KR100246824B1 - Process for electrode control of a dc arc furnace, and an electrode control device - Google Patents

Abstract

The DC arc furnace 8 includes a current controller 14 for stabilizing the current of the arc 10, and an electrode controller 18 which affects the position of the electrode 7 of the arc furnace 8 and the length of the arc 10. Has The position control of the electrode 7 is a hydraulic electrode adjusting device controlled as a function of the difference between the reference variable signal? Dos of the electrode controller which can be defined at the output of the current controller 14 and the variable signal? Act adjusted by the rectifier. Implemented by (21). As a result, the arc length is adjusted by the rectifier 5 which operates at an average drive level of 25 ° electrically, for example, ignoring the secondary voltage of the road transformer 2 and the regulated desired current value signal idos. do. The band is between the comparator or summer 17 and the output of current controller 14 to form a signal difference between the reference variable signal αdos of the electrode controller and the variable signal αact adjusted with the rectifier. Undesired frequencies are filtered out by the pass filter 16.

Description

Electrode control method and electrode control device for DC arc furnace

1 is a DC arc furnace having a current controller and an electrode controller.

2 is a characteristic curve diagram of an electrode controller-baseline signal according to a predetermined current value for various power factors.

<Description of the symbols for the main parts of the drawings>

1: AC power supply 2: furnace transformer

3: current converter 5: rectifier

6: choke 7: cathode

8: acro 9: charges

10 arc 11: melt bath

12: second electrode or anode 13, 17: summer

14 current controller 15 firing pulse transformer

16: attenuator or bandpass filter 18: electrode controller

19: valve amplifier 20: valve

21: electrode control device 22: function generator

A, B: point of FIG. 2 C: limit-power reactive power

d: electrode spacing (distance between electrode and solution)

cos : Power factor i _act : Actual current value signal

i _des : predetermined current value signal

α _act : rectifier adjustment signal at actual firing angle

α _des : Reference amount signal of electrode controller at predetermined firing angle

K1-K6: curve of the function generator

P1, P2: cos = Constant output curve

P3: Operating power curve for α _act = 35 °

The present invention relates to an electrode control method and an electrode control apparatus of a DC arc furnace.

In the preface of the present invention, reference is made to the prior art as disclosed in European Patent No. B1-0,068,180. The arc furnace with Dc current source is controlled by two control circuits. The current controller ensures a constant current corresponding to the predetermined predetermined current value. The electrode control circuit affects the position of the electrode and also affects the arc length. To lengthen the arc, the current controller either increases the voltage or drives the rectifier to keep the current constant. However, this is possible only with a margin of voltage. Control of the electrodes is carried out by an adaptive DC controller. The arc voltage supplied to the comparator or summer via the attenuator is provided as a DC voltage value. The predetermined DC voltage value is calculated taking into account the transformer voltage ratio and the electrode current for each operating point. The converter is initially limited by the limiter in accordance with the transformer ratio of the converter transformer, operating normally under the rectifier limit to the converter's possible voltage range. Even when the predetermined voltage value suddenly changes due to the interruption of the arc, the predetermined value is smoothly supplied to the summer so that the actual value is not overshooted.

Accordingly, an object of the present invention is to improve the electrode control method of the DC arc furnace as defined in claims 1 and 5, and to improve the electrode control apparatus by simple electrode control.

The present invention has the advantage that the calculation of a predetermined value for electrode control can be avoided. Instead of the DC voltage, a signal proportional to the control angle is obtained from the current controller for electrode control. The signal is passed through an attenuator, and in addition to signal matching, thresholds are also monitored, filtering out unwanted frequencies. The predetermined value is defined as a value for determining the average drive level of the rectifier.

Another advantage is that the arc length is adjusted independently of the voltage change in such a way that the required current is obtained by the specified drive level in the rectifier. Therefore, a suitable control range for stabilizing the current can always be obtained.

The constant drive level in the rectifier is also compensated for by a constant average power factor. This is particularly important in the case of static compensation, as the compensation is carried out at the specified power factor.

The power source at the operating point is very easily determined by selecting the transformer voltage ratio and specifying the direct current.

BRIEF DESCRIPTION OF THE DRAWINGS In order to assist a more complete understanding of the present invention, reference will be made in detail to the accompanying drawings.

FIG. 1 shows, on the one hand, an alternating current power supply 1 with an alternating voltage of 22 kV and, on the other hand, a furnace transformer 2 with a number of tappings connected to an alternating current voltage input of a converter or rectifier 5. It is shown. The DC voltage side of the rectifier 5 is coupled with the first electrode or cathode 7 of the arc furnace 8 via the choke 6. The second electrode or anode 12 arranged in the bottom region of the arc furnace 8 is connected to the positive terminal of the rectifier 5. An arc 10 is generated between the lower end of the cathode 7 and the lower end of the scrap or charge 9 to be melted and the surface of the melt bath 11. (d) shows the distance between the cathode 7 and the melting bath 11, that is, the electrode spacing.

The actual current value signal i _act is supplied and detected by the current converter 3 supplying alternating current to the rectifier 5 to the negative input of the comparator or summer 13. The predetermined current value signal i _des is supplied to the non-negative input of the summer 13, such as, for example, a potentiometer (not shown). At the output, a summer 13 is connected to a current controller 14 having a proportional-plus-integral control characteristic, the controller adjusting the rectifier corresponding to the turn-on angle at the outside. The amount signal α _act is transmitted to the firing pulse transformer 15, and the rectifier 5 is controlled by the output of the transformer.

The rectifier adjustment amount signal α _act is fed to the negative input of the summer 17 via an attenuator or bandpass filter 16 for signal matching, threshold monitoring and filtering of unwanted frequencies. The reference amount signal α _des of the electrode controller corresponding to the predetermined firing angle in the range, preferably in the range of 25 ° to 35 °, is supplied to the non-negative input of the summer 17. At the output, a summer 17 is connected to an electrode controller 18 having a proportional characteristic, which acts on the valve 20 of the electrode regulator 21 via a valve amplifier 19 at the output. do. The electrode adjusting device 21 is composed of, for example, a hydraulic pump having an adjusting mechanism and an electrode speed controller, and is mechanically connected to the negative electrode 7 and enables height adjustment with the negative electrode; In this way, the electrode regulator acts as a primary delay element.

The electrode control operates about 10 times later than the current control. The height adjustment of the cathode 7 is electrically operated at an average drive level, for example 25 °, regardless of the rectifier 5's secondary voltage of the furnace transformer 2 and the predetermined current value i _des adjusted. To be done. The signals and values assigned for unity are the same.

The frequency filtered by band pass filter 16 is in the range of 0.5 Hz-20 Hz.

By constantly adjusting the drive level in the rectifier 5, a constant average power factor is obtained in the power supply AC power source 1. The output of the operating point can be determined simply by selecting the voltage level of the transformer 2 and the set value of direct current.

In order to obtain various operating points or variable outputs with one voltage level of the furnace transformer 2, a predetermined current value i _des must be specified accordingly. Although reduced, in the case of maintaining the drive level of the same rectifier 5, the output becomes small. However, since the voltage loss in the AC power source 1 is small, the arc 10 becomes longer. However, this furnace process requires a shorter arc 10 at lower output. To do this, it is possible to specify a corresponding new current value for the drive level in the rectifier 5 at the same time as changing the predetermined current value i _des . For this purpose, as indicated by the dotted line in FIG. 1, a function generator 22 is provided which designates the electrode controller-reference signal [alpha] _des in dependence on a predetermined current value i _des . It is thereby possible to extend the output range.

2 shows curves K1-K6 corresponding to the functions realized by the function generator 22, which show various power factor cos. The electrode controller-reference signal (α _des ) in units of an electric angle (degree) depending on a predetermined current value i _{des in} units of kA with (0.75 1.00) as a parameter. The vertical axis additionally displays the active power P in MW units estimated by the AC power source 1. It is only coincidence that the numerical value of the electrode controller is numerically coincident with the reference amount signal α _des .

The illustrated embodiment relates to an apparatus in which the effective power P is 60 MW when the direct current is 100 kA and the set reactive power or the compensation output is 30 MVar. This device has a power factor cos at 100 kA, corresponding to point A, and with a rectifier adjustment amount signal α _act of 36 ° at AC power supply 1 to which the drive level of rectifier 5 is supplied. It is designed to be = 0.9. The connecting line AB, shown by the broken line, represents the limit of the minimum rectifier-drive level. Cos of course Curves K1 and K6 for = 0.75 and 1.0 may also be regarded as limits. The curve C corresponds to the drive level of the rectifier 5 in which the constant reactive power of the AC power supply 1 is obtained along the point A, and thus this curve is the limit line for the maximum AC power reactive power. . The function α _des = f (i _des ) will also be within such defined range, preferably cos Corresponds to a curve K3 for = 0.9.

Keeping the drive level at α _des = 35 ° and gradually decreasing the current from 100 kA to 60 kA, cos When = 1, the active power will be from 60MW to 38MW according to the operating output curve P3. This is about 60% of the maximum output.

Given α _des = f (i _des ), for example, all operating points cos according to curve (K3) When done at 0.9, a control angle α _des of 65 ° at 50 kA is required, thus obtaining an operating power of 15 MW according to the operating power curve P2, whereby 25% of the maximum power is achieved. The other curve (P1) is cos This applies to = 0.95 (schedule).

Claims (12)

In the electrode control method of the DC arc furnace 8, a) the arc current intensity is controlled by a control signal or a rectifier adjustment amount signal α _act , to a predetermined predetermined current value i _des , b) The electrode separation part d, which is the distance between the melting bath 11 of the arc furnace 8 and the one or more adjustable electrodes 7, is a function of the rectifier control amount signal α _act and the reference amount signal α _des of the definable electrode controller. A method for controlling an electrode of a DC arc furnace (8), characterized in that it is controlled according to a difference. The rectifier adjustment amount signal α _act is monitored for overshooting of the limit value, attenuated or overshooting of the limit value before comparing with the reference signal α _des of the electrode controller. Electrode control method characterized in that it is monitored and attenuated. The electrode control method according to claim 1, wherein an undesired frequency is filtered out of the rectifier adjustment amount signal (α _act ) before comparing with the reference amount signal (α _des ) of the electrode controller. 4. The firing angle signal for the rectifier 5 according to claim 2 or 3, wherein the electrode controller adjustment amount signal α _des is controlled at a predetermined firing angle α _des in a range of 15 ° to 50 °. Control method. An electrode control device for a DC arc furnace (8), having one or more adjustable electrodes (7) controlled by the electrode controller (14) and operably connected to the converter (5), the one or more electrodes (7) and the arc furnace (8). And an electrode adjusting device (21) controlled by the electrode controller (18) for adjusting the electrode spacing (d) between the melting baths (11) of the heating bath (11). Electrode control device for DC arc furnace (8), characterized in that it is operatively connected to the output of. 6. Electrode control apparatus according to claim 5, characterized in that the electrode controller (18) is connected at the input side to an output of the current controller (14) via a band pass filter (16) or an attenuator. 7. The electrode control apparatus according to claim 5 or 6, wherein a signal difference between the reference amount signal α _des of the electrode controller and the rectifier adjustment amount signal α _act is supplied to the input side of the electrode controller 18. 8. The rectifier adjustment amount signal α _act is a firing angle signal for the rectifier 5, and the electrode controller reference amount signal α _des corresponds to a predetermined point burn angle in the range of 15 ° to 50 °. Electrode control device characterized in that. The power factor according to any one of claims 1 to 3, wherein In order that the power factor can be maintained, = 0.75, cos The reference control signal? _Des of the electrode controller is formed in accordance with the target current value i _des so as not to exceed or exceed = 1). 10. The electrode control method according to claim 9, wherein the electrode controller reference amount signal (α _des ) is specified not to exceed a prescriptable limit-power reactive power (C). 5. The electrode control according to claim 4, wherein the electrode controller adjustment amount signal α _des is a firing angle signal for the rectifier 5 controlled at a predetermined firing angle α _des in a range of 25 ° to 35 °. Way. The electrode control apparatus according to claim 8, wherein the electrode controller adjustment amount signal (α _des ) corresponds to a predetermined firing angle in a range of 25 ° to 35 °.