JP2006085936A - Electrode elevation control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode elevation control device capable of preventing breakage or abnormal consumption of the electrode in a simple structure. <P>SOLUTION: The electrode elevation control device for a steel-making alternating-current arc furnace controlling elevation of electrodes 4a, 4b, 4c allocated to each phase by a speed control means having a prescribed arc impedance by supplying three-phase alternating current source; and generating arc between the electrodes of the respective phases and scraps 6 to melt the scraps 6; has a distance detecting means calculating a moving distance of the electrode position by using pulse signals from speed detectors 9a, 9b, 9c mounted on electrode elevation motors 8a, 8b, 8c, and finding the distance between the electrodes of the respective phases and the scraps. Indication of the speed or control parameter of a speed control means is made to change in compliance with the distance detected by the distance detecting means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode lifting control device used in an AC arc furnace for steel making that melts scrap with arc energy.

  In an arc furnace in which iron scrap is melted by arc discharge, it is desirable to keep the input power constant so that melting can be performed efficiently. For this reason, a control method called arc impedance constant control is adopted in which the electrode elevation control device is automatically controlled so that the ratio between the arc voltage and the arc current is constant, and the electrode is automatically raised and lowered.

  In a normal AC arc furnace, a three-phase AC power supply is stepped down to a voltage required for arc furnace operation by a furnace transformer, and power is supplied to the electrodes through a secondary conductor connected to the furnace transformer. This electrode is controlled by an electrode lifting / lowering control device, and generates arc energy necessary for melting the scrap with the scrap charged in the furnace body. Here, the electrode lift control device performs the lift control of the electrode so as to make the arc impedance between the electrode and the scrap constant as described above. The lift speed is determined by the current feedback signal on the secondary side of the furnace transformer. When the deviation is large, the vertical movement control is performed at a high speed, and when the deviation is small, the vertical movement control is performed at a low speed.

Such constant control of arc impedance does not always enable stable control at each stage of operation, and when the electrode is moved up and down while the arc is unstable, there may be an overcurrent due to excessive pulling down of the electrode. there were. As countermeasures, proposals have been made such that the instability of the arc is grasped by the frequency of the lifting / lowering operation of the electrode, and the response of the lifting / lowering operation of the electrode is made dull when this frequency increases (for example, see Patent Document 1). ).
Japanese Patent Laid-Open No. 10-335058 (page 3-4, FIG. 1)

  The method proposed in Patent Document 1 determines the lifting speed of the electrode regardless of the distance between the electrode and the scrap. Therefore, when there is a sudden disturbance when the electrode is close to the scrap, the electrode is lowered at a high speed. However, there is a problem in that the electrode is excessively pushed into the scrap, and the electrode is broken or abnormally consumed. This problem is also caused by the large weight of the electrode.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode lifting / lowering control device capable of preventing electrode breakage and abnormal wear with a simple configuration.

  In order to achieve the above object, an electrode lifting control device of the present invention supplies a three-phase AC power source, and controls the lifting and lowering of electrodes provided in each phase by means of speed control means having a constant arc impedance. In the electrode raising / lowering control apparatus for an AC arc furnace for steelmaking that generates an arc in between and melts the scrap, the moving distance of the electrode position is calculated using the pulse signal of the speed detector attached to the electrode raising / lowering motor, A distance detection means for obtaining a distance between the electrode of each phase and the scrap is provided, and a speed command or a control parameter in the speed control means is changed according to the distance detected by the distance detection means. It is said.

  According to the present invention, since the lifting operation can be slowed when the electrode is close to the scrap, the electrode lifting control device capable of preventing electrode breakage and abnormal consumption with a simple configuration. Can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  Hereinafter, an electrode lifting control apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 3.

  FIG. 1 is a block configuration diagram of an electrode elevation control apparatus according to the present invention.

  A three-phase AC power source 1 is stepped down to a voltage required for arc furnace operation by a furnace transformer 2 and is connected to an electrode 4a via secondary conductors 3a, 3b and 3c connected to the secondary side of the furnace transformer 2. AC power is supplied to 4b and 4c. The arc energy required for melting the scrap 6 is generated between the electrodes 4a, 4b and 4c and the scrap 6 charged in the furnace body 5, and the arc furnace for steelmaking is operated. In order to control the ratio of the arc voltage and the arc current to be substantially constant and perform stable operation, the electrode elevating control device 7 causes the electrode elevating motors 8a, 8b and 8c to drive the electrodes 4a, 4b and 4c up and down. 4b and 4c are provided. The electrode elevating motors 8a, 8b and 8c are respectively equipped with speed detectors 9a, 9b and 9c for outputting a pulse proportional to the number of revolutions, and supply the pulses P1, P2 and P3 to the electrode elevating control device 7, respectively. Yes. In addition, a current detector 10 and a voltage detector 11 are provided on the secondary side of the furnace transformer 2 for feedback for controlling the arc impedance constant, and a three-phase current signal Iu is supplied to the electrode lifting control device 7. , Iv and Iw, and three-phase voltage signals Eu, Ev and Ew, respectively. Hereinafter, the internal configuration and operation of the electrode elevation control device 7 will be described.

  The electrode lifting speed reference calculation circuit 71 receives the above-described three-phase current signals Iu, Iv and Iw, and the three-phase voltage signals Eu, Ev and Ew, and compares these feedback signals with the set current reference and set tap voltage. The speed command is generated by calculation, and this speed command is given to the electrode lifting motor controller 72. This comparison operation compares each phase current reference obtained by correcting the set current reference with the ratio of the set tap voltage and the voltage signals Eu, Ev, and Ew with the current signals Iu, Iv, and Iw, and the speed command is determined according to the deviation. Try to determine polarity and size. The electrode motor lift control device 72 compares this speed command with the feedback speed obtained from the output pulses of the speed detectors 9a, 9b and 9c, and outputs drive outputs V1, V2 and V3 corresponding to the deviations to the electrode lift motors 8a, 8b and Give to 8c. As described above, a speed control system for raising and lowering the electrode for performing constant arc impedance control is configured.

  The electrode position calculation circuit 73 calculates the distances L1y, L2y, and L3y between the scrap 6 and the electrodes 4a, 4b, and 4c by a method that will be described later, and supplies the distances to the electrode lifting speed reference calculation circuit 71. The electrode lifting / lowering speed reference calculation circuit 71 changes the speed command according to the values of the distances L1y, L2y, and L3y. For example, when L1y, L2y, and L3y are below a predetermined value, the speed command is lowered. If the distance L1y, L2y, and L3y between the scrap 6 and the electrodes 4a, 4b, and 4c is displayed on a display device (not shown) without any automatic control as described above, it can be confirmed by some method. It is also possible to manually control the electrode elevation.

  FIG. 2 is a block configuration diagram showing an example of the internal configuration of the electrode elevation speed reference arithmetic circuit 71.

As described above, the three-phase current signals Iu, Iv and Iw, the three-phase voltage signals Eu, Ev and Ew, the set current reference and the set tap voltage are input to the arc impedance constant control circuit 74 to make the arc impedance constant. The speed command is calculated as follows. On the other hand, the distances L1y, L2y and L3y between the scrap 6 obtained by the electrode position calculation circuit 83 and the electrodes 4a, 4b and 4c and the electrode lower limit position of each phase are compared by the comparator 75, and the distances L1y, L2y and L3y are compared. Is below the electrode lower limit position of each corresponding phase, the speed command lowering circuit 76 is operated to correct the speed command obtained by the arc impedance constant control circuit 74 described above. Although this correction is illustrated to reduce the speed command, a fixed limit may be provided for the speed command.

  Next, the operation of the electrode position calculation circuit 73 will be described with reference to FIGS. FIG. 3 is an explanatory diagram showing the relationship between the electrode positions, and FIG. 4 is a flowchart showing the operation of the electrode position calculation circuit. As shown in FIG. 3, the distances from the electrode upper limit position to the upper part of the electrode when the electrodes 4a, 4b and 4c are in contact with the scrap 6 are L1M, L2M and L3M, respectively, and the upper part of the electrodes 4a, 4b and 4c in the operating state. And L1x, L2x and L3x, and the distance between the electrode and scrap 6 are L1y, L2y and L3y, respectively. Hereinafter, the operation of the electrode position calculation circuit 73 will be described with reference to FIG.

  First, the electrode is moved to the upper limit position (ST1), and in this state, L1x, L2x and L3x are initialized to zero, and the pulse count values P1, P2 and P3 from the speed detector are initialized to zero (ST2). At the same time as the electrode is lowered, the pulses are integrated (ST3), and the integrated value is multiplied by the pulse rate α to calculate the electrode movement distance from the electrode upper limit position (ST4).

  When the electrode is further lowered and a scrap touch is detected (ST5), the movement distances L1x, L2x and L3x from the electrode upper limit position on each electrode are set as the distances L1M, L2M and L3M from the electrode upper limit position to the scrap touch position, respectively. (ST6). The detection of scrap touch can be made based on whether the phase current of each electrode is equal to or higher than a predetermined current value or whether the phase voltage is equal to or lower than a predetermined voltage value. After the distances L1M, L2M, and L3M from the electrode upper limit position to the scrap touch position are determined in this way, differences between L1M, L2M, and L3M and the current electrode positions L1x, L2x, and L3x are obtained, respectively, and the current electrode position is determined. The distances L1y, L2y and L3y from to the scrap touch position are respectively calculated (ST7).

  As described above, if the electrode is raised to the electrode upper limit position only in the initial state and the scrap touch is not performed again, the determination in step ST1 and step ST5 is NO, so the setting operation in step ST2 and step ST6 is jumped. Therefore, the distances L1y, L2y, and L3y from the current electrode position to the scrap touch position can be continuously output. The above calculation is continuously performed as long as the operation state is normal.

  In this way, it is possible to prevent breakage of the electrodes and the like by changing the speed command given to the electrode motor control device 72 by the electrode lifting speed reference arithmetic circuit 71 in accordance with the values of the distances L1y, L2y and L3y. .

  As shown in FIG. 2, the speed command given to the electrode motor control device 72 by the electrode lifting speed reference arithmetic circuit 71 is not changed, but the gain of the amplifier of the speed control system of the electrode motor control device 72 is adjusted. The operation of the electrode may be slowed down by changing the parameters of the speed control system.

  Hereinafter, an electrode lifting control apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS.

  FIG. 5 is a flowchart showing the operation of the electrode position calculation circuit of the electrode lifting control apparatus according to Embodiment 2 of the present invention. Regarding the respective parts of the second embodiment, the same parts as those in the flowchart showing the operation of the electrode position calculation circuit of the electrode lifting control device according to the first embodiment of FIG. The difference between the second embodiment and the first embodiment is that a step ST8 for performing a molten metal surface level lowering correction calculation is provided after step ST7.

  When the steelmaking arc furnace is operated, the scrap 6 is gradually melted, and the molten metal surface is lowered according to the operation duration time. For this reason, by correcting the amount of decrease in the molten metal surface, the distance between the electrodes 4a, 4b and 4c and the scrap 6 can be grasped more accurately, and the overall control accuracy can be improved.

  FIG. 6 is a flowchart showing an example of step ST8 for performing the molten metal level lowering correction calculation.

In step ST81, the arc currents Iu, Iv and Iw are controlled within a predetermined range, and it is determined whether or not the arc is in a steady state. If this determination is YES, it is determined that the position of the electrode at this time is lower than the previous position by a decrease in the molten metal surface, and in step 82,
L1M = L1M (previous) + (L1y (previous) −L1y), L2M = L2M (previous) + (L2y (previous) −L2y), L3M = L3M (previous) + (L3y (previous) −L3y) Correct the distance from the upper limit position.

  Since it is normal for this correction to increase the distance from the electrode upper limit position, a filter function is provided so that the correction is ignored when the distance from the electrode upper limit position decreases. May be.

  FIG. 7 is a flowchart showing another example of step ST8 in which the molten metal level lowering correction calculation is performed.

In step ST83, the operation time Tr of the electrode raising / lowering control apparatus of the steelmaking arc furnace is measured. According to the measured operation time Tr, the distance from the electrode upper limit position is expressed as L1M = L1M (previous) + f (Tr), L2M = L2M (previous) + f (Tr), L3M = L3M (previous) + f (Tr) Correct each one. Here, f (Tr) is prepared in advance as a time function table based on the furnace capacity of the arc furnace, scrap material, shape, charging amount, set current, and the like.

The block block diagram of the electrode raising / lowering control apparatus of this invention. The block block diagram which shows an example of the electrode raising / lowering speed reference | standard calculation circuit in the electrode raising / lowering control apparatus of this invention. Explanatory drawing which shows the relationship of an electrode position. The flowchart which shows operation | movement of the electrode position calculating circuit of the electrode raising / lowering control apparatus which concerns on Example 1 of this invention. The flowchart which shows operation | movement of the electrode position calculating circuit of the electrode raising / lowering control apparatus which concerns on Example 2 of this invention. The flowchart which shows an example of a molten metal surface fall correction | amendment calculation. The flowchart which shows the other example of a molten metal surface fall correction | amendment calculation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 3 phase alternating current power supply 2 Furnace transformer 3a, 3b, 3c Secondary side conductor 4a, 4b, 4c Electrode 5 Furnace body 6 Scrap 7 Electrode raising / lowering control apparatus 71 Electrode raising / lowering speed reference arithmetic circuit 72 Electrode raising / lowering motor control apparatus 73 Electrode Position calculation circuit 74 Arc impedance constant control circuit 75 Comparator 76 Speed command lowering circuits 8a, 8b, 8c Electrode lifting motors 9a, 9b, 9c Speed detector 10 Current detector 11 Voltage detector

Claims (6)

An AC arc furnace for steelmaking that supplies three-phase AC power, controls the elevation of the electrodes provided in each phase by means of speed control with constant arc impedance, generates an arc between each phase electrode and scrap, and melts the scrap. In the electrode lifting control device,
A distance detection means for calculating a distance of movement of the electrode position using a pulse signal of a speed detector attached to the electrode lifting motor, and obtaining a distance between the electrode of each phase and the scrap,
An electrode lifting / lowering control apparatus, wherein a speed command or a control parameter in the speed control means is changed according to the distance detected by the distance detection means. An AC arc furnace for steelmaking that supplies three-phase AC power, controls the elevation of the electrodes provided in each phase by means of speed control with constant arc impedance, generates an arc between each phase electrode and scrap, and melts the scrap. In the electrode lifting control device,
A distance detecting means for calculating a moving distance of the electrode position using a pulse signal of a speed detector attached to the electrode lifting motor, and obtaining a distance between the electrode of each phase and the scrap;
An electrode lifting / lowering control device comprising distance confirmation means for confirming the distance. When the distance detected by the distance detection means is below a predetermined value,
2. The electrode lifting / lowering control apparatus according to claim 1, wherein the speed control means prevents the speed of the electrode lifting / lowering motor from exceeding a predetermined value.   The electrode elevation control device according to claim 1, wherein the distance detection unit includes a correction unit that corrects a decrease in molten metal level caused by the progress of melting of scrap.   5. The electrode lifting / lowering control apparatus according to claim 4, wherein the correction means sets the movement amount of the electrode when the arc current is within a predetermined range as a correction amount. 5. The electrode lifting / lowering control apparatus according to claim 4, wherein the correction means is based on a time function table determined from a furnace capacity of an arc furnace, a scrap material, a shape, a charging amount, and a set arc current.

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