JPH0257888A - Electrode elevation control method for dc arc furnace - Google Patents

Abstract

PURPOSE:To improve productivity and an original unit and to stabilize a charge power by a method wherein the voltage of a moving electrode increased responding to an increase amount of a moving electrode is detected, and when an increase amount of the voltage of the moving electrode responding to an increase amount of the moving electrode is below a specified value, operation in a rise direction of the moving electrode is stopped for a specified time. CONSTITUTION:A voltage Vr applied on a moving electrode 4 for melting scraps 2 in a DC arc furnace 1 is detected by a voltage detector 9. According to a voltage deviation (Vd - Vr) between the detecting voltage Vr and a set voltage Vd set by means of a voltage set value 10, by means of a moving speed command value from a speed controller 21, elevation of the moving electrode 4 is effected. Through detection of a continuous increase of the moving electrode 4 to a value exceeding a specified value, through detection of the voltage of the moving electrode increased in response to an increase amount DELTAL of the moving electrode 4, and when an increase amount DELTAV of the voltage of the moving electrode responding to the increase amount DELTAL of the moving electrode 4, i.e. potential frequency X = DELTAV / DELTAL, is below a specified value, operation in a rise direction of the moving electrode 4 is stopped for a specified time T.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for controlling the elevation of a DC arc furnace electrode, which controls the position of a movable electrode (also referred to as an arc electrode) in a DC arc furnace, particularly during poling. The present invention also relates to a method for controlling electrode elevation in a DC arc furnace that can eliminate the occurrence of arc breakage due to the side arc phenomenon when scrap collapses.

(Prior art) Generally, in a DC arc furnace for steelmaking, for example, an arc is generated from a movable electrode, and materials to be melted such as scrap (hereinafter referred to as scrap), which are melting raw materials, are melted at the bottom of the furnace. However, when the scrap is melted, the shape of the scrap changes from time to time, and the arc current changes accordingly, so the desired arc current can be obtained reliably. That is, in order to reliably generate an arc, it is necessary to control the movement of the movable electrode in a complicated manner.

For this reason, conventionally, as shown in FIG. 3, after filling the inside of a DC arc furnace 1 with scrap 2 and closing a furnace lid 3 on the top of the furnace, a movable electrode such as a carbon electrode is inserted from the top of the furnace lid 3. Insert the furnace transformer 5, thyristor converter 6. A predetermined arc current is passed between the movable electrode 4 and the bottom electrode 8 via the smoothing reactor 7, and while controlling the position of the movable electrode 4 so as to always apply a desired voltage, the tip of the movable electrode 4 is The scrap 2 is sequentially melted by generating an arc. (The operating stage in which the movable electrode 4 is lowered while melting the scrap 2 and creating holes is called the poling stage.) In other words, when this arc occurs, the movable electrode 4 and the bottom electrode 8 A voltage V" between
The voltage deviation from the predetermined set voltage Vd is subtracted by subtractor 1.
1, the adjusting section 12 performs a proportional integral calculation so that this voltage deviation becomes zero, and the operation output (control signal) obtained thereby is given to the electric motor 13 for lifting and lowering the electrode.

The electric motor 13 for lifting and lowering the electrode rotates forward or backward based on the operation output, and the winch 14 accordingly winds or unwinds the other end of the wire 15, which has one end as a fixed end. The mast 16 is controlled to move up and down. At this time, the holder arm 17 horizontally fixed to the upper part of the mast 16 moves up and down together, so that the movable electrode 4 is raised and lowered via this holder arm 17, and a predetermined position is placed between the movable electrode 4 and the hearth bottom electrode 8. is applied, and an arc having a desired shape is generated from the tip of the movable electrode 4.

Therefore, in this type of electrode elevation 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).
d-Vr>O), control is performed to raise the movable electrode 4. In controlling the arc current, the arc current is extracted from the DC output side of the thyristor converter 6 or the output side of the hearth bottom electrode 8, and the current deviation between the detected current I' and the set current !d becomes zero. The gate control angle α is determined using an automatic current regulator, and the gate of the thyristor converter 6 is controlled in accordance with this gate control angle α.

(Issue 8 to be solved by the invention) By the way, in the electrode elevation control method as described above, basically the voltage between the movable electrode 4 and the furnace bottom electrode 8, that is, the arc voltage, and the arc length are proportional. Therefore, it is assumed that the arc voltage and the electrode position are also in a proportional relationship, and the arc voltage is controlled by controlling the entire movable electrode 4 to move up and down. That is, when the movable electrode 4 is raised, the arc voltage increases proportionally, and when the movable electrode is lowered, the arc voltage decreases proportionally. However, especially when polling or scrap collapses (scrap 2 is placed near the movable electrode 4),
2), since the arc voltage and the vertical position of the movable electrode are not necessarily in a proportional relationship, good control cannot be performed and there is a problem that arc breakage occurs. In other words, this is a phenomenon in which the arc flies to the side of the hole during poling (an arc occurs above when a thin hole is dug during poling, or scrap comes into contact with the side of the electrode due to scrap crumbling after poling), Due to the so-called side arc phenomenon, the voltage does not increase no matter how much the movable electrode is raised, and eventually the voltage is raised too much and arc breakage occurs.

When this arc breakage occurs, the movable electrode 4
must be lowered to the molten steel surface and re-ignited each time. As a result, not only does the operating time of the DC arc furnace 1 become longer, resulting in lower productivity and worse unit consumption, but also the input power is reduced until the movable electrode 4 is lowered and re-ignited. Becomes unstable.

The present invention has been made to solve the above-mentioned problems, and its purpose is to eliminate arc breakage due to side arc phenomenon during polling, improve productivity,
The object of the present invention is to provide a method for controlling the elevation of electrodes in a DC arc furnace, which is capable of improving unit consumption and stabilizing input power.

(Means and operations for solving the problem) In order to achieve the above object, the present invention detects the voltage applied to the movable electrode that melts the material to be melted in the DC arc furnace, and In a method for controlling the elevation of a movable electrode in a DC arc furnace, the elevation of the movable electrode is controlled in accordance with the voltage deviation from a predetermined set voltage. Detects the voltage of the movable electrode that has increased in accordance with the amount of rise, and when the amount of increase in the movable electrode voltage with respect to the amount of rise of the movable electrode is less than a specified value, the operation of the movable electrode in the upward direction is stopped for a specified period of time. By doing so, it is possible to prevent the movable electrode from rising above the rising limit value, to prevent arc breakage from occurring due to the side arc phenomenon during bow and ring, and to perform good electrode elevation control.

(Example) Hereinafter, an example 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 an electrode lifting control system for a DC arc furnace to which the method of the present invention is applied, and the same parts as in FIG. Only the different parts will be described here.

As shown in FIG. 1, this system includes a voltage detector 9, a voltage setter 10, a subtracter 11, a speed setting controller 18, a rise/fall switching circuit 19, a speed detector 20, and a speed It is composed of a 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 V' between the movable electrode 4 and the bottom electrode 8, and the voltage setter 10 sets the set voltage Vd in advance. 1
1 is the voltage deviation (Vd-
Vr). Further, the speed setting controller 18 inputs the voltage deviation from the subtractor 11, performs proportional integral calculation so that the voltage deviation becomes zero, and outputs a speed setting value (absolute value).

On the other hand, the rise/fall switching circuit 19 inputs the voltage deviation from the subtracter 11 and the speed setting value from the speed setting controller 18, and changes the speed setting value to positive or negative depending on the positive or negative polarity of the voltage deviation. It adds polarity and outputs it as a moving speed command value in the upward or downward direction. That is, when the voltage deviation is positive, a moving speed command value in the upward direction is output, and when the voltage deviation is negative, a moving speed command value in the downward direction is output. Further, the speed detector 20 detects the rotational speed of the electrode lifting motor 13, that is, the lifting speed of the movable electrode 4. Furthermore, the speed controller 21 increases/
The moving speed command value from the lowering switching circuit 19 and the detected speed from the speed detector 20 are input, proportional integral calculation is performed so that the deviation between the two becomes zero, and the operation output (# control signal) is used for electrode elevation. This is given to the electric motor 13.

On the other hand, the position detector 22 detects the position of the movable electrode 4. Further, the electrode rise limit calculation circuit 23 inputs the detected voltage Vr from the voltage detector 9, the set voltage Vd from the Ti pressure setting device 10, and the detected position from the position detector 22, and receives the rising amount ΔL of the movable electrode 4. Detects the voltage ΔV of the movable electrode 4 that has increased in response to the amount of increase in the movable electrode 4, and determines that the amount of increase in the movable electrode voltage with respect to the amount of rise of the movable electrode 4, that is, the potential gradient X-ΔV/ΔL as shown in FIG. It outputs an operation signal when . Furthermore, the timer circuit 24
receives the operation signal from the electrode rise limit calculation circuit 23, operates for a specified time T based on the operation signal, and supplies the operation signal to the speed setting controller 18 to set the rise speed setting value zero. be. In this case, the prescribed time T is set to correspond to the time required for the scrap caused by the side arc phenomenon (for example, scrap that has come into contact with the side surface of the movable electrode due to scrap collapse) to melt.

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

Now, by igniting the thyristor converter 6, a DC high voltage is applied between the movable electrode 4 and the furnace bottom electrode 8 of the DC arc furnace 1, and an arc is generated from the tip of the movable electrode 4, causing a DC arc. The operation of the furnace 1 is started, and the process moves to the polling period, which is the first stage. On the other hand, the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 is detected by the voltage detector 9, and this detected voltage Vr is detected by the subtractor 11, and the voltage deviation (
Vd-Vr) is calculated. Next, the speed setting controller 18
Then, proportional-integral calculation is performed so that this voltage deviation becomes zero, and the speed setting value increases /
It is input to the downward switching circuit 19. Then, in the ascending/descending switching circuit 19, a moving speed command value in the ascending or descending direction is obtained depending on the positive or negative polarity of the voltage deviation from the subtracter 11.

That is, when the voltage deviation is positive, a moving speed command value in the upward direction is obtained, and when the voltage deviation is negative, a moving speed command value in the downward direction is obtained, and this is output to the speed controller 21. Furthermore, the speed controller 21 calculates the deviation between the moving speed command value from the up/down switching circuit 19 and the detected speed from the speed detector 20, and performs proportional integral calculation so that this deviation becomes zero. An operation output (control signal) is given to the electric motor 13 for lifting and lowering the electrode. Then, in accordance with the movement speed command value from the speed controller 21, the electrode elevating motor 13 rotates forward or reverse at the commanded speed, whereby the movable electrode 4 is controlled to rise or fall.

On the other hand, the position of the movable electrode 4 is detected by the position detector 22,
This detected position is input to the electrode rise limit calculation circuit 23 together with the detected voltage Vr from the voltage detector 9 and the set voltage Vd from the voltage setter 10. In this case, for example, when a narrow hole is dug during poling, an arc is generated above, or a side arc phenomenon occurs due to the scrap 2 not coming into contact with the side surface of the movable electrode 4 due to scrap crumbling after poling. When the movable electrode 4 is raised continuously by the specified value ΔL or more, the voltage does not increase by the voltage ΔV corresponding to the increase amount, so the increase amount ΔV1 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 less than the specified value, and the electrode rise limit calculation circuit 23 outputs an operation signal to the timer circuit 24. Then, the timer circuit 24 is operated by this operating signal, and the operating signal is applied to the speed setting controller 18 for a specified time T, thereby locking the rising speed setting value, that is, the rising speed with zero magnitude. The set value is input to the rise/fall switching circuit 19. Therefore, during this specified time T required for the scrap 2 caused by the side arc phenomenon to melt, the electrode lifting motor 1
By stopping the lifting operation of No. 3, the lifting of the movable electrode 4 is also stopped, and the lifting control of the movable electrode 4 that exceeds the lifting limit is prevented, so arc breakage does not occur.

In addition, when the scrap 2 caused by the side arc phenomenon is melted and the side arc phenomenon disappears, if the movable electrode 4 is continuously raised by more than the specified value ΔL, the voltage ΔV corresponding to the amount of increase is increased. Since the voltage increases, the potential gradient X-ΔV/ΔL exceeds the specified value, and the electrode rise limit calculation circuit 23 does not output an operation signal. ``Therefore, as usual, the movable electrode 4 is controlled to move up and down based on the movement speed command value that corresponds to the speed setting value that corresponds to the voltage deviation.

As described above, in this 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 set by the voltage setter 10 are set. Depending on the voltage deviation from the set voltage Vd,
When controlling the elevation of the movable electrode 4, it is detected that the movable electrode 4 has risen continuously by more than a specified value, and the movable electrode 4 is
The voltage of the movable electrode that has increased corresponding to the amount of increase ΔL of the movable electrode 4 is detected, and when the amount of increase ΔV1 of the movable electrode voltage with respect to the amount of increase ΔL of the movable electrode 4, that is, the potential gradient The operation of the electrode 4 in the upward direction is stopped for a specified time T.

Therefore, when poling the DC arc furnace 1, if a thin hole is dug during poling, an arc may occur above.
Alternatively, when a side arc phenomenon occurs due to the scrap 2 coming into contact with the side surface of the electrode due to scrap collapse after poling, it is possible to prevent arc breakage from occurring due to the movable electrode 4 being raised too high. Therefore, it is no longer necessary to repeat the series of operations of raising the movable electrode 4 → occurrence of arc breakage → re-ignition, so the operating time of the DC arc furnace 1 is not extended, improving productivity and saving energy. In addition to making it possible to improve the unit, it also stabilizes the input power by eliminating the instability of the input power until the movable electrode 4 is lowered and re-ignition is performed, reducing the power outage time. This makes it possible to perform extremely good control even during polling.

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

(Effects of the Invention) As explained above, according to the present invention, it is possible to detect that the movable electrode has increased continuously by more than a specified value, and to detect the voltage of the movable electrode that has increased in accordance with the amount of rise of the movable electrode. , when the amount of increase in the movable electrode voltage relative to the amount of rise of the movable electrode is less than a specified value, the movement of the movable electrode in the upward direction is stopped for a specified period of time, thereby preventing the occurrence of arc breakage due to the side arc phenomenon during polling. It is possible to provide a method for controlling the electrode elevation of a DC arc furnace, which can improve productivity, improve unit consumption, and stabilize input power by eliminating the above.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing an embodiment of an electrode elevation control system for a DC arc furnace to which the present invention is applied, Fig. 2 is a diagram for explaining the apparent potential gradient in the embodiment, and Fig. 3 1 is a configuration diagram showing a conventional electrode lifting/lowering control system for a DC arc furnace. 1... DC arc furnace, 2... Scrap, 4...
Movable electrode, 5... Furnace transformer, 6... Thyristor converter, 7... Smoothing reactor, 8... Hearth bottom electrode, 9
... Voltage detector, 10... Voltage setting device, 11...
Subtractor, 18...Speed setting controller, 19...Rise/
Descending switching circuit, 20... Speed detector, 21... Speed controller, 22... Position detector, 23... Electrode rise upper limit calculation circuit, 24... Timer circuit. Figure 2

Claims (1)

[Claims] A voltage applied to a movable electrode that melts a material to be melted in a DC arc furnace is detected, and the voltage applied to the movable electrode is determined according to the voltage deviation between the detected voltage and a predetermined set voltage. In a method for controlling electrode elevation of a DC arc furnace that performs elevation control, detecting that the movable electrode has continuously risen above a specified value, and detecting the voltage of the movable electrode that has increased in accordance with the amount of rise of the movable electrode. , Electrode elevation control for a DC arc furnace, characterized in that when the amount of increase in the movable electrode voltage relative to the amount of elevation of the movable electrode is below a specified value, the operation of the movable electrode in the upward direction is stopped for a specified period of time. Method.