JP7244196B2 - Arc furnace electrode lifting device - Google Patents

Description

An embodiment of the present invention relates to an arc furnace electrode lifting device that controls electrode position by constant impedance control.

An AC arc furnace raises and lowers three electrodes in the furnace to generate arc discharge between the electrodes and scrap such as iron charged into the furnace body, and the scrap is melted by the arc heat. .

In order to optimize the melting efficiency, the electric arc furnace electrode elevating device receives current and voltage signals into a digital controller, calculates the impedance between the electrode and the scrap, and controls the elevating of the electrode by constant impedance control. Therefore, the accuracy of the measured values of the current signal and the voltage signal for calculating the impedance affects the electrode control performance of the arc furnace electrode lifting device.

JP-A-10-79293 JP-A-10-208871

Embodiments provide an arc furnace electrode lifting device with improved electrode control performance.

The arc furnace electrode lifting device according to the embodiment adjusts the distance between the electrode connected to the secondary side of the furnace transformer and the scrap when arc discharge is generated between the electrode and the scrap. Control so that the impedance is constant. The arc furnace electrode lifting device measures a first voltage between the electrode and the scrap to set a coefficient based on a tap position signal representing the secondary side voltage of the furnace transformer, a first variable coefficient unit for multiplying a voltage by the coefficient and outputting a second voltage; a first analog-to-digital converter for converting the second voltage into a digital signal and outputting it as a third voltage; and the third voltage. is divided by the coefficient to output a fourth voltage, and a second analogue receives the current flowing between the electrode and the scrap, converts it into a digital signal, and outputs it as a first current. a digital converter; and an electrode elevation master controller that generates a speed command value based on the fourth voltage and the first current so that the impedance between the electrode and the scrap becomes constant. The first variable coefficient unit sets the coefficient larger as the secondary voltage represented by the tap position signal is lower.

In this embodiment, an arc furnace electrode lifting device with improved electrode control performance is realized.

1 is a schematic block diagram illustrating an arc furnace electrode lifting device according to an embodiment; FIG. 1 is a schematic block diagram illustrating a part of an arc furnace electrode lifting device according to an embodiment; FIG. It is a conceptual diagram for demonstrating operation|movement of the arc furnace electrode raising/lowering apparatus of embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, and the like are not necessarily the same as the actual ones. Also, even when the same parts are shown, the dimensions and ratios may be different depending on the drawing.
In addition, in the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the previous figures, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a schematic block diagram illustrating an arc furnace electrode lifting device according to an embodiment.
As shown in FIG. 1, the arc furnace electrode lifting device 10 of the embodiment includes a first variable coefficient unit 12, a first analog-to-digital converter 14, a second variable coefficient unit 16, and a second analog-to-digital converter 18. and an electrode elevation master control unit 20 .

The arc furnace electrode lifting device 10 lifts and lowers the electrode 2 with respect to the fixed furnace body 3 to control the distance between the electrode 2 and the scrap 4 charged into the furnace body 3 . AC power is supplied to the electrodes 2 from a furnace transformer 5 . The electrodes 2 are connected to the secondary side of the furnace transformer 5 and are applied with an alternating voltage set by the voltage taps of the furnace transformer 5 . The electrode 2 moves up and down to an appropriate distance above the furnace body 3 and the scrap 4 .

The arc furnace electrode lifting device 10 is connected to a current transformer 6 provided on the secondary side of the furnace transformer 5 and to a potential transformer 7 provided between the electrode 2 and the furnace body 3 . A current transformer 6 detects a current I when arc discharge is generated between the electrode 2 and the scrap 4 . Potential transformer 7 detects voltage V between electrode 2 and scrap 4 when arc discharge is generated between electrode 2 and scrap 4 .

The arc furnace electrode lifting device 10 inputs the detected current I and voltage V, based on these, generates a speed command value so that the impedance during arc discharge is constant, and sends it to the drive device 30. supply. Drive device 30 drives electric motor 40 according to the supplied speed command value. The electric motor 40 acts on the lifting mechanism (not shown) of the electrode 2 to adjust the distance between the electrode 2 and the scrap 4 .

A tap changer 50 is provided on the secondary side of the furnace transformer 5 . The tap changer 50 inputs the tap position command signal and switches the connection of the tap on the secondary side of the furnace transformer 5 so as to output the voltage set by the tap position command signal. The tap changer 50 also outputs a tap position signal corresponding to the position of the tap set by the tap position command signal or the voltage output by the tap.

The arc furnace electrode lifting device 10 receives the tap position signal output from the tap changer 50 . As will be described in detail later, the arc furnace electrode lifting device 10 multiplies the input voltage V by a coefficient based on the tap position signal so that the dynamic range of the arc furnace electrode lifting device 10 can be effectively used. The tap position command signal is generated, for example, according to the settings of operation switches, jog, etc., provided on the operation panel, and supplied to the tap changer 50 . An operator of the arc furnace electrode lifting device 10 sets operation switches and the like so as to obtain an appropriate impedance while observing the melting state of the scrap 4 or the like.

The configuration of the arc furnace electrode lifting device 10 will be described in detail.
The first variable coefficient unit 12 is connected to the output of the potential transformer 7 and receives data of the voltage V measured by the potential transformer 7 . A tap position signal is input to the first variable coefficient unit 12 . The first variable coefficient unit 12 multiplies the input voltage V value by a coefficient K set based on the voltage value represented by the tap position signal, and outputs the result.

A first analog-to-digital converter (hereinafter also referred to as a first A/D converter, simply referred to as an A/D converter in the drawings) 14 is connected to the output of the first variable coefficient section 12 . The first A/D converter 14 converts the input analog value K×V into digital data and outputs the digital data.

The coefficient K set in the first variable coefficient section 12 is set to a larger value as the voltage value represented by the tap position signal is lower. That is, the coefficient K is set to a larger value as the secondary voltage of the furnace transformer 5 is lower. As will be detailed later, the secondary voltage of the furnace transformer 5 is set to an appropriate value by the tap position command signal, but depending on the impedance control between the electrode 2 and the scrap 4, one tap position , it can vary within a certain range. The higher the secondary voltage, the wider the voltage fluctuation range. Therefore, by setting the coefficient K so as to increase the secondary voltage, the first variable coefficient section 12 can utilize the wide input dynamic range of the first A/D converter 14 .

The second variable coefficient section 16 is connected to the output of the first A/D converter 14 . In the second variable coefficient section 16, the reciprocal 1/K of the coefficient K set in the first variable coefficient section 12 is set. The output of the second variable coefficient section 16 is connected to the electrode elevation master control section 20 .

A second analog-to-digital converter (hereinafter also referred to as a second A/D converter, simply referred to as an A/D converter in the drawings) 18 is connected to the output of the current transformer 6, and the current transformer 6 The data of the current I measured by is input. The output of the second A/D converter 18 is connected to the electrode elevation master controller 20 .

The electrode elevation master control unit 20 inputs the digital data of the measured voltage and the digital data of the measured current, calculates the impedance based on these, generates a speed command value so that the impedance becomes constant, and drives the driving device 30. supply to

FIG. 2 is a schematic block diagram illustrating a part of the arc furnace electrode lifting device according to the embodiment.
FIG. 2 shows the circuit configuration of the furnace transformer 5 in more detail. That is, the furnace transformer 5 has a primary winding and is connected to an external circuit by terminals P1 and P2. The secondary winding of furnace transformer 5 is connected to external circuitry by terminals S1 and S2. For example, electrode 2 is connected to terminal S1. The secondary winding of the furnace transformer 5 comprises in this example two insulated windings, each provided with a plurality of taps. Each tap of one winding is provided with terminals T1 to T6, and the tap of the other winding is provided with terminals T7 to T12.

A tap changer 50 is connected via respective taps T1 to T12 of the secondary winding of the furnace transformer 5 . The tap changer 50 is, for example, a non-voltage tap changer having a rotary connector, and the position of the connector is set according to the tap position command signal. For example, when the tap position command signal is set to the tap position A, the connector is set at the position where the terminals T1 and T12 are connected. In this case, the secondary voltage of the furnace transformer 5 is the lowest. When the tap position command signal is set to the tap position X, the connector is set at the position where the terminals T6 and T7 are connected. In this case, the secondary voltage of the furnace transformer 5 is the highest.

The first variable coefficient section 12 receives the tap position signal output from the tap switcher 50 . In this example, the factor K is set to the reference voltage when the secondary voltage is set to the highest voltage divided by the reference voltage of the secondary voltage represented by the tap position signal. In this way, the lower the secondary voltage, the larger the coefficient K can be. The reference voltage is the rated voltage output to the secondary side of the furnace transformer 5 when the tap position is set and connected. The actual secondary voltage of the furnace transformer 5 is output with a predetermined error from the reference voltage. The predetermined error is set according to the furnace transformer, and is, for example, ±100%.

For example, in the above example, the coefficient K is the reference voltage of the secondary side voltage when the terminals T6 and T7 are connected in the case of the tap position A, and the secondary side voltage when the terminals T1 and T12 are connected. is set to a value divided by the reference voltage of In the case of the tap position X, the value is set by dividing the reference voltage of the secondary side voltage when the terminals T1 and T12 are connected by the reference voltage of the secondary side voltage when the terminals T1 and T12 are connected. .

The first variable coefficient section 12 includes, for example, a non-inverting amplifier circuit using an operational amplifier. For example, the first variable coefficient section 12 includes one operational amplifier. One operational amplifier is provided with a plurality of resistors so that a plurality of gains can be set, and the gain can be set by selecting an appropriate resistor according to the tap position signal. Alternatively, the first variable coefficient unit 12 may include a plurality of operational amplifiers, each of which is set to have an amplification factor corresponding to the tap position signal, and the tap position signal selects an operational amplifier having an appropriate amplification factor. It may be selected.

The operation of the arc furnace electrode lifting device 10 of the embodiment will be described.
FIG. 3 is a conceptual diagram for explaining the operation of the arc furnace electrode lifting device of the embodiment.
FIG. 3 shows the relationship between analog data input to the first A/D converter 14 and digital data output from the first A/D converter 14. As shown in FIG. The horizontal axis is input analog data, and the vertical axis is output digital data.
As shown in FIG. 3, when the magnitude of the input analog data is small, the width of variation with respect to the reference voltage is also narrow. When the magnitude of the analog data to be input is large, the range of variation with respect to the reference voltage is also widened.

For example, "Low Voltage Tap Reference Voltage" in FIG. 3 is for tap position A in the example above. Also, the "reference voltage of the high voltage tap" is the case of the tap position X in the above example.

If the ratio of the reference voltage at the tap position A to the reference voltage at the tap position X is, for example, 1:2, the voltage fluctuation range at the tap position X is Xmin to Xmax (-100% to +100%) is 2×Amin to 2×Amax. That is, in the case of the tap position A, by setting K=2, the input dynamic range of the first A/D converter 14 can be doubled for use.

As described above, in the arc furnace electrode lifting device 10 of the embodiment, even if the secondary voltage of the furnace transformer 5 is set to be low, the first variable coefficient unit 12 allows the input voltage of the first A/D converter 14 to A wide dynamic range can be used. The voltage data multiplied by K by the first variable coefficient unit 12 is multiplied by 1/K by the second variable coefficient unit 16 connected to the output of the first A/D converter 14 to convert the original voltage data into It can be obtained as a digital value.

The setting of the coefficient K is not limited to the above, and can be arbitrarily set appropriately. For example, the input range may be set in consideration of the characteristics of the A/D converter.

Effects of the arc furnace electrode lifting device 10 of the embodiment will be described.
As described above, in the arc furnace electrode lifting device 10 of the embodiment, the first variable coefficient unit 12 multiplies the measured analog voltage data by the coefficient K corresponding to the tap position signal, and the first A/D converter 14 can be entered in Therefore, a wider input dynamic range can be used for the first A/D converter 14, so voltage data can be obtained with higher accuracy, and electrode control performance can be improved.

In the arc furnace electrode lifting device, it is necessary to finely control the constant impedance control during arc discharge according to the degree of scrap melting, etc., so the secondary side tap of the furnace transformer 5 is switched in multiple stages. In some cases, For example, there are cases where the taps are switched in 10 or more stages, and the ratio of the lowest to highest voltage of the set secondary voltage reaches 2 or even exceeds 2 in some cases. In such a case, even if an attempt is made to finely set the secondary voltage, it is difficult to achieve the desired control accuracy if there is a large error in the voltage measurement value for constant impedance control.

In the arc furnace electrode lifting device 10 of the embodiment, since the measured voltage can be obtained with high accuracy, constant impedance control can be performed with desired accuracy, and the electrode control performance can be improved.

The arc furnace electrode lifting device 10 may be configured by a programmable logic controller (PLC) or the like, and uses an existing tap position signal to recognize the setting reference value of the secondary side voltage of the furnace transformer 5. It can be easily installed in existing facilities.

As in the specific example described in FIG. 2, the value of the coefficient K is the value obtained by dividing the reference voltage of the highest voltage by the reference voltage of the secondary side voltage set by the tap position command signal and represented by the tap position signal. By doing so, voltage signal data can be input with the widest input dynamic range regardless of the reference voltage of the tap in use.

According to the embodiments described above, it is possible to realize an arc furnace electrode lifting device with improved electrode control performance.

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included within the scope and spirit of the invention, and are included within the scope of the invention described in the claims and equivalents thereof. Moreover, each of the above-described embodiments can be implemented in combination with each other.

2 Electrode 3 Furnace Body 4 Scrap 5 Furnace Transformer 6 Current Transformer 7 Instrument Transformer 10 Arc Furnace Electrode Lifting Device 12 First Variable Coefficient Section 14 First Analog-to-Digital Converter 16 Second variable coefficient unit 18 Second analog-to-digital converter 20 Electrode elevation master control unit 30 Driving device 40 Electric motor 50 Tap changer

Claims (3)

An arc furnace in which the distance between an electrode connected to the secondary side of a furnace transformer and the scrap is controlled so that the impedance when arc discharge is occurring between the electrode and the scrap is constant. An electrode lifting device,
measuring a first voltage between the electrode and the scrap to set a factor based on a tap position signal representing the secondary voltage of the furnace transformer; multiplying the first voltage by the factor to obtain a a first variable coefficient unit that outputs two voltages;
a first analog-to-digital converter that converts the second voltage into a digital signal and outputs it as a third voltage;
a second variable coefficient unit that divides the third voltage by the coefficient and outputs a fourth voltage;
a second analog-to-digital converter for inputting a current flowing between the electrode and the scrap, converting it into a digital signal and outputting it as a first current;
an electrode elevation master controller that generates a speed command value based on the fourth voltage and the first current so that the impedance between the electrode and the scrap is constant;
with
The arc furnace electrode lifting device, wherein the first variable coefficient unit sets the coefficient larger as the secondary voltage represented by the tap position signal is lower. 2. The arc furnace electrode lifting device according to claim 1, wherein said first variable coefficient section sets said coefficient so as not to exceed the input dynamic range of said first analog-to-digital converter. The first variable coefficient unit divides the highest reference value of the secondary voltage that can be represented by the tap position signal by the reference value of the secondary voltage represented by the tap position signal, and converts the coefficient 3. The arc furnace electrode lifting device according to claim 1 or 2, wherein .

Images