JPH09145254A - Electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss of electrical power and eliminate a phenomenon of unbalanced state of 3-phase by a method wherein a transformer for an electrical furnace having extending electrodes connected to a rear end of each of graphite electrodes and the extending electrodes applied as a secondary winding and an electric collecting short-circuited device for making a short-circuit of extending 3-phase electrodes to each other is arranged at an upper part of the transformer. SOLUTION: A transformer 24 for an electric furnace constructed such that a water-cooled electrical conductive pipe 26 cooperatively connected to an upper part of each of graphite electrodes is applied as a secondary winding is arranged on a fourth floor 28. An electricity collecting short-circuit device 27 for making a relative short-circuit state of extending electrodes of 3-phase is arranged at an upper part of the transformer 24 for the electric furnace. Then, the electricity collecting short-circuit device 27 can be raised or lowered by a rack part 29 cooperatively connected to an upper part of the extending electrode water- cooled electrical conductive pipe part 26 and an electrode ascending or descending driving device 31 installed at a fifth floor 30 in response to a melting state in the furnace and an operating state of the furnace. With such an arrangement as above, a loss of electrical power can be reduced, an unbalanced state of 3-phase can be eliminated and a responding characteristic of the electrode ascending or descending speed can be made fast.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric furnace for melting metal materials such as iron and stainless steel by arc heat,
The present invention mainly relates to a three-phase AC electric furnace having equipment for applying a three-phase AC power source.

[0002]

2. Description of the Related Art In recent years, a large number of electric furnaces have been installed because of effective utilization of resources and consideration of global environment for waste recycling, and demand for reduction of steelmaking cost for iron. Since electric energy is used for melting a material in an electric furnace, the electric power consumption required for melting is an important index for evaluating the performance of the electric furnace. Therefore, efforts have been made to minimize the heat dissipation loss from the furnace body and reduce the power loss in the energized section.

The conventional 3 which melts materials by arc heat
FIG. 1 shows a general equipment configuration of a phase alternating current electric furnace, and the function of each part will be outlined by taking an example of one that melts iron as an example. The power received at the extra high voltage is supplied to the primary winding of the transformer 2 for the furnace installed in the electric room via the breaker and the primary extra high voltage line 1. As the furnace transformer 2, a type in which the voltage can be adjusted under load is generally used. The secondary side of the transformer, which has been stepped down to the required voltage, has a secondary side bus bar 3 made of several copper plates, a flexible electric wire 4 made of a water cooling cable, a supporting arm bus bar 5 made of a water cooling copper tube, and an electrode clamp part 6. It is connected to the graphite electrode 7 via. The graphite electrode 7 can be replenished because it is consumed during the operation of the furnace. Since it is necessary to move the flexible wire 4 to the electrode 7 up and down according to the operating condition of the furnace, the electrode lifting device 8 can lift or lower each phase independently or collectively.

The electrode economizer 9 includes an electrode 7 and a furnace lid 10.
It is a water-cooled ring for preventing local heating of the electrode from the ejection of high-temperature gas from the gap between and. The dust collecting elbow 11 is a hood that guides the dust-containing gas from the furnace to the dust collector. Furnace stand 12,
The furnace leg 13 and the tilting device 14 are a mechanism for tilting the furnace body during tapping and tapping. The furnace body is formed by placing a refractory material or a water cooling plate on each of the furnace wall portion 16 and the hearth portion 17 on the inner surface of the iron furnace shell 15. The raw material inserted in the furnace is
It is melted by arc heat and a pool of molten steel 18 is formed in the lower part of the furnace as shown. The furnace lid 10 can be raised and lowered and swung by a furnace lid raising and turning device 19. In the upper part of the figure,
The plan view of the electrodes is shown in the auxiliary drawing. The R, S, and T three-phase electrodes are arranged in an equilateral triangle on the electrode center circle.

Performance problems in the above-described conventional electric furnace (hereinafter, the electric furnace having the conventional structure is referred to as "conventional furnace" and the electric furnace of the method according to the present invention is referred to as "main furnace") are listed below. . 1) Large power loss In an electric furnace, the power loss mainly due to resistance loss is about 4 [%] of the total electricity, but the secondary current is tens of thousands [A].
This is because the resistance loss due to the electrical resistance and the contact resistance of the conductive material from the transformer to the electrode tip is large due to such a large value. Various measures have been taken to reduce power loss, such as shortening the current-carrying path, increasing the cross-sectional area, selecting highly conductive materials, changing the structure of the furnace body, etc., but these measures are also limited. Is in a state. The energization path is a transformer, secondary side busbar (also called busbar), flexible electric wire, supporting arm busbar and electrode. These are connected at four places due to their structure and function, so contact at each connection part Resistance is hard to avoid. The power loss at the connecting part occupies a large proportion. In addition, overheating due to loosening may cause catastrophic disasters such as damage to components.

2) In a conventional furnace having a large three-phase imbalance, generally, the paths for feeding power from the furnace transformer installed in the electric chamber to the electrodes via the conductive materials must be geometrically uneven. I don't get it. Electrically, the nonuniformity of the reactance components is remarkable. As a result, the unbalance rate of the amount of power input to each phase is as high as 8 to 20%. This non-equilibrium causes non-uniform melting rate of the raw material in the circumferential direction in the furnace and non-uniform melt-down of the sidewall refractory. In addition, the non-uniformity of the power in each phase deteriorates the power input efficiency and limits the power supply capacity of the power system. From the above, various measures have been taken for the conductor arrangement method in order to reduce this imbalance, but these measures have reached the limit.

3) In an electric furnace having a slow electrode up-and-down response speed, the arc length is apt to change during the melting process because the raw material mainly made of scrap is indefinite. Therefore, it is necessary to independently move each of the three-phase electrodes up and down to control the arc length to a predetermined value. In the conventional furnace, a large “Π-shaped (uppercase Greek letter“ pie ”)” structure consisting of the electrode columns, the electrode supporting arms 20, and the graphite electrodes 7 is lifted and lowered collectively. Therefore, if the graphite electrode is rapidly moved up and down, the electrodes vibrate, and the shear stress in the lateral direction of the graphite electrode is weak, which causes breakage, so that the response speed cannot be increased. If you try to increase the responsiveness by force, hunting of the entire system will occur. Generally, only a slow control of 4 to 6 [m / min] is possible. As a result, if there is a rapid change in arc length,
The movement of the electrodes cannot follow this, and the current changes drastically, causing excessive flicker in the related power supply system and degrading the quality of the power supply. Occasionally, a short circuit occurs, making it impossible to continue operation of the electric furnace, which impedes productivity.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the problems in the conventional furnace as described above, reduces power loss,
An object of the present invention is to provide a three-phase AC electric furnace which eliminates the three-phase unbalance phenomenon, accelerates the response of the electrode ascending / descending speed, and has a low construction equipment cost. The problems to be solved by the present invention are the following items.

1) The length of the high-current conductive path on the secondary side of the transformer for the furnace and the number of connecting parts are minimized, and as a result, the resistance loss in the conductive path is reduced, and the ratio of the power used for melting the material to the input power. Higher than conventional furnaces. 2) By making the conduction path on the secondary side of the transformer for the furnace completely symmetrical with respect to the center of the furnace, the impedance of each phase of the three phases is equalized, and the imbalance of input power as in the conventional furnace is avoided. 3) To increase the ascending / descending speed of the electrode so that it can follow the variation of the arc length due to collapse during melting of the material, and as a result, suppress the occurrence of flicker in the power supply system. 4) In solving the above problems of the conventional furnace, the cost for remodeling or newly installing the conventional electric furnace should be low.

[0010]

According to the results of designing, manufacturing, operating and equipment maintenance of conventional electric furnaces by the present inventors, the root of the above-mentioned problems arises when the electric furnace body is placed in parallel with the furnace. It was found to be in the configuration of the electric furnace facility where the transformer for use and related electric equipment are arranged.

The means for solving the above-mentioned problems is to arrange an extension electrode connected to the rear end of a graphite electrode, arrange a furnace transformer configured as a secondary winding, and extend the extension electrode above the transformer. Is to arrange a current collecting and shorting device for short-circuiting each other.

The extension electrode, which also functions as the secondary winding of the furnace transformer, is connected to the rear end of the graphite electrode, and the nonmagnetic structural steel is used as a core tube for ensuring the mechanical strength, and concentric with the core tube. The cooling fluid (air or water) reciprocating pipe line consisting of a plurality of pipes is provided, and the conductive pipe is provided on the outer periphery thereof. The graphite electrode and the extension electrode connected to it are straight type as a whole, but since it is necessary to move them up and down, a rack is connected to the rear end of the extension electrode, and a "rack and pinion mechanism" described later is used. It is necessary to be able to move up and down, and whatever kind of mechanism is used, it is indispensable for constructing the electric furnace of the present invention.

Further, the current collector short-circuit device is installed above the furnace transformer and short-circuits each phase to form a closed loop of the arc current. In order to secure the reliability of the short circuit at the short circuit part and to avoid the occurrence of ohmic loss here, it is not a good idea to use an incomplete contact mechanism consisting of, for example, a brush and an electric brush. We have devised a current collector short-circuit device. The current collecting and shorting device needs to move up and down as the electrodes move up and down, so a lifting device is required. In order to keep the arc length constant, it is necessary to secure the flexibility of the positional relationship for each phase. Such an elevating mechanism is indispensable when the electrode elevating mechanism of the present invention is a batch furnace.

If an extension electrode is arranged so as to be connected to the rear end of the graphite electrode for each phase and the extension electrode itself functions as the secondary winding of the furnace transformer, the transformer for the furnace 2
The secondary winding is no longer required, and the transformer for the furnace can be installed adjacent to the upper part of the furnace body, eliminating the need for busbars, flexible wires, and supporting arm busbars as in conventional furnaces. The number of connecting points can be reduced by shortening the number of conductive path members of different types. as a result,
Power loss can be reduced to the limit.

In the conventional method of arranging the electric furnace main body and the furnace transformer together, it was impossible to geometrically equalize the conductive paths. By arranging it on the graphite electrode, it becomes possible to make the geometrical arrangement of each of the three phases symmetrical in the circumferential direction of the electric furnace. As a result, electrical balancing is achieved and the imbalance of the three-phase input power can be eliminated.

Further, by avoiding the "Π-shaped" arrangement as in the conventional electrode elevating device and adopting the "straight type", it is possible to eliminate the lateral shake when the electrode is elevating. Further, the responsiveness of the electrode ascending / descending speed is enhanced by the reduction of the total amount of the conductive path members and the straight type effect. As a result, the ascending / descending of the electrode can follow a rapid change in the arc length, the arc length can be kept more constant than in the conventional case, the change in the arc current value can be reduced, and flicker can be reduced.

As a countermeasure against flicker of a conventional furnace, there is also a method of remodeling into a DC electric furnace, and it is also known that the flicker at that time is remarkably reduced compared to the conventional one. Since the furnace itself and the power supply system are very different from the electric furnace, a large amount of capital investment is required. However, when the electric furnace according to the present invention is modified as described above, the electric furnace main body hardly needs to be modified and the conventional technical heritage can be inherited.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The outline of the main constituent parts of the furnace and the function of each part will be described with reference to FIG. In FIG. 2, the variable voltage transformer 21 is a transformer for changing the voltage supplied to the primary winding of the transformer for a furnace, and the primary side special high voltage line 22 is connected to a special high voltage power supply system via a switch. The secondary-side special high-voltage line 23 is connected to the primary-side winding of the furnace transformer 24. The transformer 24 for the furnace is a winding core type transformer in which the water-cooled conductive tube portion 26 of the extension electrode connected to the upper part of the graphite electrode 27 is configured as a secondary winding, and is a three-phase transformer having a secondary winding number of "1". Is. A current collector short-circuit device 27 is installed above the furnace transformer 24. The other parts of the graphite electrode and the furnace body are almost the same as those of the conventional electric furnace.

The furnace transformer 24 is fixedly installed on the fourth floor 28, and the current collector short-circuit device 27 can be moved up and down according to the melting condition in the furnace and the operating condition of the furnace. Rack portion 29 connected above the extension electrode water-cooled conductive tube portion 26
And an electrode lifting drive device 31 installed on the fifth floor 30
By the "rack and pinion mechanism" composed of the pinion part of the electrode 27, the electrode 27 is moved up and down in the combined mode of the large amplitude low speed mode and the small amplitude high speed mode.

Further, the current collecting short-circuit portion is composed of a current collecting short-circuiting device composed of a short-circuit block for short-circuiting the electrode-side current collecting ring, the semi-fixed current collecting ring and three semi-fixed current collecting rings, as will be described later. And a flexible conducting wire portion (hereinafter referred to as a semi-fixed side current collecting ring and a short-circuit block side) that connects with the current collecting short-circuiting device lifting / lowering device 32 installed on the fourth floor 28. The "bolt and nut mechanism" on the installation base of the shaft and the current collector short-circuit device makes it possible to move up and down at low speed.

The low-speed mode is an operation mode in which the electrode is slowly lowered from the initial stage of melting to the final stage of melting, and after the completion of melting, the electrode is raised for tilting the furnace or inserting material, which is different from the conventional electric furnace. It is also a slow operating mode. The high-speed mode is a mode in which the electrode is moved up and down following a rapid change in arc length during melting.

Although the transformer for the furnace is fixed in the embodiment,
Both can be lifted and lowered by a bolt and nut mechanism. In the figure, illustrations of sensors such as voltage and current detectors and utility supply paths such as water cooling and drainage pipes of the furnace body are omitted. Further, although there is a mechanism for replenishing the graphite electrode according to the wear of the graphite electrode and a heat retaining mechanism for the graphite electrode, these are shown by a broken line frame 34 between the third floor 33 and the fourth floor 28 in the drawing. Was omitted. In addition, the auxiliary positions in the upper part of FIG. 2 show the positions of the R, S, and T3 phase electrodes and the arrangement of the three guide shafts between them.

The general structure of the furnace is such that the conventional furnace is arranged in a plane, whereas the present furnace is characterized by a vertical arrangement. Next, a transformer, a current collecting short-circuit device and an extension electrode, which are the points of the present invention, and a lifting drive device for them will be described based on examples of the present inventors.

The target furnace is a furnace shell inner diameter of 6,100 [mm], a conventional power source capacity of 25,000 [kVA], and a nominal capacity of 6
Since 0 [ton] and auxiliary materials are additionally inserted, it was dealt with by modifying the existing furnace whose actual production amount is 80 [ton] per charge. The diameter of the graphite electrode is 20 [inch] (50
8 [mm]) and the distance between the electrodes is 1,350 [mm] (electrode circle diameter is 1,560 [mm]), which is the same as the previous specifications before modification.

FIGS. 3 and 4 show one of the above-mentioned furnace transformers.
A longitudinal sectional view of the phase and a lateral sectional view of the three phases are shown. Primary winding is Δ (delta) connection, secondary winding is Y
(Star) Connected. One phase is a hollow cylinder shape,
The outer diameter is about 1,300 [mm] and the height is about 2,600 [mm]. The iron core is divided into 5 stages in order to facilitate cooling and ease of material procurement and manufacturing. It is a wound iron core type using magnetic steel sheet with high magnetic flux density and low iron loss. The height is 450 [mm]. The capacity of the transformer and the secondary voltage follow the specifications of the conventional type before modification, and the capacity of each is 2
5 [MVA], maximum line voltage 460 [V], and rated line voltage 380 [V]. The maximum phase voltage corresponding to the line voltage is 266 [V] and the rating is 219 [V]. The primary side supply voltage of the transformer was 22 [kV] in the past,
In this method, the power was changed to 66 [kV]. The line current at rated voltage is 38 [kA] at the rating and 48 [kA] at the maximum.
And The number of primary windings that are wound in a chain with the iron core is 1
At 73, the maximum current density was suppressed to 2.5 [A / mm ² ] with a margin, and an insulating coated square conductor wire having a cross-sectional area of 127 [mm ² ] was used. Spacers were intermittently inserted between the split cores in the circumferential direction so that insulating oil could easily permeate.

3 and 4, the extended water-cooled conductive tube portion 26 functioning as the secondary winding of the transformer and the graphite electrode 27 are shown in broken lines for size comparison. FIG. 4 shows a partially enlarged view of the cross section. From the center direction of the transformer, the extension electrode 26 acting as a secondary winding, the gap gap 37 between the transformer and the extension electrode, the inner frame 38 for one phase of the transformer 1,
An insulating oil layer 39 for cooling the secondary winding and the iron core to ensure insulation between the frames, an inner winding layer 40 of the primary winding, an insulating layer 41 between the iron core and the primary winding, and a silicon steel plate are wound and predetermined. Core layer 42 that secures the magnetic path area of the core, the insulating layer 43 between the iron core and the primary winding outer winding layer, the primary winding outer winding layer 44, the insulating oil layer 39, the one-phase outer frame 46, the outer frame of the entire transformer The order is 47.

FIG. 5 and FIG. 6 show a vertical sectional view of the current collecting short circuit portion and a lateral sectional view of three phases. The collector short-circuit device section includes the electrode-side collector ring 48 and the semi-fixed-side collector ring 4.
9. A current collecting short-circuit device including a short-circuit block 50 and a flexible flat conductor wire 51 connecting them. The current collector short-circuit device is slowly moved up and down together with its installation base according to the operating condition. Electrode side collector ring 4
Reference numeral 8 serves as an equalizer for fixing the flexible flat conductor 51 and equalizing the potential level. Since the current collector short-circuit device moves up and down at a relatively low speed as compared with the electrodes, the flexible flat conductor plays a role in absorbing the difference in displacement caused thereby. The current from the plurality of flexible flat conductors 51 is connected to the semi-fixed side current collecting ring 49. This current collecting ring also plays the same role as the electrode side. Total 4 between the center of 3 rings and each phase ring
The individual short-circuit blocks 50 play a role of short-circuiting the three-phase currents with each other. The flexible flat conductor wire 51 bridges between both current collecting rings, and is made up of a total of 24 flexible flat conductor wires in two stages for each phase.

FIG. 6 (b) shows an auxiliary drawing for explaining the mounting of the flexible flat conductor wire. Both ends are connected to the current collecting ring by three mounting bolts 52, respectively. As the flexible flat conductor wire, a flat type twisted wire having a cross-sectional area of about 240 [mm ² ] and excellent flexibility was used. Maximum current density is about 8.3 [A / m
m ² ]. The semi-fixed side current collecting ring 49 is equipped with a cooling water pipe 53 under a flat conductor fixing base and is cooled. The reason for limiting the number of steps to two is to make maintenance easier. Since the electrode moves up and down according to the melting condition during the operation of the furnace, this movement allowance was set to ± 300 [mm] with a sufficient margin. In the auxiliary diagram for explaining the movement allowance of FIG. 6C, the electrode side at the electrode rising upper limit and the electrode lower limit is shown by broken lines, and the positional relationship and the state of bending of the flexible flat conductor wire are shown.

The overall dimensions of the transformer and the current collector short-circuit device were taken into consideration so that the outer frame had substantially the same size. The height of the current collector short-circuit device is about 150 including the flexible conductor.
It is 0 [mm]. Here, the current collector short-circuit device is used as described above, but when the arc current is small in a small-capacity electric furnace, a brush system such as that used in a synchronous motor can be applied. Here, the above method was adopted to ensure contact reliability and minimize contact resistance.

7 to 9 show the structure of the extension electrode. FIG.
Shows an overall view of one phase of the electrode, FIG. 8 shows an external view of a joint portion and the like, and FIG. 9 shows a cross-sectional view of a main portion. 7A is a diagram showing the positional relationship with the floor when the electrode is at the lowest position, and FIG. 7B is a diagram showing the positional relationship with the floor when the electrode is at the highest position. A graphite electrode is used by connecting a normal pole with a nipple, and up to four poles can be connected. The length of each pole is 1,500 [mm], and the maximum length of graphite electrode is 6,000.
It is 0 [mm] and is connected by the first joint on the extension electrode side. The extension electrode is divided into a water-cooled conductive pipe portion and a rack portion, and a space between these is connected by a second joint. The positions of the transformer for the furnace and the current collector short-circuit device are shown by the broken-line blocks. The arrangement of the electrodes viewed from above is shown in the auxiliary drawing on the right side.
An electrode side current collecting ring is attached to the portion of the current collecting short-circuit device. The second joint has an inlet and an outlet for cooling water, from which cooling water is supplied to the water-cooled conductive pipe portion. A block is attached to the upper end of the electrode to prevent the electrode from descending. The movement allowance in FIG. 7 is a margin for the electrode to move up and down according to the operating condition, and is set to 5,400 [mm] in the embodiment. The total length of the electrodes with the graphite electrodes connected is about 26 [m] at the longest.

FIG. 8 shows an external view of the joint portion and the upper end block including the front and rear thereof. The first joint of FIG. 8 (a) connects the graphite electrode and the water-cooled conductive tube portion,
It is composed of a graphite electrode joint block for connecting the graphite electrode with an electrode nipple, a water cooling conductive tube lower end block which is a turning point of a reciprocating path of cooling water, and a first coupling connecting them.

The second joint shown in FIG. 8 (b) connects the water-cooled conductive pipe section and the rack section. The water-cooled conductive tube upper end block has an inlet / outlet for cooling water, and the rack lower end attached to the lower end of the rack section. Blocks, and second connecting these
It consists of a coupling. FIG. 8C shows the rack upper end block.

FIG. 9 shows a sectional view of the main part of FIG. FIG. 9A shows a cross section taken along the line AA ′ in FIG. 8A. The cross section shows a gap from the center, an extension electrode core tube 54 as a structure for supporting a heavy object, and cooling inside the cooling water outward path. Channel 5
5. Cooling water outflow path 56 that flows downward from above the electrode
Further, a cooling water outward passage partition plate 57 arranged in the circumferential direction therein and functioning as a support beam, a cooling water passage partition pipe 58 which is a partition of the cooling water reciprocating passage, a cooling water return passage 60 having a partition plate 59 similar to the outward passage, and conductive. It is a multi-layer tube composed of an inner tube 61 and a main conductive tube 62 for passing a large current which is an arc current and a secondary current for a transformer for a furnace. The main conductive tube and the inner tube of the conductive tube were made of lightweight and highly conductive material. Here, Al-Mg-
An aluminum alloy pipe used for a Si-based power bus was used. Non-magnetic structural stainless steel was used as the material for the other parts. FIG. 9B is a sectional view taken along the line BB ′ in FIG. 8B, and has a structure similar to that of the sectional view taken along the line AA ′. The pipe 64 is connected, and similarly, the cooling water outlet pipe 65 and the cooling water outlet flexible pipe 66 are connected to the tip thereof. FIG. 9C is a cross section C- of FIG.
C'denotes a rack part of a rack and pinion mechanism for raising and lowering an electrode, which will be described later, and has a double-toothed rack. The material used was ordinary structural steel.

FIG. 10 is a view for explaining the electrode lift control mechanism installed on the fifth floor 30. FIG. 10 (a) shows a rack consisting of a double-toothed rack 67 and two pinions 68.
The pinion mechanism is shown in FIG. 10B, including its drive system. Insulation base 6 from the 5th floor 30
It is electrically insulated via 9. Electrode upper end block 70 and stopper 7 on top of rack and pinion outer frame 71
With 2, it is structured to prevent the electrode from falling. Pinion 6
Reference numeral 7 is driven by an AC servomotor 75 via a coupling 73 and a speed reducer 74. An electromagnetic brake 76 is connected to the motor for maintaining the state when stopped or for emergency stop. The motor capacity is about 6 which is the total weight of one electrode.
In order to move [ton] at a maximum ascending / descending speed of 1,000 [mm / sec], 300 [kW] and a rated speed of 900 [rpm] were used. The pinion has a pitch circle diameter of 690 [mm] and the reduction gear has a reduction ratio of 32.49.

FIG. 11 is a view for explaining the current collecting and shorting device lifting drive mechanism installed on the fourth floor 28. The part consisting of the current collecting ring and the short-circuit block is the current collecting ring installation base 79
Is installed via an insulating base 80. Installation base 79
There are installation base nut portions 81 at three positions on the outer periphery of the electrode equidistant from the center of the electrode. The nut and the guide shaft bolt portion 82 constitute a "bolt / nut mechanism", and the installation base 79 moves up and down. A bevel gear 84 is provided at the lower end of the guide shaft 83, and the bevel gear 85 on the drive system side rotates the guide shaft. The bevel gear 85 on the drive system side is driven by an AC servomotor 88 via a coupling 86 and a speed reducer 87. The screw portion of the guide shaft bolt is a square screw, the effective operating diameter is 110 [mm], the lead of the screw is 40 [mm], and the rotation speed of the guide shaft is 150 [rpm] at the maximum. AC servo motor capacity is 15 [kW], rated speed is 900 [rpm]
], The reduction ratio of the reduction gear is 5.97. Between RS, ST
And the up-and-down drive system between TSs are synchronously operated by the motor control system.

The maximum lifting speed of the above electrode lifting device is about 1,000 [mm / sec], which is about 10 times the lifting speed of the conventional furnace. The maximum lifting speed of the current collector short-circuit device is about 100 [mm / sec], which is almost the same as the lifting speed of the conventional furnace.

As described above, the current collector short-circuit device operates in the low speed ascending / descending mode in which the current gradually moves downward during tapping and as the material is melted. On the other hand, it is necessary for the electrode to move up and down in the same low speed mode as the lifting speed of the current collector short-circuiting device, while rapidly moving up and down in response to the arc length variation. The mode that follows this arc length variation is called the high speed ascent / descent mode. During normal material melting, it essentially operates in a combined mode of slow and fast modes.

FIG. 12 shows a block diagram of an arc voltage control system which is closely related to the elevation control of the electrodes and the current collecting and short-circuit device, and these control systems. Although one phase is shown in the figure, the behavior of each phase of R, S, and T is closely related to each other as in the conventional electric furnace, and the consistency adjustment control between each layer is also performed. The control is performed by a control PLC, which calculates a control signal from various operating condition set values and sensor information, and outputs it to each drive device and the like. Only electrode position detection, current collector short-circuit device position detection, current detection and voltage detection information are shown as sensor information in the figure. Since the optimum arc length for the arc voltage is determined along with the progress of melting of the material, the output voltage of the variable voltage transformer is controlled according to the arc voltage, and the same logic as in the conventional furnace is used.

Since the arc current fluctuates according to the fluctuation of the actual arc length, the electrode is moved up and down in order to maintain it at a predetermined value calculated from the amount of electric power supplied. Since the voltage and current signals are AC signals containing harmonics, they are converted into effective values by the detection / smoothing circuit. After that, the high-speed fluctuation component that is difficult to control is removed by the ultra-high-speed fluctuation component removal circuit, and is input to the control device as a feedback signal. In the current collector short-circuit control system, a component that gradually changes as the melting of the material in the furnace progresses is extracted and input by the low-speed fluctuation extraction circuit. In a normal operation state while the melting is in progress, the position of the current collector short-circuit device is thereby feedback-controlled in the low speed mode described above. A faster current fluctuation record including a lower speed is input to the electrode lift drive control system, and feedback control is performed so as to maintain the set current value. As a result, high-speed electrode lift control including the low-speed region is realized. In the electrode up-and-down drive control circuit, the variation component obtained by subtracting the low-speed mode component is used as the high-speed variation component, and the component obtained by adding both modes is output as the control output. Since the low-speed mode doubles as a large-amplitude electrode lift during material charging and tapping, the two modes are handled separately.

The operating speed of the low speed mode described above is 10
0 [mm / sec] or less, that of high speed mode is 100 to 1,0
It is 00 [mm / sec]. In the high-speed mode, it was impossible to follow the conventional electric furnace, for example, it was not possible to deal with the rapid fluctuation of the arc length due to the collapse of a large material in the furnace. This was made possible by the fact that the response speed of elevating and lowering the electrode of was achieved. In the conventional furnace, the responsiveness could not be structurally enhanced, and hunting was sometimes performed when the control system was forced to improve the responsiveness. Above, the features of the furnace, such as the transformer for the furnace, the current collecting short-circuit device, the extension electrode and the operation thereof, have been described in detail including examples.

[0041]

As a result of modifying the existing electric furnace to realize the above electric furnace and modifying the parts according to the present invention, the following effects are obtained. First, regarding the power loss reduction effect, analysis results are shown for a conventional type furnace before remodeling and an electric furnace according to the present invention in accordance with a conventional method using static characteristics. The electrical equivalent circuit of the electric furnace which is the premise of the analysis is shown in FIG. 13 for the conventional furnace and FIG. 14 for the main furnace. FIGS. 13A and 14A show an equivalent circuit of three phases, and FIGS. 13B and 14B show one phase as an average value of three phases for each member of the arc current conducting portion. The detailed equivalent circuit is shown.

In the figure, V ₀ is the secondary side line voltage of the transformer for the furnace, and V _S is the phase voltage. Assuming that the three phases are in an equilibrium state, there is a relationship of V _S = V ₀ / sqr (3). Z _CR ,
Z _CS and Z _CT are circuit impedances of R, S, and T phases, respectively, and R _AR , R _AS , and R _AT are arc resistances of each phase. The reactance of the arc is negligible because it is minimal. I _R , I _S ,
I _T is the current of each phase. In the static characteristic analysis, the average circuit constant of each phase is used to treat the three phases as being in an equilibrium state for analysis. Therefore, the circuit impedance configuration for one phase is shown using the average value. In the conventional furnace of FIG. 13B, the circuit impedance Z _C = R _C + jX _C is the impedance of the transformer for the furnace Z _T = R _T + jX _T , the impedance of the secondary side bus bar Z _B = R _B + jX _B , the flexible wire. Impedance Z _F = R _F + jX _F , support arm bus impedance Z _S = R _S + jX _S , graphite electrode impedance Z _K
= R _K + jX _K, and the contact resistance of each part and the impedance Z _I = R _I + jX _I due to the induction of the structure.

In the case of the main furnace of FIG. 14 (b), Z _C is the impedance of the current collecting short-circuit portion Z _E = R _E + jX _E , the impedance of the furnace transformer Z _U = R _U + jX _U , and the impedance of the water-cooled extension electrode. _{Z W = R W + jX W} , the impedance of the graphite electrodes Z _K, composed of the impedance Z _I by induction and contact resistance of each part. The real part of impedance represents resistance, and the imaginary part represents reactance, which is a vector quantity. The average line current, that is, the arc current is represented by I _A.

The values obtained by calculating the resistance and reactance of each part according to the impedance calculation formula are shown in Table 1 for the conventional furnace.
Table 2 shows this furnace. Impedance calculation values are calculated separately for the flexible wire and the supporting arm bus for the middle phase (here, S phase) and both phases (here, R phase and T phase). Since | Z | is a vector quantity whose impedance is composed of a resistance component and a reactance component, | Z | represents its absolute value. The distribution of impedance for each component section is shown in%. For example, in Table 1, the ratio of transformer impedance to total impedance: Z _T /
Z _Cav is a value calculated by | Z _T | / | Z _Cav |
[%].

Further, the above-described impedance imbalance between the middle phase and the both-sided phase is expressed by an unbalance rate. In the conventional furnace of Table 1, it is 17.7 [%]. The average value of the total impedance is the average of the absolute values in the case of the conventional furnace: ｜ Z _Cav ｜
Has a value of 3.14 [mΩ], and in the case of this furnace, | Z _c |
It became 26 [mΩ]. In the conventional furnace, the suffix "av" is added because there is a difference in the impedance of each phase, which means an average value. In principle, this difference does not appear in the calculation in this furnace and can be ignored in practice. Since the calculated value is based on the assumption of contact resistance from the results of other conventional furnaces, this is not used directly for static characteristic calculation,
Correct based on the results of the short circuit test. Letting Z _CM be the impedance obtained in consideration of the short-circuit test results for each furnace, the average value for the conventional furnace is Z _CM = R _CM +
jX _CM = 0.692 + j3.44, | Z _CM | = 3.51
[MΩ], Z _CM = R _CM + jX _CM = 0.290 in this furnace
+ J 3.25, | Z _CM | = 3.26 [mΩ].
Strictly speaking, since the arc current contains harmonics, the impedance value changes depending on the operating state, but here, static characteristic analysis was performed using Z _CM .

[0046]

[Table 1]

[0047]

[Table 2]

Of the results of analyzing the static characteristics of the conventional furnace and the main furnace in FIGS. 15 and 16, the rated voltage: V _O =
An example of characteristics at 380 [V] will be shown. The voltage was analyzed for 9 taps of V _O = 300 to 460 [V] in 20 [V] steps according to the tap voltage. The horizontal axis represents the arc current: I _a [kA]. The vertical axis shows the circuit power: P _t [M
W], effective arc power: P _a [MW] and power factor: cos
φ [%], efficiency: η [%],% impedance:% Z _C
[%]. P _t and P _a are left vertical scales, cos φ, η,
% Z _C is shown on the right vertical axis scale. In the figure, "S
"HORT" represents when the arc length is "zero" and there is a short circuit.
From the static characteristic curve, under the condition of maximum power input (“MA in the figure
X "), when the optimum power input condition (" OPT "in the figure),
When% Z _C = 60 [%] (“% Z60” in the figure),% Z
When c = 40 in [%] (in the figure "% Z40"),% Z _C =
At 20 [%] (“% Z20” in the figure), read P _t and P _a , plot line voltage: V _O (phase voltage: V _S ) on the horizontal axis, and graph it to change the arc length. Analyze the characteristics when In FIG. 15 and FIG. 16, P _t , P _a , cos φ, η, and% Z _C under the maximum power input condition are each “◯”,
The optimum power input conditions are marked with "●", and the other cases are marked with "・". Under the optimum power input conditions, the horizontal axis and the vertical axis are drawn with broken lines to make each value easier to see.

V of each variable under the optimum power input condition
_The characteristics with respect to _O (V _S ) are shown in FIG. 17 for the conventional furnace.
This furnace is shown in FIG. The following can be seen by comparing the two figures. The maximum power input condition, that is, P _t under the condition where the input power is maximum is about 6 [%] larger in this furnace than in the conventional furnace. The optimum power input condition, that is, the condition under which the arc power is maximized, _Pa is about 18% larger than that of the conventional furnace. Efficiency: η is 8 in the conventional furnace under optimum power input conditions
In contrast to 3.5 [%], the present furnace has 91.8 [%], which is as efficient as 8.3 [%]. When% Z _C is small (for example, 20%), the efficiencies of the conventional furnace and the main furnace are close to each other. (Characteristic diagrams such as when% Z _C = 20 [%] are omitted)

Generally, the arc furnace is operated at a point where the arc current is slightly smaller than the optimum power input condition. Under the initial melting conditions, long arcs have a small% Z _C , and at the end of the period, short arcs operate at a point close to the optimum melting conditions. Considering this, it can be seen from the analysis results that this furnace is expected to be improved in efficiency by about 5 to 8% as compared with the conventional furnace. In addition, when compared with a power source with the same capacity, it is 18
It can be understood that a large amount of power can be input also for [%], which enables efficient use of the power supply. It can be seen that this furnace can reduce power loss to the limit.

The imbalance of the electric power of each phase has been improved both in terms of calculation and performance. Regarding the improvement in the response speed of the electrode elevation, in the high-speed operation mode, it was improved about 10 times compared to the conventional furnace, and 60 [m / min] was achieved.

As a result of the improvement of these characteristics, the following economic merit was obtained by using this furnace. The merits obtained are listed below. 1) power loss is reduced, the power-on condition improved power consumption rate in consideration of the power efficiency, it average to the% Z _C is operating in a small point than the optimum power input conditions,
Most of the resistance loss in the graphite electrode is regarded as active power as heat inside the furnace, and power is required for pumps such as water cooling in each part. In this case, the power loss is about 4.5 [%], and in the case of this furnace, it is about 1.2 [%], and the power loss is 3.3 [%].
It was reduced by a minute. As a result, the electric power consumption required for steelmaking has improved by this amount.

2) Improved productivity Since the power source is designed with the same power supply capacity as the conventional one, as described above, the amount of arc power that can be applied is large, the energization time per charge is reduced, and the responsiveness of electrode elevation is improved. As a result of the improvement, the dead time from tapping to the start of the next charging current is reduced, and the productivity is improved by about 10%.

3) Flicker is reduced In order to maintain the quality of the power supply system, the flicker regulation will be severe in the future, but a DC electric furnace is introduced to suppress it. In this furnace, the effect of suppressing the instability phenomenon similar to the current control in the DC furnace is obtained by the fast response of the electrode elevation, and it is improved to 40 points in the flicker value when the conventional furnace is 100 points. The effect was surpassed.

4) Construction cost and maintenance load,
Cost reduction The furnace transformer in this furnace is a wound iron core type, and because it is easy to manufacture, it could be manufactured at low cost. Moreover, since the conventional furnace has flexible electric wires and many contact portions, the maintenance frequency, work amount, and cost for maintenance and management of these have to be increased, but in this furnace, these are about 2 /
Reduced to 3.

Although the above is an effect from a small number of actual performances of this furnace, other expected effects by introducing this furnace in consideration of future improvement will be listed below. 1) High-voltage power can be received. If the capacity of the electric furnace becomes too large, it will have to receive power from an extra high voltage instead of receiving power from the conventional extra high voltage line, but in this case, the winding side core type transformer of the secondary side of this method is used. It is advantageous to use the transformer because it can receive power from a higher voltage due to the relationship between the turns ratio of the transformer and the input / output voltage ratio.

2) A high efficiency transformer can be realized. The winding core transformer is easy to manufacture, but the magnetic path direction matches the good magnetic direction of the grain-oriented electrical steel sheet and does not have a cutting joint as in the case of the iron core used in conventional furnace transformers. It is possible to utilize 100% of the characteristics of materials and realize a highly efficient transformer. Therefore, the power loss in the transformer can be reduced to the limit. Further, because of its structure, the manufacturing cost is low, so that the construction cost of the electric furnace can be reduced.

3) The electrodes can be rotated. In a three-phase electric furnace, even if the input power of each phase is made uniform, the arc heat must hit the material unevenly between the electrode positions. Due to the structure of the conventional furnace, it is difficult to rotate the electrodes in the circumferential direction of the furnace. Therefore, as a measure to deal with the non-uniform melting of materials and the non-uniform melting loss of the furnace wall, for example, the number of electrodes is set to six. Although some measures have been taken,
No substantial improvement effect is obtained. On the other hand, in the present method, it is possible to easily rotate the constituents located above the electrodes all at once, and the electrode position is oscillated in the circumferential direction during the melting or is repeatedly displaced by 30 [deg]. Is feasible. As a result, it becomes possible to eliminate the non-uniform melting in the furnace or positively direct the position of the electrode to the unmelted portion to control the melting rate of that portion.

4) A high-efficiency smelting furnace for special steel can be realized at low cost. Although the introduction and construction of a DC electric furnace with excellent flicker suppression characteristics are in progress, the DC furnace requires a bottom electrode, and it is necessary to carry out unmelted water operation after each melting charge. Not suitable as a smelting furnace. Further, the DC furnace requires a rectifier circuit for converting alternating current to direct current, which increases the initial equipment investment cost and maintenance cost. For this reason, this furnace can be used as a smelting furnace for special steel, and is advantageous in terms of operation and cost as compared with introducing a DC electric furnace.

5) Bottom tapping can be easily realized. This furnace has no bottom electrode like DC furnace,
Since a highly efficient electric furnace with few flicker can be realized,
The bottom tapping required for highly efficient continuous operation of the electric furnace can be adopted.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a general configuration of a conventional electric furnace.

FIG. 2 is a diagram showing a main part of a furnace body structure of a three-phase AC electric furnace configured by utilizing the present invention.

FIG. 3 is a design diagram of the implemented transformer, namely, transformer 1
It is a longitudinal cross-sectional view of phases. Peripheral devices installed along with a general transformer are omitted.

FIG. 4 is a design view of the implemented transformer and is a transverse cross-sectional view of the entire transformer. Peripheral devices installed along with a general transformer are omitted. In addition, an enlarged view of the cross section is shown.

FIG. 5 is a design view of a current collector short-circuit portion that has been carried out, showing a vertical cross-sectional view of one phase.

FIG. 6 is a design view of an implemented current collector short-circuit portion, showing a cross-sectional view of the whole. In addition, an auxiliary diagram for attaching the flexible flat conductor wire and an auxiliary diagram for explaining the movement allowance when the electrode is moved up and down are shown.

FIG. 7 is an overall view of one phase of an electrode, where (a) is a view when the electrode is at the lowest position and (b) is a view when the electrode is at the highest position.

FIG. 8 is a view of a joint part of an electrode and an upper end block. (A) is a 1st joint, (b) is a 2nd joint, (c) is an external view including the front-back block, respectively.

9 is a cross-sectional view taken along the line AA ′ of the main part of FIG.
The BB 'section is shown in (b), and the CC' section is shown in (c).

10A and 10B are views showing an electrode lift control mechanism, in which FIG. 10A is a view including a rack and pinion mechanism which is a lift mechanical mechanism, and FIG.

FIG. 11 is a view showing an elevating mechanism of the current collector short-circuit device of the current collector short-circuit portion.

FIG. 12 is a diagram showing a control block of an arc voltage / electrode lifting control device and a current collecting short-circuit device lifting control device.

FIG. 13 shows an equivalent circuit showing a configuration of an equivalent circuit for three phases and an impedance for one phase of the conventional furnace main furnace.

FIG. 14 shows an equivalent circuit of a three-phase equivalent circuit and a one-phase impedance configuration of a conventional furnace main furnace.

FIG. 15 shows a conventional furnace and a main furnace as an example of static characteristic diagrams when the line voltage setting value: V _O is 380 [V] based on the impedance values obtained from Tables 1 and 2.

FIG. 16 shows the conventional furnace and the main furnace as examples of static characteristic diagrams when the line voltage setting value: V _O is 380 [V] based on the impedance values obtained from Table 1 and Table 2.

FIG. 17 is a graph showing, as an example, the characteristic of each variable under the optimum power input condition obtained by obtaining the static characteristic diagram as shown in the examples of FIGS. 15 and 16 for each line voltage. Similar characteristics are obtained under other conditions, and analysis / study is performed.

FIG. 18 is a diagram showing, as an example, the characteristics of each variable under the optimum power-on condition obtained by obtaining static characteristic diagrams as shown in the examples of FIGS. 15 and 16 for each line voltage. Similar characteristics are obtained under other conditions, and analysis / study is performed.

[Explanation of symbols]

1 Transformer for transformer Primary side special high voltage wire 2 Transformer for furnace 3 Transformer for reactor Secondary side bus bar 4 Flexible wire 5 Support arm bus bar 6 Electrode clamp 7 Graphite electrode 8 Electrode lifting device 9 Electrode economizer 10 Furnace lid 11 For dust collection Elbow 12 Furnace base 13 Furnace pedestal 14 Furnace tilting device 15 Furnace shell 16 Furnace wall 17 Hearth 18 Molten steel 19 Furnace lid lifting swivel device 20 Electrode support arm 21 Variable voltage transformer 22 Variable voltage transformer Primary high voltage line 23 Variable voltage transformer Secondary side special high voltage line 24 Reactor transformer 26 Extended electrode water-cooled conductive tube section 27 Current collector short circuit 28 Fourth floor 29 Extended electrode rack section 30 Fifth floor 31 Electrode lift drive 32 Current collector short drive lift 33 3 floor 34 graphite electrode and heat insulating portion 35 1st floor 36 2nd floor 37 transformer-extension electrode gap 3 1-phase inner frame 39 Insulating oil 40 Primary winding inner winding 41 Iron core-inner winding insulation 42 Iron core (silicon steel plate) 43 Iron core-outer winding insulation 44 Primary winding outer winding 46 1-phase outer frame 47 Transformer Outer frame 48 Electrode side current collecting ring 49 Semi-fixed side current collecting ring 50 Short circuit block 51 Flexible flat conductor wire 52 Conductor wire mounting bolt 53 Cooling water pipe 54 Extension electrode core pipe 55 Cooling water passage inner pipe 56 Cooling water outward passage 57 Cooling water outward passage partition plate 58 Cooling water divider pipe 59 Cooling water return pipe partition plate 60 Cooling water return pipe 61 Conductive pipe inner pipe 62 Main conductive pipe 63 Cooling water inlet pipe 64 Cooling water inlet flexible pipe 65 Cooling water outlet pipe 66 Cooling water outlet flexible pipe 67 Both tooth rack 68 Pinion 69 Insulation base 70 Electrode upper end block 71 Rack and pinion outer frame 72 Stopper 73 Coupling 74 Speed reducer 75 A Servo motor 76 Electromagnetic brake 77 Drive system installation base 78 Pinion bearing 79 Collection ring, short-circuit block installation base 80 Insulation base 81 Installation base nut part 82 Guide shaft bolt part 83 Guide shaft 84 Guide shaft side bevel gear 85 Drive system side bevel gear 86 Coupling 87 Speed reducer 88 AC servo motor 89 Electric brake 90 Drive system installation stand

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 20, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

1) The length of the high-current conductive path on the secondary side of the transformer for the furnace and the number of connecting parts are minimized, and as a result, the resistance loss in the conductive path is reduced, and the ratio of the power used for melting the material to the input power. Higher than conventional furnaces. 2) Impedance of each phase of the three phases by perfect symmetry of the secondary transformer conductive path with respect to the center of the furnace
To make the input power unbalanced as in conventional furnaces. 3) To increase the ascending / descending speed of the electrode so that it can follow the variation of the arc length due to collapse during melting of the material, and as a result, suppress the occurrence of flicker in the power supply system. 4) In solving the above problems of the conventional furnace, the cost for modifying or newly installing the conventional electric furnace should be low.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

The extension electrode, which also functions as the secondary winding of the furnace transformer, is connected to the rear end of the graphite electrode, and the nonmagnetic structural steel is used as a core tube for ensuring the mechanical strength, and concentric with the core tube. The cooling fluid (air or water) reciprocating pipe line consisting of a plurality of pipes is provided, and the conductive pipe is provided on the outer periphery thereof. The graphite electrode and the extension electrode connected to it are straight type as a whole, but since it is necessary to move them up and down, a rack is connected to the rear end of the extension electrode, and a "rack and pinion mechanism" described later is used. To be able to go up and down
I am .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

If an extension electrode is arranged so as to be connected to the rear end of the graphite electrode for each phase and the extension electrode itself functions as the secondary winding of the furnace transformer, the transformer for the furnace 2
The secondary winding is no longer required, and the transformer for the furnace can be installed adjacent to the upper part of the furnace body, eliminating the need for busbars, flexible wires, and supporting arm busbars as in conventional furnaces. can be shortened, it is possible to reduce the number of connecting points by reducing the number of or the conductive path member. As a result, the power loss can be reduced to the limit.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The outline of the main constituent parts of the furnace and the function of each part will be described with reference to FIG. In FIG. 2, the variable voltage transformer 21 is a transformer for changing the voltage supplied to the primary winding of the transformer for a furnace, and the primary side special high voltage line 22 is connected to a special high voltage power supply system via a switch. The secondary-side special high-voltage line 23 is connected to the primary-side winding of the furnace transformer 24. The transformer 24 for the furnace is a wound iron core type transformer having a water-cooled conductive tube portion 26 of an extension electrode connected to the upper portion of the graphite electrode 7 as a secondary winding, and is a three-phase transformer having a number of secondary windings of “1”. Is. A current collector short-circuit device 27 is installed above the furnace transformer 24. The other parts of the graphite electrode and the furnace body are almost the same as those of the conventional electric furnace.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

The furnace transformer 24 is fixedly installed on the fourth floor 28, and the current collector short-circuit device 27 can be moved up and down according to the melting condition in the furnace and the operating condition of the furnace. Rack portion 29 connected above the extension electrode water-cooled conductive tube portion 26
And an electrode lifting drive device 31 installed on the fifth floor 30
By the "rack and pinion mechanism" composed of the pinion section, the electrode 7 is moved up and down in the combined mode of the large amplitude low speed mode and the small amplitude high speed mode.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

3 and 4, the outer diameter of the graphite electrode 7 is shown by a broken line for the purpose of size comparison and the extended water-cooled conductive tube portion 26 functioning as the secondary winding of the transformer. FIG. 4 shows a partially enlarged view of the cross section. From the center of the transformer,
An extension electrode 26 acting as a secondary winding, a gap gap 37 between the transformer and the extension electrode, an inner frame 3 for one phase of the transformer
8, an insulating oil layer 39 for cooling the primary winding and the iron core to ensure insulation between the frames, a primary winding inner winding layer 40, an insulating layer 41 between the iron core and the primary winding, and a silicon steel plate. An iron core layer 42 for winding and securing a predetermined magnetic path area, an insulating layer 43 between the iron core and the primary winding outer winding layer, a primary winding outer winding layer 44, an insulating oil layer 39,
The outer frame 46 for one phase and the outer frame 47 of the entire transformer are arranged in this order.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

FIG. 9 shows a sectional view of the main part of FIG. FIG. 9A is a sectional view taken along the line AA ′ in FIG. 8A. The sectional view shows a gap from the center, an extension electrode core tube 54 as a structure for supporting a heavy object, and an inside of the cooling water outward path. Cooling channel inner pipe 5
5. Cooling water outflow path 56 that flows downward from above the electrode
Further, a cooling water outward passage partition plate 57 arranged in the circumferential direction therein and functioning as a support beam, a cooling water passage partition pipe 58 which is a partition of the cooling water reciprocating passage, a cooling water return passage 60 having a partition plate 59 similar to the outward passage, and conductive. It is a multi-layer tube composed of an inner tube 61 and a main conductive tube 62 for passing a large current which is an arc current and a secondary current for a transformer for a furnace. The main conductive tube and the inner tube of the conductive tube were made of lightweight and highly conductive material. Here, Al-Mg-
An aluminum alloy pipe used for a Si-based power bus was used. Non-magnetic structural stainless steel was used as the material for the other parts. FIG. 9B is a sectional view taken along the line BB ′ in FIG. 8B, and has a structure similar to that of the sectional view taken along the line AA ′. The pipe 64 is connected, and similarly, the cooling water outlet pipe 65 and the cooling water outlet flexible pipe 66 are connected to the tip thereof. FIG. 9C is a cross section C- of FIG.
C'denotes a rack part of a rack and pinion mechanism for raising and lowering an electrode, which will be described later, and has a double-toothed rack. The material used was ordinary structural steel.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

The maximum lifting speed of the above electrode lifting device is about 1,000 [mm / sec], which is about 10 times the lifting speed of the conventional furnace. The maximum lifting speed of the current collector short-circuit device is about 200 [mm / sec], which is about twice the lifting speed of the conventional furnace.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

The operating speed of the low speed mode described above is 20.
0 [mm / sec] or less, high speed mode is 200 to 1,0
It is 00 [mm / sec]. In the high-speed mode, it was impossible to follow the conventional electric furnace, for example, it was not possible to deal with the rapid fluctuation of the arc length due to the collapse of a large material in the furnace. This was made possible by the fact that the response speed of elevating and lowering the electrode of was achieved. In the conventional furnace, the responsiveness could not be structurally enhanced, and hunting was sometimes performed when the control system was forced to improve the responsiveness. Above, the features of the furnace, such as the transformer for the furnace, the current collecting short-circuit device, the extension electrode and the operation thereof, have been described in detail including examples.

[Procedure amendment 10]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction contents]

Further, the above-described impedance imbalance between the middle phase and the both-sided phase is expressed by an unbalance rate. In the conventional furnace of Table 1, it is 17.7 [%]. The average value of the total impedance is the average of the absolute values in the case of the conventional furnace: ｜ Z _Cav ｜
Value 3.14 [mΩ], the case of this furnace | Z _c | 2.
It became 89 [mΩ]. In the conventional furnace, the suffix "av" is added because there is a difference in the impedance of each phase, which means an average value. In principle, this difference does not appear in the calculation in this furnace and can be ignored in practice. Since the calculated value is based on the assumption of contact resistance from the results of other conventional furnaces, this is not used directly for static characteristic calculation,
Correct based on the results of the short circuit test. Letting Z _CM be the impedance obtained in consideration of the short-circuit test results for each furnace, the average value for the conventional furnace is Z _CM = R _CM +
jX _CM = 0.692 + j3.44, | Z _CM | = 3.51
[MΩ], Z _CM = R _CM + jX _CM = 0.290 in this furnace
+ J 3.25, | Z _CM | = 3.26 [mΩ].
Strictly speaking, since the arc current contains harmonics, the impedance value changes depending on the operating state, but here, static characteristic analysis was performed using Z _CM .

[Procedure amendment 11]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

[Fig. 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsu Fukuyama 5893 Tamura, Hiratsuka, Kanagawa Pref.Induction Technology Co., Ltd. Within the development headquarters

Claims (4)

[Claims] 1. An electric furnace using a three-phase alternating current for melting a metal material such as iron by arc heat, wherein a furnace transformer having a graphite electrode rear end connected to an extension electrode as a secondary winding is provided. An electric furnace characterized in that a current collecting and shorting device for shorting the three-phase extension electrodes to each other is arranged above the transformer. 2. The extension electrode is connected to a rear end of a graphite electrode, has a nonmagnetic structural steel as a core tube, and has a reciprocating flow path of a cooling fluid composed of a plurality of concentric tubes, and has a conductive outermost periphery. 2. The electric furnace according to claim 1, further comprising a cooling conductive tube portion having a three-layer structure having a tube, and further having a rack portion for raising and lowering the electrode at the rear end thereof. 3. The electric furnace according to claim 1, further comprising a mechanism for moving up and down the current collector short-circuit device alone or in conjunction with a furnace transformer in accordance with the operating condition of the electric furnace. 4. A mechanism for raising or lowering the height of the extension electrode connected to the graphite electrode individually or collectively for controlling the arc voltage of each phase of the three-phase alternating current to a predetermined value. It has, The electric furnace of any one of Claims 1-3 characterized by the above-mentioned.