JP2769326B2 - Control method for raising and lowering electrodes of DC arc furnace - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for controlling an electrode elevation of a DC arc furnace for controlling the position of a movable electrode (also referred to as an arc electrode) of a DC arc furnace, and more particularly to a method for boring and scrapping. The present invention relates to a method of controlling an electrode rise of a DC arc furnace, which can prevent occurrence of arc breakage due to a side arc phenomenon at the time of collapse.

(Prior Art) In general, for example, in a DC arc furnace for iron making, a material to be melted such as scrap as a raw material for melting (hereinafter referred to as scrap) while generating an arc from a movable electrode.
Is melted to obtain molten steel at the furnace bottom, but the shape of the scrap changes moment by moment when the scrap is melted,
Since the arc current changes accordingly, in order to reliably obtain a desired arc current, that is, to surely generate an arc, it is necessary to frequently raise and lower the movable electrode.

For this reason, conventionally, as shown in FIG. 3, after filling the scrap 2 inside the DC arc furnace 1 and closing the furnace lid 3 on the upper part of the furnace, a movable electrode such as a carbon electrode is placed from the upper part of the furnace lid 3. 4 and a predetermined arc current is passed between the movable electrode 4 and the furnace bottom electrode 8 via the furnace transformer 5, the thyristor converter 6, and the smoothing reactor 7, so that a desired voltage is always applied. While the position of the movable electrode 4 is controlled, an arc is generated from the tip of the movable electrode 4 to melt the scrap 2 sequentially. (Thus, the operation stage in which the scrap 2 is melted to form holes while the movable electrode 4 is lowered is called a boring period.) That is, when the arc is generated, the movable electrode 4 and the furnace bottom electrode 8 are connected to each other. Is detected by the voltage detector 9, a voltage deviation between the detected voltage Vr and a preset voltage Vd determined by the voltage setting device 10 is obtained by the subtractor 11, and the voltage deviation becomes zero. As described above, the proportional integral calculation is performed by the adjustment unit 12, and the operation output (control signal) obtained by the operation is supplied to the electrode lifting / lowering motor 13. The electrode lifting / lowering motor 13 rotates forward or backward based on the operation output, and the winch 14 winds or rewinds the other end of the wire 15 having one end as a fixed end. The mast 16 is controlled to move up and down. At this time, the mast
The movable electrode 4 is moved up and down via the holder arm 17 by vertically moving the holder arm 17 fixed horizontally on the upper portion 16, and a predetermined voltage is applied between the movable electrode 4 and the furnace bottom electrode 8. As a result, an arc having a desired shape is generated from the tip of the movable electrode 4.

Therefore, in this type of electrode lifting / lowering control method, when the set voltage is smaller than the detected voltage (Vd−Vr <0), the movable electrode 4 is lowered, and the set voltage is larger than the detected voltage (Vd−Vr−0).
When there is a relationship of Vr> 0), control is performed so as to raise the movable electrode 4. In controlling the arc current, an arc current is extracted from the DC output side of the thyristor converter 6 or the output side of the hearth electrode 8 so that the current deviation between the detected current Ir and the set current Id becomes zero. The gate control angle α is obtained by the automatic current regulator, and the gate of the thyristor converter 6 is controlled according to the gate control angle α.

(Problems to be Solved by the Invention) In the above-described electrode elevation control method, basically, the voltage between the movable electrode 4 and the furnace bottom electrode 8, that is, the arc voltage is proportional to the arc length. The arc voltage and the electrode position are also in a proportional relationship, and the control of the arc voltage is performed by controlling the movable electrode 4 to move up and down. That is, when the movable electrode is raised, the arc voltage is increased proportionally, and when the movable electrode is lowered, the arc voltage is reduced proportionally. However, particularly during boring and scrap collapse (when the scrap 2 is present at a position near the movable electrode 4), the arc voltage and the position of the movable electrode are not necessarily in a proportional relationship. There is a problem that it is not possible to perform the operation and an arc break occurs. That is, this is a phenomenon in which the arc flies to the side surface of the hole at the time of boring (an arc occurs upward when a thin hole is dug during boring, or scrap contacts the electrode side surface due to scrap collapse after boring), When the so-called side arc phenomenon occurs, no matter how much the movable electrode is raised, the voltage does not rise, but finally the arc is broken due to the excessive rise. When this arc break occurs, the movable electrode 4 must be lowered to the molten steel surface and re-ignition must be repeated each time. As a result, the DC arc furnace 1
Not only does the operating time increase, which leads to a decrease in productivity and a deterioration in basic unit, but also the input power decreases and becomes unstable until the movable electrode 4 is lowered and re-ignition is performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to eliminate the occurrence of arc breakage due to a side arc phenomenon at the time of boring, thereby improving productivity, improving the basic unit, and supplying electric power. It is an object of the present invention to provide a method for controlling the elevation of an electrode of a DC arc furnace capable of stabilizing the temperature.

(Means and Actions for Solving the Problems) In order to achieve the above object, according to the present invention, a voltage applied to a movable electrode for melting a substance to be melted in a DC arc furnace is detected, and this detected voltage is preliminarily determined. In an electrode lift control method for a DC arc furnace, in which a movable electrode is lifted and lowered according to a voltage deviation from a predetermined set voltage, it is detected that the movable electrode continuously rises above a specified value, and the movable current rises. The voltage of the movable electrode increased according to the amount is detected, and when the amount of increase in the movable electrode voltage with respect to the amount of rise of the movable electrode is equal to or less than a specified value, the operation of the movable electrode in the rising direction is stopped for a specified time. Thereby, it is possible to prevent the movable electrode from rising above the rising limit value, prevent an arc break due to a side arc phenomenon at the time of boring, and perform a good electrode elevation control. You.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example of the overall configuration of a DC arc furnace electrode elevation control system to which the method of the present invention is applied.
The same parts as those in the drawings are denoted by the same reference numerals, and the description thereof will be omitted.
Here, only different parts will be described.

The system comprises a voltage detector 9 as shown in FIG.
Voltage setting device 10, Subtractor 11, Speed setting controller 18, Up / Down switching circuit 19, Speed detector 20, Speed controller 21
, A position detector 22, an electrode rise limit calculation circuit 23, and a timer circuit 24.

Here, the voltage detector 9 detects the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8, and the voltage setter 10 sets the set voltage Vd in advance. Also, the subtractor 11
A voltage deviation (Vd−Vr) between the voltage Vr detected by the voltage detector 9 and the set voltage Vd set by the voltage setting device 10 is calculated. Further, the speed setting controller 18 receives the voltage deviation from the subtracter 11 as input, performs a proportional-integral operation so that the voltage deviation becomes zero, and outputs a speed setting value (absolute value).

On the other hand, the up / down switching circuit 19 receives the voltage deviation from the subtractor 1 and the speed setting value from the speed setting controller 18 as inputs, and outputs a positive or negative speed setting value according to the positive or negative polarity of the voltage deviation. A polarity is added to output the moving speed command value in the ascending or descending direction. That is, when the voltage deviation is positive, the moving speed command value in the rising direction is output, and when the voltage deviation is negative, the moving speed command value in the falling direction is output. The speed detector 20 is a motor 13 for raising and lowering the electrode.
, That is, the moving speed of the movable electrode 4. Further, the speed controller 21 receives the moving speed command value from the ascending / descending switching circuit 19 and the detected speed from the speed detector 20 as inputs, performs a proportional-integral operation so that the deviation between them becomes zero, and outputs an operation output. (Control signal) to the motor 13 for raising and lowering the electrode.

On the other hand, the position detector 22 detects the position of the movable electrode 4. Further, the electrode rise limit calculation circuit 23 detects the detection voltage Vr from the voltage detector 9 and the set voltage Vr from the voltage setter 10.
d, the detection position from the position detector 22 is input and the movable electrode 4
The voltage ΔV of the movable electrode 4 increased in accordance with the rise amount ΔL of
Is detected, and the amount of increase of the movable electrode voltage with respect to the amount of increase of the movable electrode 4, that is, the potential gradient X = Δ as shown in FIG.
An operation signal is output when V / ΔL is equal to or less than a specified value. Further, the timer circuit 24 receives the operation signal from the electrode rising limit calculation circuit 23 as input, operates by the operation signal for a specified time T, and gives the operation signal to the speed setting controller 18 to set the rising speed set value to zero. Is set. In this case, the specified time T is set to a time corresponding to the time required for melting a scrap caused by the side arc phenomenon (for example, a scrap in contact with the side surface of the movable electrode due to scrap collapse).

Next, a method for controlling the electrode elevation of the DC arc furnace in the present embodiment will be described.

Now, by firing the thyristor converter 6,
DC high voltage is applied between the movable electrode 4 and the bottom electrode 8 of the DC arc furnace 1, an arc is generated from the tip of the movable electrode 4, and the operation of the DC arc furnace 1 is started, which is an initial stage. Transition to the boring period. On the other hand, a voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 is detected by a voltage detector 9, and the detected voltage Vr is subtracted by a subtractor 11 from a voltage deviation (Vd−V) from a set voltage Vd.
r) is required. Next, the speed setting controller 18 performs a proportional-integral operation so that the voltage deviation becomes zero, and a speed setting value corresponding to the voltage deviation is increased / decreased by the up / down switching circuit.
Entered in 19. The ascending / descending switching circuit 19 obtains a moving speed command value in the ascending or descending direction according to the positive or negative polarity of the voltage deviation from the subtractor 11. That is, when the voltage deviation is positive, a moving speed command value in the rising direction is obtained, and when the voltage deviation is negative, a moving speed command value in the falling direction is obtained, which is output to the speed controller 21. further,
The speed controller 21 calculates a deviation between the moving speed command from the ascending / descending switching circuit 19 and the detected speed from the speed detector 20, performs a proportional-integral operation so that the deviation becomes zero, and outputs an operation output ( Control signal) is supplied to the electrode lifting / lowering motor 13. Then, in accordance with the moving speed command value from the speed controller 21, the electrode raising / lowering motor 13 rotates forward or backward at the command speed, whereby the movable electrode 4 is controlled to be raised or lowered.

On the other hand, the position of the movable electrode 4 is detected by the position detector 22,
This detection position is input to the electrode rise limit calculation circuit 23 together with the detection voltage Vr from the voltage detector 9 and the set voltage Vd from the voltage setting device 10. In this case, for example, when an arc is generated upward when a thin hole is dug during boring, or when the scrap 2 comes into contact with the side surface of the movable electrode 4 due to the scrap collapse of boring, a side arc phenomenon occurs. , Even if the movable electrode 4 is continuously raised by the specified value ΔL or more, the voltage ΔV corresponding to the amount of increase
Since the voltage does not increase only, the increase amount ΔV of the movable electrode voltage with respect to the increase amount ΔL of the movable electrode 4, that is, the potential gradient X
= ΔV / ΔL becomes equal to or less than the specified value, and the electrode rise limit calculation circuit
An operation signal is output to the timer circuit 24 from 23.
Then, the timer circuit 24 is operated by this operation signal, and the operation signal is given to the speed setting controller 18 for the specified time T, so that the ascending speed set value is locked, that is, the ascending speed of zero magnitude. The set value is input to the up / down switching circuit 19. Therefore, during the specified time T required for melting the scrap 2 caused by the side arc phenomenon, the ascending operation of the electrode lifting / lowering motor 13 is stopped, so that the ascending of the movable electrode 4 is also stopped, and the ascending limit is exceeded. Since the rising control of the movable electrode 4 is prevented, there is no occurrence of arc breakage.

When the scrap 2 caused by the side arc phenomenon is completely melted and the side arc phenomenon disappears, if the movable electrode 4 is continuously raised by the specified value ΔL or more, the voltage is increased by the voltage ΔV corresponding to the amount of increase. Rise, the potential gradient X = ΔV / ΔL becomes greater than or equal to a specified value, and no operation signal is output from the electrode rise limit calculation circuit 23. Accordingly, the control of moving the movable electrode 4 up and down is performed based on the moving speed command value corresponding to the speed setting value corresponding to the voltage deviation as originally.

As described above, in the present embodiment, the voltage Vr applied to the movable electrode 4 for melting the scrap 2 in the DC arc furnace 1 is detected by the voltage detector 9, and the detected voltage Vr and the voltage setter 10 are detected.
When performing the elevation control of the movable electrode 4 according to the voltage deviation from the set voltage Vd set in the above, it is detected that the movable electrode 4 has continuously risen by a specified value or more, and the rise amount ΔL of the movable electrode 4 is determined. The voltage of the movable electrode correspondingly increased is detected, and the increase amount Δ of the movable electrode voltage with respect to the increase amount ΔL of the movable electrode 4 is detected.
When V, that is, the potential gradient X = ΔV / ΔL is equal to or less than a specified value, the operation of the movable electrode 4 in the ascending direction is stopped for a specified time T.

Therefore, during boring of the DC arc furnace 1, an arc is generated upward when a thin hole is dug during boring, or a side arc phenomenon occurs due to the scrap 2 coming into contact with the electrode side surface due to scrap collapse after boring. In this case, it is possible to prevent the occurrence of arc breakage due to the movable electrode 4 being raised too much. Therefore, it is not necessary to repeatedly perform a series of operations of raising the movable electrode 4 → occurrence of an arc break → re-ignition, so that the operation time of the DC arc furnace 1 does not increase, thereby improving the productivity and reducing the unit consumption. And it is possible to stabilize the applied power by lowering the movable electrode 4 to perform re-ignition, stabilize the applied power, and reduce the power cutoff time. This makes it possible to perform very good control even during boring.

In the above embodiment, since the arc voltage fluctuates greatly, a low pie filter is provided between the voltage detector 9 and the subtracter 11 to average the detection voltage Vr, and an integrating circuit or a statistical processing circuit is provided. Alternatively, the detection voltage Vr may be averaged.

(Effects of the Invention) As described above, according to the present invention, it is detected that the movable electrode continuously rises by a predetermined value or more, and the voltage of the movable electrode that is increased according to the amount of rise of the movable electrode is detected. When the amount of increase of the movable electrode voltage with respect to the amount of rise of the movable electrode is equal to or less than a specified value, the operation of the movable electrode in the rising direction is stopped for a specified time. Thus, it is possible to provide a method of controlling the elevation of an electrode of a DC arc furnace, which can improve the productivity, improve the basic unit, and stabilize the input power.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of an electrode elevation control system of a DC arc furnace to which the present invention is applied, FIG. 2 is a diagram for explaining an apparent potential gradient in the embodiment, and FIG. 1 is a configuration diagram illustrating an electrode lifting / lowering control system of a DC arc furnace of FIG. DESCRIPTION OF SYMBOLS 1 ... DC arc furnace, 2 ... Scrap, 4 ... Movable electrode, 5 ... Transformer for furnace, 6 ... Thyristor converter, 7 ...
... Smoothing reactor, 8 ... Bottom electrode, 9 ... Voltage detector, 10 ... Voltage setting device, 11 ... Subtractor, 18 ... Speed setting controller, 19 ... Up / down switching circuit, 20 ... ... speed detector, 21 ... speed controller, 22 ... position detector, 23 ... electrode rising upper limit calculation circuit, 24 ... timer circuit.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Shoichi Takahashi, 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Toshimichi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Inside (72) Inventor Kinzo Okazaki 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (56) References JP-A-62-113383 (JP, A) JP-A-61- 285693 (JP, A) JP-B 63-5571 (JP, B2) JP-B 33-5590 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) F27B 3/08, 3 / 28 F27D 11/08 H05B 7/148

Claims (1)

(57) [Claims] A voltage applied to a movable electrode for melting an object to be melted in a DC arc furnace is detected, and the movable electrode is raised and lowered according to a voltage deviation between the detected voltage and a predetermined voltage. In the electrode raising / lowering control method of a DC arc furnace for performing control, detecting that the movable electrode continuously rises by a predetermined value or more, detecting a voltage of the movable electrode increased in accordance with the amount of rise of the movable electrode, When the amount of increase in the movable electrode voltage with respect to the amount of rise of the movable electrode is equal to or less than a specified value, the operation of the movable electrode in the rising direction is stopped for a specified time. .