JPH02420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrometallurgy, and more particularly to a method and apparatus for smelting raw ore material in an electric arc furnace.

The invention can be applied to steel production, non-ferrous metallurgy, chemical industry and production of heat-resistant materials.

The raw ore smelting method is described in "Elektro" by FP Edneral.
metallurgiya stali ifdrrosplavov/Electrometallurgy of Steels and Iron Alloys, published by ``Metallurgiya'', Moscow 1977 edition, pp. 103-157, 378-454), in which alternating current at commercial frequency (50 Hz) is used. Ore smelting or arc smelting furnaces are known which can be filled with raw ore material, melted to allow a reduction reaction to proceed, and discharge the final molten metal. In addition, an electric furnace plant implementing the above-mentioned method (LE Nikol'skii et al.
"nagrevai ikh parametry"/Industrial plant for arc heating and its parameters "Energiya"
Published by Moscow, 1971 edition pp. 16-26, 94-109)
is known, and it consists of a transformer connected to the power supply equipment connected to the electrode inserted into the melting tank of the arc furnace, an electrode movement and positioning mechanism, an automatic raw ore material feeding device, and a power input adjustment device. It is made up of.

However, the above-mentioned method has an excessive loss of energy since there is no means for continuous adjustment of the voltage and continuous positioning of the electrode. The device has an inherently low power coefficient due to large reactance losses, with reactive power amounting to 50-60% of the total power. The greater the energy loss, the greater the electric furnace rating. Additional equipment is required to compensate for reactive power. Furthermore, the devices described above also require a large amount of copper as a conductor since the effective energy losses in the power supply equipment are also large due to skin and proximity effects.

During smelting, it is necessary to frequently adjust the position of the electrodes of the arc furnace in order to adjust the power supply, which disturbs the heat balance in the tank of the arc furnace.

The above-mentioned devices have large inherent electromagnetic losses in the metal structure, and therefore the mechanical resistance of the components made of magnetic material also decreases due to their overheating.

Another drawback is power transfer between phases, which results in uneven energy distribution within the arc furnace, resulting in reduced furnace throughput and reduced durability of the furnace's refractory lining. Due to the skin effect, the cross section of the power conductor is not used effectively, and the mass and dimensions of the power supply equipment are required to be even larger.

Furthermore, another method of smelting raw ore in a 21000KVA electric arc furnace ("Spravochnik po
Electrothermal Technology Handbook, published by Energiya, Moscow, 1979, chapter 9), in which raw ore (coke, quartzite and iron It consists of a device that continuously fills waste (waste). In the vessel of an arc furnace, thermal energy is released in the form of joule heat due to the alternating current flowing through the raw ore and heat generated by the arc of the electrodes buried within the vessel. The continuous release of thermal energy overheats the raw ore and melts it at the bottom of the tank. Melting proceeds by internal thermal reduction of iron and silicon oxide by the carbon of the coke, and the carbon is removed from the arc furnace in the form of gases in the form of carbon monoxide and carbon dioxide. The reduced silicon dissolves in the melted reduced iron, and the final molten metal collects in the tank.
It is extracted as a silicon-iron alloy and a small amount of entanglement.

A device that incorporates this method for smelting raw ore materials in an electric arc furnace ("Spravochnik po
Electrotermicheskomu oborudovaniyu''/Handbook of Electrothermal Technology (1971, Chapter 9) states that the electric heating technology has a transformer connected to the secondary winding, which is the power supply equipment connected to the arc furnace electrode inserted in the arc furnace vessel. There is. The power supply equipment is coupled to a device for controlling input power into the arc furnace using an electrode positioning mechanism whose output is coupled to control the input power into the arc furnace.

Such devices inherently have large heat losses due to the cooling water poured into the internal space of the structural elements made of magnetic material and the electromagnetic field prevailing in the furnace. These are 6 of the effective power consumed in the furnace.
It has reached ~7%. The high current intensity compared to the voltage and the possible reactance of the furnace circuit makes it impossible to obtain a monthly average power factor of more than 0.8-0.82, which implies a high specific power consumption.

Copper power supply equipment has a large cross section (21600mm ² )
This is because the cross section is not used effectively.

According to the above method, the characteristics of the transformer and the power supply situation are inappropriate, so the electrical resistance in the melting tank,
electrodes due to high voltage fluctuations at transformer taps.
It has to move as much as 1000mm, making it nearly impossible to smoothly adjust the operating voltage during smelting.

The purpose of the present invention is to improve the method and device for smelting raw ore materials in an electric furnace, increase the electrical efficiency of the electric furnace, lower electromagnetic losses, and lower the operating frequency of alternating current below industrial alternating current. A special purpose frequency converter is inserted into the electrical circuit of the equipment to continuously adjust the current frequency and voltage during smelting to increase the power factor of the arc furnace.

The purpose of this invention is to provide a device for smelting raw ore materials in an electric furnace supplied with alternating current, in which the raw ore materials are filled, melted by reduction, and the final molten metal and tangles are removed. 0.05 to 30
It can be filled with a device that converts the frequency to Hz and feeds it to an electrode inserted into the melting tank of the arc furnace.

According to the present invention, a method is provided for smelting raw ore materials in an electric furnace supplied with alternating current, which comprises filling the raw ore materials, reducing and melting them, and removing the final molten metal and entanglements. It consists of an extraction device in which, according to the invention, the supplied current is converted to a frequency between 0.05 and 30 Hz and supplied to an electrode inserted into a melting vessel in an arc furnace.

By setting the frequency of the supplied current as described above, power efficiency can be improved, a conventional power supply line can be used without using a special power supply line, and the smelting process can be performed.

In order to carry out the method described above effectively, it is appropriate to equip the equipment with the following equipment, which connects the electrodes inserted into the melting tank of the electric furnace through power supply equipment. a transformer with a secondary winding connected to the power supply equipment with a device for controlling the power input to the arc furnace and coupled to the electrodes of the arc furnace via an electrode positioning mechanism according to the invention; Frequency converter inserted between the secondary winding of the transformer and the electrode of the arc furnace as part of the power supply equipment; a frequency converter controller coupled to both the converter and the frequency converter controller.

Frequency converters and power supply equipmentIn order to minimize reactive power losses in the conductors, according to the invention, the following frequency converters are preferred, which are direct A frequency conversion circuit is used in which each rectifier group has three arms of rectifiers connected in opposite directions, and the primary lead of the rectifier arm of each rectifier group is connected to the power supply on the converter side. connected to one phase of the equipment;
The secondary leads of the rectifier arms of one group are connected to the short circuit busbars, and the short circuit busbars belonging to a pair of rectifier groups are insulated from each other and connected to the electrodes in the arc furnace, the power supply on the current side The equipment part consists of two busbars, with forward and reverse rectifiers alternating with an adjustable ON-OFF cycle.
The leads of the frequency converter control device are connected to the frequency converter rectifier to turn on and off the frequency converter.

The device according to the invention has a frequency converter made up of a direct frequency conversion circuit consisting of pairs of rectifier groups of the same specification, each pair of rectifier groups being electrically connected to each other and connected to corresponding electrodes in the arc furnace. The short circuit busbars of the rectifier groups are set parallel to each other, and the secondary leads of the first, second and third phase arms of a single rectifier group are connected to the same pair, respectively. 3rd, 2nd and 1st of other rectifier groups
Advantageously, it is coaxial with the phase leads.

Exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an apparatus for carrying out the above-described method for smelting raw ore material, which includes a transformer 1 for transforming the voltage and current. The secondary winding of the transformer 1 (not shown in FIG. 1) is connected to an electrode 3 inserted into a melting tank 4 of an electric furnace 5 via a power supply equipment 2, and is connected to a frequency converter. 6 is inserted into the middle part of the power supply equipment 2. The power converter 7 is a part of the power supply equipment 2 and is arranged near the electrode 3 .

The power supply equipment, which is a component of the device, is composed of pipe conductors, flexible cables, wiring materials and contacts and is intended to supply current from the transformer 1 to the frequency converter 6 and its output to the electrodes 3. ing. Frequency converter 6 converts the commercial frequency current from 0.05
This is for converting the frequency to 30Hz and supplying it to the electrode 3. The melting tank 4 is designed to receive the raw ore material 8, melt it with Joule heat and the radiant heat of the arc 9, proceed with a reduction reaction, and remove the molten metal 10 from the melting tank 4 through the outlet 11. .

Power input to the device includes a device 12 for controlling power input to the arc furnace and an electrode positioning mechanism 13.
controlled by and. Some of the input signals of the device 12 for controlling the power input are connected to the output of the frequency converter 6 of the power supply installation 2 for monitoring voltage fluctuations, while other input signals of the device 12 are connected to the output of the frequency converter 6 of the power supply installation 2 for monitoring voltage fluctuations, while the other input signals of the device 12 are connected to the output of the frequency converter 6 of the power supply installation 2 for monitoring voltage fluctuations. It is connected to a power converter 7 set on the power supply equipment 2 in series with the electrode 3 to detect the intensity. The output of the device 12 is connected to the excitation winding of the motorized part (not shown in FIG. 1) of the electrode positioning mechanism 13. The circuits of the electrode positioning mechanism input control device 12 and the power converter 7 are, for example,
The circuit follows the known circuit as described in "Industrial Arc Heating Plants and Their Constants," by LENikol'skii, Moscow, published by "Energiya", 1971, pages 100-109.

FIG. 1 also shows a device 14 for frequency converter control, the input signals of which are connected to the power supply 2 via a power converter 7. The output of the device 14 is connected to a control input of the frequency converter 6 and is used to control the frequency of the output current of the frequency converter 6 and its direction. The circuit of the control device 14 of the frequency converter 6 is described by I. Ya, Bernshtein, for example.
Author: Tiristornye preobrazovateli Chastoty bez
zvena postyannogo toka” / Thyristor frequency converter without direct current network Moscow,
It follows the known circuit as described in Energiya, 1968, page 75.

FIG. 2 is a circuit diagram of an apparatus implementing the method for smelting raw ore materials according to the invention.

The transformer 1 has a primary winding 1 whose leads are connected to a high-voltage three-phase mains power supply (not shown in Figure 2).
5 and a secondary winding 1 connected to the frequency converter 6
It consists of 6. The number of phases of transformer 1 and the number of phases of power supply equipment 2 are both 3, and power supply equipment 2
, the first, second and third phases are indicated as 2', 2'' and 2, respectively.The frequency converter 6 is connected to a rectifier group 1 in pairs (in this case 3 pairs) of identical specifications.
7', 17'' and 17, each of which has rectifiers 18 and 1 connected in parallel in opposite directions.
Contains 9 three arms. In the following, the arms of the rectifiers 18, 19 are connected to the respective rectifier groups 17', 1
7'', 17 elements, the rectifier 18 is represented by the forward rectifier 19 in the reverse direction, and the two rectifiers are connected to one phase 2', 2'' or 2 of the power supply equipment 2.
That is, it is connected to one part of the secondary winding 16 of the transformer 1. The arms of rectifiers 18 and 19 of each rectifier group 17', 17'' and 17
The lead wires of the rectifier groups 17', 17'', and 17 are respectively connected to the phases of the power supply equipment 2 on the transformer 1 side, the first phase 2', the second phase 2'', and the third phase 2. The second lead wire 20 of the arm of the rectifier 18, 19 is connected to the short circuit bus 21. The short-circuit buses 21 of the rectifier groups 17', 17'' and 17 belonging to one pair are insulated from each other and are connected to the same corresponding current 3 via a power converter 7 formed, for example, by a shunt 22. The part of the power supply equipment 2 on the electrode 3 side is made of a parallel two-wrap type, such as a sandwich type, for example.
Adjacent rectifier groups 17' and 1 belonging to different pairs
7'', 17'' and 17, 17 and 17' are connected to short circuit busbars 21. By arranging the conductors of the power supply equipment 2 in this way, the electromagnetic field in this area is canceled out, and the reactive power in the secondary and primary circuits of the frequency converter 6 is reduced, resulting in an increase in the power factor. do.

The controller 14 connects the rectifiers 18 and 1 at appropriate intervals.
9 is used to alternately switch ON and OFF. The device constructed with the circuit shown in FIG. 2 is intended to produce three-phase currents and voltages with a frequency of 0.05 to 30 Hz to avoid voltage distortions in the circuit network. The device depicted in FIG. 2 has a higher power factor than an electric furnace supplied with commercial frequency.

FIG. 3 shows yet another circuit of the frequency converter 6. In FIG. Here, as in Figure 2,
The frequency converter 6 is composed of a circuit for direct frequency conversion, and includes a group of rectifiers 17', 17'', and 17'' having the same specifications.
17, each of which incorporates three pairs of rectifiers 18 and 19 connected in opposite directions.
In each rectifier group 17', 17'', 17,
Each arm of the rectifiers 18 and 19 is connected with its primary lead to one phase 2', 2'', 2 of the power supply equipment 2 on the transformer 1 side.
The secondary leads 20 of all the arms belonging to 7′, 17″, and 17 are connected to the corresponding short circuit busbars 21. In each pair, the rectifier group 1
7', 17'' and 17 are electrically connected to each other and to the corresponding electrodes 3.

FIG. 4 shows, for example, the first pair of rectifiers 17'.
1 shows a pair of embodiments of rectifier groups such as .
The secondary leads 20 of the arms of the rectifiers 18 and 19 of each rectifier group 17' are connected to a short circuit bus 21. The short-circuit busbars 21 of the rectifier group 17' belonging to one pair are placed in parallel with each other in opposite directions, forming a two-wire arrangement. The arms of the rectifier group 17', which are connected to the 12' (Figure 3), 22'' and 32nd phases of the power supply equipment 2, are connected to the 1st, 2nd and 3rd phase arms of the power supply equipment 2, respectively. The details of the mutual relationship of the arms of the rectifier group 17' belonging to one phase will be explained with reference to FIG. 4.The first phase arm of the rectifier group 17' It is coaxial with the third phase of one rectifier group 17'.Similarly, the third phase of one rectifier group 17'
The arm of phase 2 is coaxial with the arm of the first phase 2' of the other rectifier group 17', and the arms of the second phase 2'' of the two rectifier groups 17' are coaxial with each other. The rectifiers 18 and 19 and the shorting bus 21 in groups 17'' and 17 (FIG. 3) are in a similar condition.

Figures 5a to 5j show rectifier groups 17', 17'',
17 instantaneous current intensity i (Figures 5a to 5f),
The current intensity i in the electrode 3 (Figs. 5g, 5h and 5j) and the main current intensity i (Fig. 5k) are shown during one period T of the output voltage as a function of time t. .

Melting tank 4 of arc furnace 5, which is the device shown in FIG.
is constantly filled with raw mineral materials consisting of metal and non-metal oxides (ores), reducing agents and solvents.
A commercial frequency is supplied to the power input of the frequency converter 6 through the transformer 1 and the power supply equipment 2 . The current converted to a lower frequency band between 0.05Hz and 30Hz is transferred from the output of the frequency converter 6 to the electrode 3.
is given to. This converted current flows through the raw material 8 and the deep thermally insulated arc 9. Frequency converter 6 is controlled by device 14, which will be discussed in more detail below.

The Joule heat released by the raw ore material 8 and the heat radiated by the arc 9 heat the raw ore material 8, and the temperature increases.
Create an altitude area that reaches 2000 to 4000 degrees Celsius. At these temperatures, the oxide ore volatilizes and becomes a vapor. The melting furnace gas from the reduction reaction, consisting mostly of carbon monoxide, passes through the overlying raw ore materials and heats them.

As the raw ore material 8 gradually descends, it is heated, softened, and melted. Since the main reduction reaction occurs in the liquid phase, the reduced molten metal 10 and non-metals gradually accumulate at the bottom.

When the molten metal 10 accumulates, it is removed from the outlet 1.
1 and taken out from the melting tank 4.

The electrodynamic resistance of the area of each electrode 3 in the melting vessel 4 of the arc furnace 5 changes constantly during smelting, and the current intensity of the electrode 3 therefore also changes from its installed value. This is monitored by power converter 7. The signal from the power converter 7 is sent to the rectifier 1 of the frequency converter 6.
8, 19 enters the device 14 for adjusting the firing angle. Variations in the firing angles of the rectifiers 18 and 19 change the voltage and current supplied to the electrodes 3 and thus adjust the power input to the device. This does not require changing the position of the electrode 3 and, as a result, stabilizes the thermal energy distribution in the melting tank of the arc furnace 5 (Fig. 1) and the position of the reaction zone, resulting in a stable distribution of the elements contained in the ore. Furthermore, faster and more complete reduction is achieved, resulting in higher operating efficiency in the arc furnace 5.

If the current intensity fluctuation exceeds 10%, the power input regulator 12 (FIG. 1) raises and lowers the electrode 3 in a manner similar to well-known devices to restore the current intensity to the designed value. The positioning mechanism 13 is excited to issue a signal to cause the positioning mechanism 13 to move. If it is not possible to restore the power input to the designed value by adjusting the position of the electrodes, the voltage supplied to the electrodes 3 is adjusted by switching the taps of the transformer 1.

The frequency of the voltage and current supplied to the electrode 3 is
0.05 to 30Hz even during the smelting process or processing
can be changed to the optimal frequency between. The change in current frequency redistributes the energy released in the melter 4 (power input) through the change in the effective and reactive resistance of the current circuit in the melter 4; the energy generated in the part of the arc 9 is It increases as the current frequency decreases. The reduction in the current frequency also increases the power coefficient cos of the arc furnace 5 and the electrical efficiency of the device, which ie increases the voltage at the arc 9.

The current frequency is determined by the electrical parameters (power coefficient, power usage efficiency, subharmonic components, and other parameters) available during smelting, and the rectifier 18 and 1
9 (FIG. 2) is changed discontinuously using a frequency converter 6 controlled by a device 14 for turning on and off. For example, if the frequency converter 6 in FIG. 2 is used, first the device 14 outputs a signal that turns on the forward rectifiers 18 for a certain period of time, and then turns them off. After some suitable time interval Δ (FIG. 5), the device 14 (second
The signal from FIG.) turns on the reverse rectifier 19. The current flowing through the rectifier groups 17', 17'', 17 naturally commutates.
Interval to turn off the rectifier 19 and turn on the rectifier 19 △
(Figures 5a to 5j) indicate the period T of the output voltage (5th
It is one-sixth of that in Figures a to 5j).

The operation of the frequency converter 6 (Fig. 2) is shown in Fig. 5a~
This can best be explained using the diagram depicted in Figure 5k. At time t _p (Fig. 5a), group 1
7' forward rectifier 18 (FIG. 2) and group 17''
The reverse rectifier 19 (see Figure 5b) is turned on. At time t ₁ after T/3 has elapsed, rectifiers 18 and 19 (Fig. 2) are turned off, which means that T
is held for a time Δ (FIGS. 5a to 5j) equal to 1/6 of . At time _t2 , rectifier 19 of rectifier group 17' and rectifier 18 of rectifier group 17'' (see FIGS. 5a and 5b, respectively) are turned on.

At time t ₃ after 1/3 of T, the rectifier 18,
19 (Fig. 2) is turned OFF and held for a time △. The process for these rectifier groups 17', 17'' is then repeated.The remaining rectifier groups 17'' and 17 (FIGS. 5c, 5d) and rectifier group 1
The rectifiers 18 and 19 of 7 and 17' (Figs. 5e and 5f) carry out the operation described above at 1/3 of the period T.
ON and OFF operations are performed using a mold that is shifted by 2/3. This effect balances the magnetic fields in that the currents flowing in the two conductors of the power supply 2 (FIG. 2) are equal in magnitude and in opposite directions. 5th g
Figures 5h and 5i show the current intensity i _g of the electrode 3,
i _h and i _j are the sum of the current intensities depicted in Figures 5a and 5f, Figures 5b and 5c, Figures 5d and 5e, respectively. . The main current intensity i _k depicted in Figure 5j
Since there is a no-current section, there is no low frequency fluctuation, which reduces the fractional frequency component contained in the power supply voltage and increases the power coefficient of the frequency converter 6.

Next, the frequency converter 6 shown in FIGS. 3 and 4
Let us consider the operation of . In Figure 3,
Arrow lines B ₁ A ₁ , C ₁ B ₁ , A ₁ C ₁ , and B ₂ A ₂ , C ₂ B ₂ ,
A ₂ C ₂ indicates the direction of the current flowing when, for example, the first, second, and third phase arms of the group 17' are opened and closed. As can be seen in the figure, the directions of the switching currents in the above circuit are opposite to each other, and this is because the arrangement of the two short-circuiting buses 21 of these groups 17' balances the magnetic fields, and the rectifier The firing angles of 18 and 19 are decreased to increase the power factor of frequency converter 6.

Each process carried out in the arc furnace 5 (FIG. 1) is characterized by adjusting the electrical resistance of the raw material 8 and the fluctuations in the energy required to carry out the reduction reaction. This is the arc furnace from 0.05 to
This is possible by operating with an alternating current at a frequency variable between 30 Hz or at a certain fixed frequency within this range.

For example, in the smelting of high-grade iron ore, the highest performance is achieved when 60 to 90% of the total energy supplied to the melting tank 4 in the arc furnace 5 is released in the arc 9 section, depending on the silicon content. can get. In the smelting of 75% silicon iron, by converting the frequency to 5Hz, the energy ratio released in the arc 9 can be reduced to 15~
20% increase, guaranteeing high smelting performance in the same melting tank as in the case of smelting 45% silicon iron. Substitution of other types of alloys does not require a different furnace. For example, in the smelting of 45% silicon iron, arc furnace 5
Operation with a current having a frequency of 12 to 45 Hz is required in the same melting vessel 4.

Therefore, a decrease in frequency increases the effective voltage at the electrode 3 on the one hand, but on the other hand promotes a redistribution of the power input within the melting vessel 4 and reduces the proportion of current flowing through the raw material 8, which It enables operation at high effective phase voltage without disturbing the smelting process. This increases the electrical efficiency of the arc furnace 5 and its total throughput.

When smelting 75% silicon iron using the method and apparatus according to the invention in a 16.5 MVA electric furnace at 5 Hz current, the plant efficiency is from 0.82 to 0.92, and the electrical efficiency is 0.897.
From 0.914 to 0.914, total processing capacity increases by 15% and power consumption decreases by 2%.

The above coefficients improve the performance of existing electric furnaces and point the way to large-scale high-performance furnace fabrication.

The smelting method according to the present invention makes it possible to discontinuously change the current frequency and voltage in each smelting process, and as a result, it is possible to operate the arc furnace 5 with the electrode 3 fixed (stationary). Therefore, the heat distribution in the melting tank 4, the area of the raw material 8, the arc 9 and the position of the molten metal 10 remain stable, so that through efficient utilization of power input and (calendar time) (power consumption, total processing Performance improvements (consisting of capacity and other parameters) are made. Another advantage of the above-described smelting method according to the invention is that it reduces energy losses due to electric field-induced currents in the metal structure of the arc furnace 5 and in the manufacturing plant. This minimizes the heating of these metal structures and prevents a reduction in their mechanical strength, so that a wider range of magnetic materials can be used as materials for the arc furnace 5 and the factory building.

Since the low frequency smelting method according to the present invention also reduces skin and proximity effects, the power supply equipment 2 and the transformer 1
can be made with less copper since its cross section is more effectively utilized.

With the method according to the invention at a frequency current of 5Hz
When smelting raw ore materials in a 24MVA arc furnace 5, the power factor is lower than when using a commercial frequency.
Total processing capacity of 1.5% furnace increases by 1.4%.

As described above, the present invention has the following features (1) to
(4).

(1) A transformer transforms the voltage and current of a commercial power supply, and then a frequency converter converts the frequency to a polyphase frequency within a predetermined range (0.05 to 30Hz). )
It is driven by Therefore, a frequency converter converts the commercial frequency to a lower frequency in the above range,
As a result, the size, weight, and cost of the transformer can be reduced compared to the case where the transformer is driven to transform current and voltage.

(2) If the fundamental frequency of the current supplied to the electric arc furnace is
It converts into multiphase frequency current in the range of 0.05 to 30Hz. By setting this to a low frequency range, the period during which a half-wave current of opposite polarity to the supply current applied to the electrode exists (no-current period) can be easily and accurately adjusted (within an error of 0.1%). ), the reactance of the arc furnace can be lowered, and the electromagnetic loss of the conductor can be reduced.

(3) Controls the non-current period of the supplied current applied to the electrodes, which provides the following advantages. For example, if the voltage of the first electrode increases and the voltage of the third electrode decreases, if you lengthen the no-current period, the voltage of the first electrode decreases, the voltage of the third electrode increases, and the voltage of the second electrode decreases. is kept constant. Therefore, the energy released from the electrodes remains constant and the temperature inside the furnace remains constant. Therefore, since the electrodes can be stably positioned in the furnace without the need to move them up and down, the temperature distribution in the furnace can be maintained stably without the need for extra power to drive the electrodes. Furthermore, since the no-current period is controlled without changing the phase and waveform of the primary current of the frequency converter, the power factor of the device is always kept at a high value, which is even more noticeable due to feature (2) above. become. That is, if the phase and waveform of the primary current are changed by controlling the phase of the thyristor of the frequency converter, it is possible to control the voltage applied to the electrodes, but this has the disadvantage that the effective power supplied to the furnace decreases. This drawback can be eliminated by controlling the no-current period.

(4) By controlling the fundamental frequency of the frequency-converted supply current within the above frequency range based on the measured values and fundamental frequency of the supply voltage and current applied to the electrodes, the impedance of the furnace can be kept low and stable. It is possible to minimize power consumption, stabilize the temperature distribution in the furnace, stabilize the position of the reaction zone, prevent local overheating in the arc furnace, and reduce consumption of alloy.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus implementing the method for smelting raw ore material in an electric arc furnace according to the invention. FIG. 2 is a circuit diagram of an apparatus implementing the method for smelting raw ore material in an electric arc furnace according to the invention. FIG. 3 shows one embodiment of the frequency converter of the device according to the invention. FIG. 4 shows one embodiment of a frequency conversion circuit according to the present invention. Figures 5a to 5j show the instantaneous current intensity flowing through the various arms of the rectifier over time. 1... Transformer, 2... Power supply equipment, 3... Electrode, 4... Melting tank, 5... Arc furnace, 6... Frequency converter, 7... Power converter, 8... Raw ore material ,
DESCRIPTION OF SYMBOLS 10... Molten metal, 12... Electric power input control device to an arc furnace, 13... Electrode positioning mechanism, 14...
... Frequency converter control device, 16 ... Transformer secondary winding, 17', 17'', 17 ... Rectifier group, 18
...forward rectifier, 19 ...reverse rectifier, 20
...Secondary lead wires of the arms of rectifiers 18 and 19, 21
...Short circuit bus.

Claims (1)

[Claims] 1. The output of a commercial power source is input to the transformer 1, the raw ore material 8 is filled, the raw ore material 8 is melted, the reduction reaction is allowed to proceed, and the final molten metal 10 and entanglements are taken out. A method for smelting raw ore material in a melting tank of an electric arc furnace comprising electrodes supplied with an alternating current, wherein the output current of the transformer has a fundamental frequency of 0.05 Hz to 0.05 Hz.
converted into a multi-phase frequency current in the range of 30 Hz and supplied to an electrode 3 of an arc furnace 5, said electrode being stably positioned in the melting tank of said arc furnace, the frequency converted supply applied to said electrode; measuring current and voltage fluctuations and controlling the period of no current between half-waves of opposite polarity of the current applied to the electrodes based on the measurements; A method for smelting raw ore material in an arc furnace, characterized in that the fundamental frequency of the frequency-converted supply current is controlled within the frequency range based on the fundamental frequency. 2. In claim 1, when the deviation of the frequency-converted supply current and voltage is below a predetermined value, the electrode is kept stationary in the melting tank of the electric arc furnace; a transformer 1 for moving said electrode in the melting tank of said electric arc furnace if the deviation exceeds a predetermined value and supplying said supply current and voltage if said supply current and voltage deviate significantly from nominal values;
A method for smelting raw ore materials in an arc furnace, characterized by switching the taps. 3 Transformer 1 having a primary winding and a secondary winding 16
, an electric arc furnace 5 for filling and melting the raw ore material to advance the reduction reaction, an electrode 3 inserted into the melting tank 4 of the arc furnace, and an input for controlling the power supply to the arc furnace. Frequency converter 6 with a control device 12 and a frequency converter control device 14
and a current lead connecting a secondary winding 16 of the transformer to a first output terminal of the frequency converter and a second output terminal of the frequency converter to the electrode. In an apparatus for smelting raw ore materials in ,17″,
17 pairs, the secondary output terminal 2 of each arm circuit of the commutator group is connected to a short circuit bus 21, and one set of short circuit buses in the pair of commutator groups are insulated from each other and connected to the electrodes. the current lead between the second output terminal of the commutator group and the electrode consists of two wires, the current lead from the frequency converter at the electrode in the melting vessel being connected to a corresponding one of the electrodes; Smelting raw ore material in an arc furnace comprising power converters 7 and 22 for detecting supplied current and voltage, the output of the power converter being given to the input of the control device 14. equipment for. 4. In claim 3, the input control device 12 includes a mechanism 13 for shifting the electrodes and a voltage changeover switch in the transformer 1, and the output of the input control device for smelting raw ore material in an electric arc furnace, connected to the outputs from power converters 7, 22, characterized in that said power converters detect frequency-converted currents and voltages at said electrodes; equipment.