Power supply device and smelting method for multi-electrode direct current electric arc furnace and submerged arc furnace

Abstract

The present invention relates to the technical field of industrial smelting, and in particular to a power supply device and a smelting method for a multi-electrode direct current electric arc furnace and submerged arc furnace, used for solving problems arising from operating conditions in which the furnace charge of the multi-electrode direct current furnace exhibits abnormal conductivity. The device consists of components such as a phase-shifting transformer, a rectifier module, a direct current conversion module, and an isolation switch; the components are connected according to a specific rule, thereby forming a top-electrode attribute transformation loop within a device topology. By means of the smelting method described herein, anode-cathode attribute transformation of a top electrode in a multi-electrode direct current furnace can be achieved, so that smelting can still be carried out by means of a top-electrode loop under complex conditions such as poor furnace charge conductivity, and once a molten pool forms in the furnace and the furnace charge conductivity is enhanced, normal production procedures can be resumed, thereby reducing the time required to handle abnormal faults, and improving the smelting efficiency of industrial smelting, especially in the fields of ferroalloys and specialty steels.

Description

A multi-electrode DC electric arc furnace, a power supply device for a submerged arc furnace, and a smelting method. Technical Field

[0001] This invention belongs to the field of industrial smelting technology, and relates to a multi-electrode DC electric arc furnace, a power supply device for a submerged arc furnace, and a smelting method. Background Technology

[0002] With the increasing demand for efficient and high-quality smelting in industry, traditional AC furnaces are gradually showing their limitations. DC furnaces, with their unique advantages, have become an important development trend in the industrial smelting field.

[0003] The DC furnace exhibits a stable electric arc, reducing the likelihood of flashover and short circuits, thus improving the stability of the smelting process and reducing electrode consumption. Its high heat transfer efficiency shortens smelting time, increases production efficiency, and lowers energy consumption. The DC furnace has minimal impact on the power grid, improving grid stability and reducing interference. Its high grid-side power factor enhances grid utilization efficiency and reduces electricity costs. Finally, the DC furnace is environmentally friendly, reducing pollutant emissions and aligning with green manufacturing principles.

[0004] To further improve efficiency, high-power DC furnaces and submerged arc furnaces typically employ a multi-top cathode + bottom anode structure. This structure can provide greater power and increase production efficiency, while also enhancing the contact area between the electrodes and the furnace charge through the configuration of multiple electrodes, thereby improving the stability of the electric arc.

[0005] However, existing multi-electrode DC furnace technology faces the following challenges when dealing with complex operating conditions such as poor conductivity of the furnace charge and uneven distribution of non-metallic materials:

[0006] Poor conductivity of the furnace charge or uneven distribution of non-metallic materials results in a small electrode contact area, making it difficult to establish current and causing a significant drop in current during the early stages of smelting. In severe cases, the current is too low to ignite an arc, requiring refilling of the furnace charge, which prolongs smelting time and disrupts production. When the furnace charge has poor conductivity, refilling or adjusting the charge structure is necessary, further extending smelting time. Poor conductivity also makes it difficult to establish current, leading to reduced smelting efficiency. Conductivity grades include: High conductivity (good conductivity): resistivity below 1×10⁻⁶. -6 Ω·m; Medium conductivity: resistivity between 1×10 -6 Ω·m and 1×10 -4 Between Ω·m; low conductivity (poor conductivity): resistivity higher than 1×10 -4 Ω·m.

[0007] For example, CN111952986A discloses a high-performance DC electric arc furnace power supply and method, but it cannot solve the problem of low smelting efficiency caused by poor conductivity of furnace charge in a timely manner, and requires the configuration of reactive power compensation and filtering devices.

[0008] Therefore, it is necessary to develop a multi-electrode DC electric arc furnace, a power supply device for an electric arc furnace, and a smelting method suitable for various complex working conditions, in order to solve the problem of abnormal conductivity of the furnace charge, improve smelting stability and efficiency, reduce smelting time, increase production efficiency, and broaden the application range of DC furnaces in the smelting of special steels and ferroalloys. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a power supply device and smelting method for a multi-electrode DC electric arc furnace and a submerged arc furnace, to solve the problem of abnormal conductivity of the furnace charge in a multi-electrode DC furnace. The DC power supply device provided by this invention adds a top electrode property transformation circuit to the traditional DC device topology. Combined with the smelting method provided by this invention, it reduces the processing time under abnormal furnace charge conditions with very little increase in hardware cost, and greatly improves smelting stability and efficiency.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A power supply device for a multi-electrode DC electric arc furnace and a submerged arc furnace, comprising:

[0012] A phase-shifting transformer has a primary side connected to the AC power grid and a secondary side with multiple output windings and multiple phase-shifting output terminals.

[0013] A rectifier module, the input of which is connected to multiple phase-shifting outputs of the phase-shifting transformer;

[0014] The DC-DC converter module has its input terminal connected to the output terminal of the rectifier module, and its multiple output terminals are connected according to a specific rule to form multiple sets of positive and negative outputs after the connection is completed.

[0015] A disconnecting switch is used to connect the multiple sets of positive and negative outputs to different electrodes;

[0016] The multiple phase-shifting output terminals on the secondary side of the phase-shifting transformer are respectively connected to the input terminals of different rectifier modules;

[0017] The rectifier module is composed of one or more rectifier units connected in parallel, and each rectifier unit is composed of power devices forming a fully controlled, semi-controlled, or uncontrolled rectifier circuit.

[0018] Furthermore, the DC-DC converter module is composed of an input reactance, a supporting capacitor, a DC chopper circuit, and an output reactance connected in sequence. The DC chopper module is composed of a full-bridge or half-bridge DC-DC circuit made of power devices.

[0019] Furthermore, the multiple output terminals of the DC-DC converter module are connected according to a specific rule, which is as follows:

[0020] Multiple DC-DC converter modules connected to the same rectifier module output terminal are directly connected in parallel, forming a set of positive and negative outputs through an isolating switch;

[0021] The DC power supply device will generate multiple sets of positive and negative outputs. Among them, multiple sets of positive outputs are directly connected in parallel to form a set of anode outputs, which are then connected to the bottom anode of the furnace body through a short anode network.

[0022] Multiple sets of negative electrode outputs are connected in parallel to form multiple sets of cathode outputs, the same number as the number of top cathodes in the furnace body, and then connected to different top cathodes through cathode short networks;

[0023] The anode output is connected to one or more cathode outputs via a disconnect switch.

[0024] Furthermore, the disconnecting switch is composed of one or more disconnecting switches connected in parallel.

[0025] A smelting method for a multi-electrode DC electric arc furnace and a submerged arc furnace includes the following steps:

[0026] S1: Close the isolating switches at the output terminals of all DC-DC converter modules, open the isolating switch between the anode output and the cathode output, control the power supply to output a voltage of preset amplitude, control the top cathode to descend, and collect the loop current signal and pressure signal.

[0027] S2: During the electrode descent, a threshold judgment is performed on the detection signal. If the pressure is greater than the threshold, the current is less than the arc initiation current, and the duration is greater than the threshold, then the electrode contact area is considered abnormal or the conductivity of the furnace charge is abnormal, and the process jumps to S3.

[0028] S3: Based on the furnace body and furnace charge conditions, one or more furnace top cathodes are transformed into top anodes. All output isolation switches of the DC-DC converter module corresponding to the electrode to be adjusted are disconnected, and the isolation switch between the short network circuit of the electrode and the original anode output is closed to complete the anode-cathode attribute transformation of the top electrode.

[0029] S4: Re-control the descent of the top electrode, and perform threshold judgment on the detection signal according to S2. If the electrode contact area or the conductivity of the furnace charge is found to be abnormal, jump to S5; otherwise, the furnace charge at the contact point is considered to be normal. Adjust the smelting current and power, and after smelting for 5 to 15 minutes, jump to S1.

[0030] S5: If the number of abnormal cases is too high, jump to S7; otherwise, jump to S6.

[0031] S6: Control the top electrode to rise, add conductive material to the surface of the furnace charge, and then jump back to S4;

[0032] S7: If the power supply equipment, short circuit circuit, or furnace charge is deemed to be faulty, the system will stop smelting for investigation.

[0033] S8: The power supply equipment, short circuit, and furnace charge are considered to be normal, and the system is smelting normally.

[0034] Furthermore, in S2, the pressure threshold is a percentage of the compressive strength of the electrodes used in the electric arc furnace, the arc ignition current is a percentage of the rated current of the power supply device for the electric arc furnace, and the time threshold is a value determined by smelting experience.

[0035] Furthermore, in step S3, if the furnace body has two top electrodes, then one top electrode can be selected for property transformation. If the furnace body has multiple top electrodes, then the condition of the furnace charge is observed, and the bottom charge with a resistivity lower than 1×10⁻⁶ is selected. -6 The properties of the top electrode with an Ω·m value are transformed. After the property transformation, at least one anode and one cathode are retained in the top electrode.

[0036] Furthermore, in S4, during the process of re-controlling the descent of the top electrode, the top anode is first lowered to contact the furnace charge, and the top cathode is lowered after keeping the anode stationary. The threshold judgment is then performed according to S2. At this time, the current threshold judgment is only performed on the top electrode with anode or cathode attributes.

[0037] Furthermore, in step S4, the pressure signal of the top anode electrode is used to determine whether the electrode is in contact with the furnace charge.

[0038] If the furnace charge at the contact point is considered to be normal, the smelting current and power are adjusted according to the conductivity of a single top electrode, and smelting is carried out for 5 to 15 minutes to form a molten pool in the furnace, which facilitates the subsequent restoration of normal smelting.

[0039] Furthermore, in step S6, a conductive material is added between the bottoms of different top electrodes to facilitate the formation of a conductive circuit after the electrodes descend.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) The multi-electrode DC electric arc furnace and electric arc furnace power supply device provided by the method of the present invention has no change in the main topology compared with the traditional power supply device, only the top electrode attribute transformation circuit is added, and the attribute transformation function of the top electrode is realized with very low cost increase.

[0042] (2) The method of the present invention provides a multi-electrode DC electric arc furnace, a power supply device for an electric arc furnace and a smelting method, which solves the problem of low smelting efficiency caused by poor conductivity of the furnace charge, reduces the processing time of furnace charge handling and backfilling under abnormal conditions, improves production and smelting efficiency, and broadens the application scope of DC furnace in special steel and ferroalloy smelting.

[0043] (3) The method of the present invention provides a multi-electrode DC electric arc furnace and smelting method for electric arc furnace. The algorithm is easy to implement, does not affect the original smelting process, and the whole process is simple to operate and has obvious effects. It can be widely applied to various DC furnace smelting occasions.

[0044] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0046] Figure 1 is a flowchart of a multi-electrode DC electric arc furnace and submerged arc furnace smelting method according to the present invention;

[0047] Figure 2 is a schematic diagram of the power supply device connection for the dual-top electrode DC furnace in Embodiment 1;

[0048] Figure 3 is a schematic diagram of the DC-DC converter module topology in Embodiment 1;

[0049] Figure 4 is a schematic diagram of the connection of the power supply device for the three-top electrode DC furnace in Example 2.

[0050] Reference numerals in the attached figures: Phase-shifting transformer 201, First rectifier module 211, Second rectifier module 212, Third rectifier module 213, First DC-DC converter module 221, Second DC-DC converter module 222, Third DC-DC converter module 223, Fourth DC-DC converter module 224, Fifth DC-DC converter module 225, Sixth DC-DC converter module 226, First disconnecting switch K1, Second disconnecting switch K2, Third disconnecting switch K3, Fourth disconnecting switch K4, Fifth disconnecting switch K5, Sixth disconnecting switch K6, Seventh disconnecting switch K7, Eighth disconnecting switch K8, First furnace top electrode E1, Second furnace top electrode E2, Third furnace top electrode E3. Detailed Implementation

[0051] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0052] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0053] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0054] For ease of understanding, two implementation examples of the method of this invention are provided. In the first embodiment, the DC furnace has a dual-top electrode structure. The multi-electrode DC power supply device provided by this invention consists of a phase-shifting transformer 201, a first rectifier module 211, a second rectifier module 212, a first DC-DC converter module 221, a second DC-DC converter module 222, a third DC-DC converter module 223, a fourth DC-DC converter module 224, a first isolating switch K1, a second isolating switch K2, a third isolating switch K3, a fourth isolating switch K4, and a fifth isolating switch K5. In this embodiment, the DC-DC converter module is composed of an input reactance, a supporting capacitor, a DC chopper circuit, and an output reactance connected in sequence. The DC chopper module is composed of a half-bridge DC-DC circuit formed by IGBTs. The schematic diagram of the module is shown in Figure 3.

[0055] In this embodiment, the system connection diagram is shown in Figure 2. The primary side of the phase-shifting transformer 201 is connected to the AC power grid, and the two sets of secondary sides of the phase-shifting transformer 201 are respectively connected to the input terminals of the first rectifier module 211 and the second rectifier module 212. The output terminal of the first rectifier module 211 is connected to the input terminals of the first DC-DC converter module 221 and the second DC-DC converter module 222, and the output terminal of the second rectifier module 212 is connected to the input terminals of the third DC-DC converter module 223 and the fourth DC-DC converter module 224. The same-pole output terminals of the first DC-DC converter module 221 and the second DC-DC converter module 222 are directly connected in parallel, wherein the positive output terminal forms a positive output through the first isolating switch K1, and the negative output terminal forms a negative output through the second isolating switch K2. Similarly, the third DC-DC converter module 223 and the fourth DC-DC converter module 224 form another set of positive and negative outputs through the third isolating switch K3 and the fourth isolating switch K4. The positive output of the first isolating switch K1 is directly connected in parallel with the positive output of the third isolating switch K3, and short-circuited to form a set of anode outputs, which are then connected to the bottom anode of the DC furnace. The negative output of the second isolating switch K2 is directly connected to the first top electrode E1 of the DC furnace. Similarly, the negative output of the fourth isolating switch K4 is connected to the second top electrode E2 of the DC furnace. The negative output of the fourth isolating switch K4 and the anode output short circuit are connected through the fifth isolating switch K5.

[0056] The basic parameters of the overall system of the DC furnace power supply device in this embodiment are as follows: rated capacity 4MVA, rated voltage 500V, rated current 8kA, and graphite electrode compressive strength 21MPa. Based on the on-site furnace charge material and graphite electrode performance data, a preset amplitude voltage U is set. s =80V, electrode pressure threshold P th =5MPa, arcing current I st =200A, duration threshold T th =2s. The smelting method provided by the present invention is shown in Figure 1. Based on the parameters of this embodiment, the specific implementation steps include the following eight steps:

[0057] S1: Close the first isolation switch K1 to the fourth isolation switch K4 at the output terminals of all DC-DC converter modules, open the fifth isolation switch K5 between the anode output and the cathode output, and control the power supply to output a voltage U of a preset amplitude. s =80V, and simultaneously control the first furnace top electrode E1 and the second furnace top electrode E2 to descend, and collect the circuit current signals I1, I2 and pressure signals P1, P2 of the electrodes;

[0058] S2: During the electrode descent, a threshold judgment is performed on the detection signal. If the pressure feedback signals P1 and P2 of both electrodes are greater than the threshold of 5MPa, it indicates that the top electrode has made sufficient contact with the furnace charge. At this time, the timing is started to judge the magnitude of the circuit current. If the total circuit current I1+I2 of the two electrodes is less than the arc initiation current threshold of 200A, and this state is maintained for more than 2s, it is considered that the electrode contact area is abnormal or the conductivity of the furnace charge is abnormal. Then, the two top electrodes are controlled to rise to the initial position and then descend again, and the threshold judgment of the detection signal is performed again. If the abnormality is still observed after 5 attempts, the process jumps to S3. In other cases, the furnace charge at the contact point is considered normal, and the process jumps to S8.

[0059] S3: In this embodiment, the DC furnace has a dual-top electrode structure, so any one top electrode can be selected and transformed into an anode. In this embodiment, the second furnace top electrode E2 is transformed into an anode. Disconnect the third isolation switch K3 and the fourth isolation switch K4 corresponding to the third DC conversion module 223 and the fourth DC conversion module 224 of the second furnace top electrode E2, and close the fifth isolation switch K5 between the short circuit of this electrode and the anode output to complete the anode-anode attribute transformation of the second furnace top electrode E2;

[0060] S4: Re-control the descent of the top electrode. First, lower the second top electrode E2 after the attribute change. When the pressure feedback signal P2 is greater than the threshold of 5MPa, it is considered that the second top electrode E2 has contacted the furnace charge. At this time, keep the second top electrode E2 stationary and control the descent of the first top electrode E1. During the descent, the detection signal is judged according to the threshold judgment in S2. At this time, only the feedback signals I1 and P1 of the first top electrode E1 are judged. If it is determined that the contact area of ​​the first top electrode E1 is abnormal or the conductivity of the furnace charge is abnormal, then jump to S5; otherwise, it is considered that the furnace charge at the contact point is normal, and the smelting power and smelting current are reduced according to the electrode conductivity. Since this case is essentially changing from dual-electrode energization to single-electrode energization, the smelting power and current are reduced to half of the rated values, that is, smelting is carried out according to the smelting power of 2MVA and the smelting current of 4kA. The device can jump to S1 after smelting for 5 minutes.

[0061] S5: If the number of abnormalities is greater than 5, then jump to S7; otherwise, jump to S6.

[0062] S6: Control the first furnace top electrode E1 and the second furnace top electrode E2 to rise to their initial positions, and add conductive material or material with a resistivity lower than 1×10⁻⁶ between the bottoms of the two top electrodes. -6 The furnace charge of Ω·m is switched back to S4;

[0063] S7: If the power supply equipment, short circuit circuit, or furnace charge is deemed to be faulty, the system will stop smelting for investigation.

[0064] S8: The power supply equipment, short circuit, and furnace charge are considered to be normal, and the system is smelting normally.

[0065] The above embodiment 1 illustrates the application of the apparatus and method provided by the present invention in a double-top electrode DC furnace. When the conductivity of the furnace charge is poor, the smelting power circuit and its conductivity can be adjusted by changing the anode and cathode properties of the top electrode and adding conductive material to the surface of the furnace charge. After the molten pool is formed and the conductivity of the furnace charge is enhanced, the process can be switched back to normal smelting mode, reducing the time for handling abnormal conditions and improving smelting efficiency.

[0066] In Embodiment 2, the DC furnace has a three-electrode structure. The multi-electrode DC power supply device provided by this invention consists of a phase-shifting transformer 201, a first rectifier module 211, a second rectifier module 212, a third rectifier module 213, a first DC-DC converter module 221, a second DC-DC converter module 222, a third DC-DC converter module 223, a fourth DC-DC converter module 224, a fifth DC-DC converter module 225, a sixth DC-DC converter module 226, a first isolating switch K1, a second isolating switch K2, a third isolating switch K3, a fourth isolating switch K4, a fifth isolating switch K5, a sixth isolating switch K6, a seventh isolating switch K7, and an eighth isolating switch K8. In this embodiment, the DC-DC converter module is also composed of an input reactance, a supporting capacitor, a DC chopper circuit, and an output reactance connected in sequence. The DC chopper module is composed of a half-bridge DC-DC circuit formed by IGBTs. The schematic diagram of the module is shown in Figure 3.

[0067] In this second embodiment, the system connection diagram is shown in Figure 4. The primary side of the phase-shifting transformer 201 is connected to the AC power grid, and the three sets of secondary sides of the phase-shifting transformer 201 are respectively connected to the input terminals of the first rectifier module 211, the second rectifier module 212, and the third rectifier module 213. The output terminal of the first rectifier module 211 is connected to the input terminals of the first DC-DC converter module 221 and the second DC-DC converter module 222. The output terminal of the second rectifier module 212 is connected to the input terminals of the third DC-DC converter module 223 and the fourth DC-DC converter module 224. The output terminal of the third rectifier module 213 is connected to the input terminals of the fifth DC-DC converter module 225 and the sixth DC-DC converter module 226. The same-pole output terminals of the first DC-DC converter module 221 and the second DC-DC converter module 222 are directly connected in parallel, wherein the positive output terminal forms a set of positive outputs through the first isolating switch K1, and the negative output terminal forms a set of negative outputs through the second isolating switch K2. Similarly, the third DC-DC converter module 223 and the fourth DC-DC converter module 224 form a second set of positive and negative outputs through the third disconnect switch K3 and the fourth disconnect switch K4, and the fifth DC-DC converter module 225 and the sixth DC-DC converter module 226 form a third set of positive and negative outputs through the fifth disconnect switch K5 and the sixth disconnect switch K6. The positive outputs of the first disconnect switch K1, the third disconnect switch K3, and the fifth disconnect switch K5 are directly connected in parallel, short-circuited to form a set of anode outputs, and then connected to the bottom anode of the DC furnace. The negative output of the second disconnect switch K2 is directly connected to the first top electrode E1 of the DC furnace. Similarly, the negative output of the fourth disconnect switch K4 is connected to the second top electrode E2 of the DC furnace, and the negative output of the sixth disconnect switch K6 is connected to the third top electrode E3 of the DC furnace. The negative output of the fourth disconnect switch K4 is connected to the anode output short network through the seventh disconnect switch K7, and the negative output of the sixth disconnect switch K6 is connected to the anode output short network through the eighth disconnect switch K8.

[0068] The basic parameters of the DC furnace power supply system in this embodiment are as follows: rated capacity 6MVA, rated voltage 500V, rated current 12kA, and graphite electrode compressive strength 21MPa. Based on data such as the furnace charge material and graphite electrode performance, a preset amplitude voltage U is set. s =80V, electrode pressure threshold P th =5MPa, arcing current I st =300A, duration threshold T th =2s. The smelting method provided by the present invention is shown in Figure 1. Based on the parameters of this embodiment two, the specific implementation steps include the following eight steps:

[0069] S1: Close the first isolation switch K1 to the sixth isolation switch K6 at the output terminals of all DC-DC converter modules, open the seventh isolation switch K7 and the eighth isolation switch K8 between the anode output and the cathode output, and control the power supply to output a voltage U of a preset amplitude. s =80V, and simultaneously control the first furnace top electrode E1, the second furnace top electrode E2 and the third furnace top electrode E3 to descend, and collect the circuit current signals I1, I2, I3 and pressure signals P1, P2, P3 of the electrodes;

[0070] S2: During the electrode descent, threshold judgment is performed on the detection signals. If the pressure feedback signals P1, P2, and P3 of the three electrodes are all greater than the threshold of 5MPa, it indicates that the top electrode has made sufficient contact with the furnace charge. At this time, the timing is started to judge the magnitude of the circuit current. If the total circuit current I1+I2+I3 of the three electrodes is less than the arc initiation current threshold of 300A, and this state is maintained for more than 2 seconds, it is considered that the electrode contact area is abnormal or the conductivity of the furnace charge is abnormal. Then, all top electrodes are controlled to rise to the initial position and then descend again, and the threshold judgment of the detection signals is performed again. If the abnormality is still observed after 5 attempts, the process jumps to S3. In other cases, the furnace charge at the contact point is considered normal, and the process jumps to S8.

[0071] S3: In this embodiment, the DC furnace has a three-top electrode structure. One or two top electrodes can be selected as anodes. In this embodiment, both the second top electrode E2 and the third top electrode E3 are selected as anodes. The output third isolation switches K3 to K6 of the third DC converter module 223 to the sixth DC converter module 226 corresponding to the second and third top electrodes E2 and E3 are disconnected. The seventh isolation switch K7 and the eighth isolation switch K8 between the second and third top electrodes E2 and E3 and the anode output short network are closed, completing the anode / anode attribute conversion of the second and third top electrodes E2 and E3.

[0072] S4: Re-control the descent of the top electrode. First, lower the second and third top electrodes E2 and E3 after attribute changes. When the pressure feedback signals P2 and P3 are both greater than the threshold of 5MPa, it is considered that the second and third top electrodes E2 and E3 have contacted the furnace charge. At this time, keep the second and third top electrodes E2 and E3 stationary, and control the first top electrode E1 to descend. During the descent, the detection signals are judged according to the threshold judgment in S2. At this time, only the feedback signals I1 and P1 of the first top electrode E1 are judged. If the electrode contact area or the conductivity of the furnace charge is found to be abnormal, jump to S5; otherwise, it is considered that the furnace charge at the contact point is normal, and smelting is carried out according to the adjustment of smelting power and smelting current. Since this case is essentially changing from three-electrode energization to single-electrode energization, the smelting power and current are reduced to one-third of the rated values, that is, smelting is carried out according to a smelting power of 2MVA and a smelting current of 4kA. The device can jump to S1 after smelting for 5 minutes.

[0073] S5: If the number of abnormalities is greater than 5, then jump to S7; otherwise, jump to S6.

[0074] S6: Control the first furnace top electrode E1, the second furnace top electrode E2, and the third furnace top electrode E3 to rise to their initial positions, and add conductive material or a material with a resistivity lower than 1×10⁻⁶ between the bottoms of the three top electrodes. -6 The furnace charge of Ω·m is switched back to S4;

[0075] S7: If the power supply equipment, short circuit circuit, or furnace charge is deemed to be faulty, the system will stop smelting for investigation.

[0076] S8: The power supply equipment, short circuit, and furnace charge are considered to be normal, and the system is smelting normally.

[0077] The above embodiment two illustrates the application of the apparatus and method provided by the present invention in a three-top electrode DC furnace. Similar to the embodiment, the conductivity of the furnace charge can be optimized and the time for handling abnormal conditions can be reduced by changing the anode and cathode properties of the top electrode and adding conductive material to the surface of the furnace charge.

[0078] In summary, by employing the method of this invention to provide a multi-electrode DC electric arc furnace, a power supply device for an electric arc furnace, and a smelting method, the smelting process of the multi-electrode DC furnace can be optimized. In complex situations such as poor conductivity of the furnace charge, smelting can be carried out through the top electrode circuit. Once the molten pool appears in the furnace and the conductivity of the furnace charge is good, the normal production process can be restored, thereby reducing the time for handling abnormal faults and improving the efficiency of industrial smelting, especially ferroalloy and special steel smelting. It is applicable to smelting applications of multi-electrode DC furnaces.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A power supply device for a multi-electrode DC electric arc furnace and a submerged arc furnace, characterized in that: include: A phase-shifting transformer has a primary side connected to the AC power grid and a secondary side with multiple output windings and multiple phase-shifting output terminals. A rectifier module, the input of which is connected to multiple phase-shifting outputs of the phase-shifting transformer; The DC-DC converter module has its input terminal connected to the output terminal of the rectifier module, and its multiple output terminals are connected according to a specific rule to form multiple sets of positive and negative outputs after the connection is completed. A disconnecting switch is used to connect the multiple sets of positive and negative outputs to different electrodes; The multiple phase-shifting output terminals on the secondary side of the phase-shifting transformer are respectively connected to the input terminals of different rectifier modules; The rectifier module is composed of one or more rectifier units connected in parallel, and each rectifier unit is composed of power devices forming a fully controlled, semi-controlled, or uncontrolled rectifier circuit.

2. The power supply device for a multi-electrode DC electric arc furnace and a submerged arc furnace according to claim 1, characterized in that: The DC-DC converter module is composed of an input reactance, a supporting capacitor, a DC chopper circuit, and an output reactance connected in sequence. The DC chopper module is composed of a full-bridge or half-bridge DC-DC circuit made of power devices.

3. The power supply device for a multi-electrode DC electric arc furnace and a submerged arc furnace according to claim 1, characterized in that: The multiple output terminals of the DC-DC converter module are connected according to a specific rule, which is as follows: Multiple DC-DC converter modules connected to the same rectifier module output terminal are directly connected in parallel, forming a set of positive and negative outputs through an isolating switch; The DC power supply device will generate multiple sets of positive and negative outputs. Among them, multiple sets of positive outputs are directly connected in parallel to form a set of anode outputs, which are then connected to the bottom anode of the furnace body through a short anode network. Multiple sets of negative electrode outputs are connected in parallel to form multiple sets of cathode outputs, the same number as the number of top cathodes in the furnace body, and then connected to different top cathodes through cathode short networks; The anode output is connected to one or more cathode outputs via a disconnect switch.

4. The power supply device for a multi-electrode DC electric arc furnace and a submerged arc furnace according to claim 1, characterized in that: The disconnecting switch is composed of one or more disconnecting switches connected in parallel.

5. A smelting method for a multi-electrode DC electric arc furnace and a submerged arc furnace, characterized in that: Includes the following steps: S1: Close the isolating switches at the output terminals of all DC-DC converter modules, open the isolating switch between the anode output and the cathode output, control the power supply to output a voltage of preset amplitude, control the top cathode to descend, and collect the loop current signal and pressure signal. S2: During the electrode descent process, the detection signal is judged by a threshold. If the pressure is greater than the threshold, the current is less than the arc ignition current and the duration is greater than the threshold, it is considered that the electrode contact area is abnormal or the conductivity of the furnace charge is abnormal, and the process jumps to S3. S3: Based on the furnace body and furnace charge conditions, one or more furnace top cathodes are transformed into top anodes. All output isolation switches of the DC-DC converter module corresponding to the electrode to be adjusted are disconnected, and the isolation switch between the short network circuit of the electrode and the original anode output is closed to complete the anode-cathode attribute transformation of the top electrode. S4: Re-control the descent of the top electrode, and perform threshold judgment on the detection signal according to S2. If the electrode contact area or the conductivity of the furnace charge is found to be abnormal, jump to S5; otherwise, the furnace charge at the contact point is considered to be normal. Adjust the smelting current and power, and after smelting for 5 to 15 minutes, jump to S1. S5: If the number of abnormal cases is too high, jump to S7; otherwise, jump to S6. S6: Control the top electrode to rise, add conductive material to the surface of the furnace charge, and then jump back to S4; S7: If the power supply equipment, short circuit circuit, or furnace charge is deemed to be faulty, the system will stop smelting for investigation. S8: The power supply equipment, short circuit, and furnace charge are considered to be normal, and the system is smelting normally.

6. The smelting method of the multi-electrode DC electric arc furnace and the submerged arc furnace according to claim 5, characterized in that: In S2, the pressure threshold is a percentage of the compressive strength of the electrodes used in the electric arc furnace, the arc ignition current is a percentage of the rated current of the power supply device for the electric arc furnace, and the time threshold is a value determined by smelting experience.

7. The smelting method of the multi-electrode DC electric arc furnace and the submerged arc furnace according to claim 5, characterized in that: In step S3, if the furnace body has two top electrodes, then one top electrode can be selected for property transformation; if the furnace body has multiple top electrodes, then the condition of the furnace charge is observed, and the bottom charge with a resistivity lower than 1×10⁻⁶ is selected. -6 The properties of the top electrode with an Ω·m value are transformed; after the property transformation, at least one anode and one cathode are retained in the top electrode.

8. The smelting method of the multi-electrode DC electric arc furnace and the submerged arc furnace according to claim 5, characterized in that: In S4, during the process of re-controlling the descent of the top electrode, the top anode is first lowered to contact the furnace charge. After keeping the anode stationary, the top cathode is lowered, and a threshold judgment is performed according to S2. At this time, the current threshold judgment is only performed on the top electrode with anode or cathode attributes.

9. The smelting method of the multi-electrode DC electric arc furnace and the submerged arc furnace according to claim 5, characterized in that: In step S4, the pressure signal of the top anode electrode is used to determine whether the electrode is in contact with the furnace charge. If the furnace charge at the contact point is considered to be normal, the smelting current and power are adjusted according to the conductivity of a single top electrode, and smelting is carried out for 5 to 15 minutes to form a molten pool in the furnace, which facilitates the subsequent restoration of normal smelting.

10. The smelting method of the multi-electrode DC electric arc furnace and the submerged arc furnace according to claim 5, characterized in that: In step S6, a conductive material is added between the bottoms of different top electrodes to facilitate the formation of a conductive circuit after the electrodes descend.

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