JPH0254892A - Voltage control method of dc arc furnace - Google Patents

Abstract

PURPOSE:To prevent a reduction in input power level while sufficiently utilizing the capacity of a power source by sequentially setting the value of a set voltage to a value lower than the no-load voltage value of the power source by a specified value. CONSTITUTION:The voltage between a movable electrode 4 and a furnace bottom electrode 8 is detected by a voltage detector 10, and this voltage is inputted to both a maximum voltage setting equipment 18 and a subtracter 20. In the setting equipment 18, the detected voltage is subjected to sampling and A/D exchange, and a histogram of amplitude distribution within a fixed time is obtained by a deflection calculating means 18-2. Based on this histogram, a standard deviation omicron of the detected voltage is obtained. Further, the maximum set voltage Vdmax at each time is sequentially calculated according to the scheme I by a set voltage calculating means 18-3. In the scheme, k is a predetermined value, and Vmax is a no-load voltage of the power source. in a subtracter 20, the voltage of a detector 10 is subtracted from the calculated voltage Vmax to determine a voltage deviation. Based on this voltage deviation, the raising/falling of the electrode 4 is controlled.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a voltage control method for a DC arc furnace, which controls the arc voltage by controlling the position of a movable electrode (also referred to as an arc electrode) of the DC arc furnace. In particular, the present invention relates to a voltage control method for a DC arc furnace that can improve productivity by effectively utilizing equipment.

(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 moment to moment, and the arc voltage changes accordingly, so the desired arc voltage can be obtained reliably. That is, in order to connect the arc reliably, it is necessary to control the movable electrode in a complicated manner.

For this reason, conventionally, as shown in FIG. 3, after filling a DC arc furnace 1 with scrap 2 and closing a furnace lid 3 on the top of the furnace, a movable electrode 4 such as a carbon electrode is inserted from the top of the furnace M3. 5. Insert the furnace transformer from the power supply (not shown). Cyrisk converter 6. A predetermined voltage is applied between the movable electrode 4 and the furnace bottom electrode 8 via the smoothing reactor 7, and the tip of the movable electrode 4 is controlled while the position of the movable electrode 4 is controlled so that the desired arc current is always flowing. The scrap 2 is sequentially melted by generating an arc. That is, when this arc occurs, the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 is detected by the voltage detector 10, and the voltage between this detected voltage Vr and the preset voltage Vd determined by the voltage setting device 11 is determined. The adjustment unit 12 performs proportional-integral calculation so that the deviation becomes zero, and the resulting repulsion output (control signal) is provided to the electrode lifting motor 13. 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. A voltage of 1 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 Id is adjusted to zero. A gate control angle α is determined using an automatic current regulator, and the gate of the cyrisk converter 6 is controlled in accordance with this gate control angle α.

(Problem to be Solved by the Invention) By the way, in the above-mentioned DC arc furnace, from the viewpoint of maximizing the effective use of the equipment capacity and improving productivity, the power supply that applies voltage to the DC arc furnace 1 has been changed. It is desirable to make full use of their abilities. However, as a characteristic of the arc phenomenon in a DC arc furnace, the arc changes as the melting of scrap progresses, and in particular, the voltage changes greatly from moment to moment. At this time, if the arc voltage value becomes higher than the no-load voltage value of the power supply, arc breakage will occur.
It is necessary to lower the movable electrode 4 for ignition, and then raise the movable electrode 4 until the set voltage is reached. If such arc breakage occurs frequently, the input power level will be lowered accordingly, making it impossible to operate the equipment to its maximum capacity, resulting in a decrease in productivity.

Therefore, conventionally, the maximum set voltage value is set to about two-thirds (about 70%) of the no-load voltage value of the power supply, and the level is set so that the arc voltage does not reach the no-load voltage. Therefore, the voltage control does not reflect changes in the situation of the DC arc furnace (the presence or absence of scrap), and tends to be set at a low level that does not cause arc breakage. In other words, if the voltage is set so as not to exceed the no-load voltage value for an unstable arc as shown in Figure 4(a), the voltage will change as shown in Figure 4(b) due to changes in the conditions of the DC arc furnace. Even though it is possible to increase the input power by increasing the set voltage when the arc becomes stable, the DC arc furnace has no choice but to operate with the set voltage still low. For this reason, the actual situation is that the capacity of the power source cannot be fully utilized, making it impossible to effectively utilize equipment and improve productivity.

The present invention was made to solve the above-mentioned problems, and its purpose is to maximize productivity by making the most of equipment capacity without causing a drop in input power level due to arc breakage. It is an object of the present invention to provide a voltage control method for a DC arc furnace that can improve the voltage.

(Means and operations for solving the problem) In order to achieve the above object, the present invention detects the voltage applied from the power source to the movable electrode that melts the material to be melted in the DC arc furnace, and detects the detected voltage. and according to the voltage deviation from the predetermined set voltage.

In a voltage control method for a DC arc furnace that controls voltage by controlling the moving speed and elevation of a movable electrode,
By detecting the standard deviation σ of the voltage, setting a predetermined value as k, and sequentially setting the set voltage value to a value lower than the no-load voltage value of the power supply by σ, the capacity of the power supply can be improved. While making full use of the voltage, it is possible to eliminate the occurrence of arc breakage, suppress a drop in the input power level, and always perform good voltage 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 a voltage control system for a DC arc furnace to which the method of the present invention is applied. The same parts as in FIG. Now, I will only discuss the different parts.

As shown in FIG. 1, this system includes a voltage detector 10,
Voltage setting device 11, maximum voltage setting device 18, and switch 1
9, subtractor 20, speed setting controller 2], and upper y1/
Downward switching circuit 22, speed detector 23, and speed controller 2
It consists of 4.

Here, the voltage detector 10 is for detecting the voltage Vr between the movable electrode 4 and the bottom electrode 8, and the voltage setting device 11 is for setting the set voltage Vd in advance. Further, the maximum voltage setting device 18 has an A/D conversion/sampling means 18-
1, a standard deviation calculation means 18-2, and a set voltage calculation means 18-3, which performs amplitude distribution analysis (statistical processing) on the amplitude of the voltage waveform detected by the voltage detector 10, and calculates the value at that point. Maximum set voltage V d m at the time
This is to set ax sequentially. This maximum voltage setting device 1
8 is composed of, for example, a computer.

That is, the A/D conversion/sampling means 18-1 is
The waveform of the voltage Vr detected by the voltage detector 10 is sampled at equal time intervals and then A/D converted. Further, the standard deviation calculation means 18-2 specifies a memory address corresponding to the amplitude value of the voltage waveform sampled by the A/D conversion/sampling means 18-1, and executes an operation for a certain period of time to add 1 to the contents. By doing so,
A histogram of the amplitude distribution within the time period is obtained, and the standard deviation σ of the voltage Vr is calculated based on this histogram. Further, the set voltage calculation means 18-3
Based on the standard deviation σ of the voltage Vr calculated by the standard deviation calculating means 18-2, the no-load voltage VIllaX of the power supply, and the predetermined value k, the highest set voltage V d ff1ax at that point in time is calculated one after another. This is what is output.

On the other hand, the switch 19 is set to the maximum voltage setting device 18 side when the DC arc furnace 1 is in the stable period after polling, during the shelving period, during the reloading period, and during the melting period until burn-through, that is, when scrap is present. Also, when there is no more scrap due to melting, the voltage setting device 11 is manually switched by an operator. The subtracter 20 also outputs a voltage deviation (VdIIlax-Vr) or (V
d-Vr). Further, the speed setting controller 21 inputs the voltage deviation from the subtracter 20, performs a 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 22 inputs the voltage deviation from the subtracter 20 and the speed setting value from the speed setting controller 21, and changes the speed setting value to positive or negative depending on the 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 difference is negative, a moving speed command value in the downward direction is output. Further, the speed detector 23 detects the rotational speed of the electrode lifting motor 13, that is, the lifting/lowering speed of the movable electrode 4. Furthermore, the speed controller 24 inputs the movement speed command value from the rise/fall switching circuit 22 and the detected speed from the speed detector 23, performs proportional integral calculation so that the deviation between the two becomes zero, and outputs the operation output. (control signal) is given to the electric motor 13 for lifting and lowering the electrode.

Next, a voltage control method for a DC arc furnace in this embodiment will be explained.

Now, by igniting the Cyrisk converter 6, a high DC voltage is applied between the movable electrode 4 and the bottom electrode 8 of the DC arc furnace 1, and an arc is generated from the tip of the movable electrode 4. When the operation of the DC arc furnace 1 is started and the polling period, which is the first stage, is completed, the operation quality is determined by manually closing the switch 19 to the highest voltage setting device 18 side.

On the other hand, voltage Vr between movable electrode 4 and furnace bottom electrode 8 is detected by voltage detector 10, and this detected voltage Vr is input to maximum voltage setter 18 and subtractor 20, respectively. In the maximum voltage setter 18, the waveform of the detection voltage Vr or A/
A/D conversion is performed while being sampled at equal time intervals by the D conversion/sampling means 18-1. Then, the standard deviation calculation means 18-2 specifies the memory address corresponding to the amplitude value of the voltage waveform to be sampled and increments the contents by 1 for a certain period of time, thereby calculating the amplitude within the period. A histogram of the distribution is obtained, and the standard deviation σ of the voltage Vr is calculated based on this histogram. FIG. 2(a') is a diagram showing temporal changes in arc voltage, and FIG. 2(b) is a diagram showing an example of a histogram.

Furthermore, the set voltage calculation means 18-3 calculates the drift deviation σ of the calculated voltage Vr, the no-load voltage VIIla of the power supply,
X, and a predetermined value k (-2 in this example)
Based on the maximum set voltage V d at that point in time
wax is V d flaX −V laX −k cy −V
It is calculated sequentially according to IaX -2U. The calculated maximum set voltage V d max is then input to the subtracter 20 through one switch.

On the other hand, in the subtracter 20, the maximum set voltage V d m
Voltage deviation between ax and detection voltage Vr (V d ll1aX
-Vr) is obtained. Next, the speed setting controller 21 performs a proportional-integral calculation so that this voltage deviation becomes zero, and outputs the speed setting value to the rise/fall switching circuit 22. In the rise/fall switching circuit 22, a subtracter 20
A moving speed command value in the upward or downward direction is obtained depending on the positive or negative polarity of the voltage deviation from . That is, when the voltage deviation is positive, a moving speed command value in the -L ascending direction is obtained, and when the voltage deviation is negative, a descending direction moving speed command value is obtained.
This is output to the speed controller 24.

In addition, the speed controller 24 determines the deviation between the moving speed command value from the ascending/descending switching circuit 22 and the detected speed from the speed detector 23, 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. And this speed controller 2
According to the movement speed command value from 4, the electrode lifting motor 1
3 rotates forward or reverse at the commanded speed, the movable electrode 4 is controlled to rise or fall. In addition, when transitioning from the stable period after polling, to the shelving period, to the refilling period, to the melting period until burn-through, to the refining period where there is no scrap, the switch 19 should be switched to the voltage setting device 11 side at that point. As a result, normal electrode elevation control is performed based on the voltage deviation between the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 and the set voltage Vd.

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 10, and the amplitude 13 of this detected voltage waveform is
Then, amplitude distribution analysis was performed to calculate the standard deviation σ of the voltage, and the operation pattern of DC arc furnace 1, from the stable period after polling to the shelving period, refilling period, and melting period until burn-through, was determined. When the voltage is present, the set voltage value V d a + ax is changed to the no-load voltage value V of the power supply.
The value is successively set to a value 2σ lower than max.

Therefore, during the operation pattern of the DC arc furnace 1, which is the stable period after the end of polling, the shelving period, and the melting period until burnout during the refilling period, that is, the period when scrap is present, the input power level due to the occurrence of arc breakage is It becomes possible to perform operations that make the most effective use of equipment capacity without causing a decrease in productivity, and productivity can be improved.

It should be noted that the present invention is not limited to the above-described embodiments, but can be similarly implemented in the following manner.

(a) In the above embodiment, amplitude distribution analysis is performed on the amplitude of the detected voltage waveform to calculate the voltage standard deviation σ, and the set voltage value V d InaX is calculated from the no-load voltage value V of the power supply.
Although the values are successively set to values 2σ lower than ll1aX, the present invention is not limited to this, and if the histogram shows an almost normal distribution as shown in Fig. 2 as a result of amplitude distribution analysis of the detected voltage waveform, for example, Find the voltage V at which the probability of a certain time being below a certain voltage V is P% (the set voltage at this time (
The average voltage) is ■o), and the difference Δ■ between this voltage V and the no-load voltage viax of the power supply is determined, and the set voltage value V
d 01ax may be successively set to a value of Vo+ΔV. By using such a method, it becomes possible to simplify calculations in the maximum voltage setting device.

(b) In the above embodiment, the predetermined value k was explained as −2, or it is most efficient if the value of k is selected in the range of −1.5 to 2.

(c) In the above embodiment, the explanation was given on the assumption that the primary voltage of the furnace transformer 5 does not fluctuate, but if this primary voltage fluctuates, the no-load voltage viax of the power supply also fluctuates.
It is preferable to correct this variation. That is, −
When a fluctuation in the secondary voltage occurs, the no-load voltage v max of the power supply is determined each time by multiplying the negative voltage by the fluctuation rate, and the determined no-load voltage v max is applied to the maximum voltage setting device 18 in FIG. The correction may be performed by giving the no-load voltage v wax of the set voltage calculation means 18-3. This makes it possible to perform voltage control with even higher precision.

(d) In the above embodiment, the set voltage is varied by analyzing the amplitude distribution of the waveform of the detected voltage Vr. may be made variable. That is, when the arc current is approximately constant, the voltage or primary voltage v1 ・
Since it is proportional to COSα, the firing angle may be varied to turn on as quickly as possible by managing COSα.

(Effects of the Invention) As explained below, according to the present invention, the standard deviation σ of the voltage is set sharply, the predetermined value is set as k, and the value of the set voltage is determined from the no-load voltage value of the power supply. Since both σ and σ are successively set to lower values, it is possible to maximize the equipment capacity and improve productivity without reducing the input power level due to arc breakage. A voltage control method for a DC arc furnace can be provided.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing one embodiment of a voltage control system for a DC arc furnace to which the present invention is applied, Fig. 2 is a diagram for explaining the operation of the same embodiment, and Fig. 3 is a diagram showing a conventional DC arc furnace voltage control system. FIG. 4 is a block diagram showing a voltage control system for a furnace, and is a diagram for explaining conventional problems. 1... DC arc furnace, 2... Scrap, 4...
Movable electrode, 5... Furnace transformer, 6... Cyrisk converter, 7... Smoothing reactor, 8... Hearth bottom electrode, 10
... Voltage detector, 11... Voltage setting device, 18...
Maximum voltage setting device, 18-1...A/D conversion/sampling means, 18-2...Standard deviation calculation means, 18-3
...Setting voltage calculation means, 1...Switch, 2o.
...Subtractor, 21...Speed setting controller, 22...Up/down switching circuit, 23...Speed detector, 24...
Speed controller. Applicant's agent Patent attorney Takehiko Suzue (a) (b) Figure No.

Claims (1)

[Claims] A voltage applied from a power source to a movable electrode that melts a material to be melted in a DC arc furnace is detected, and the movable In a voltage control method for a DC arc furnace that controls the voltage by controlling the moving speed and elevation of the electrode, the standard deviation σ of the voltage is detected, a predetermined value is set as k, and the value of the set voltage is set as follows: k than the no-load voltage value of the power supply
A voltage control method for a DC arc furnace, characterized in that the voltage is sequentially set to a lower value by σ.