JPH0261988A - Power control method for dc arc furnace - Google Patents

Abstract

PURPOSE:To improve the efficiency of dissolution by varying the preset voltage when the ascent speed is the preset value or above and when the arc voltage at the time of a short circuit is increased from zero to voltage generation based on the ascent speed of a movable electrode and the arc voltage detected when the movable electrode and solved scrap are short-circuited. CONSTITUTION:When scrap 6 collapses into contact with a movable electrode 5 and the arc voltage becomes zero, an adjusting unit 21 quickly lifts the movable electrode 5, and the number of pulses generated by a pulse generator 31 is quickly increased. A short circuit judging unit 33 compares the ascent speed dv obtained by a position change detecting unit 32 with the judgment speed V0 and sends the change signal to a preset voltage changing unit 34 after the short circuit is released. The changing unit 34 sends the change rate beta1 to a multiplier 35 and changes and sets the set voltage Vs from a voltage setter 20 to Vs.beta1 and sends it to an adder 19. As a result, the power feed quantity fed to the movable electrode is stabilized by the movable set voltage when the ascent speed is the preset value or above and the arc voltage at the time of a short circuit is increased from zero to voltage generation, and the dissolution time can be shortened.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to reducing the amount of power supplied to the movable electrode of a DC arc furnace when the movable electrode comes into contact with scrap, which is the material to be melted, and is short-circuited. This invention relates to a power control method for a DC arc furnace.

[Conventional technology]

FIG. 4 is an overall configuration diagram of a DC arc furnace, in which a DC arc furnace main body 1 is provided with a furnace bottom electrode 2 at the bottom and a furnace cover 3 at the top so that it can be closed.

Further, a hole 4 is formed in the center of this furnace 'M3, and a movable electrode 5 is arranged in this hole 4. Note that scrap 6, which is a material to be melted, is placed inside the DC arc furnace main body 1.

Furthermore, the movable electrode 5 is raised and lowered within the DC arc furnace 1 by a lifting device 7.

That is, the lifting device 7 is provided with an electric motor 8 for lifting and lowering electrodes, and a rotating shaft of this electric motor 8 is connected to a winch 9. A wire 10 having one end fixed is hung on this winch 9, and a roller 12 of a mast 11 is hung on this wire 10. A holder arm 13 is provided on the mast 11, and the movable electrode 5 is provided on this 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 the primary side of the furnace transformer 14, and a cyrisk converter 16 is connected to the secondary side of the transformer 14.
is connected. And this thyristor converter 16
The movable electrode 5 is connected to the output side of the movable electrode 5 via a reactor 17.

Further, this power supply system is provided with arc voltage and arc current control systems. That is, in the arc voltage control system, a voltage detector 18 is connected between the hearth bottom electrode 2 and the movable electrode 5, and the detected voltage output from the voltage detector 18, that is, the arc voltage is sent to the adder 19. There is. This adder 19 has a set voltage VS set in the voltage setter 20.
is input, and the adder 19 inputs the detected voltage and the set voltage Vs
The voltage deviation between the voltage and the voltage is determined and sent to the adjustment section 21.

Accordingly, the adjustment section 21 obtains a lifting control signal according to the voltage deviation according to the PI control, and sends this signal to the electrode lifting motor 8. As a result, the position of the movable electrode 5 is controlled so that an arc is generated in the gap between the movable electrode 5 and the scrap 6.

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, and the detected current output from the current detector 22, that is, the arc current is sent to the adder 23. ing. This adder 23 has a set current (constant t8 current) I set in the current setter 24.
s is input, and the adder 23 inputs the detected current and the set current I.
The deviation current with respect to s is determined and sent to the gate control section 25.

In this way, this gate control section 25 controls the gate firing angle of the Cyrisk converter 16 in accordance with the deviation current.

However, with the above configuration, an arc Q is generated between the movable electrode 5 and the scrap 6, and the scrap 6 is melted. This state of melting will be explained with reference to FIG. 5. First, as shown in FIG. 5(a), as the scrap 6 melts, the movable electrode 5 is lowered. In other words, it is polling in the operating pattern. As a result of this poling, the movable electrode 5 reaches the bottom of the DC arc furnace main body 1, as shown in FIG. 5(b), and enters a stable period. After this stable period has passed, the scrap 6 on the wall side of the DC arc furnace main body 1 collapses due to the melting of the scrap 6, as shown in FIG. 6(C). Then, an arc is generated between the fallen scrap 6 and the movable electrode 5, and the scrap 6 is melted.

[Problem to be solved by the invention]

However, while the scrap 6 is being melted as described above, the scrap 6 falls down, and although it is fine if the scrap 6 does not come into contact with the movable electrode 5 when it falls down, it may come into contact with the movable electrode 5, or the scrap 6 that has fallen down may come into contact with the movable electrode 5. 5 and may cause a short circuit. When a short circuit occurs in this way, the arc voltage between the movable electrode 5 and the scrap 6 becomes "0" and the arc current becomes a short circuit current. Therefore, the voltage deviation between the arc voltage and the set voltage VS becomes very large, and the adjustment section 21 sends out a command to rapidly raise the movable electrode 5. This causes the movable electrode 5 to rise rapidly until the short circuit is released. An arc voltage is generated from the moment the movable electrode 5 separates from the scrap 6, the short circuit current is eliminated, the arc is re-ignited, and the scrap 6 is remelted, resulting in a polling state.

On the other hand, the poling after the short circuit is released often has a form in which the scrap 6 that has collapsed forms a bridge, and differs from the poling at the initial stage of melting in terms of the density of the scrap 6 directly under the movable electrode 5. Therefore, during polling at this time, the arc voltage often exceeds the allowable arc voltage of the equipment, and arc breakage often occurs. Each time the arc breaks, the movable electrode 5 is lowered until short-circuited with the scrap 6 for re-ignition, and after the short-circuit, the movable electrode 5 is raised until the arc voltage approaches the set voltage. Usually, at this time of year, high voltage and large current are set, so the arc voltage limit allowed by the equipment is quickly reached, causing the arc to break. Therefore, the wasted time increases, the dissolution efficiency decreases, and the dissolution time becomes longer.

Therefore, the present invention provides a power control method for a DC arc furnace that can automatically change the setting of the voltage and current supplied to the movable electrode after a short circuit caused by a pile-up of scrap, thereby achieving stable poling without cutting off the arc and shortening the melting time. The purpose is to

[Means and actions to solve the problem]

The present invention provides a power control method for a DC arc furnace in which DC voltage is supplied to the movable electrode of the DC arc furnace and the movable electrode is raised and lowered according to the voltage deviation between the DC voltage and a set voltage. The rising speed and arc voltage of the movable electrode are detected during a short circuit with scrap, and the set voltage is variably set when the rising speed exceeds a predetermined speed or when the arc voltage at the time of a short circuit reaches zero voltage. This is a power control method for a DC arc furnace that attempts to achieve the above object.

Further, the present invention provides a power control method for a DC arc furnace in which a DC voltage is supplied to a movable electrode of a DC arc furnace and the movable electrode is raised and lowered according to a voltage deviation between this DC voltage and a set voltage. The speed and arc voltage are detected, and when the rising speed exceeds a predetermined speed or when the short circuit is released and arc voltage is generated, the set voltage is variably set, and the set current for the current flowing through the movable electrode is variably set. This is a power control method for a DC arc furnace that attempts to achieve the above object.

〔Example〕

A first embodiment of the present invention will be described below with reference to the drawings. Note that the same parts as in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 1 is an overall configuration diagram of a power control device for a DC arc furnace to which a power control method for a DC arc furnace is applied. In the same figure, 30 is a set voltage changing means, which is the movable electrode 5.
The rising speed V is detected, and this rising speed V is the predetermined speed V.

Polling after the short circuit is released when the
It has a function to variably set the set voltage during re-entry).

The specific configuration is as follows. Reference numeral 31 denotes a pulse generator, which is connected to the rotating shaft of the electrode lifting/lowering motor 8 and generates a pulse signal having a pulse number corresponding to the rotational speed of the motor 8.

Further, the position change amount detection unit 32 receives the pulse signal from the pulse generator 31 at every predetermined sampling period, counts up and down the number of pulses, calculates the position H of the movable electrode 5, and compares this position with the previous one. Difference from position d
It has a function of calculating the ascending and descending speed v1 of the movable electrode 5, especially the rising speed dv dv-dH/dt, from H and the elapsed time dt. And this rising speed d
v is sent to the short circuit determining section 3. This short circuit determination unit 33 has a determination speed ν0 for determining a short circuit in advance.
1. For example, the maximum speed v□ allowed by the installation is set, and this judgment speed V□ is compared with the rising speed dv to determine the rising speed d.
It has a function of determining that a short circuit has occurred when v is equal to or higher than the determination speed vo and a short circuit current is flowing, and transmitting a change signal to the set voltage changing section 34.

This set voltage change section 34 normally sends a signal of "1" to a multiplier 35 connected between the voltage setter 20 and the adder 19, and upon receiving the change signal, changes the change rate β1 to the multiplier 35.
5. Note that the set voltage that is changed by multiplying the set voltage VS by this change rate β1 is set higher.

Further, a timer 36 is connected to the short-circuit determining section 33, and is configured to be reset after a certain period of time after the change signal is sent by the timer 36.

Next, the operation of the apparatus configured as described above will be explained.

When DC voltage is supplied to the movable electrode 5 and an arc Q is generated between the movable electrode 5 and the scrap 6, the scrap 6 is melted by this arc. At this time, the arc voltage is detected by the voltage detector 18 and sent to the adder 19 to determine the voltage deviation from the set voltage VS, and this voltage deviation is sent to the adjustment section 21. Then, from this adjustment section 21, a lift control signal that eliminates the voltage deviation is sent to the electrode lifting motor 8, and the movable electrode 5 is controlled to rise and fall. While the position of the movable electrode 5 is controlled in this way, as it descends as shown in FIG. 2 and reaches Hl, the scrap 6 inside the DC arc furnace main body 1 collapses as shown in FIG. 5(C). becomes. When the position of the movable electrode 5 reaches Hl in this way, the position change amount detection unit 32 receives the pulse signal from the pulse generator 31 to determine the current position of the movable electrode 5, and calculates the current position of the movable electrode 5 from this current position and the previously determined position. Movable electrode 5
The rising speed dv of is calculated and sent to the short circuit determining section 33. This short circuit determination section 33 receives the rising speed dv and determines the determination speed vO.
If the rising speed dv is equal to or higher than the judgment speed vo and a short circuit current is flowing, a change signal is sent to the setting voltage changing section 34.
Send to. However, if the scrap 6 inside the DC arc furnace main body 1 is in a state where it easily collapses as shown in FIG. 5(C), the scrap 6 may collapse and come into contact with the movable electrode 5.

At two points, when the scrap 6 collapses and comes into contact with the movable electrode 5, the arc voltage becomes zero. Thereby, the adjustment unit 21 sends out a command to rapidly raise the movable electrode 5. With that,
The movable electrode 5 rises rapidly as shown in FIG. 2a.

At this time, the number of pulses generated by the pulse generator 31 increases rapidly, and this pulse signal causes the position change amount detection unit 3 to
2 determines the rising speed dv of the movable electrode 5. Then, the short circuit determination section 33 compares the rising speed dv at this time with the determination speed V□, and based on this comparison result and the fact that a short circuit current is flowing, it determines that there is a short circuit, and sends change No. 1J to the set voltage change section 34. do. The set voltage changing unit 34 sends the change rate β1 to the multiplier 35, and the set voltage Vs sent from the voltage setter 20 is changed to VS·β1, and the set voltage Vs is changed to the adder 19.
sent to. As a result, as the movable electrode 5 rises, the movable electrode 5
The set arc voltage between and the scrap 6 becomes lower.

The movable electrode 5 continues to rise and is re-ignited the moment it leaves the scrap 6. The movable electrode 5 rises in accordance with the voltage deviation until the gap with the scrap 6 becomes equal to the set arc voltage. After ignition, the fallen scrap 6 is polled again. This polling speed is so fast that the scrap 6 immediately melts and falls to the bottom. Therefore, the arc voltage generated tends to exceed the allowable voltage that the equipment can produce, resulting in arc breakage. However, since the set voltage is lowered as described above, the gap between the movable electrode 5 and the scrap 6 becomes smaller, and the dissolution rate of the scrap 6 is overcome, and the movable electrode 6 follows and descends. In this case, although the voltage generated by the arc may increase, it remains within the voltage range allowed by the equipment, and melting can be continued without the arc Q breaking.

In this way, in the first embodiment, the rising speed dv of the movable electrode 5 is detected, and this rising speed dv is the determination speed V.

Since the set voltage VS is variably set when the above occurs, the movable electrode 5 can be lowered to follow the scrap melting and the arc Q can be cut when repoling occurs after a short circuit. It disappears. Therefore, the average value of the amount of electric power supplied to melt the subrack 6 is stabilized, and the time for dissolving the subrack 6 can be shortened, so that the efficiency of melting is improved. However, the power consumption rate improves.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

Now, the device shown in the same figure is equipped with a set voltage changing means 30 and a set current changing means 40, of which the set voltage changing means 30 detects the rising speed dv of the movable electrode 5, and detects the rising speed dv of the movable electrode 5. It has a function of variably setting the set voltage Vs when dv becomes equal to or higher than the determination speed VO.

Note that the configuration is exactly the same as the configuration in the first embodiment, so the explanation thereof will be omitted. Moreover, the set current changing means 4
0 detects the rising speed dv of the movable electrode 5, and when this rising speed dv exceeds the judgment speed VQ, the setting current (rated current) Is for the arc current flowing through the movable electrode 5 during polling after short-circuit release is varied. It has a function to set. The specific configuration includes a pulse generator 312, a position change amount detection section 32. Short circuit determination section 33. Multiplier 4 connected between set current changing section 41 and current setting device 24 and adder 23
It is composed of 2. The setting current changing section 41 normally
'' signal to the multiplier 42, and has a function of sending the change rate β2 to the multiplier 42 upon receiving the change signal. Note that the setting current Is is changed and set by being multiplied by this change rate β2. β2 is the setting current Is
decreases more than

Next, the operation of the device configured as described above during a short circuit and during polling (re-entry) after the short circuit is released will be explained.

When the scrap 6 collapses and comes into contact with the movable electrode 5 and the arc voltage becomes zero, the adjustment section 21 sends out a command to rapidly raise the movable electrode 5. As a result, the movable electrode 5 rises rapidly, and the number of pulses generated by the pulse generator 31 rapidly increases. However, at this time, the short-circuit determination unit 33 uses the rising speed dv determined by the position change amount detection unit 32 and the determination speed V.
. Based on the comparison result, a change signal is sent to the set voltage change section 34 after the short circuit is released. As a result, the set voltage change unit 34 sends the change rate β1 to the multiplier 35, and changes the set voltage VS sent from the voltage setter 20 to VS・β
Change the setting to 1 and send it to one adder. As a result, as the movable electrode 5 rises, the set voltage between the movable electrode 5 and the scrap 6 becomes lower, and during polling after the short circuit is released, the voltage deviation becomes smaller than before changing the set voltage.

At the same time, the change signal is sent to the set current change section 41, so the set current change section 41 sends the change rate β2 to the multiplier 42. As a result, the set current Is is
- The setting is changed to β2 and sent to the adder 23.

As a result of the above, the set current is changed to match the changed set arc voltage. Therefore, the descending speed of the movable electrode 5 is accelerated during re-entry after the short circuit is released, and is controlled to a gap between the movable electrode 5 and the scrap 6 in which the arc Q does not break. Then, when a certain period of time has elapsed since the timer 36 sent out the change signal, the short-circuit determining section 33 resets the change signal. As a result, the set voltage is returned to VS again, position control of the movable electrode 5 is executed, and the set current is returned to Is again.

In this way, in the second embodiment, the rising speed dv of the movable electrode 5 is set sharply, and this rising speed dv is the determination speed V.

When this happens, the set voltage VS is variably set and the set current Is is variably set, so the power supply is switched to the first level without cutting off the arc Q during polling (re-entry) after the short circuit is released. It can be supplied more stably and consistently compared to the example. Therefore, the time for dissolving the subrack 6 can be shortened and the efficiency of dissolution can be improved.

Note that the present invention is not limited to the above embodiments, and may be modified without departing from the spirit thereof.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a power control method for a DC arc furnace that can stabilize the amount of power supplied to the movable electrode and shorten the melting time.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a power supply device for a DC arc furnace to which the first embodiment of the power supply method for a DC arc furnace according to the present invention is applied, FIG. 2 is a diagram showing the elevation and descent of the movable electrode, and FIG. 3 1 is an overall configuration diagram of a power supply device for a DC arc furnace to which the second embodiment of the power supply method for a DC arc furnace according to the present invention is applied, FIG. It is a figure showing the operating state of an arc furnace. 1... DC arc furnace main body, 2... Furnace bottom electrode, 5...
・Movable electrode, 6... Scrap, 7... Lifting device,
16... Cyrisk converter, 18... Voltage detector,
19... Adder, 20... Voltage setting device, 21...
Adjustment unit, 22... Current detector, 23... Adder, 2
4... Current setting device, 25... Gate control section, 30.
... Setting voltage changing means, 31... Pulse generator, 32... Position change amount detection section, 33... Short circuit determination section, 34... Setting voltage changing section, 35... Multiplier, 36
...Timer, 40...Setting current changing means, 41...
- Setting current changing unit, 42...multiplier. Diagram

Claims (2)

[Claims] (1) In a power control method for a DC arc furnace in which a DC voltage is supplied to a movable electrode of the DC arc furnace and the movable electrode is raised and lowered according to a voltage deviation between the DC voltage and a set voltage, the movable electrode and the movable electrode are moved up and down during melting. The rising speed and arc voltage of the movable electrode are detected when the movable electrode is short-circuited with the scrap, and the set voltage is adjusted when the rising speed exceeds a predetermined speed and when the arc voltage at the time of the short-circuit goes from zero to voltage generation. A power control method for a DC arc furnace characterized by variable setting. (2) In a power control method for a DC arc furnace, in which a DC voltage is supplied to a movable electrode of the DC arc furnace, and the movable electrode is raised and lowered according to a voltage deviation between the DC voltage and a set voltage, the rate of rise of the movable electrode is detects the arc voltage, and when the rate of rise exceeds a predetermined speed or when the short circuit is released and arc voltage is generated, the set voltage is variably set, and the set current with respect to the current flowing through the movable electrode is variable. A power control method for a DC arc furnace, characterized in that: