JP6566439B2 - Arc furnace electrode lifting device - Google Patents

Description

  Embodiments described herein relate generally to an arc furnace electrode lifting device.

  The arc furnace supplies three-phase AC power to the electrodes provided in each phase via a furnace transformer, generates an arc discharge between each phase electrode and scrap, and melts the scrap by the arc heat. . The arc furnace electrode lifting / lowering device controls the distance between the electrode and the scrap by raising / lowering the electrode of each phase so that the optimum arc discharge is maintained.

  In the arc furnace electrode lifting / lowering apparatus, the impedance at the time of arc discharge based on the current and voltage between the electrode and scrap is controlled so as to approach the reference impedance by moving the electrodes of each phase up and down. The arc furnace electrode lifting device maintains the optimum arc discharge by controlling the impedance in this way. In the arc discharge, the impedance described above fluctuates drastically, for example, fluctuates greatly at the time of switching between periods such as immediately after the start of charging, a boring period, a melting period and a refining period. For this reason, it is preferable to provide an appropriate dead zone for each period (for example, Patent Document 1).

  On the other hand, in an arc furnace, because the phase of the three-phase AC power supply is controlled up and down between scraps, the impedance during arc discharge affects each other and impedance in other phases that are not controlled. Fluctuations may be detected as fluctuations in the self-phase impedance. When the up / down control is performed using the impedance fluctuation in the other phase as the impedance fluctuation in the own phase, there is a possibility that the arc length that has been optimal until then is changed to an inappropriate arc length. Therefore, the scrap melting efficiency may be lowered by raising and lowering the electrode even though the arc length of the self phase does not fluctuate.

Japanese Patent No. 5343421

  The embodiment determines whether the impedance variation during arc discharge is due to the variation of the arc length of the own phase or the variation of the arc length of the other phase, and when the arc length of the other phase varies Stops raising and lowering the electrodes. This provides an arc furnace electrode lifting apparatus that can stably operate.

The arc furnace electrode lifting apparatus according to the embodiment lifts and lowers one of the three electrodes connected to each phase of the three-phase alternating current to form an arc discharge formed between the one electrode and scrap. To control. The arc furnace electrode lifting device generates a speed command value based on a first current value flowing between the one electrode and the scrap and a first voltage value between the one electrode and the scrap. And a drive device that performs speed control of an electric motor that raises and lowers the one electrode based on the speed command value. The control device calculates a first impedance related to the arc discharge based on the first current value and the first voltage value, and generates an impedance deviation between the first impedance and a preset second impedance. A calculation unit; a control switching unit that outputs a deviation signal that stops the deviation or the motor; and a sensitivity correction unit that generates the speed command value based on the deviation or the stop signal. The control switching unit is configured such that the first current value is greater than a preset second current value and the first voltage value is equal to or greater than a preset second voltage value, or the first current value When the value is smaller than the second current value and the first voltage value is less than or equal to the second voltage value, the stop signal is output.

  In the present embodiment, since it includes a control switching unit that can detect the variation direction of the arc length of the other phase by detecting the direction of variation of each of the current value and the voltage value related to the impedance of the arc discharge. With respect to the arc length fluctuation of the other phase, the raising / lowering of the electrode can be stopped, and stable operation can be continued.

It is a block diagram which illustrates the arc furnace electrode raising / lowering apparatus which concerns on 1st Embodiment. FIG. 2A and FIG. 2B are schematic views for explaining the operation of the arc furnace electrode lifting apparatus of the first embodiment. It is a flowchart explaining operation | movement of the arc furnace electrode raising / lowering apparatus of 1st Embodiment. It is a block diagram which illustrates the arc furnace electrode raising / lowering apparatus which concerns on 2nd Embodiment. It is a block diagram which illustrates a part of arc furnace electrode raising / lowering apparatus of 2nd Embodiment. It is a block diagram which illustrates the arc furnace electrode raising / lowering apparatus which concerns on 3rd Embodiment. It is a flowchart explaining operation | movement of the arc furnace electrode raising / lowering apparatus of 3rd 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 size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
In the present specification and drawings, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

(First embodiment)
FIG. 1 is a block diagram illustrating an arc furnace electrode lifting apparatus according to this embodiment.
FIG. 2A and FIG. 2B are schematic views for explaining the operation of the arc furnace electrode lifting apparatus of the present embodiment.
FIG. 3 is a flowchart for explaining the operation of the arc furnace electrode lifting apparatus of the present embodiment.
As shown in FIG. 1, the arc furnace electrode lifting / lowering apparatus 1 of this embodiment includes an impedance control device 10 and a drive device 30. The arc furnace electrode lifting / lowering device 1 raises and lowers the electrode 2 with respect to the fixed furnace body 3 to control the distance between the electrode 2 and the scrap 4 charged in the furnace body 3. The electrode 2 is set with a voltage supplied from an AC power supply on the primary side by a voltage tap of the furnace transformer 5. The electrode 2 moves up and down so as to be an appropriate distance above the furnace body 3 and the scrap 4.

  The arc furnace electrode lifting / lowering device 1 is connected to a current transformer 6 provided on the secondary side of the furnace transformer 5 and an auxiliary transformer 7 provided between the electrode 2 and the furnace body 3. The current transformer 6 detects an arc current Iarc which is a current when an arc discharge is generated between the electrode 2 and the scrap 4 and outputs a current value IFB corresponding to the arc current Iarc. The auxiliary transformer 7 detects an arc voltage Varc that is a voltage between the electrode 2 and the scrap 4 when an arc discharge is generated between the electrode 2 and the scrap 4, and generates a voltage VFB corresponding to the arc voltage Varc. Output. The arc furnace electrode lifting / lowering device 1 inputs a current value IFB corresponding to the detected arc current Iarc and a voltage value VFB corresponding to the arc voltage Varc, and sets the lifting drive system 8 for lifting / lowering the electrode via the electric motor 32. Drive to raise and lower the electrode 2. The current value IFB corresponding to the arc current Iarc is IFB = Iarc / K, where K is the current transformation ratio of the current transformer 6. The voltage value VFB corresponding to the arc voltage Varc is VFB = Varc / N, where N is the transformation ratio of the auxiliary transformer 7.

  In the arc furnace in which the arc furnace electrode lifting / lowering device 1 is used, each of the three electrodes connected to each phase of the three-phase AC power supply generates an arc discharge with the scrap 4 and is installed in one furnace body 3. The entered scrap 4 is melted. The distance between the electrode 2 and the scrap 4 in each phase of the three-phase alternating current is controlled independently. That is, a set of arc furnaces includes three raising / lowering mechanisms for the electrodes 2 and three arc furnace electrode raising / lowering devices 1 for driving the raising / lowering mechanisms. Hereinafter, unless otherwise specified, one of the three lifting mechanisms and the arc furnace electrode lifting device 1 will be described.

  The impedance control device 10 includes an impedance deviation calculation unit 12, a control switching unit 14, and a sensitivity correction unit 16. The impedance control device 10 is connected to each secondary side of the current transformer 6 and the auxiliary transformer 7. The output of the impedance control device 10 is connected to the drive device 30.

  The impedance deviation calculation unit 12 is connected to the secondary side of the current transformer 6 and the auxiliary transformer 7 and receives a current value IFB corresponding to the arc current Iarc and a voltage value VFB corresponding to the arc voltage Varc. The impedance deviation calculation unit 12 calculates the impedance Z between the electrode 2 and the scrap 4 based on the current value IFB and the voltage value VFB. The impedance deviation calculation unit 12 calculates a deviation ΔZ between the calculated impedance Z and a preset reference impedance Zr, and supplies the result to the control switching unit 14.

  The control switching unit 14 is connected to the secondary side of the current transformer 6 and the auxiliary transformer 7 and receives a current value IFB corresponding to the arc current Iarc and a voltage value VFB corresponding to the arc voltage Varc. The timing at which the control switching unit 14 inputs the current value IFB and the voltage value VFB is the same as the timing at which they are input to the impedance deviation calculation unit 12. That is, the current value IFB and the voltage value VFB that are the same as those of the impedance deviation calculation unit 12 are input to the control switching unit 14. The control switching unit 14 receives the current value IFB and calculates a difference from a preset current set value ISET. The control switching unit 14 receives the voltage value VFB and calculates a difference from a preset voltage setting value VSET. The current set value ISET and the voltage set value VSET are values obtained in advance through experiments or the like. When the difference between the current value IFB and the current set value ISET is 0 or more and the difference between the voltage value VFB and the voltage set value VSET is 0 or more, the control switching unit 14 calculates the calculation result of the impedance deviation calculation unit 12. Regardless of whether 0 (zero) is output. Even when the difference between the current value IFB and the current set value ISET is 0 or less and the difference between the voltage value VFB and the voltage set value VSET is 0 or less, regardless of the calculation result of the impedance deviation calculation unit 12, The control switching unit 14 outputs 0 (zero). In cases other than the above, the control switching unit 14 outputs a deviation ΔZ that is a calculation result of the impedance deviation calculation unit 12. That is, the control switching unit 14 switches the output to the deviation ΔZ or 0 depending on the difference between the current values IFB and ISET and the difference between the voltage values VFB and VSET.

  The sensitivity correction unit 16 generates a speed command value V for the drive device 30 based on the output from the control switching unit 14. The sensitivity correction unit 16 generates a speed command value V by multiplying the input impedance deviation ΔZ by a sensitivity function. The sensitivity function includes, for example, a sensitivity dead zone characteristic including a dead zone in which the speed command value V is 0 during a predetermined period when the impedance deviation ΔZ is input.

  The drive device 30 receives the supply of the speed command value V from the sensitivity correction unit 16 and controls the speed of the electric motor 32. The drive device 30 is, for example, an inverter device, and outputs an alternating current having a frequency set based on the input speed command value V and supplies the alternating current to the electric motor 32. The electric motor 32 rotates at a speed according to the alternating current supplied from the drive device 30.

Operation | movement of the arc furnace electrode raising / lowering apparatus 1 of this embodiment is demonstrated.
An arc discharge is generated between the electrode 2 and the scrap 4, and an arc corresponding to the distance between the electrode 2 and the scrap 4 is formed. The shape of the scrap 4 changes depending on the stage of melting or the processing time. Therefore, the distance between the electrode 2 and the scrap 4 changes according to time or the like, and the arc length (arc length) changes accordingly.

  In FIG. 2A, a state in which the shape of the scrap 4 is changed according to the processing time is indicated by a solid line, a broken line, and an alternate long and short dash line. For example, in the initial state of arc discharge, the scrap 4 has a solid line shape, and the distance between the electrode 2 and the scrap 4 is L1. When arc discharge is generated in this state, the arc length is substantially equal to L1. When the scrap 4 is melted with time and the shape of the scrap 4 becomes a broken line, the distance between the electrode 2 and the scrap 4 is L2. When arc discharge is generated in this state, the arc length is substantially equal to L2. Since the shape of the scrap 4 changes depending on the degree of melting, the distance between the electrode 2 and the scrap 4 may be shortened. When the scrap 4 has a one-dot chain line shape, the distance between the electrode 2 and the scrap 4 is L3. When arc discharge is generated in this state, the arc length is substantially equal to L3. Thus, the arc length varies depending on the state and shape of the scrap 4.

  The arc current Iarc and the arc voltage Varc vary depending on the arc length. The relationship between the variation of the arc length and the variation of the arc current Iarc and the arc voltage Varc was found by actual measurement. According to this actual measurement, the relationship between the fluctuation of the arc current Iarc and the fluctuation of the arc voltage Varc due to the fluctuation of the arc length of the control target self-phase is the relationship between the fluctuation of the arc current Iarc due to the fluctuation of the arc length of the other phase. This is different from the relationship between the fluctuation and the fluctuation of the arc voltage Varc.

  In FIG. 2 (b), it is uniquely determined how the arc current and the arc voltage of the self-phase fluctuate when the arc length of the other phase varies with the arc length of the self-phase to be controlled. It has been shown. In FIG. 2B, the self-phase electrode 2 to be controlled is connected to the U phase, for example, and the arc length is constant (L1). The other-phase electrode 2a is connected to, for example, the V-phase, and the arc length becomes longer as time elapses (dashed line, L4 to L5). Further, the case where the arc length is shortened depending on the degree of melting of the scrap 4 is also shown (dashed line, L4 to L6).

  As shown in FIG. 2 (b), when the arc length of the other phase becomes longer, the arc current Iarc of the own phase decreases and the arc voltage Varc is substantially constant. When only the decrease of the arc current Iarc is detected in the control target self-phase, it is determined that the arc length of the other phase is long. Further, when only an increase in the arc current Iarc is detected in the own phase to be controlled, it is determined that the arc length of the other phase is short. Therefore, when such a value is detected, the own phase elevation control is stopped.

  Thus, it is calculated whether the arc current Iarc and the arc voltage Varc at the control-target self-phase electrode 2 are increasing or decreasing, respectively, and the arc length varies in the self-phase depending on the direction of each variation. Or whether it is occurring in another phase. If it is determined that the arc length variation occurs in the self phase, constant impedance control is performed for the self phase. If the arc length variation occurs in the other phase, the self-phase electrode is moved up and down. Stop control.

A series of operation | movement of the arc furnace electrode raising / lowering apparatus 1 of this embodiment is demonstrated using FIG.
As shown in FIG. 3, in step S1, the control switching unit 14 reads a current value IFB and a voltage value VFB.

  In step S2, the control switching unit 14 uses the read current value IFB and voltage value VFB and the preset current set value ISET and voltage set value VSET to make a determination according to the following equation (1).

  IFB-ISET ≧ 0 and VFB-VSET ≧ 0 (1)

  If it is determined that the expression (1) is not satisfied, the process proceeds to the next step S3.

  In step S3, the control switching unit 14 performs determination according to the equation (2).

  IFB-ISET ≦ 0 and VFB-VSET ≦ 0 (2)

  If it is determined that the expression (2) is not satisfied, the process proceeds to the next step S4.

  In step S <b> 4, the control switching unit 14 determines that the arc length of the controlled phase is changing, and supplies the impedance deviation ΔZ supplied from the impedance deviation calculation unit 12 to the sensitivity correction unit 16. .

  In step S <b> 5, the sensitivity correction unit 16 multiplies the impedance deviation ΔZ by the sensitivity function to generate a speed command value V, and supplies the generated speed command value V to the drive device 30. The drive device 30 drives the electric motor 32 according to the speed command value V, and the electrode 2 is moved to an appropriate position by the electric motor 32 and the elevating drive system 8.

  When it determines with satisfy | filling Formula (1) by step S2, a process transfers to step S6.

  In step S <b> 6, the control switching unit 14 determines that the influence of the change in the arc length of the other phase has been received, and the sensitivity correction unit 16 determines whether the impedance deviation ΔZ supplied from the impedance deviation calculation unit 12. On the other hand, an output for generating a signal for stopping the drive device 30 is supplied. This signal is a signal for setting the speed command value V to zero, for example, and ΔZ = 0.

  In step S <b> 7, the sensitivity correction unit 16 supplies a stop signal to the drive device 30 based on the signal for setting the speed command value V to zero from the control switching unit 14.

  When it determines with satisfy | filling Formula (2) by step S3, a process transfers to step S6. Thereafter, the same processing as described above is performed.

The operation and effect of the arc furnace electrode lifting apparatus 1 of this embodiment will be described.
As described above, in the arc furnace electrode lifting apparatus 1 of the present embodiment, the control switching unit 14 uses the current value IFB corresponding to the arc current Iarc to be controlled, the voltage value VFB corresponding to the arc voltage Varc, and the current set value. The difference between the ISET and the voltage set value VSET is calculated. And the control switching part 14 determines whether each difference is 0 or more or 0 or less. The control switching unit 14 determines that the current value IFB and the voltage value VFB have changed due to the fluctuation of the arc length of the other phase that is not the control target when each difference is equal to or greater than 0 or equal to or less than 0. Outputs a signal to stop lifting control. As a result, the arc furnace electrode lifting apparatus 10 changes the current value IFB and / or the voltage value VFB even though the arc length between the electrode 2 and the scrap 4 that are actually controlled is not changed. Since the raising / lowering control of the electrode is not performed, a stable arc discharge state can be maintained, and a stable operation can be continued.

(Second Embodiment)
FIG. 4 is a block diagram illustrating an arc furnace electrode lifting apparatus according to this embodiment.
FIG. 5 is a block diagram illustrating a part of the arc furnace electrode lifting device of the present embodiment.
The arc furnace electrode lifting / lowering apparatus 1a according to the present embodiment is different from that of the first embodiment in that the impedance control device 10a includes a differential correction unit 22. Other components are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and detailed description thereof is omitted as appropriate.
As shown in FIG. 4, the impedance control device 10 a of the arc furnace electrode lifting apparatus 1 a according to the present embodiment further includes a differential correction unit 22.

  The differential correction unit 22 is connected to the output of the impedance deviation calculation unit 12. The output of the differential correction unit 22 is connected to the control switching unit 14. The differential correction unit 22 corrects and outputs the deviation ΔZ1 by multiplying the differential value of the impedance deviation ΔZ1 calculated by the impedance deviation calculation unit 12 by a predetermined coefficient k.

  More specifically, as shown in FIG. 5, the differential correction unit 22 includes a differential circuit 23a, a coefficient circuit 23b, and an adder 23c. The differentiation circuit 23a and the coefficient circuit 23b are connected in cascade. The impedance deviation ΔZ1 is added to kdΔZ1 / dt by the cascade-connected circuit and the adder 23c. Therefore, the differential correction unit 22 outputs the impedance deviation ΔZ of the following equation (3).

The operation and effect of the arc furnace electrode lifting / lowering apparatus 1a of this embodiment will be described.
In the arc furnace electrode lifting / lowering apparatus 1a of the present embodiment, the impedance control device 10 includes a differential correction unit 22 that corrects the impedance deviation ΔZ1 output from the impedance deviation calculation unit 12 with the time differential value. For this reason, it is possible to add a differential correction to fluctuations in the arc length of the self-phase to be controlled, improving followability to the target arc length and improving melting efficiency.

(Third embodiment)
FIG. 6 is a block diagram illustrating an arc furnace electrode lifting device according to this embodiment.
FIG. 7 is a flowchart for explaining the operation of the arc furnace electrode lifting apparatus of the present embodiment.
As shown in FIG. 6, in the arc furnace electrode lifting apparatus 1b of the present embodiment, the configuration of the control switching unit 14a of the impedance control apparatus 10b is different from that of the first embodiment. Other components are the same as those in the first embodiment, and the same components are denoted by the same reference numerals and detailed description thereof is omitted as appropriate.
As shown in FIG. 6, the arc furnace electrode lifting / lowering device 1 b of the present embodiment includes an impedance control device 10 b and a drive device 30. The impedance control device 10b includes an impedance deviation calculation unit 12, a control switching unit 14a, and a sensitivity correction unit 16. The control switching unit 14a calculates the difference between the current value IFB corresponding to the arc current Iarc and the voltage value VFB corresponding to the arc voltage Varc, and the preset current setting value ISET and voltage setting value VSET, respectively. When the difference between the current value IFB and the current set value ISET is equal to or greater than the increase determination threshold value KUi, and the difference between the voltage value VFB and the voltage set value VSET is equal to or greater than the increase determination threshold value KUv The control switching unit 14a outputs 0 (zero) regardless of the calculation result of the impedance deviation calculation unit 12. As a result of comparison, the difference between the current value IFB and the current set value ISET is smaller than the decrease determination threshold value KDi, and the difference between the voltage value VFB and the voltage set value VSET is the decrease determination threshold value KDv. The control switching unit 14 a outputs 0 (zero) regardless of the calculation result of the impedance deviation calculation unit 12 even when the value is smaller than the value. In cases other than the above, the control switching unit 14 outputs a deviation ΔZ that is a calculation result of the impedance deviation calculation unit 12.

The operation of the arc furnace electrode lifting apparatus 1b of this embodiment will be described with reference to FIG.
FIG. 7 is a flowchart of the operation of the control switching unit 14a of the arc furnace electrode lifting / lowering apparatus 1b of the present embodiment, which is different from the flowchart of the first embodiment (FIG. 3) in steps S2a and S3a. The steps are the same. Steps S2a and S3a will be described.
As shown in FIG. 7, in step S2a, the control switching unit 14a performs determination according to the equation (4).

  IFB-ISET ≧ KUi and VFB-VSET ≧ KUv (4)

  Here, the increase determination thresholds KUi and KUv are positive real values set in advance. These threshold values are obtained and set in advance by experiments or the like.

  If it is determined that the expression (4) is not satisfied, the process proceeds to the next step S3a.

  In step S3a, the control switching unit 14a performs determination according to the equation (5).

  IFB-ISET ≦ KDi and VFB-VSET ≦ KDv (5)

  Here, the decrease determination threshold values KDi and KDv are negative real values set in advance. These threshold values are obtained and set in advance by experiments or the like. The absolute value of the decrease determination threshold value KDi regarding the current value may be the same as or different from the absolute value of the increase determination threshold value KUi regarding the current value. The absolute value of the decrease determination threshold value KDv related to the voltage value may be the same as or different from the increase determination threshold value KUv related to the voltage value.

  If it is determined that Expression (5) is not satisfied, the process proceeds to the next step S4, and firstly operates in the same manner as in the embodiment.

The operation and effect of the arc furnace electrode lifting / lowering apparatus 1b of the present embodiment will be described.
In the arc furnace electrode lifting / lowering apparatus 1b of this embodiment, the impedance control device 10b includes a control switching unit 14a having a plurality of preset threshold values KUi, KUv, KDi, and KDv. Since the arc current Iarc and the arc voltage Varc include noise, the current value IFB obtained by converting the arc current Iarc and the arc voltage Varc and the stepped-down VFB also include noise. Therefore, when calculation is performed using such current values and voltage values, it may be difficult to determine whether the current value IFB or the voltage value VFB is rising or falling. Therefore, the influence of noise can be reduced by setting a discrimination threshold according to the noise level. Therefore, the increase determination threshold values KUi and KUv are set to positive real numbers, and the decrease determination threshold values KDi and KDv are set to negative real numbers. By setting each discrimination threshold in this manner, stable operation can be realized without causing malfunction even if the control switching unit 14a is operated using the current value IFB and the voltage value VFB including noise. Can do.

  The thresholds KUi, KUv, KDi, and KDv can be set to optimum values through experiments or the like, so that more effective noise removal can be performed.

  According to the embodiment described above, it is possible to realize an arc furnace electrode lifting apparatus that can stop the lifting of the electrode when the arc length of the other phase fluctuates, and can continue the operation stably.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and the equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

  1, 1a, 1b Arc furnace electrode lifting device, 2 electrodes, 3 furnace body, 4 scrap, 5 furnace transformer, 6 current transformer, 7 auxiliary transformer, 10, 10a, 10b impedance control device, 12 impedance deviation calculation 14, 14a Control switching unit, 16 Sensitivity correction unit, 22 Differential correction unit, 23a Differentiation circuit, 23b Coefficient circuit, 30 Drive device, 32 Electric motor

Claims (3)

An arc furnace electrode lifting / lowering device for controlling an arc discharge formed between the one electrode and scrap by raising / lowering one of three electrodes connected to each phase of a three-phase alternating current. ,
A control device for generating a speed command value based on a first current value flowing between the one electrode and the scrap and a first voltage value between the one electrode and the scrap;
A drive device that performs speed control of an electric motor that raises and lowers the one electrode based on the speed command value;
With
The controller is
An impedance deviation calculator that calculates a first impedance related to the arc discharge based on the first current value and the first voltage value, and generates a deviation between the first impedance and a preset second impedance;
A control switching unit for outputting a deviation signal for stopping the deviation or the motor;
A sensitivity correction unit that generates the speed command value based on the deviation or the stop signal;
Including
The control switching unit is configured such that the first current value is greater than a preset second current value and the first voltage value is equal to or greater than a preset second voltage value, or the first current value An arc furnace electrode lifting / lowering device that outputs the stop signal when the value is smaller than the second current value and the first voltage value is less than or equal to the second voltage value.   The arc furnace electrode lifting / lowering apparatus according to claim 1, wherein the control device further includes a differential correction unit that calculates a time differential value of the output from the impedance deviation calculation unit and outputs a deviation corrected by the time differential value. The difference between the first current value and the second current value is not less than a first threshold value, and the difference between the first voltage value and the second voltage value is not less than a second threshold value. Yes or
The difference between the first current value and the second current value is a third threshold value or less, and the difference between the first voltage value and the second voltage value is a fourth threshold value or less. Yes,
3. The first threshold value and the second threshold value are values larger than 0, and the third threshold value and the fourth threshold value are values smaller than 0. The arc furnace electrode lifting device described in 1.

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