Electrode lifting device for arc furnace

Abstract

To provide an electrode lifting device of an arc furnace, which appropriately sets a speed sensitivity characteristic of electrode elevation control in accordance with a furnace period, and improves an operation efficiency.SOLUTION: In an embodiment, an electrode lifting device of an arc furnace comprises: an impedance deviation operation part that calculates an impedance deviation on the basis of an arc current between an electrode and a scrap, an arc voltage, a set current previously set to an input current calculating part, and a set voltage; and a target speed operation part having a plurality of speed sensitivity characteristics obtained by plotting a speed command value against the impedance deviation. In the input current calculating part, a plurality of pairs of the set current and the set voltage are set. The impedance deviation operation part determines a corresponding furnace period from the plurality of furnace periods on the basis of the set current and the set voltage by sequentially inputting the pair of the set current and the set voltage from the input current calculating part. The target speed operation part selects and sets the speed sensitivity characteristic corresponding to the determined furnace period from the plurality of speed sensitivity characteristics.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an electrode lifting device for a steelmaking arc furnace.

Background Art

[0002] An arc furnace supplies power to electrodes via a furnace transformer, generates an arc discharge between the electrodes of each phase and the scrap, and melts the scrap. The electrode lifting device of the arc furnace controls the lifting and lowering of the electrodes by motor speed control and controls the arc length to an appropriate length.

[0003] An arc furnace is divided into furnace conditions such as initial charging, additional charging, and refining for each operation, and further, the furnace conditions are divided into each furnace period such as the initial melting period, boiling period, melting period, and final melting period. The furnace period has different states inside the furnace respectively.

[0004] In a conventional electrode lifting device, the furnace period is judged by time counting, and the dead zone is changed according to the furnace period judged by time counting, thereby changing the characteristics of electrode lifting control according to the state inside the furnace and improving the operation efficiency (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since time counting varies depending on the furnace condition and the type of scrap, there are not only a large number of patterns corresponding to each situation, but also due to the influence of the distribution of scrap and the component adjustment work of molten steel, etc., the time of each furnace period is not constant for each operation. For example, there are cases where the time of that furnace period changes when an operator manually intervenes while judging the furnace condition visually or the like.

[0007] The present invention was made to solve the above-mentioned problems, and aims to provide an electrode lifting device for an arc furnace that can more appropriately set the speed sensitivity characteristics of electrode lifting control according to the furnace period, thereby improving operational efficiency. [Means for solving the problem]

[0008] Embodiments of the present invention are electrode lifting devices for an arc furnace that generate speed command values ​​to control an electrode lifting mechanism that raises and lowers an electrode positioned at a distance on molten scrap, thereby controlling the arc formed between the electrode and the scrap. This electrode lifting device for an arc furnace is Regarding the operation of the aforementioned arc furnace Multiple reactor eras of each Corresponding to Multiple set currents, each of the multiple furnace periods Corresponding to An input power calculation unit, which has a preset input power pattern including multiple sets of time series consisting of multiple periods in which multiple set voltages, multiple set currents, and multiple set voltages are applied, outputs the multiple set currents and the multiple set voltages. One of the inputs for set current and set voltage One set at a time, in order received The impedance deviation calculation unit calculates the impedance deviation based on the set current and set voltage, the arc voltage applied between the electrode and the scrap, and the arc current flowing through the electrode when the arc is formed, and the impedance deviation and the above Speed ​​command value Represents the relationship It comprises a target velocity calculation unit having velocity sensitivity characteristics. The impedance deviation calculation unit is The table data represents the correspondence between the plurality of set currents and the plurality of set voltages and the plurality of furnace periods. Based on the set of set current and set voltage that are input sequentially By referring to the table data, the furnace period corresponding to one set of set current and set voltage among the multiple furnace periods is determined, and a command value representing the determined furnace period is set. The target speed calculation unit outputs to the target speed calculation unit. Each of the aforementioned plurality of reactor periods has a plurality of speed sensitivity characteristics, and a command value representing the reactor period A speed sensitivity characteristic corresponding to the above is selected and set from the plurality of speed sensitivity characteristics, and based on the set speed sensitivity characteristic, the speed command value corresponding to the impedance deviation output from the impedance deviation calculation unit is output to the electrode lifting mechanism. [Effects of the Invention]

[0009] According to the embodiment, an electrode lifting device for an arc furnace is provided that more appropriately sets the speed sensitivity characteristics of electrode lifting control according to the furnace period, thereby improving operational efficiency. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic block diagram illustrating an electrode lifting device for an arc furnace according to the first embodiment. [Figure 2] This is a schematic graph illustrating the speed sensitivity characteristics of the electrode lifting device of an arc furnace according to the first embodiment. [Figure 3] This is a schematic block diagram illustrating an electrode lifting device for an arc furnace according to the second embodiment. [Modes for carrying out the invention]

[0011] The embodiments will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

[0012] (First embodiment) Figure 1 is a schematic block diagram illustrating an electrode lifting device for an arc furnace according to the first embodiment. Figure 1 shows the various components that make up the arc furnace 100, along with the electrode lifting device 8. First, the configuration of the arc furnace 100 will be explained. As shown in Figure 1, the arc furnace 100 includes a furnace transformer 1, a current transformer 2, an auxiliary transformer 3, electrodes 4, a furnace body 6, an input power calculation unit 7, an electrode lifting device 8, an inverter 12, and a motor 13.

[0013] On the primary side of the furnace transformer 1, the plant busbar is connected and power is supplied from the busbar. On the secondary side of the furnace transformer 1, the electrode 4 is connected. On the secondary side of the furnace transformer 1, a current transformer 2 is provided to detect the current supplied to the electrode 4. The current transformer 2 is connected to the electrode lifting device 8.

[0014] Below the electrode 4, the furnace body 6 is arranged, and scrap 5 is charged into the furnace body 6. The furnace body 6 is connected to, for example, the neutral point and grounded. An auxiliary transformer 3 is connected to detect the voltage between the electrode 4 and the furnace body 6, and the output of the auxiliary transformer 3 is connected to the electrode lifting device 8. Hereinafter, it is assumed that the scrap 5 has the same potential as the furnace body 6, and the auxiliary transformer 3 detects the voltage between the electrode 4 and the scrap 5.

[0015] The furnace transformer 1 has a primary winding and a secondary winding, and a plurality of taps are provided on the secondary winding. The furnace transformer 1 has a tap changer function. The tap changer function of the furnace transformer 1 is a function in which the furnace transformer 1 inputs a tap position command and selects and connects a tap corresponding to the input tap position from a plurality of taps. In relation to the tap changer function, on the secondary side of the furnace transformer 1, there are terminals for inputting a tap position command and terminals for outputting a signal representing the current tap position.

[0016] The input power calculation unit 7 is connected to the terminal for inputting the tap position command of the furnace transformer 1. The input power calculation unit 7 is connected to the terminal for outputting the signal representing the tap position of the furnace transformer 1. The input power calculation unit 7 is connected to the electrode lifting device 8.

[0017] The input power calculation unit 7 is pre-set with an input power pattern, which is a pattern of input power corresponding to the furnace stage. The input power pattern is set with multiple sets of combinations of a set current Iref, a set voltage Vref, and a period during which power is to be input. The input power calculation unit 7 outputs the set current Iref and the set voltage Vref to the electrode lifting device 8 according to the input power pattern. The input power calculation unit 7 calculates a tap position for the voltage applied between the electrode 4 and the scrap 5 according to the set voltage Vref, generates a tap position command corresponding to the tap position, and outputs it to the furnace transformer 1. The furnace transformer 1 sets the tap position according to the tap position command and outputs a signal representing the set tap position to the input power calculation unit 7 and the electrode lifting device 8.

[0018] The input power pattern set in the input power calculation unit 7 is time-series data of a set of combinations of a set current Iref, a set voltage Vref, and a period during which the power is input, corresponding to the furnace stage. For example, in the steelmaking process of a certain material, the input power pattern includes a combination of a first set current Iref1 [kA], a first set voltage Vref1 [V], and a period T1 [Hr], a combination of a second set current Iref [kA], a second set voltage Vref2 [V], and a second period T2 [Hr], a combination of a third set current Iref3 [kA], a third set voltage Vref3 [V], and a third period T3 [Hr], and a combination of a fourth set current Iref4 [kA], a fourth set voltage Vref4 [V], and a period T4 [Hr]. These combinations are configured to be executed in this order. Note that the input power pattern may include a period during which the set current Iref and the set voltage Vref become 0. The period during which the set current Iref and the set voltage Vref are 0 is, for example, the period for additional charging of scrap.

[0019] The set of first set current Iref1 [kA], first set voltage Vref1 [V], and period T1 [Hr] corresponds, for example, to the initial stage of dissolution. The set of second set current Iref2 [kA], second set voltage Vref2 [V], and second period T2 [Hr] corresponds, for example, to the boring stage. The set of third set current Iref3 [kA], third set voltage Vref3 [V], and third period T3 [Hr] corresponds, for example, to the dissolution stage. The set of fourth set current Iref4 [kA], fourth set voltage Vref4 [V], and period T4 [Hr] corresponds, for example, to the final stage of dissolution. The input power calculation unit 7 outputs the set current Iref and set voltage Vref to the electrode lifting device according to such input power patterns, generates tap positions, and outputs them to the furnace transformer 1.

[0020] The power input pattern may be modified by manual intervention by the operator of the arc furnace 100, thereby extending or shortening the power input period. The power input calculation unit 7 outputs the set current Iref and set voltage Vref for that pattern according to the modified period.

[0021] The power input pattern may be set to be the same for each plant, for example. Alternatively, the power input pattern may be set to be the same for each arc furnace or for each type of scrap. Such patterns are set by the plants operating the arc furnaces or by steel manufacturers, and these power input patterns are set in the power input calculation unit 7.

[0022] The electrode lifting device 8 receives the arc current IFB detected by the current transformer 2 and the arc voltage VFB detected by the auxiliary transformer 3. The electrode lifting device 8 receives the set current Iref and set voltage Vref from the power input calculation unit 7. The electrode lifting device 8 calculates the impedance deviation ΔZ according to the following equation (1).

[0023] ΔZ = (IFB / Iref) - (VFB / Vref) (1)

[0024] The electrode lifting device 8 has pre-set furnace stages corresponding to the set current Iref and set voltage Vref output from the input power calculation unit 7. In the example above, if the input set is the first set current Iref1 and the first set voltage Vref1, the electrode lifting device 8 determines that the furnace stage is the initial stage of melting. If the input set is the second set current Iref2 and the second set voltage Vref2, the electrode lifting device 8 determines that the furnace stage is the boring stage. If the input set is the third set current Iref3 and the third set voltage Vref, the electrode lifting device 8 determines that the furnace stage is the melting stage. If the input set is the fourth set current Iref4 and the fourth set voltage Vref4, the electrode lifting device 8 determines that the furnace stage is the final stage of melting.

[0025] The electrode lifting device 8 has speed sensitivity characteristics corresponding to the furnace stage. The speed sensitivity characteristics have an appropriate dead zone set for each furnace stage. The dead zone of the speed sensitivity characteristics is the impedance deviation value at which the speed command value for raising and lowering the electrode 4 is set to 0 even if the impedance deviation is not 0. For example, the dead zone is set to be narrower as the furnace stage progresses. When the dead zone is narrow, the electrode 4 can be raised and lowered more precisely in accordance with the impedance deviation. On the other hand, when the dead zone is wide, raising and lowering the electrode 4 is stopped even when the impedance deviation is of a certain magnitude. Therefore, even if the impedance fluctuates greatly in the initial stages of melting, accidents such as the electrode 4 colliding with the scrap 5 and being damaged can be made less likely. The dead zone may be set for each furnace stage, regardless of the progress of the furnace stage. For example, the impedance deviation may fluctuate greatly during the boring stage or the final stages of melting, and in the speed sensitivity characteristics corresponding to the boring stage or the final stages of melting in such cases, the dead zone is set to be wider.

[0026] The electrode lifting device 8 selects and sets a speed sensitivity characteristic corresponding to the reactor period determined by the set current Iref and set voltage Vref. Using the set speed sensitivity characteristic, the electrode lifting device 8 outputs a speed command value corresponding to the impedance deviation ΔZ to the inverter 12.

[0027] The inverter 12 drives the motor 13 at a speed corresponding to the speed command value, and the motor 13 raises and lowers the electrode 4 connected via the lifting mechanism, controlling the distance between the electrode and the scrap 5 so that the desired arc current IFB is achieved.

[0028] The configuration of the electrode lifting device 8 according to this embodiment will be described below. The electrode lifting device 8 according to this embodiment includes an impedance deviation calculation unit 9, a target speed calculation unit 10, and an acceleration / deceleration calculation unit 11.

[0029] The impedance deviation calculation unit 9 is connected to the output of the input power calculation unit 7. The impedance deviation calculation unit 9 uses the set current Iref and set voltage Vref output from the input power calculation unit 7 to determine the reactor period. The impedance deviation calculation unit 9 has a table pre-configured that shows the correspondence between the set current Iref and set voltage Vref pairs and the reactor period. The impedance deviation calculation unit 9 determines the reactor period by referring to the table and outputs a command value representing the reactor period to the target speed calculation unit 10.

[0030] The impedance deviation calculation unit 9 calculates the impedance deviation ΔZ by substituting the set current Iref, the set voltage Vref, the arc current IFB detected by the current transformer 2, and the arc voltage VFB detected by the auxiliary transformer 3 into equation (1), and outputs it to the target speed calculation unit 10.

[0031] The target speed calculation unit 10 has multiple speed sensitivity characteristics corresponding to the reactor period. The target speed calculation unit 10 selects and sets a speed sensitivity characteristic from among the multiple speed sensitivity characteristics that corresponds to the command value representing the reactor period output from the impedance deviation calculation unit 9.

[0032] Let's explain the speed sensitivity characteristics. Figure 2 is a schematic graph illustrating the speed sensitivity characteristics of the electrode lifting device of an arc furnace according to the first embodiment. In Figure 2, the horizontal axis represents the impedance deviation ΔZ, and the vertical axis represents the velocity command value V. Figure 2 shows the velocity sensitivity characteristics for three different reactor phases. In this example, the solid line plots represent the velocity sensitivity characteristics for the initial melting and boring phases, the dashed line plots represent the velocity sensitivity characteristics for the melting phase, and the dashed-dotted line plots represent the velocity sensitivity characteristics for the final melting phase. In the velocity sensitivity characteristics, the velocity command value is set to 0 in the interval between the impedance deviation ΔZ and D, and "D" is called the dead zone. The size of the dead zone is set to differ depending on the reactor phase.

[0033] As shown in Figure 2, in the electrode lifting device 8 according to this embodiment, the velocity sensitivity characteristics are set such that the dead zone D narrows as the furnace phase progresses from the initial melting and boring phases to the melting phase and the final melting phase. This makes it possible to control the lifting and lowering operation of the electrode 4 more precisely as the arc discharge stabilizes and the lifting and lowering operation of the electrode 4 becomes slower as the furnace phase progresses.

[0034] Furthermore, in the electrode lifting device 8 according to this embodiment, the velocity sensitivity is set to be high in the early stages of melting. High velocity sensitivity means that the slope of the plot in the graph in Figure 2 is steep. In the electrode lifting device 8 according to this embodiment, by setting the velocity sensitivity to be high and widening the dead zone D during the furnace stage in the early stages of melting, the electrode 4 can be rapidly raised and lowered while the shape of the scrap remains, thereby improving operational efficiency and effectively preventing accidents such as collisions between the electrode 4 and the scrap 5.

[0035] As mentioned above, the width of the dead zone D and the velocity sensitivity of the velocity sensitivity characteristics are not limited to those described above, and can be arbitrarily selected and set to suit the situation. For example, if the impedance deviation ΔZ fluctuates significantly during the boring phase or the final stages of dissolution, the dead zone D may be made wider and the velocity sensitivity higher than in the case shown in Figure 2.

[0036] Thus, in the electrode lifting device 8 according to this embodiment, by selecting and setting an appropriate speed sensitivity characteristic according to the furnace period, it becomes possible to control the impedance to a constant value more precisely and safely, and to control the arc length to an appropriate level.

[0037] Returning to Figure 1, we continue the explanation. As shown in Figure 1, the target speed calculation unit 10 applies the impedance deviation output from the impedance deviation calculation unit 9 to the speed sensitivity characteristics set according to the reactor period to calculate the speed command value and output it to the acceleration / deceleration calculation unit 11.

[0038] The acceleration / deceleration calculation unit 11 performs acceleration / deceleration calculations on the speed command value output from the target speed calculation unit 10. The acceleration / deceleration calculation unit 11 outputs the calculated value as the speed command value to the inverter 12. For example, the acceleration / deceleration calculation unit 11 has a preset acceleration / deceleration rate, and applies the acceleration / deceleration rate to the change in the speed command value to sequentially calculate the speed command value.

[0039] The effects of the electrode lifting device according to this embodiment will be explained. The impedance deviation calculation unit 9 has a pattern of reactor phase determination criteria that corresponds to the input power pattern set in the input power calculation unit 7. Therefore, it can reliably determine the reactor phase according to the input power pattern set in the input power calculation unit 7. The input power pattern may be modified by manual intervention by the operator, but in the electrode lifting device 8 according to this embodiment, the impedance deviation calculation unit 9 calculates and determines the estimated value of the input power set in the input power calculation unit 7, so it can accurately determine the reactor phase regardless of time counting.

[0040] Furthermore, in the electrode lifting device 8 according to this embodiment, the target speed calculation unit 10 has multiple speed sensitivity characteristics corresponding to the reactor stage. In the speed sensitivity characteristics corresponding to the reactor stage, the dead zone is narrowed as the reactor stage progresses. This makes it possible to control the speed of the lifting and lowering operation of the electrode 4 even with a smaller impedance deviation, thus enabling more precise control.

[0041] Furthermore, in the electrode lifting device 8 according to this embodiment, the speed sensitivity characteristics of the target speed calculation unit 10, which correspond to the furnace stage, are set according to the rate of change of speed with respect to impedance deviation. In the initial furnace stage, a wider dead zone and steeper speed sensitivity characteristics are used to allow melting to proceed more safely and quickly, and as the furnace stage progresses, the dead zone is narrowed and the speed sensitivity characteristics are made gentler, allowing for more precise control of the lifting and lowering operation of the electrode 4.

[0042] Furthermore, the velocity sensitivity characteristics can be arbitrarily set to be appropriate for each arc furnace. If the impedance deviation ΔZ fluctuates significantly during the boring phase or the final melting phase, the dead zone during these phases can be widened compared to the dead zone during the preceding furnace phase, thereby increasing the velocity sensitivity. In this way, it becomes possible to apply more appropriate velocity sensitivity characteristics according to the characteristics of the arc furnace and the scrap being charged, enabling the operation of the arc furnace with high precision and productivity.

[0043] (Second embodiment) Figure 3 is a schematic block diagram illustrating an electrode lifting device for an arc furnace according to the second embodiment. As shown in Figure 3, the arc furnace 200 includes a furnace transformer 1, a current transformer 2, an auxiliary transformer 3, electrodes 4, a furnace body 6, an input power calculation unit 7, an electrode lifting device 208, and a hydraulic cylinder 215. The hydraulic cylinder 215 replaces the inverter 12 and motor 13 of the arc furnace 100 shown in Figure 1. The electrode lifting device 208 generates a speed command value for the hydraulic cylinder 215 and outputs it to the hydraulic cylinder 215. Other components are the same as those in the arc furnace 100 shown in Figure 1. The same reference numerals are used for identical components, and detailed explanations are omitted as appropriate.

[0044] The electrode lifting device 208 comprises an impedance deviation calculation unit 9, a target speed calculation unit 210, and an acceleration / deceleration calculation unit 211. The target speed calculation unit 210 and the acceleration / deceleration calculation unit 211 are configured and operate in the same manner as the electrode lifting device 8 shown in Figure 1, except that they generate speed command values ​​for the hydraulic cylinder 215.

[0045] By operating in the same manner as the electrode lifting device 8 in Figure 1, the electrode lifting device 208 according to this embodiment also achieves the same effects as the electrode lifting device 8.

[0046] In this way, it is possible to realize an electrode lifting device for an arc furnace that can more appropriately set the speed sensitivity characteristics of electrode lifting control according to the furnace period, thereby improving operational efficiency.

[0047] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0048] 1... Furnace transformer, 2... Current transformer, 3... Auxiliary transformer, 4... Electrodes, 5... Scrap, 6... Furnace body, 7... Input power calculation unit, 8, 208... Electrode lifting device, 9... Impedance deviation calculation unit, 10, 210... Target speed calculation unit, 11, 211... Acceleration / deceleration calculation unit, 12... Inverter, 13... Motor, 100, 200... Arc furnace

Claims

1. An electrode lifting device for an arc furnace that generates a speed command value to control an electrode lifting mechanism that raises and lowers an electrode positioned at a distance on molten scrap, thereby controlling the arc formed between the electrode and the scrap, An impedance deviation calculation unit receives inputs one set at a time from an input power calculation unit, which has a preset input power pattern including a plurality of set currents corresponding to each of a plurality of furnace periods for the operation of the arc furnace, a plurality of set voltages corresponding to each of the plurality of furnace periods, and a plurality of time series consisting of a plurality of periods in which the plurality of set currents and the plurality of set voltages are applied, and calculates the impedance deviation based on the set current and set voltage, the arc voltage applied between the electrode and the scrap, and the arc current flowing through the electrode when the arc is formed. A target speed calculation unit having speed sensitivity characteristics that represent the relationship between the impedance deviation and the speed command value, Equipped with, The impedance deviation calculation unit has table data representing the correspondence between the plurality of set currents and the plurality of set voltages and the plurality of furnace periods, and by referring to the table data based on the set current and set voltage that are input sequentially, it determines the furnace period corresponding to the set current and set voltage among the plurality of furnace periods, and outputs a command value representing the determined furnace period to the target speed calculation unit. The electrode lifting device for an arc furnace has a target velocity calculation unit which has a plurality of velocity sensitivity characteristics which correspond to each of the plurality of furnace periods which select and set a velocity sensitivity characteristic which corresponds to a command value which represents the furnace period which from the plurality of velocity sensitivity characteristics which, and based on the set velocity sensitivity characteristic which outputs a velocity command value which corresponds to the impedance deviation output from the impedance deviation calculation unit which to the electrode lifting mechanism.

2. The electrode lifting device for an arc furnace according to claim 1, wherein the target velocity calculation unit has a dead zone that narrows as the furnace period progresses in the plurality of velocity sensitivity characteristics, and is set such that the rate of change of velocity with respect to impedance deviation decreases as the furnace period progresses.

3. The electrode lifting device for an arc furnace according to claim 1, wherein the target velocity calculation unit has, in the plurality of velocity sensitivity characteristics, the first velocity sensitivity characteristic corresponding to the boring phase has a wider dead zone than the second velocity sensitivity characteristic corresponding to the initial melting phase, and the rate of change of velocity with respect to impedance deviation is larger.

4. The electrode lifting device for an arc furnace according to claim 1, wherein the target velocity calculation unit has a wider dead zone in the plurality of velocity sensitivity characteristics, and the third velocity sensitivity characteristic corresponding to the final stage of dissolution has a wider dead zone than the fourth velocity sensitivity characteristic corresponding to the dissolution stage, and the rate of change of velocity with respect to impedance deviation is larger.

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