JPH0261489A - Control of electric power for dc arc furnace - Google Patents

Abstract

PURPOSE:To shorten smelting time by supplying the maximum electric power to a movable electrode when an arc is stabilized. CONSTITUTION:When a DC voltage is supplied to a movable electrode 5 and an arc Q is generated between the movable electrode 5 and scrap 6, the scrap 6 is smelted while the movable electrode 5 is descended gradually and enters into poling. In this case, a pulse generator 31 generates a pulse in accordance with the rotating number of a motor 8 for elevating the electrode. A poling speed detecting unit 32 counts the pulse signal at every predetermined sampling period to obtain the present position of the movable electrode 5. The poling speed detecting unit 32 operates the poling sped of the movable electrode 5 from a difference between the present position and a position detected at previous time and the sample period. A change of setting judging unit 33 changes the setting of a set voltage Vs and a set current Is to the maximum allowable values when a deceleration is detected as the result of comparison between the operated poling speed and a speed operated at previous time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power control method for a DC arc furnace that controls the amount of power supplied to a movable electrode.

[Conventional technology]

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

Further, a hole 4 is formed in the center of the furnace lid 3, and this hole 4
A movable electrode 5 is arranged at. 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, that is, the arc voltage output from the voltage detector 18 is input to one adder. being sent. This adder 19 has a set voltage V set in the voltage setter 20.
s is input, and the adder 19 inputs the detected voltage and the set voltage V
The voltage deviation with S is determined and sent to the adjustment section 21.

Thus, the adjustment section 21 determines a lifting control signal corresponding to the PI sub-control and thus the voltage deviation, 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 (rated current) Is set in the current setting device 24.
is input, and the adder 23 inputs the detected current and the set current Is
The deviation current from the current is calculated 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, when ignition is performed, 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. 4. First, Fig. 4 (a) shows the state of ignition;
When ignited in this state, the scrap 6 is melted. The movable electrode 5 then descends as the melt dissolves. In other words, it is polling in the operating pattern. Then,
As this poling progresses, the movable electrode 5 reaches the bottom of the DC arc furnace main body 1, as shown in FIG. 3(c), and enters a stable period.

[Problem to be solved by the invention]

By the way, when melting scrap 6 using the above operation pattern, the arc voltage fluctuates greatly and is unstable at the beginning of melting, but as the melting of scrap 6 progresses, the arc voltage stabilizes and the arc Q The state of occurrence becomes stable. This makes it possible to supply a large amount of power to the movable electrode 5. However, in the DC arc furnace configured as described above, the scrap 6 is always melted at a set voltage and a set current regardless of the melting state of the scrap 6.

Therefore, the amount of power supplied to the movable electrode 5 cannot be varied depending on the melting status of the scrap 6, and therefore the melting time becomes long and the melting efficiency is poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power control method for a DC arc furnace that can shorten the melting time by supplying maximum power to the movable electrode from when the arc is stabilized.

[Means and actions to solve the problem]

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 the DC arc furnace, and the movable electrode is raised and lowered according to the voltage deviation between this DC voltage and a set voltage. The above purpose is achieved by detecting the polling speed of the movable electrode from , and changing the set voltage and the set current for the current flowing through the movable electrode to the maximum allowable value when the polling speed becomes slower than the polling start speed. This is a method for controlling power 11 of a DC arc furnace.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Note that the same parts as in FIG. 3 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, reference numeral 30 denotes a power control means, which detects the polling speed of the movable electrode 5 after ignition, and when the polling speed has decreased from the start of polling, the set voltage Vs
It also has a function of changing the setting current IS to the maximum allowable value. The specific configuration is as follows. 31
is a pulse generator, and this pulse generator 31 is connected to the rotating shaft of the electric motor 8 for raising and lowering the electrode, and generates a pulse signal having a number of pulses corresponding to the number of rotations of the electric motor 8. Also, the polling speed detection section 32 receives a pulse signal from the pulse generator 31 at every predetermined sampling period, counts up and down the number of pulses, and activates t! i! ! It has a function of determining the position H of the movable electrode 5 and calculating the polling speed of the movable electrode 5 from the difference between this position and the previous position and the sampling period. This polling speed dv is then sent to the setting change determination section 33. The setting change determination section 33 receives the polling speed determined by the polling speed detection section 32, and has a function of comparing the polling speed received this time with the polling speed received last time to detect whether the polling speed has decreased. ing. The setting change determining section 33 has a function of sending a change signal to the setting voltage changing section 34 and the setting current changing section 35 when detecting deceleration. That is, when the poling speed is reduced, the melting of the scrap 6 progresses and the fluctuation in the arc voltage decreases. The set voltage change unit 34 normally sends a signal of "1" to the multiplier 36 connected between the voltage setter 20 and the adder 19, and upon receiving the change signal, changes the change rate α1.
is sent to the multiplier 36 to calculate the maximum allowable set voltage Vs・α
The setting must be changed to 1. Further, the set current changing section 35 normally sends a signal of "1" to the current setter 24 and the adder 2.
When the change signal is received, the change rate α2 is sent to the multiplier 37, which changes the setting to the maximum allowable set current Is・α2. .

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. When the scrap 6 is melted while the movable electrode 5 is controlled to rise and fall in this manner, the movable electrode 5 gradually descends, that is, enters poling. At this time, the pulse generator 31 generates a pulse signal with a number of pulses corresponding to the number of rotations of the electric motor 8 for lifting and lowering the electrode.

The polling speed detection unit 32 receives this pulse signal at every predetermined sampling period, performs counting, and determines the current position of the movable electrode 5 from this count value. Then, the polling speed of the movable electrode 5 is calculated from the difference between this current position and the previously detected position and the sampling period. Then, the setting change determination section 33 receives the polling speed determined by the polling speed detection section 32, compares this speed with the previously received speed, and detects whether there has been a deceleration. by the way,
At the beginning of polling, the speed is vl as shown in FIG. Therefore, the movable electrode 5 descends at the polling speed v1 and melts the scrap 6. Note that this polling speed v1 differs depending on the type of scrap 6.

As the melting of the scrap 6 progresses in this manner, the poling speed of the movable electrode 5 is reduced to vl due to the molten steel. As a result, the polling speed detected by the polling speed detection section 32 becomes vl. Therefore, the setting change determination unit 33 detects that the polling speed has decreased by comparing the previous polling speed ■1 and the current polling speed v2. At this time, the fluctuation of the arc voltage is reduced, and the setting change determination unit 33 sends a change signal to the set voltage change unit 34 and the set current change unit 35 based on the deceleration determination result. Thus, the set voltage changing section 34
sends the change rate α1 to the multiplier 36 to change the setting voltage Vs to the maximum allowable setting 7u voltage Vs·α1. Also, at the same time, the set current changing section 35 changes the multiplier 3
By sending the change rate α2 to 7, the set current Is is changed to the maximum allowable set current Is·α2. As a result, the maximum allowable power is supplied to the movable electrode 5 and the scrap 6 is melted. Accordingly, if the maximum allowable power is supplied, the rate of dissolution of the scrap 6 will be faster.

In this way, in the above-mentioned embodiment, the polling speed of the movable electrode 5 is detected after ignition, and when the polling speed becomes slower than the polling start speed, the set voltage VS and the set current Is are set to the maximum allowable values. Since the settings are changed, the amount of power supplied to the movable electrode 5 can be set to the maximum allowable amount of the equipment after the generation of the arc Q is stabilized.

Therefore, the time for melting the scrap 6 can be shortened, the efficiency of melting can be improved, and the power supplied to the movable electrode 5 is not wasted.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. For example, the polling speed of the movable electrode 5 may be determined by directly detecting the displacement of the movable electrode 5 instead of detecting the rotational speed of the electrode lifting/lowering motor 8. Further, the setting voltage and setting current may be changed and set by separately providing setting devices for maximum allowable voltage and current, without using a multiplier.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to provide a power control method for a DC arc furnace that can shorten the melting time by supplying maximum power to the movable electrode from when the arc is stabilized.

[Brief explanation of the drawing]

Figure 1 shows the overall configuration of a power control device for a DC arc furnace to which an embodiment of the DC arc furnace power control method according to the present invention is applied, and Figure 2 shows the poling speed of the movable electrode. , FIG. 3 is a diagram for explaining the prior art, and FIG. 4 is a diagram showing an operation pattern of a DC 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...
Controller, 22... Current setting device, 23... Adder, 2
4... Current setting device, 25... Gate control section, 3o.
...Power changing means, 31...Pulse generator, 3
2 River polling speed steep part, 33...setting change part, 3
4... Setting voltage changing unit, 35... Setting 7 is a current changing unit, 36.37... Multiplier. Applicant's agent Patent attorney Takehiko Suzue 3rd diagram

Claims (1)

[Claims] 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 this DC voltage and a set voltage, the movable electrode is A DC arc furnace characterized in that the poling speed of the electrode is detected, and when the poling speed becomes slower than the poling start speed, the set voltage and the set current for the current flowing through the movable electrode are changed to maximum allowable values. power control method.