode elevating device for an arc furnace, for example, obtains the deviation between the detected value of the impedance of the arc discharge and the preset value, and uses this deviation so that the detected value of the impedance follows the set value. Control the ascent and descent. As a result, the distance between the electrode and the scrap can be controlled to be constant.

Further, in such an electrode elevating device for an arc furnace, the sensitivity of the electrode elevating drive and the dead zone are set. As a result, it is possible to suppress the sensitive ascending / descending motion of the electrodes. For example, it is possible to prevent the electrodes from being too far apart from each other and causing arc breakage.

The sensitivity and dead zone are set by manually selecting from fixed values set in advance in several patterns. However, the sensitivity and dead zone need to be changed according to the situation in the arc furnace. Therefore, in the configuration set by manual selection, a value that is not optimal for the situation inside the arc furnace may be set. In addition, it may take time to change the settings.

Japanese Unexamined Patent Publication No. 10-335508

An embodiment of the present invention provides an electrode elevating device for an arc furnace, which can easily and surely set the sensitivity and dead zone of the electrode elevating operation.

The electrode elevating device for an arc furnace according to the embodiment is used in an arc furnace for steelmaking, is connected to a drive device for elevating and lowering an electrode for performing arc discharge, and is for an arc furnace that controls the elevating and lowering of the electrode by the drive device. In the electrode elevating device, a current-voltage detector that detects the measured current value of the current supplied to the electrode and detects the measured current value of the voltage applied to the electrode, and a reference of the current supplied to the electrode. It is obtained from the current measured value and the voltage measured value, as well as the current / voltage setting unit that enables the setting of the current set value to be used and the reference voltage set value of the voltage applied to the electrode. Based on the impedance deviation calculation unit that calculates the impedance deviation between the measured impedance of the arc discharge, the current set value, and the set impedance of the arc discharge obtained from the voltage set value, and the measured impedance. A constant impedance control unit that generates a control signal for controlling the drive device so as to follow the set impedance, and a furnace condition determination unit that determines the status inside the steelmaking arc furnace based on the impedance deviation. Based on the determination result of the situation in the steel arc furnace, the sensitivity dead zone automatic setting unit that automatically sets the sensitivity and dead zone of the ascending / descending drive of the electrode, the control signal, and the set sensitivity and dead zone. Based on the above, the arc furnace electrode elevating device includes a command value generating unit that generates a command value to be input to the driving device and inputs the generated command value to the driving device.

Provided is an electrode elevating device for an arc furnace, which can easily and surely set the sensitivity and dead zone of the electrode elevating operation.

It is a block diagram which shows typically the electrode elevating apparatus for an arc furnace which concerns on embodiment. It is a graph which shows an example of the operation of the command value generation part schematically. It is a table which shows an example of the operation of the furnace condition determination part typically. It is a table which shows an example of the operation of the sensitivity dead zone automatic setting part typically. It is a flowchart which shows typically an example of the operation of the electrode elevating apparatus for an arc furnace which concerns on embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same parts are represented, the dimensions and ratios may be different from each other depending on the drawings.
In the specification of the present application and each of the drawings, the same elements as those described above with respect to the above-described drawings are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically showing an electrode elevating device for an arc furnace according to an embodiment.
As shown in FIG. 1, the electrode elevating device 10 for an arc furnace includes a current transformer 12, a transformer 14, and a main control device 16.

The arc furnace electrode elevating device 10 is used in the steelmaking arc furnace 2. The steelmaking arc furnace 2 is, for example, a three-phase AC arc furnace. However, the steelmaking arc furnace 2 is not limited to the three-phase AC arc furnace, and may be a DC arc furnace or the like. Hereinafter, the steelmaking arc furnace 2 will be described as a three-phase AC arc furnace.

The steelmaking arc furnace 2 includes a furnace body 3 and an electrode 4. The furnace body 3 can be charged with scrap 5. The electrode 4 is arranged above the furnace body 3. The electrode 4 is connected to the drive device 6 and is moved up and down by the drive device 6. Further, the electrode 4 is connected to the secondary side of the furnace transformer 7. The primary side of the furnace transformer 7 is connected to a three-phase AC power supply (not shown). As a result, a current is supplied to the electrode 4 via the transformer for the furnace 7.

The drive device 6 may be an electric type including a motor, an inverter, or the like, or may be a hydraulic type including a hydraulic cylinder, a motor, or the like. The configuration of the drive device 6 may be any configuration in which the electrode 4 can be raised and lowered.

In the steelmaking arc furnace 2, the electrodes 4 are arranged above the scrap 5 so as to be separated from each other. Then, an electric current is supplied to the electrode 4 to generate an arc discharge between the electrode 4 and the scrap 5, so that the scrap 5 charged into the furnace body 3 is melted by the heat of the discharge. As a result, steelmaking is performed by the steelmaking arc furnace 2.

Although not shown in FIG. 1, in a three-phase AC arc furnace, three electrodes 4 corresponding to each phase of the three-phase AC are provided. The drive device 6 raises and lowers each of the three electrodes 4 individually, for example. The operation of the three electrodes 4 in each phase is substantially the same. Therefore, in the following, only the operation of one electrode 4 of one phase will be described.

The current transformer 12 is magnetically coupled to the secondary side of the furnace transformer 7. As a result, the current transformer 12 detects the current supplied to the electrode 4. The current supplied to the electrode 4 is, in other words, the arc current of the arc discharge between the electrode 4 and the scrap 5. The current transformer 12 is connected to the main control device 16. _{The current transformer 12 inputs the measured current value I 1} of the current supplied to the electrode 4 to the main control device 16. The current transformer 12 actually _{detects the measured current value I 1} of each phase, _{and inputs the measured current value I 1} of each phase to the main control device 16. The current supplied to the electrode 4 is not limited to the current transformer 12, and may be any current detector capable of detecting the current supplied to the electrode 4.

The primary side of the transformer 14 is connected to the secondary side of the furnace transformer 7. As a result, the transformer 14 detects the voltage applied to the electrode 4. More specifically, the transformer 14 detects the voltage applied between the electrode 4 and the scrap 5. The voltage applied to the electrode 4 is, in other words, the arc voltage of the arc discharge between the electrode 4 and the scrap 5. The secondary side of the transformer 14 is connected to the main control device 16. Transformer 14 inputs the voltage measured value V ₁ of the voltage applied to the electrode 4 to the master controller unit 16. The transformer 14 actually _{detects the measured voltage value V 1} of each phase _{and inputs the measured voltage V 1} of each phase to the main control device 16. The voltage applied to the electrode 4 is not limited to the transformer 14, and any voltage detector capable of detecting the voltage applied to the electrode 4 may be used.

The main control device 16 calculates the impedance of the arc discharge between the electrode 4 and the scrap 5 based on the input current measured value I ₁ and the voltage measured value V _1. Then, the main control device 16 generates a command value for controlling the elevation of the electrode 4 by the drive device 6 based on the calculated impedance, and inputs the generated command value to the drive device 6. For example, the main control device 16 generates a speed reference signal representing the ascending / descending speed of the electrode 4 as a command value and inputs it to the drive device 6. The drive device 6 raises and lowers the electrode 4 so as to have a speed corresponding to the input speed reference signal. As described above, the arc furnace electrode elevating device 10 is used in the steelmaking arc furnace 2 and is connected to the drive device 6 that elevates and elevates the electrode 4 for performing arc discharge, and controls the elevating and lowering of the electrode 4 by the drive device 6. do.

The main controller 16 generates, for example, a speed reference signal so that the impedance is substantially constant. In other words, the main controller 16 generates a speed reference signal so that the distance between the electrode 4 and the scrap 5 is substantially constant. The main control device 16 controls the raising and lowering operation of the electrode 4 by the driving device 6 so that the distance between the electrode 4 and the scrap 5 is substantially constant. As a result, it is possible to suppress the occurrence of arc breakage and overcurrent state between the electrode 4 and the scrap 5, and perform stable arc discharge.

The command value generated by the main control device 16 is not limited to the speed reference signal, but is an arbitrary command value capable of controlling the impedance (distance between the electrode 4 and the scrap 5) substantially constantly. good. The command value may be appropriately set according to, for example, the configuration of the drive device 6.

The main control device 16 includes a current / voltage detection unit 31, a current / voltage setting unit 32, an impedance deviation calculation unit 33, an impedance constant control unit 34, a furnace condition determination unit 35, a sensitivity dead zone automatic setting unit 36, and a command. It has a value generation unit 37 and.

The current-voltage detection unit 31 detects the measured current value I _{1 based on the input from the current transformer 12, and also detects the measured voltage V 1} based on the input from the transformer 14.

_{The current-voltage setting unit 32 enables the setting of the current setting value I 2} which is the reference of the current supplied to _{the electrode 4, and also sets the voltage setting value V 2} which is the reference of the voltage applied to the electrode 4. to enable. The current / voltage setting unit 32 has, for example, an operation unit that accepts a manual operation by an operator or the like, _{and sets the current setting value I 2} and the voltage setting value V ₂ according to the operation of the operation unit. In other words, the current / voltage setting unit 32 sets the current value and the voltage value input by the operation of the operation unit as the current set value I ₂ and the voltage set value V ₂ , respectively.

The configuration of the current / voltage setting unit 32 is not limited to the configuration in which the _{current set value I 2} and the voltage set value V _{2 are set by manual operation.} The current / voltage setting unit 32 may be connected to an external device via a network or the like, _{and may set the current set value I 2} and the voltage set value V ₂ based on the input from the external device.

The impedance deviation calculation unit 33 is connected to the current / voltage detection unit 31 and the current / voltage setting unit 32. The current / voltage detection unit 31 _{inputs the detected current actual measurement value I 1} and the voltage actual measurement value V ₁ to the impedance deviation calculation unit 33. The current / voltage setting unit 32 _{inputs the set current set value I 2} and the voltage set value V ₂ to the impedance deviation calculation unit 33.

The impedance deviation calculation unit 33 calculates the impedance deviation Z _{D from the input current measured value I 1} , the voltage measured value V ₁ , the current set value I ₂ , and the voltage set value V ₂ . The impedance deviation calculation unit 33 determines the impedance deviation _{between the measured impedance of the arc discharge obtained from the measured current value I 1} and the measured voltage V ₁ and the set impedance of the arc discharge obtained from the current set value I ₂ and the voltage set value V _2. Calculate Z _D. Impedance deviation calculation unit 33, for _example, by _{Z D = V 1 / I 1} -V 2 / I 2, and calculates the impedance deviation _{Z D.}

The impedance deviation calculation unit 33 is connected to the impedance constant control unit 34 and the furnace condition determination unit 35. The impedance deviation calculation unit 33 _{inputs the calculated impedance deviation Z D} to the impedance constant control unit 34 and the furnace condition determination unit 35.

Based on the input impedance deviation Z _D , the constant impedance control unit 34 drives the drive device 6 (the height of the electrode 4) so that the measured impedance (V ₁ / I ₁ ) follows the set impedance (V ₂ / I _2). Generates a control signal to control. Impedance stabilization controller 34, for example, by VVVF control, generates a control signal based on the impedance difference _{Z D.} The constant impedance control unit 34 is connected to the command value generation unit 37. The constant impedance control unit 34 inputs the generated control signal to the command value generation unit 37.

Ro況determination unit 35 based on the impedance difference Z _D input, determines the status (Ro況) of steel-making arc furnace 2. Ro況determination unit 35 determines, for example, by continued time of the impedance deviation Z _D and the impedance deviation Z _D, the status of the steel-making arc furnace 2. The situation in the steelmaking arc furnace 2 is, for example, a situation related to a melting process of scrap 5 by the steelmaking arc furnace 2 such as a melting period, a boring period, and a refining period. The furnace condition determination unit 35 is connected to the sensitivity dead zone automatic setting unit 36. The furnace condition determination unit 35 inputs the determination result of the condition in the steelmaking arc furnace 2 to the sensitivity dead zone automatic setting unit 36.

The sensitivity dead zone automatic setting unit 36 automatically sets the sensitivity and the dead zone of the ascending / descending drive of the electrode 4 based on the input determination result of the situation in the steelmaking arc furnace 2. The sensitivity is, for example, a proportional gain with the output of the constant impedance control unit 34 as 100%. The dead zone represents the range of the _{impedance deviation Z D} that sets the command value generated by the command value generation unit 37 to 0%. By setting the sensitivity and the dead zone in this way, it is possible to suppress the sensitive ascending / descending operation of the electrode 4. The sensitivity dead zone automatic setting unit 36 is connected to the command value generation unit 37. The sensitivity dead zone automatic setting unit 36 inputs the set sensitivity and dead zone to the command value generation unit 37.

The command value generation unit 37 generates a command value to be input to the drive device 6 based on the control signal input from the constant impedance control unit 34 and the sensitivity and dead zone input from the sensitivity dead zone automatic setting unit 36. , The generated command value is input to the drive device 6. The command value generation unit 37 generates, for example, a speed reference signal based on the input control signal, sensitivity, and dead zone, and inputs the speed reference signal to the drive device 6.

FIG. 2 is a graph diagram schematically showing an example of the operation of the command value generation unit.
As shown in FIG. 2, the command value generation unit 37 generates the sensitivity function Fs based on the input sensitivity S and the dead zone Sn. Sensitivity S represents, for example, the maximum value when the impedance deviation _{Z D} is 100% (S), and the impedance deviation _{Z D} is the minimum value when the 100% of (-S). The command value generation unit 37 generates the sensitivity function Fs by, for example, a linear function connecting the upper limit value of the dead zone Sn and the maximum value S, and a linear function connecting the lower limit value of the dead zone Sn and the minimum value −S.

After generating the sensitivity function Fs, the command value generation unit 37 determines the proportional gain based on _{the impedance deviation Z D calculated by the impedance deviation calculation unit 33 and the sensitivity function Fs.} For example, in the example shown in FIG. 2, when the impedance deviation Z _D calculated by the impedance deviation calculation unit 33 is −50%, the command value generation unit 37 determines −50% as the proportional gain.

Then, the command value generation unit 37 determines the proportional gain, and then multiplies the control signal input from the constant impedance control unit 34 by the proportional gain to obtain the command value (speed reference signal) input to the drive device 6. Generate.

In FIG. 2, _{the positive side of the impedance deviation Z D} corresponds to the rising direction of the electrode 4. That is, in this example, the dead zone Sn is set only on the rising side of the electrode 4. Dead zone Sn is based on the 0% of the impedance deviation Z _D, it may be set on both the rising side and the falling side. The dead zone Sn may be set in a predetermined range based on 0% of the impedance deviation Z _D. However, it is preferable that the dead zone Sn is set to at least the rising side. As a result, it is possible to suppress the arc breakage due to the excessive rise of the electrode 4.

FIG. 3 is a table schematically showing an example of the operation of the furnace condition determination unit.
As shown in FIG. 3, Ro況determination unit 35 has, for example, the impedance variation Z _D, and the duration of the impedance deviation Z _D, and status of steelmaking arc furnace 2, a table data that associates.

For example, when the operation is started, the furnace condition determination unit 35 determines that the condition inside the steelmaking arc furnace 2 is “melting period 1”. The furnace condition determination unit 35 determines that the "dissolution period 1" has ended and the process has shifted to the "dissolution period 2" when the state in which the _{impedance deviation Z D} is a _{1 or more continues for Ta 1 second.} Then, the furnace condition determination unit 35 states that when the impedance deviation Z _D is b ₁ or more and less _{than a 1 for Ta 2} seconds, the “dissolution period 2” ends and the process shifts to the “dissolution period 3”. judge. The furnace condition determination unit 35 determines the condition inside the steelmaking arc furnace 2 based on the impedance deviation Z _{D and the duration of the impedance deviation Z D by performing the same processing thereafter.} The impedance deviation Z _D becomes smaller as the operation progresses. Therefore, b ₁ is smaller than _{a 1 and c 1} is smaller than _{b 1.}

FIG. 4 is a table schematically showing an example of the operation of the sensitivity dead zone automatic setting unit.
As shown in FIG. 4, the sensitivity dead zone automatic setting unit 36 has, for example, table data in which the situation in the steelmaking arc furnace 2, the sensitivity, and the dead zone are associated with each other. The sensitivity dead zone automatic setting unit 36 refers to the table data based on the determination result input from the furnace condition determination unit 35. Then, the sensitivity dead zone automatic setting unit 36 automatically sets the sensitivity and dead zone by reading the sensitivity and dead zone associated with the situation in the steelmaking arc furnace 2 from the table data. As described above, the sensitivity automatically set by the sensitivity dead zone automatic setting unit 36 is, for example, the maximum value (minimum value) for generating the sensitivity function Fs.

Sensitivity increases, for example, as the operation progresses. Therefore, for example, in the example of FIG. 4 _{, the values} increase in the order of _{x a1} , x _a2 , and x a3. On the other hand, the dead zone becomes smaller as the operation progresses, for example. Thus, for example, in the example of FIG. _4, it decreases in the order of _{y a1, y a2, y a3} . However, the sensitivity and the dead zone are not limited to the above, and may be appropriately set according to the situation in the steelmaking arc furnace 2.

FIG. 5 is a flowchart schematically showing an example of the operation of the electrode elevating device for an arc furnace according to the embodiment.
As shown in FIG. 5, the arc furnace electrode elevating device 10 starts the elevating drive of the electrode 4 of the steelmaking arc furnace 2 in response to the input of the operation command (step S1 in FIG. 5).

When the elevating drive of the electrode elevating device 10 for an arc furnace is started, the current / voltage detection unit 31 detects the measured current value I ₁ based on the input from the current transformer 12, and is based on the input from the transformer 14. The voltage measurement value V ₁ is detected, and the detected current measurement value I ₁ and the voltage measurement value V ₁ are input to the impedance deviation calculation unit 33 (step S2 in FIG. 5).

_{Further, the current set value I 2} and the voltage set value V ₂ are set by the current / voltage setting unit 32, and the set current set value I ₂ and the voltage set value V ₂ are input to the impedance deviation calculation unit 33 (FIG. 5). Step S3).

The impedance deviation calculation unit 33 calculates the impedance deviation Z _{D from the input current measured value I 1} , the voltage measured value V ₁ , the current set value I ₂ , and the voltage set value V ₂ , and calculates the calculated impedance deviation Z _D. Inputs are made to the constant impedance control unit 34 and the furnace condition determination unit 35 (step S4 in FIG. 5).

The constant impedance control unit 34 controls the drive device 6 so that the measured impedance (V ₁ / I ₁ ) follows the set impedance (V ₂ / I _{2 ) based on the input impedance deviation Z D.} A control signal is generated, and the generated control signal is input to the command value generation unit 37 (step S5 in FIG. 5).

Ro況determination unit 35 based on the impedance difference Z _D input, determines the status of the steel-making arc furnace 2, and inputs the determination result to the sensitivity deadband automatic setting unit 36 (step S6 in FIG. 5). The furnace condition determination unit 35, for example, in the steelmaking arc furnace 2 by referring to the table data based on the _{input impedance deviation Z D} and the duration of the impedance deviation Z _{D, as described above.} Judge the situation of.

The sensitivity dead zone automatic setting unit 36 automatically sets the sensitivity and dead zone of the ascending / descending drive of the electrode 4 based on the input determination result of the situation in the steelmaking arc furnace 2, and sets the set sensitivity and dead zone as command values. Input to the generation unit 37 (steps S7 and S8 in FIG. 5). The sensitivity dead zone automatic setting unit 36 is associated with the situation in the steelmaking arc furnace 2 by referring to the table data based on the input situation in the steelmaking arc furnace 2 as described above. The sensitivity and dead zone are set automatically.

The command value generation unit 37 generates a command value to be input to the drive device 6 based on the control signal input from the constant impedance control unit 34 and the sensitivity and dead zone input from the sensitivity dead zone automatic setting unit 36. , The generated command value is input to the drive device 6 (step S9 in FIG. 5).

For example, as described above, the command value generation unit 37 generates a sensitivity function Fs based on the input sensitivity S and the dead zone Sn, and the impedance deviation Z _D and the sensitivity function calculated by the impedance deviation calculation unit 33. A command value is generated by determining the proportional gain based on Fs and multiplying the control signal input from the constant impedance control unit 34 by the proportional gain.

The drive device 6 moves the electrode 4 up and down based on the input command value. As a result, the distance between the electrode 4 and the scrap 5 (of the electrode 4) so that the impedance of the arc discharge becomes constant based on _{the current set value I 2} and the voltage set value V ₂ set by the current / voltage setting unit 32. Height) is controlled. Hereinafter, the arc furnace electrode elevating device 10 repeats the above steps S2 to S9 until a command to end the operation is input (step S10 in FIG. 5). The end of the operation may be automatically determined, for example, based on the determination result of the condition in the steelmaking arc furnace 2 by the furnace condition determination unit 35.

As described above, in the arc furnace electrode lifting device 10 according to the present embodiment, Ro況determination unit 35, based on the impedance difference Z _D, to determine the status of the steel-making arc furnace 2, the sensitivity deadband The automatic setting unit 36 automatically sets the sensitivity and dead zone of the ascending / descending drive of the electrode 4 based on the determination result of the situation in the steelmaking arc furnace 2.

As a result, it is possible to prevent the sensitivity and dead zone from being set that are not optimal for the situation inside the steelmaking arc furnace 2, and it also takes time to change the sensitivity and dead zone settings. It can be suppressed. Therefore, it is possible to provide an electrode elevating device 10 for an arc furnace that can easily and surely set the sensitivity and dead zone of the elevating operation of the electrode 4.

Although some embodiments of the present invention have been described above, 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 embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention and its equivalents described in the claims. Moreover, each of the above-described embodiments can be implemented in combination with each other.

2 Arc furnace for steelmaking, 3 Reactor body, 4 Electrodes, 5 Scrap, 6 Drive device, 7 Transformer for furnace, 10 Electrode elevating device for arc furnace, 12 Transformer, 14 Transformer, 16 Main controller, 31 Current Voltage detection unit, 32 Current / voltage setting unit, 33 Impedance deviation calculation unit, 34 Constant impedance control unit, 35 Arc furnace condition determination unit, 36 Sensitivity dead zone automatic setting unit, 37 Command value generation unit

Claims (3)

In an arc furnace electrode elevating device used in an arc furnace for steelmaking, which is connected to a drive device for elevating and lowering electrodes for performing arc discharge and controls the elevating and lowering of the electrodes by the drive device.
A current-voltage detector that detects the measured current value of the current supplied to the electrode and also detects the measured voltage of the voltage applied to the electrode.
A current-voltage setting unit that enables setting of a current setting value that serves as a reference for the current supplied to the electrode and a voltage setting value that serves as a reference for the voltage applied to the electrode.
An impedance deviation calculation unit that calculates the impedance deviation between the measured impedance of the arc discharge obtained from the measured current value and the measured voltage value, the set impedance of the arc discharge obtained from the current set value, and the set impedance of the arc discharge obtained from the voltage set value.
A constant impedance control unit that generates a control signal for controlling the drive device so that the measured impedance follows the set impedance based on the impedance deviation.
Based on the impedance deviation, a furnace condition determination unit that determines the condition inside the steelmaking arc furnace, and a furnace condition determination unit.
Based on the determination result of the situation in the steelmaking arc furnace, the sensitivity dead zone automatic setting unit that automatically sets the sensitivity and dead zone of the ascending / descending drive of the electrode, and the sensitivity dead zone automatic setting unit.
A command value generator that generates a command value to be input to the drive device based on the control signal and the set sensitivity and dead zone, and inputs the generated command value to the drive device.
Electrode lifting device for arc furnaces. The furnace condition determination unit has table data associating the impedance deviation, the duration of the impedance deviation, and the situation in the steelmaking arc furnace, and the calculated impedance deviation and the impedance deviation. The arc furnace electrode elevating device according to claim 1, wherein the state in the steelmaking arc furnace is determined by referring to the table data based on the duration of the above. The sensitivity dead zone automatic setting unit has table data in which the situation in the steelmaking arc furnace is associated with the sensitivity and the dead zone, and the table data is referred to based on the determination result of the furnace condition determination unit. The electrode elevating device for an arc furnace according to claim 1 or 2, wherein the sensitivity and the dead zone are automatically set.

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