JP4815175B2 - Electrode lifting device for arc furnace - Google Patents

Description

  The present invention relates to an arc furnace electrode lifting apparatus for melting scrap by arc energy generated from an arc furnace electrode.

  In general, an electrode raising / lowering device for an arc furnace is used to melt scrap (steel scrap or the like) charged in the furnace body. The arc furnace electrode lifting device includes three lifting support masts that are lifted and lowered by the driving force of the electric motor, a horizontal arm that is individually fixed to each lifting support mast, and suspended at the tip of each horizontal arm. And three electrodes arranged at a predetermined interval on the top of the furnace body. A predetermined alternating voltage is supplied to each of these electrodes from each phase secondary winding of the furnace three-phase transformer.

  When melting the scrap charged in the furnace body, the raising / lowering support mast of each electrode raising / lowering device for the arc furnace is lowered, and the three electrodes are made to approach the scrap in the furnace body through the furnace lid at the top of the furnace body. To go. At this time, since a predetermined alternating voltage is applied to each electrode, an arc is generated between each electrode end and the scrap in the furnace body, and the scrap is melted by the generated arc.

  By the way, in a conventional arc furnace electrode lifting device, high-speed lowering control is performed when the electrode is initially lowered, and the arc voltage appearing between the one-phase secondary winding with the three-phase transformer and scrap is near zero. When reaching the value, it is regarded as a scrap touch, and control is performed to switch all three electrodes to the automatic operation mode (impedance constant control).

  FIG. 4 is a block diagram for explaining an electrode lifting control unit in a conventional arc furnace electrode lifting apparatus.

  In this arc furnace electrode lifting device, the AC power supply voltage supplied to the primary winding is stepped down to a voltage required for arc operation by the furnace three-phase transformer 1, and the secondary of the furnace three-phase transformer 1 is reduced. It supplies to the electrode 2 connected to a side winding. In this state, when the electrode 2 is brought closer to the scrap 4 charged in the furnace body 3, arc energy is generated between the electrode 2 and the scrap 4 in the furnace body 3.

Therefore, the electrode lifting / lowering control unit 10 in the arc furnace electrode lifting / lowering apparatus performs the following process. At the time of initial descent accompanying the start of energization, the electrode 2 is manually lowered at a high speed to approach the scrap 4. At this time, the auxiliary transformer 5 connected to the secondary winding of the furnace three-phase transformer 1 is used. The arc voltage is detected and sent to an arc voltage check circuit 11 provided in the electrode elevation control unit 10. The arc voltage check circuit 11 compares the actual arc voltage V detected by the auxiliary transformer 5 with the set arc voltage Vs regarded as a scrap touch, and although not shown, any of R phase, S phase, and T phase is not shown. When the actual arc voltage V corresponding to one phase becomes equal to or lower than the set arc voltage Vs (V ≦ Vs), the R, S, and T phases are switched to the constant arc impedance control circuit 12, and the actual arc voltage V Using the arc current I detected by the instrument current transformer 6, automatic operation control is performed to make the arc impedance constant so that desired arc energy is generated from the three electrodes 2 (Patent Document 1).
JP-A-5-217671 (see FIG. 3)

  However, in the arc furnace electrode lifting apparatus as described above, the actual arc voltage V can be obtained even when only one phase of the three-phase secondary winding of the furnace three-phase transformer 1 is involved at the start of energization, regardless of the arc current. When the voltage becomes equal to or lower than the set arc voltage Vs, it is considered that the electrode 2 has reached the scrap 4 and the three electrodes 2 are switched to the constant impedance control. Therefore, a phase in which no arc is generated occurs because no arc current flows. In addition, there is a problem that the melting operation efficiency of the scrap 4 is lowered and the operation time is lost, for example, an unstable phase is generated even when an arc is generated.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an arc elevator electrode lifting apparatus and electrode lifting method that stabilizes the arc current of all phases when shifting to constant impedance control for each electrode and shortens the operation time. The purpose is to provide.

In order to solve the above-mentioned problems, an arc furnace electrode lifting apparatus according to the present invention is an arc furnace electrode that melts scrap in the furnace body by arc energy generated from an electrode for each phase to which a predetermined AC power is supplied. In the lifting device, rapid lowering drive control means for rapidly lowering the electrodes for each phase at the time of initial lowering, and between each phase AC power input line and the grounding line of the furnace body when the respective phase electrodes are rapidly lowered. Detects the arc voltage that appears, checks the scrap touch of the electrode for each phase, and if it is judged as a scrap touch, stops the electrode of the corresponding phase and stops by this arc voltage check means and phase response of the arc current checking means for checking the phase of the arc current of only the electrode obtained by, a by the arc current checking means If it is determined that the leakage current is flowing relative to the electrodes of the corresponding phase and control means for executing the arc impedance constant control is provided, the arc impedance constant control through each section in the same manner as described above for the electrodes of the other phases It is the structure provided with the electrode raising / lowering control part which transfers .

  Further, the method for raising and lowering the electrode for an arc furnace according to the present invention is the method for raising and lowering the electrode for an arc furnace in which the scrap in the furnace body is melted by the arc energy generated from the electrode for each phase to which predetermined AC power is supplied. Each time, a scrap touch is detected from the voltage appearing between each phase electrode and the scrap in the furnace body, and the rapid drop is sequentially stopped from the scrap touch and the detected phase electrode, and an arc current is applied to the phase electrode. The arc impedance constant control is executed when the current flows.

  ADVANTAGE OF THE INVENTION According to the present invention, an arc furnace electrode lifting apparatus and electrode lifting method capable of stabilizing the arc current of all phases when shifting to constant impedance control for each electrode and shortening the operation time are provided. it can.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of an electrode raising / lowering control unit of an arc furnace electrode raising / lowering apparatus according to the present invention. In the figure, the same parts as those in FIG.

  In FIG. 1, 1 is a furnace transformer, for example, a three-phase furnace transformer is used. The furnace transformer 1 converts the AC power supply voltage supplied to the primary winding into a desired voltage necessary for arc operation and supplies the converted voltage to the electrode 2. As shown in FIG. 2, the electrode 2 comprises three electrodes 2a (R phase), 2b (S phase), and 2c (T phase), and is disposed on the top of the furnace body 3 as described above. Are individually suspended by, for example, horizontal arms (not shown) corresponding to each phase, and are individually moved up and down according to the lifting operation by the electrode lifting device. Each electrode 2a, 2b, 2c is connected to each phase secondary winding of a three-phase transformer, which is a furnace transformer 1, and supplied with an AC voltage stepped down by the furnace transformer 1.

  The furnace body 3 is charged with scrap 4 to be melted and is normally closed by a furnace lid (not shown). Therefore, the electrodes 2 a, 2 b, 2 c lowered by the raising / lowering operation of the electrode raising / lowering device pass through the opening formed in the furnace lid and are inserted into the furnace body 3.

  Reference numeral 5 denotes an auxiliary transformer, which is connected between each phase secondary winding of the furnace transformer 1 and the furnace body 3 in a grounded state, and detects an arc voltage between the electrode 2 and the scrap 4. And sent to the electrode elevation control unit 20. 6 is an instrument current transformer, which detects an arc current from the secondary side of each phase of the furnace transformer 1 and sends it to the electrode lift control unit 20 in the same manner as the auxiliary transformer 5.

  The electrode raising / lowering control unit 20, which is the main part of the present invention, includes a rapid lowering drive control means 21 (21R, 21S, 21T) for rapidly lowering the electrodes 2a, 2b, 2c corresponding to each phase when starting energization, and an arc voltage checking means. 22 (22R, 22S, 22T), arc current check means 23 (23R, 23S, 23T), and arc impedance constant control means 24 (24R, 24S, 24T) are provided.

  The arc voltage check means 22 considers the actual arc voltage and scrap touch of each phase detected by the auxiliary transformer 5 connected between each phase secondary side of the furnace transformer 1 and the furnace body 3 ground line. Compared with the set arc voltage, when the actual arc voltage falls below the set arc voltage, only the electrode 2 of the corresponding phase is regarded as a scratch touch, and after stopping the electrode 2 corresponding to the phase, the arc current check An instruction is sent to the arc current check means 23. This set arc voltage is a voltage value corresponding to when the electrode 2 reaches the scrap 4 and is determined from experiments and other past knowledge and experience.

  Upon receiving a check instruction from the arc voltage check means 22, the arc current check means 23 takes in the actual arc current detected by the above-described current transformer 6 for each phase, and the actual arc current and a predetermined arc current are taken. Is compared with the set arc current that is regarded as flowing, and if there is a phase in which the actual arc current I exceeds the set arc current Is, the arc impedance constant control means 24 corresponding to the phase is selected. .

  The arc impedance constant control means 24 uses the actual arc voltage V detected by the auxiliary transformer 5 and the arc current I detected by the instrument current transformer 6 so that the actual arc current I exceeds the set arc current Is. Only the electrode 2 corresponding to the corresponding phase is subjected to arc arc impedance constant control, and is automatically operated so as to obtain desired arc energy.

  In addition, although the said electrode raising / lowering control part 20 is generally implement | achieved using a microprocessor (CPU), it is also possible to set it as a hardware structure using a logic circuit etc., for example.

  Next, regarding the operation of the electrode lifting control unit 20 in the arc furnace electrode lifting apparatus as described above, the operation of the electrode lifting control unit 20 when a microprocessor (CPU) is used will be described.

  When energization starts (S1), the electrode lifting control unit 20 performs a predetermined process according to the flow shown in FIG. That is, the electrode rapid lowering drive control means 21R, 21S, 21T for each phase of the electrode lifting control unit 20 sends out a rapid lowering drive control signal and gives it to an electric motor (not shown). When the electrodes 2a, 2b, and 2c are initially lowered, the electric motor rapidly lowers the electrodes 2a, 2b, and 2c that are suspended on the horizontal arm via, for example, the lifting support mast and the horizontal arm corresponding to each phase. As a result, the electrodes 2a, 2b, 2c corresponding to each phase pass through the furnace lid on the top of the furnace body 3 toward the scrap 4 in the furnace body 3, and approach the scrap 4 (S2R, S2S, S2T).

  At this time, the arc voltage check means 22R, 22S, 22T for each phase of the electrode lifting / lowering control unit 20 is the actual arc voltage that appears between the secondary winding side of the corresponding phase of the furnace transformer 1 and the ground. V is monitored (S3R, S3S, S3T). That is, the arc voltage check means 22R, 22S, 22T take in the actual arc voltage V from the auxiliary transformer 5 provided for each phase, and obtain the actual arc voltage V of each phase and the set arc voltage Vs regarded as scrap touch. In comparison, when the actual arc voltage V corresponding to any one phase, for example, the R phase is equal to or lower than the set arc voltage Vs (V ≦ Vs), it is regarded as a scrap touch and the electrode 2a corresponding to the R phase is stopped. (S4R).

  At this time, if the actual arc voltage V corresponding to the other S phase and T phase is not less than or equal to the set arc voltage Vs, the process proceeds to steps S2S and S2T, the electrode automatic rapid drop is continued, and the actual arc voltage V Are monitored (S3S, S3T).

  In step S4R, after stopping the electrode 2a, the arc current check means 23R corresponding to the R phase is executed. This arc current check means 23R compares the actual arc current I detected by the current transformer 6 corresponding to the R phase with the set arc current Is that the arc current is assumed to flow (S5R), and the actual arc current I Is determined to be greater than or equal to the set arc current Is (I ≧ Is), the arc impedance constant control means 24R is executed (S6R). That is, the constant arc impedance control means 24R takes in the actual arc voltage V detected by the auxiliary transformer 5R and the actual arc current I detected by the current transformer 6 for the corresponding phase, and the actual arc voltage V and the actual arc voltage V are detected. The automatic control operation is performed so that the ratio with the arc current i is constant (S6R). In this automatic control operation, the elevator control is performed at a speed slower than the manual control operation (rapid ascending / descending speed), and is controlled so as not to cause arc breakage in response to a change in the situation inside the furnace body 3.

  By the way, when the electrode 2a corresponding to the R phase is in the arc impedance constant control, the arc voltage check means 22S, 22T corresponding to the S phase and the T phase, as described above, the actual arc voltage V and the set arc voltage Vs. (S3S, S3T), for example, when the actual arc voltage V of the S phase becomes equal to or lower than the set arc voltage Vs, the electrode 2b corresponding to the S phase is stopped for the first time, and the arc current is similar to the R phase. Monitoring (S5S) and transition to arc impedance constant control (S6S).

  In the T phase, the same procedure is followed to stop the electrode (S4T), monitor the arc current (S5T), and control the constant arc impedance (S6T).

  Therefore, according to the embodiment as described above, the actual arc voltage V and the set arc voltage Vs are compared for each phase, and the arc current is sequentially from the phase in which the actual arc voltage V is equal to or less than the set arc voltage Vs. When the process moves to the check means 23, it is determined whether or not the arc current is actually flowing, and when the stable arc current is flowing, the process shifts to the constant arc impedance control. Then, it is possible to shift to the constant impedance control sequentially. As a result, there is no phase in which no arc is generated because no arc current flows, and there is no phase that is unstable even when an arc is generated, and the scrap 4 can be melted and operated in a stable state. As a result, the efficiency of the melting operation of the scrap 4 can be increased, and the operation time can be shortened.

  In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

The block diagram which shows one Embodiment of the electrode raising / lowering control system among the electrode raising / lowering apparatuses for arc furnaces which concern on this invention. The figure which shows the example by which the electrode is arrange | positioned for every phase. The flowchart explaining the operation | movement of the electrode raising / lowering control in the electrode raising / lowering apparatus for arc furnaces which concerns on this invention. The block diagram which shows the electrode raising / lowering control system of the conventional electrode raising / lowering apparatus for arc furnaces.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Furnace transformer, 2 (2a, 2b, 2c) ... Electrode, 3 ... Furnace body, 4 ... Scrap, 5 ... Auxiliary transformer, 6 ... Current transformer for instrument, 20 ... Electrode raising / lowering control part, 21 ( 21R, 21S, 21T) ... Electrode rapid drop drive control means, 22 (22R, 22S, 22T) ... Arc voltage check means, 23 (23R, 23S, 23T) ... Arc current check means, 24 (24R, 24S, 24T) … Arc impedance constant control means.

Claims (3)

In an arc furnace electrode lifting device for melting scrap in the furnace body by arc energy generated from electrodes for each phase supplied with predetermined alternating current power,
Rapid descent drive control means for rapidly lowering the electrodes for each phase at the time of initial descent, and arc voltage appearing between each phase AC power input line and the ground line of the furnace body at the time of high descent of each phase electrode Detect and check the scrap touch of the electrode for each phase, and when it is judged as scrap touch, only the arc voltage check means corresponding to each phase that stops the electrode of the corresponding phase, and the electrode stopped by this arc voltage check means Arc current check means corresponding to each phase for checking the arc current of each phase, and control for executing arc impedance constant control for the electrode of the corresponding phase when it is determined by the arc current check means that the arc current is flowing and means is provided for the electrodes of the other phase electrode shifts to the arc impedance constant control through each section in the same manner as described above Noboru Arc furnace electrode lifting device being characterized in that a control unit. The electrode lifting apparatus for an arc furnace according to claim 1,
The arc voltage check means of the electrode elevation control unit compares the arc voltage corresponding to each phase with a set arc voltage that is regarded as a scrap touch in advance, and when the arc voltage is equal to or lower than the set arc voltage, An electrode lifting apparatus for an arc furnace characterized in that only the electrodes are individually stopped. In an arc furnace electrode lifting / lowering method of melting scrap in the furnace body by arc energy generated from an electrode for each phase to which a predetermined AC power is supplied,
For each phase, the scrap touch is detected from the voltage appearing between the electrode of each phase and the scrap in the furnace body, and the rapid drop is sequentially stopped from the electrode of the detected phase with the scrap touch, A method for raising and lowering an electrode for an arc furnace, which performs constant control of arc impedance when an arc current is flowing.

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