JP2683374B2 - How to prevent arc breakage in a DC arc furnace - Google Patents

Description

The present invention relates to a method for preventing arc breakage in a DC arc furnace.

[Prior Art] FIG. 2 is an overall configuration diagram of a DC arc furnace, in which a DC arc furnace body 1 is provided with a furnace bottom electrode 2 on the bottom and a furnace lid 3 on the top to be closed. ing. A hole 4 is formed in the center of the furnace lid 3, and a movable electrode 5 is arranged in the hole 4. In addition, a scrap 6 which is an object to be melted is charged into the DC arc furnace main body 1. The movable electrode 5 is moved up and down inside the DC arc furnace 1 by a lifting device 7. That is, the lifting device 7 is provided with the electrode lifting motor 8, and the rotating shaft of the motor 8 is connected to the winch 9. A wire 10 having one end fixed to the winch 9
And a roller 12 of a mast 11 is hung on the wire 10. A holder arm 13 is provided on the mast 11, and the movable electrode 5 is provided on the holder arm 13.

On the other hand, the power supply system to the movable electrode 5 is as follows. A power transmission system 15 is connected to a primary side of the furnace transformer 14, and a thyristor converter 16 is connected to a secondary side of the transformer 14. The movable electrode 5 is connected to the output side of the thyristor converter 16 via a reactor 17. The power supply system is provided with an arc voltage and arc current control system. That is, the arc voltage control system includes a voltage detector between the bottom electrode 2 and the movable electrode 5.
The detection voltage output from the voltage detector 18, that is, the arc voltage is sent to the adder 19. The set voltage Vs set in the voltage setter 20 is input to the adder 19, and the adder 19 calculates the voltage deviation between the detected voltage and the set voltage Vs and sends it to the motor drive control unit 21. . Then, the motor drive control unit 21 executes PI control to obtain an elevation control signal according to the voltage deviation, and sends this signal to the electrode elevation motor 8. As a result, the gap between the movable electrode 5 and the scrap 6 is properly maintained.

On the other hand, in the arc current control system, a current detector 22 is connected between the reactor 17 and the movable electrode 5.
The detection current, that is, the arc current output from the controller is sent to the adder 23. The set current Is set in the current setter 24 is input to the adder 23, and the adder 23
Detects the deviation current between the detection current and the set current Is and sends it to the gate controller 25. Thus, this gate control unit 25
Controls the gate firing angle of the thyristor converter 16 according to the deviation current. Further, the detected current of the current detector 22 is sent to the falling determination unit 26. The descending determination unit 26 has a function of sending a signal for descending the movable electrode 5 at the maximum speed to the motor drive control unit 21 when the detected current becomes a predetermined value or less. Therefore, when the arc current becomes equal to or lower than a predetermined value during melting of the scrap 6, the movable electrode 5 rapidly descends.

[Problems to be solved by the invention]

By the way, the arc Q during melting of the scrap 6 does not always have the same direction. This is partly due to the gas atmosphere when the scrap 6 is melted.
Further, when the scrap 6 is melted, the scruff 6 becomes a molten metal, so that an arc Q is generated between the scrap 6 and another scrap 6, or the direction of the arc Q is changed due to the scrap 6 falling down or the like. By the way, such a change in the generation direction of the arc Q means, in other words, a change in the gap between the movable electrode 5 and the scrap 6 and a change in the arc length. In this case, the gap between the movable electrode 5 and the scrap 6 becomes large, the arc voltage becomes very high, the arc current decreases, and the arc may break. However, in such a case, the descent determination unit
The decrease of the arc current is detected by 26 and the movable electrode 5 is lowered. However, in the detection of the arc current, the time when the gap between the movable electrode 5 and the scrap 6 becomes large does not coincide with the time when the arc current decreases.
Since the constant current control is performed by 25, the arc current decreases with a delay after reaching the equipment limit. Therefore, the timing of lowering the movable electrode 5 may be delayed and the arc may be broken.

Therefore, an object of the present invention is to provide a method of preventing arc breakage in a DC arc furnace that can immediately lower the movable electrode to prevent arc breakage when the gap between the movable electrode and scrap becomes large.

[Means and actions for solving the problem]

The present invention provides a direct current voltage to a movable electrode of a direct current arc furnace to generate an arc between a melted object and a direct current which raises and lowers the movable electrode according to a voltage deviation between an arc voltage and a set voltage at this time. In the arc cut prevention method of the arc furnace,
A method for preventing arc breakage in a DC arc furnace, which detects an arc voltage, and lowers the movable electrode at a maximum speed when the arc voltage exceeds a predetermined voltage lower than the no-load maximum voltage.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 1 is an overall configuration diagram of an arc break prevention device for a DC arc furnace to which the method of the present invention is applied. In the figure, 30 is a rapid lowering means, which detects an arc voltage, and this arc voltage is a predetermined voltage V ₀ · V lower than the no-load maximum voltage V _0.
When β ₁ or more, the movable electrode 5 is lowered at the maximum speed V max, and when the arc voltage drops to V ₀ · β ₂ , the movable electrode 5 is stopped from descending and feedback is performed by the arc voltage. It has a function of returning to the control. Specifically, it is composed of a rapid fall determination unit 31 and a determination voltage setting unit 32. In the judgment voltage setting device 32, the judgment voltage V ₀ · β ₁ and the recovery voltage V ₀ · β ₂ for returning to the feedback control by the arc voltage are set in advance. In addition, the rapid-fall determination unit 31 compares the detection voltage from the voltage detector 18 with the determination voltage V ₀ · β ₁ set in the determination voltage setting device 31 to determine that the detection voltage is the determination voltage V ₀ · β. When it becomes higher than _{1, the} function of continuing to send the descending command to descend the movable electrode 5 at the maximum speed V max to the motor drive control unit 21, and the detection voltage and the recovery voltage when the descending command is sent. V ₀ · β ₂
It has a function of resetting the descending command when the detected voltage becomes equal to or lower than the recovery voltage V ₀ · β ₂ by comparing with.

Next, the operation of the device configured as described above will be described with reference to the drawings.

When a DC voltage is supplied to the movable electrode 5 and an arc Q is generated between the movable electrode 5 and the scrap 6, this arc Q
Due to this, the scrap 6 is melted. At this time, the arc voltage is detected by the voltage detector 18 and sent to the adder 19 to obtain the voltage deviation from the set voltage Vs, and this voltage deviation is sent to the motor drive control unit 21. Then, the motor drive control unit 21 sends an elevation control signal for zeroing the voltage deviation to the electrode elevation motor 8, and the movable electrode 5 is elevated. Then, the scrap 6 is melted by the arc Q between the movable electrode 5 and the scrap 6 while the movable electrode 5 is vertically controlled in this manner.

At this time, the arc voltage detected by the voltage detector 18 is also sent to the rapid fall determination unit 31. Then, the rapid fall determination unit 31 compares the detection voltage with the determination voltage V ₀ · β ₁ ,
If the detected voltage is equal to or lower than the determination voltage V ₀ · β ₁ , a normal drive command is sent to the motor drive control unit 21. By the way, during the melting of the scrap 6, the direction in which the arc Q is generated may change and the arc length, that is, the gap between the movable electrode 5 and the scrap 6 may become wide. Then, the arc voltage increases and becomes equal to or higher than the determination voltage V ₀ · β ₁ . At this time, the rapid fall determination unit 31 determines that the detected voltage becomes equal to or higher than the determination voltage V ₀ · β ₁ and forces the motor drive control unit 21 to issue a lowering command to lower the movable electrode 5 at the maximum speed V max. To send out. As a result, the motor drive control unit 21 sends a lifting control signal for lowering the electrode lifting motor 8 at the maximum speed V max. Then, the movable electrode 5 descends at the maximum speed V max. As the movable electrode 5 descends, the gap between the movable electrode 5 and the scrap 6 becomes narrower and the arc voltage decreases. During this period, the rapid descent determination unit 31 continues to send the descent command. Then, when the arc voltage decreases and the arc voltage decreases to the voltage for restoration V ₀ · β ₂ or less, the rapid descending determination unit 31 resets the sending of the descending command. As a result, the arc Q is not broken, and the raising / lowering control of the movable electrode 5 is performed again by the feedback of the arc voltage.

As described above, in the above-described embodiment, the arc voltage is detected, and the movable electrode 5 is lowered when the arc voltage becomes equal to or higher than the determination voltage V ₀ · β ₁ which is higher than the no-load maximum voltage V _0. Therefore, even if the gap between the movable electrode 5 and the scrap 6 widens due to the gas atmosphere in the DC arc furnace body 1, the melting of the scrap 6, the collapse of the scrap 6, etc. The arc voltage can be lowered by lowering 5 at the maximum speed V max. As a result, even if the arc voltage fluctuates during melting of the scrap 6, the arc breakage disappears. In particular, since the arc voltage is detected to prevent the arc from being broken, it is possible to detect that the arc voltage has become faster than the arc current.

The present invention is not limited to the above-described embodiment, and may be modified without departing from the gist thereof.

〔The invention's effect〕

As described in detail above, according to the present invention, even if the gap between the movable electrode and the scrap becomes large and the arc voltage becomes very high due to the collapse of scrap or the like, the arc can be reduced by lowering the movable electrode at the maximum speed. It is possible to provide a method for preventing arc breakage in a DC arc furnace, which can prevent breakage and can prevent arc breakage against fluctuations in arc voltage during scrap melting.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an arc interruption prevention device for a DC arc furnace to which an embodiment of an arc interruption prevention method for a DC arc furnace according to the present invention is applied, and FIG. 2 is a prior art configuration diagram. 1 ... DC arc furnace main body, 2 ... furnace bottom electrode, 5 ... movable electrode, 6 ... scrap, 7 ... lifting device, 16 ... thyristor converter, 18 ... voltage detector, 19 ... addition Vessels, 20…
… Voltage setting unit, 21 …… Motor drive control unit, 22 …… Current detector, 23 …… Adder, 24 …… Current setting unit, 25 …… Gate control unit, 30 …… Rapid descent means, 31 …… Rapid descent determination unit,
32 …… Judgment voltage setting device.

(72) Inventor Toshimichi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Norio Ao 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Kiyoshi Kato 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (56) Reference JP-A-60-112289 (JP, A)

Claims (1)

(57) [Claims] 1. A direct current voltage is supplied to a movable electrode of a direct current arc furnace to generate an arc between the molten substance and the movable electrode, and the movable electrode is moved up and down according to a voltage deviation between the arc voltage and a set voltage at this time. In the method for preventing arc breakage of a DC arc furnace, the arc voltage is detected, and when the arc voltage is equal to or higher than a predetermined voltage lower than the no-load maximum voltage, the movable electrode is lowered at a maximum speed. Method for preventing arc breakage in a DC arc furnace.