JP2002208472A - Arc furnace device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an arc furnace device enabled to make the setting error small for the arc current, caused by the output voltage fluctuation of a furnace transformer. SOLUTION: Electrodes 11 of an arc furnace 1 is elevated by an electrode elevating device 13, and the scrap 12 in the arc furnace 1 is melted by alternating current power supplied from a three-phase furnace transformer 25 to the electrodes 11. The arc furnace device comprises an arithmetic circuit 41 calculating an effective value of secondary voltage of the furnace transformer 25 by imputing respective detected values of three-phase arc voltage; a circuit 43 multiplying the effective values obtained at the arithmetic circuit 41 by a proportionality constant, and averaging them afterwards; a voltage deviation output circuit 44, inputting the value of one phase out of the detected values of three-phase arc voltage and the average value obtained at the circuit 43, and calculating the voltage deviation depending on the difference between them; an arc current setting circuit 45, calculating the current deviation from the detected value of arc current and the value obtained by multiplying the detected value of arc current by a proportionality constant; and an electrode elevation sensitivity setting device 46 calculating a standard velocity to be given to the electrode elevating device 13 by reducing the voltage deviation of the voltage deviation output circuit from the current deviation of the arc current setting circuit 45.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc furnace apparatus capable of controlling the impedance of an arc furnace.

[0002]

2. Description of the Related Art As shown in a system diagram of FIG. 11, a conventional steelmaking arc furnace 1 includes a power transmission system 21 and a power distribution transformer 22.
Power distribution system 23, series reactor 24, three-phase reactor transformer 2
5 are connected.

The arc furnace 1 generates a large current arc of a commercial frequency between a graphite electrode 11 connected to a three-phase furnace transformer 25 and a scrap material 12 as shown in FIG. The scrap 12 is melted by arc heat. In addition, the scrap 12 is stored in a furnace main body in which a refractory 17 is disposed at the bottom of the furnace body 16. Furnace body 1
6 is grounded by a grounding device 18.

[0004] The melting of the scrap 12 causes the scrap 12 to collapse, causing the electrode 11 to be short-circuited, and the arc length to be constantly varied, so that the magnitude of the arc current repeats irregular time variation.

The electric power of the arc furnace 1 is supplied through a furnace transformer 25, and the secondary side of the furnace transformer 25 has a low voltage of about 200 V to 700 V and several hundred to 100,000 A in accordance with the arc characteristics. Large current. The electrode 11 is controlled by an electrode lifting / lowering device 13 including a furnace cover 14 and a driving mechanism 15 to control the arc length and stabilize the arc.

At this time, in order to obtain a stable arc, the reactance of the arc furnace circuit is 30 to 30 based on the furnace transformer 25.
About 50% is necessary, and in a small arc furnace, a series reactor 24 is provided to obtain a necessary reactance.

As shown in FIG. 13, one cycle of the operation of the arc furnace includes a melting period, an oxidizing period, and a reducing period. The cycle starts with charging of scrap and ends with tapping.
It takes about 5 to 4 hours. Scrap 12 during melting
Due to the direct arc between the electrode and the electrode 11, the arc length fluctuates and moves as the scrap 12 melts, and the arc is a very unstable period, so that the arc is frequently cut off and the current is intermittent. When dissolution proceeds to some extent, electrode 1
1 descends, and the electrode 11 is surrounded by the wall of the scrap 12 as shown in FIG.

[0008] Since the portion of the scrap 12 near the arc melts, the wall of the scrap 12 becomes unstable, the scrap 12 suddenly collapses, a two-phase short circuit of the electrode 2 occurs, and the arc current fluctuates rapidly.

In the last stage of melting, the molten steel is accumulated on the furnace bottom and the arc is stabilized. When the melting is completed, iron ore and oxygen are added while raising the temperature, oxidative refining is performed, and then reductive refining is performed with reducing auxiliary materials, and lime, coke breeze, fluorite, etc. are added to desulfurize and deoxidize To make steel. At this time, the arc was stable, the current hardly fluctuated, and the molten steel was 1600
After the temperature is raised to 1700 ° C., the furnace body 15 is tilted for tapping.

FIG. 14 is a diagram for explaining a circuit for giving a speed reference to the above-mentioned electrode lifting / lowering device 13, and FIG. 14 (a) is a schematic configuration diagram thereof. This is a line voltage effective value calculator 29, a phase voltage converter 30 that converts the line voltage effective value Vrms obtained by the calculator 29 into a phase voltage Vphase, and a phase voltage converted by the phase voltage converter 30. * 1 and an impedance scale 31 for calculating a voltage deviation Zref between the actually detected arc voltages Va for three phases, an arc current detection gain (proportional constant G1) 32 for inputting an arc current I2 and calculating a current deviation Zfbk. , FIG. 14 (b)
As shown in the figure, the voltage deviation Zref and the current deviation Zfbk are inputted, and an electrode lifting / lowering sensitivity setting unit 33 for obtaining a speed reference ZΔ given to the drive mechanism 15 of the electrode lifting / lowering device 13 is constituted.

The arc current I2 and the arc voltage Va
Are detected by detectors (not shown) on the secondary side of the furnace transformer 25.

The output of a furnace voltage drop compensating circuit (IR drop compensating circuit) for compensating for a furnace voltage drop caused by the arc current I2 and a tap position signal of the furnace transformer 25 (furnace) For the data by the TR tap answer) 26, a fixed value 27, that is, a line voltage effective value Vrms is input.

As described above, a circuit (a voltage deviation generating circuit for controlling the impedance of the arc furnace 1) for giving a speed reference to the conventional electrode lifting / lowering device 13 is a target based on the tap position signal of the furnace transformer 25. The voltage deviation is set, the voltage drop is obtained from the actual value of the arc current as a compensation for the fluctuation, and this is added to the target voltage deviation to make a correction.

[0014]

The conventional arc furnace apparatus described above has the following problems.

1) Data from the tap position signal (furnace TR tap answer) 26 of the furnace transformer 25 is a fixed value 27, which deviates from the target value when the system voltage fluctuates. The arc load is an unbalanced load, and since various disturbances affect the tap voltage, for example, only one pole does not arc discharge,
The error is large if the value is fixed.

2) There is a voltage drop compensation circuit (IR drop compensation circuit) 28, but compensation cannot be made unless the impedance drop of the system is clearly understood. In order to compensate for the voltage drop from the arc current, it is difficult to adjust the voltage drop after the equipment is in operation, and it is difficult to make adjustments.

3) When the voltage drop compensating circuit 28 is used, an error is promoted when the system voltage rises. This is because the conventional arc furnace apparatus does not have a function (circuit) for lowering the voltage deviation target value when the received voltage changes to a higher level.

That is, in the conventional arc furnace apparatus,
The behavior of the electrode 11 is determined only by the comparison between the voltage deviation and the current deviation. The voltage deviation Zref as a reference deviates from the true value, and the value of the current deviation as a feedback deviates from the target. No.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an arc furnace apparatus capable of reducing an arc current setting error caused by output voltage fluctuation of a furnace transformer.

[0020]

To achieve the above object, an invention according to claim 1 is to raise and lower an electrode of an arc furnace by an electrode lifting / lowering device, and to supply the electrode with AC power from a furnace transformer. For melting the scrap in the arc furnace by supplying a voltage deviation target value from the detected arc voltage value in the electrode lifting device, and a voltage deviation target value calculated by the calculating device. And a device for calculating a speed reference given to the pole lifting device from the current deviation obtained based on the detected arc current value.

According to a second aspect of the present invention, an electrode of a three-phase arc furnace is raised and lowered by an electrode lifting device, and AC power from a three-phase furnace transformer is applied to the electrode. An effective value calculation circuit that supplies and melts scrap in the arc furnace, and calculates an effective value of a secondary voltage of the furnace transformer by inputting three-phase arc voltage detection values, respectively; An averaging circuit that multiplies the rms value obtained by the rms calculating circuit by a proportional constant and then averages the values, and inputs a one-phase value of the arc voltage detection values and the average value obtained by the averaging circuit. A voltage deviation output circuit for obtaining a voltage deviation from the difference between the two; an arc current setting circuit for obtaining a current deviation from an arc current detection value and a value obtained by multiplying the arc current detection value by a proportional constant; From the deviation, the voltage of the voltage deviation output circuit And electrode elevation sensitivity setter deviation by subtracting seek speed reference given to the electrode lifting device, which is an arc furnace device provided with a.

According to a third aspect of the present invention, an electrode of a single-phase arc furnace is raised and lowered by an electrode lifting device, and AC power from a single-phase furnace transformer is applied to the electrode. An effective value calculating circuit that supplies and melts scrap in the arc furnace, and calculates an effective value of a secondary voltage of the furnace transformer by inputting a single-phase arc voltage detection value, respectively; An averaging circuit for multiplying the rms value obtained by the rms calculation circuit by a proportional constant and then averaging the values, inputting one of the arc voltage detection values and the averaging value obtained by the averaging circuit. A voltage deviation output circuit for obtaining a voltage deviation from the difference between the two, an arc current setting circuit for obtaining a current deviation from an arc current detection value and a value obtained by multiplying the arc current detection value by a proportional constant, and a current deviation of the arc current setting circuit. From the voltage deviation output circuit. And electrode elevation sensitivity setter deviation by subtracting seek speed reference given to the electrode lifting device, which is an arc furnace device provided with a.

According to the present invention, the arc voltage is calculated from the voltage between the output terminal of the furnace transformer and the ground without depending on the fluctuation of the receiving power supply voltage and the correction of the voltage drop due to the arc current, and the impedance (continuous impedance) is calculated. (Arc current). As a result, the impedance control using the voltage deviation generation method of the present invention can perform arc impedance control (arc current control) without being affected by fluctuations in the power supply voltage.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram for explaining an embodiment of an arc furnace apparatus according to the present invention. The present invention is different from the above-described conventional arc furnace device in that an impedance control device 4 for obtaining a speed reference given to the electrode lifting device 13 is provided.

As shown in FIG. 2, the impedance control device 4 includes an arc voltage / tap voltage effective value calculation circuit (arc voltage / tap voltage effective value conversion circuit) 41, a voltage deviation target value conversion circuit 42, and an averaging circuit. Circuit 43 and voltage deviation output circuit (arc voltage / impedance conversion circuit) 44
A proportional constant circuit 47, an arc current setting circuit 45,
An arc elevating / lowering sensitivity setting unit 46, which detects the arc voltage detected by the arc voltage detector 3 (relatively indicating the strength of the load impedance) Va, Vb, Vc, and the arc current detected by the arc current detector 2. An arc current, for example, Ia is input and the following processing is performed to obtain a speed reference.

Arc voltage / tap voltage effective value calculation circuit 4
Numeral 1 is to input the arc voltage detection values Va, Vb, and Vc and calculate the effective value of the secondary voltage of the furnace transformer 25. The voltage deviation target value conversion circuit 42 includes an effective value conversion circuit 4
The effective value obtained in step 1 is multiplied by a proportional constant (1 / 定 数 3). The averaging circuit 43 is a primary delay element for preventing vibration, and averages the output of the voltage deviation target value conversion circuit 42, that is, the value multiplied by the proportional constant.

The voltage deviation output circuit (impedance scale) 44 is provided for detecting the arc voltage and the averaging circuit 43.
Is input to obtain the voltage deviation (impedance reference) Zref from the difference between them, and outputs the percentage of Va with respect to the target voltage as the voltage deviation Zref. Specifically, the averaging circuit 4
When the arc voltage, for example, the value of Va reaches the output value of No. 3, a voltage deviation of 100% is output.

The proportional constant circuit 47 multiplies the detected arc current, for example, Ia by a proportional constant. The arc current setting circuit 45 calculates a current deviation (impedance feedback) Zf from a value obtained by multiplying the detected arc current value Ia by a proportional constant and the current set value.
bk is obtained. The electrode elevation sensitivity setting device 46 is
The speed reference given to the electrode lifting mechanism of the electrode lifting device 13 is obtained by subtracting the voltage deviation Zref of the voltage deviation output circuit 44 from the current deviation Zfbk of the arc current setting circuit 45.

In such a configuration, the secondary side (secondary side) of the furnace transformer 25 is connected to the electrode 11 via the scrap 12 inside the arc furnace 1.
Inside, the scrap 12 and the electrode 11
It is controlled by the electrode lifting / lowering device 13 so that a gap (impedance) is maintained between them.

When the load is balanced or open, the arc voltage V between the secondary terminal of the furnace transformer 25 and the neutral point (furnace)
a, Vb, and Vc are approximately 1 / √3 (phase voltage) of the terminal voltage.
Is shown.

Since the arc furnace 1 is unbalanced during operation, the arc voltage Va does not always reach Va = Vb = Vc. This point is that, in the conventional arc furnace apparatus, the detected voltages (arc voltages) Va, Vb, and Vc are used in the arc voltage deviation circuit only as one element that relatively represents the strength of the load impedance.

On the other hand, in the embodiment of the present invention, the measured arc voltages Va, Vb, and Vc are converted into an arc voltage / tap voltage effective value calculation circuit 41 and a voltage deviation target value conversion circuit 4.
After the arithmetic processing of the averaging circuit 43, the coordinate axis (scale on the parameter side) of the voltage deviation output circuit 44 is set as the voltage deviation target value. As a result, it is possible to reduce the setting error of the arc current due to the output voltage fluctuation of the furnace transformer 25.

FIGS. 3 to 6 are waveform diagrams of the arc voltage and the arc current for explaining the operation and effect of the present embodiment. FIG. 3 is a waveform diagram of the arc voltage and the arc current according to the embodiment of the present invention. FIG. 4 is an enlarged waveform diagram of an arc voltage showing a note portion of FIG. 3, FIG. 5 is a waveform diagram of an arc current showing an enlarged portion of a note portion of FIG. 3, and FIG. FIG. 3 is a waveform diagram of an arc voltage and an arc current of FIG.
From these figures, it can be seen that the device of the present embodiment has a smaller behavior of the arc current when the arc voltage fluctuates as compared to the conventional device, as compared with the difference in the arc voltage fluctuation.

In the embodiment of the present invention described above, the portion of the effective value Vrms in FIG. 14 which has been set to the fixed value by changing the target voltage from the fixed value to the reactor transformer output has already been compensated. In other words, since the measured value is used as an impedance scale, the voltage deviation Zref can be accurately output, and an arc current with a small setting error can be obtained.

FIGS. 7 to 9 are diagrams for explaining the principle of the present invention, in which the output side of the three-phase transformer whose secondary side of the above-mentioned furnace transformer 25 is △ -connected, and a grounding device ( It is a description of a circuit for estimating a line voltage or a phase voltage from a measured voltage value between the grounds 18.

Now, when voltage is measured with the circuit configuration as shown in FIG. 7, it is not possible to directly measure the output side phase voltage and line voltage. This is because what is measured at this time is the neutral point O (zero potential) and the output terminal on the load side, not the neutral point at the center (core) of the secondary side circuit.

Therefore, in the secondary circuit of FIG.
It is assumed that the voltages generated at −C and CA flow through the loads Ra, Rb and Rc via the neutral point O, and the values of the loads Ra, Rb and Rc can be varied. At this time, the neutral point O is connected to the ground and fixed at 0 potential. However, no current is exchanged between the ground and the neutral point O, and the neutral point O functions only as the neutral point O. When the values of the loads Ra, Rb, Rc are balanced, the values of Va, Vb, Vc are terminals AB, BC, C
−A (hereinafter referred to as “secondary line voltage”) is one-third of the voltage route (√). Here, assuming that the load Ra is 0 ohm and Rb and Rc are open, Va generates 0V, and Vb and Vc generate voltages equivalent to the secondary side line voltage.

After all, the values of Va, Vb, and Vc measured with respect to the change in the load impedance do not indicate the phase voltage because the secondary circuit itself floats with respect to the 0 potential. Can be said to represent the relative strength of In other words, when the load is a balanced load, that is, when Ra = Rb = Rc, almost represents a phase voltage.

(1) Here, Va, Vb, Vc of the present invention
A circuit for estimating the secondary side line voltage will be described. First, when it is assumed that the load Ra = Rb = Rc and the load is balanced,
The detected voltages shown in FIG. 1 are replaced with the vector points Va, Vb,
Attention is paid to the relationship between the area S surrounded by Vc and the voltage between the secondary side lines in FIG.

If the load is balanced, Va = Vb = Vc, and is equal to 1 / √3 times the phase voltage between the secondary lines (phase voltage). It can be seen as the voltage between. From this, the relationship between the secondary side line voltage: the square root of the area S is obtained by comparing the side and the square root of the area in FIG. The meaning of the square root of the area is to make the units uniform, but this is because the relationship between the area and the side is not proportional when the lengths of the sides are different.
This is to be compared with the secondary side line voltage.

(1) In the case of one balanced load, where Va, Vb, and V when balanced with Va = Vb = Vc
As shown in FIG. 7, the area surrounded by c is S1 + S2 +
It becomes S3.

Here, S1 = S2 = S3, and for example, S
The area of 1 is as follows.

I = Va × Vc × cos 30 ° / 2 = (1
/ √3 × 1 / √3 cos30 °) / 2 = cos30 ° /
6 (S2 and S3 are the same) Therefore, S = S1 + S2 + S3 = 3 × cos30 ° / 6 = c
os30 ° / 2, and the square root is √ (cos30 °
/ 2)-Equation.

After all, the square root of the area: secondary side line voltage = √
(Cos 30 ° / 2): 1 is obtained.

(2) When one phase is floating at 0 potential,
That is, when Vb in FIG. 9 approaches the neutral point O, the points Va ′ and V
The square root of the area S surrounded by c 'and O is √S = √Va'
× Vc ′ × cos 30 ° / 2) = √ (1 × 1 × cos3
0 ° / 2) = √ (cos 30 ° / 2), which is the same value as the equation.

It is assumed that Va 'and Vc' are on the extension of Va and Vc.

(3) Unbalance of each phase By analogy with the results of (1) and (2), even if all three phases are unbalanced, that is, when Va 'と き W' ≠ Vc '(2 The secondary side line voltage is “1”. The square root of the area = Ｓ (S1 + S2 + S3) = √ (cos3
0 ° / 2), S1 = (Va ′ × Vc ′ × cos30 °) / 2 S2 = (Vb ′ × Vc ′ × cos30 °) / 2 S3 = (Vb ′ × Vc ′ × cos30 °) / 2 into the equation, and cos30 ° / 2 × (Va ′ × Vc ′ + Vb ′ × V
a ′ + Vb ′ × Vc ′) = √ (cos 30 ° / 2), therefore, √ (Va ′ × Vc ′ + Vb ′ × Va ′ + V
b ′ × Vc ′) = 1−Equation is obtained.

The relationship between the square root of the area and the line voltage is √ (co
s30 ° / 2): 1, the right term of the equation can be used as it is as the secondary side line voltage.

As a result, the secondary side line voltage = √ (Va ′ ×
Vc '+ Vb'.times.Va' + Vb'.times.Vc ')-Expression is obtained.

Where Va ', Vb' and Vc 'are Va, V
b, Vc.

From the above, the following can be said.

1) Only the scalar of the central effective value is calculated from the square number of the detected voltage in the above equation.

2) Even if an imbalance occurs on the load side in FIG. 8, the detected voltage conforms to the phase of the original vectors A, B and C. (Thus, the above calculation is possible). At this time, naturally, there is also a difference between the values of the line voltages of the furnace transformer, but the result of the above equation shows only a central value.

Equation 3) can be applied as an impedance scale in a voltage deviation generating circuit.

FIG. 10 is a block diagram for explaining a second embodiment of the present invention. In the first embodiment described above, the main circuit is a three-phase circuit. However, the present embodiment is configured to be applicable to a case where the main circuit is a single-phase circuit.

Specifically, only the configurations of the arc voltage / tap voltage effective value conversion circuit 48, the voltage deviation target value conversion circuit 49, and the averaging circuit 50 are different. The arc voltage / tap voltage effective value conversion circuit 48 adds the arc voltages Va and Vc. The voltage deviation target value conversion circuit 49 divides the value obtained by the arc voltage / tap voltage effective value conversion circuit 48 by two. The averaging circuit 50 averages the values converted by the voltage deviation target value conversion circuit 49. Other configurations are the same as those of the first embodiment.

[0058]

According to the present invention, it is possible to provide an arc furnace apparatus capable of reducing the setting error of the arc current accompanying the output voltage fluctuation of the furnace transformer.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an arc furnace device of the present invention.

FIG. 2 is a block diagram for explaining a first embodiment of the arc furnace device of the present invention.

FIG. 3 is a waveform chart of an arc voltage and an arc current for explaining the operation and effect in the embodiment of FIG. 2;

FIG. 4 is an enlarged view of the waveform diagram of the arc voltage in FIG. 3;

FIG. 5 is an enlarged view of the waveform diagram of the arc current in FIG. 3;

FIG. 6 is a waveform diagram of an arc voltage and an arc current of a conventional arc furnace device.

FIG. 7 is a diagram for explaining the principle of the present invention, in which the secondary side of the furnace transformer has a line voltage or a phase voltage based on the measured value of the voltage between the three-phase output terminal of the Δ connection and the earthing device (earth). The figure which shows the circuit which converts (predicts) voltage.

FIG. 8 is a diagram for explaining the function of FIG. 7;

FIG. 9 is a diagram for explaining the function of FIG. 7;

FIG. 10 is a block diagram for explaining a second embodiment of the arc furnace device of the present invention.

FIG. 11 is a system diagram of an arc furnace device.

FIG. 12 is a cross-sectional view illustrating FIGS. 1 and 10 and a conventional arc furnace.

FIG. 13 is a diagram showing one cycle of operation of the arc furnace and the average power input during each operation.

FIG. 14 is a diagram showing a schematic configuration of a conventional arc furnace device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Arc furnace 4 ... Impedance control device 11 ... Graphite electrode 12 ... Scrap 13 ... Electrode raising / lowering device 14 ... Furnace lid 15 ... Drive mechanism 16 ... Furnace 17 ... Refractory 18 ... Grounding device 21 ... Power transmission system 22 ... Distribution transformer 23 ... power distribution system 24 ... series reactor 25 ... three-phase furnace transformer 27 ... fixed value 28 ... voltage drop compensation circuit 29 ... line voltage effective value calculator 30 ... phase voltage converter 31 ... impedance scale 32 ... arc current Detection gain 33 ... Electrode elevating sensitivity setting device 41 ... Tap voltage effective value calculating circuit 42 ... Voltage deviation target value conversion circuit 43 ... Averaging circuit 44 ... Voltage deviation output circuit 45 ... Arc current setting circuit 46 ... Electrode elevating sensitivity setting device 47: proportional constant circuit 48: tap voltage effective value conversion circuit 49: voltage deviation target value conversion circuit 50: averaging circuit

Claims (3)

[Claims] An electrode of an arc furnace is raised and lowered by an electrode lifting device, and AC power from a furnace transformer is supplied to the electrode to melt the scrap in the arc furnace. An apparatus for calculating a voltage deviation target value from an arc voltage detection value in the apparatus; and applying the voltage deviation target value calculated by the calculation apparatus and a current deviation obtained based on the arc current detection value to the pole lifting / lowering apparatus. An arc furnace device comprising: a device for calculating a speed reference; 2. An electrode for a three-phase arc furnace is raised and lowered by an electrode lifting device, and AC power from a three-phase furnace transformer is supplied to the electrode to melt the scrap in the arc furnace. An effective value calculating circuit for inputting the detected values of the three-phase arc voltages to calculate the effective value of the secondary voltage of the furnace transformer, respectively, and multiplying the effective value obtained by the effective value calculating circuit by a proportional constant. An averaging circuit for post-averaging, and a voltage deviation output circuit for inputting a one-phase value of the arc voltage detection value and the average value obtained by the averaging circuit and obtaining a voltage deviation from a difference between the two. An arc current setting circuit for obtaining a current deviation from an arc current detection value and a value obtained by multiplying the arc current detection value by a proportional constant; and subtracting the voltage deviation of the voltage deviation output circuit from the current deviation of the arc current setting circuit. Speed base given to the electrode lifting device Arc furnace apparatus having an electrode elevation sensitivity setter, the seeking. 3. An electrode for a single-phase arc furnace is raised and lowered by an electrode lifting device, and AC power from a single-phase furnace transformer is supplied to the electrode to melt the scrap in the arc furnace. A single-phase arc voltage detection value is inputted, and an effective value calculating circuit for calculating an effective value of the secondary voltage of the furnace transformer, and an effective value obtained by the effective value calculating circuit is multiplied by a proportional constant. An averaging circuit for post-averaging, a voltage deviation output circuit for inputting one of the arc voltage detection values and the average value obtained by the averaging circuit and obtaining a voltage deviation from a difference between the two; An arc current setting circuit for obtaining a current deviation from an arc current detection value and a value obtained by multiplying the arc current detection value by a proportional constant; and subtracting the voltage deviation of the voltage deviation output circuit from the current deviation of the arc current setting circuit. Velocity base given to electrode lifting device Arc furnace apparatus having an electrode elevation sensitivity setter, the seeking.