DE1765526A1 - Three-phase electric arc furnace - Google Patents

Description

DR.-ING. G. EICHENBERG - ί «/ L ₀

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DIPL-ING. H. SAUERLAND ceciuenauee76 Ill / Sch.

DR.-ING. R. KÖNIG telephone432732

PATENT LAWYERS

The United Steel Companies limited, The Mount, Broomhill, Sheffield, Yorkshire, England

"Three-phase arc furnace"

The invention relates to a three-phase electric arc furnace, especially the electrical connections between the transformer and the electrode holders.

In conventional electric furnaces, three electrodes protrude vertically into the furnace chamber, with each electrode from one Electrode holder is held in the intended position. Usually the electrode holders are arranged so that the electrode axes are at the corners of an equilateral triangle. Each electrode holder is at the end attached to a horizontally extending electrode arm. The three electrode arms lie above the furnace and run generally parallel, although they also often diverge at a small angle towards the furnace. As a result, there are two outer electrode arms, each with an outer electrode holder and in plan view a middle electrode arm that supports the middle electrode holder. Each electrode arm is usually made of

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BANK ACCOUNT: DEUTSCHE BANK AG., DOSSELDORF 1672161 POST CHECK ACCOUNT: ESSEN 8/34

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carried by a vertical mast, through which he adjusted with the electrode for setting the arc in the vertical can be. Each of the three masts is between the furnace and the transformer, the one with the electrodes above flexible and rigid lines in the form of pipe rails is electrically connected. The flexible lines are required in view of the relative movement between the electrode arms and the transformer · They are with the rigid lines connected over the electrode lines and run to the electrode holders that are electrically connected to the electrodes.

Such electric furnaces can be divided into three categories with a power of 10 MVA, 10 to 20 MVA and over 20 MVA. In all furnaces it is important that the power loss is the same for the three phases, so that the impedance of the electrical connections between the transformer and the electrode holders should be the same for each phase in order to achieve phase compensation. In the case of electric furnaces with an output of more than 10 MVA, phase balancing is becoming increasingly difficult. It is equally important that the inductance of the secondary connections, for example that between the secondary terminals of the transformer and the electrode holders, be low, otherwise the furnace will operate with a low and inefficient power factor. However, with regard to the desired low inductance of the seconds

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Därrerbindungen in electric ovens with an output of more than 20 MVA considerable difficulties, These are caused by the increasing length and the greater spacing of the secondary conductors in larger ovens and by the current flowing through the secondary part required for a higher input power. Accordingly, the Phasing put in furnaces with a capacity over 10 MVA and furnaces with a capacity over 20 MVA the Phasenbalanoe and equilateral low inductance difficult problems. The m latter problem, of course, 1st much more difficult to solve when the current frequency, such as in North America, 60 Hz instead of the usual 50 Hz.

Attempts have been made in the past to reduce the inductance of the secondary lines and at the same time equalize the inductance of each phase to bring about a phase adjustment. For example, the secondary delta connections of the transformer were relocated from it to the vicinity of the electrode holder, ^ for which, however, a special mast and support arm are required. Also were saturable auxiliary reactors for the proposed automatic inductance change of the secondary connections in order to maintain a phase balance. A fixed reactor was arranged on the middle secondary lines of at least one arc. Except the this required expensive and complicated constructions have these attempts with regard to the desired

109883/0467

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Phase compensation while reducing the inductance led to no result.

According to the invention, it is now proposed, in the case of a * Three-phase electric arc furnace of the type mentioned at the beginning, doho in an electric furnace with three electrodes each held by its own electrode holder and three generally parallel, horizontally extending and vertically adjustable electrode arms for one electrode holder each, that at least two rigid lines connected in parallel horizontally from each of the two outer electrode holders at a distance above the arms the concerned with The flexible lines connected to the transformer run and with the rigid lines of each electrode holder in one of two planes which are substantially vertical and substantially parallel at a distance from one another while at least two rigid lines connected in parallel extend horizontally from the central electrode holder run at a distance above the arms to the relevant flexible lines connected to the transformer and essentially symmetrical between the two vertical planes in a common, essentially horizontal one Lie level. Such a furnace with six or more substantially parallel ducts, usually in shape of pipe rails, has the significant advantage that it has a particularly low inductance with suitable distances between the lines.

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sits. In addition, the spacing of the lines can be selected so that, in addition to a low inductance, the Inductance of all secondary lines to the three electrode holders is the same and therefore a phase balance results. In this respect, the aforementioned difficulties are made easier and more economical by the furnace according to the invention Way overcome.

Of course, the flexible lines also have a certain inductance. For this reason, the flexible lines of each phase are usually combined into a bundle. The effect of such a bundling on the lines of a phase is that the conductor bundle between the other two conductor bundles for the central electrode holder has a lower inductance than the outer ones Phases and consequently no phase compensation results. In the furnace according to the invention, such an effect is no longer absolutely undesirable, since with a suitable choice of the distance between the rigid lines, for example pipe rails, which lie in a substantially horizontal plane or planes, the inductance of these lines can be made lower, equal or greater than that of the rigid leads extending to the outer electrode holders. Accordingly, if the difference between the inductance of the central and the outer rigid lines is equal to and opposite to the difference between the internal

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ductance of the middle and outer flexible lines, the overall effect being that the oeeamtinduktanz of the phases is equal, provided that the inductances en of the electrodes and the furnace transformer are symmetrical are. This is particularly desirable when the flexible lines are arranged in a conventional manner can achieve. On the other hand, the distance between the rigid lines can also be adjusted so that these have the same inductance. This has a certain arrangement of the flexible lines with the same inductance result if a phase balance is to be achieved.

Although cliiening only six pipes or other rigid conduits is satisfactory Achieve results, if there are more than six lines, an equal number of lines is preferable, so that each pair enables a current path leading back and forth for cooling water. “For example, you can have two Use outer conductors, each eight in one corresponding substantially vertical plane lying conductor comprises; and eight center conductors, four of which are in one substantially horizontal plane and the other four are in a second, also essentially horizontal plane immediately above it. In this way surrendered calibrate a total of two vertical and two horizontal levels. In the context of the invention, however, the number of conductors can be increased even further.

BAD ORIGINAL 109383/0 ^ 67

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Decreasing the inductance of the secondary lines also allows the delta connection to be completed of the furnace transformer at the connection of the flexible

_N len and the rigid lines. This makes six Sr-- -

Bundle of flexible cables that connect the six transformer terminals

f ■. Connect * men with the rigid lines. The ones on the outside .... Flexible lines arranged in Traneformatorklems lie »between the rigid lines of the outer and inner phases _; ββη, while the two inner bundles of flexible lines BWisohen the inner transformer terminals and the rigid lines of the outer phase are arranged.

In the drawing, a three-phase arc furnace according to the invention with a line is shown as an exemplary embodiment. :. power of 36 MVA and an arc current of 42 KA. In the drawing you can see:

ffigο 1 the side view of a furnace according to the invention,

? lg, 2 a thematic representation of the electrical lines,

gjg.2a a schematic representation of another line arrangement,

gjg, 3 in an enlarged view the rigid pipe rails for the electrodes,

4 a plan view of the electrical lines of the Mg. 3,

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Π65526

5 shows a vertical section along line VV in FIG. 3, FIG. 6 shows a section along line VI-VI in FIGS

7 shows a graphic representation of the effect of a change in the distance between the pipe rails for the middle phase on the inductance «

The furnace system shown in FIGS. 1 to 4 includes a furnace transformer 1 with three primary or input terminals 2 and six secondary or output terminals 3, which are designated with a., A ", b .., b ₂ , c" c " . Each of the three secondary transformer windings lies between a pair of corresponding secondary terminals 3. Six sets of flexible leads 4, each consisting of a bundle of eight individual conductors, connect each secondary terminal 3 to a corresponding pair of rigid pipe rails (Figure 2). This arrangement of the flexible lines results in a low inductance, since the two bundles of each phase hang close to each other and their mutual inductance are 180 ° apart and therefore completely cancel each other out. The alternative arrangement of FIG. 2a, on the other hand, results in a higher inductance, since the mutually canceling inductances between the phases are 120 ° apart and therefore only half cancel each other out. The reference symbols a ^, a ₂ , b ^, t> ₂ , C ₁ and C ₂ denote corresponding parts in FIGS. 2 and 2a.

The electric furnace is six pipe rails 6 to 11,

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of which are siehtbar 3? ig _e 1, only the Rohrsohienen 6, 7 and 8. FIG. The pipe rails 6 and 7 are carried by an electrode arm 12, from which they are electrically insulated. The electrode arm 12 is arranged at the end of a vertically adjustable lifting mast 15. The two pipe rails 6 and 7 are connected in parallel via a connector 27. At the end of the electrode arm 12 there is an electrode holder 18 with a cylindrical electrode 21. In a similar way, the pipe rails 8 and 9 are held by a horizontal electrode arm 13 from which they are insulated. The electrode arm 13 is in turn arranged at the end of a lifting mast 16, which is also vertically adjustable. The two pipe rails are connected to an electrode holder 19 with an electrode 22; they are connected in parallel via a connector 28. Likewise, the two remaining pipe rails 10 and 11 are carried by a corresponding horizontal electrode arm 14, from which they are electrically insulated. The third electrode arm 14 is also arranged on a vertically adjustable lifting mast 17. The pipe rails 10 and 11 are held in parallel with a corresponding electrode holder 20 with a third electrode 23 and via a connector 29. As can be seen from FIG. 3, the three electrode arms 12 to 14 run essentially parallel to one another, although they converge at a small angle in the direction of the electrodes 21 to 23. The longitudinal axes of the electrodes 21 to 23 lie

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at the corners of an equilateral triangle and extend down into an oven 24. In this oven, the Batch to be melted brought by the three arcs between the electrodes 21, 22, 23 and the metal surface is melted in the usual way. During the melting, the lifting masts 15, 16 and 17 are adjusted vertically, to adjust the arc lengths and create optimal melting conditions. At the end of the melting process the furnace 24 is tilted on toothed rims 25 to pour the metal.

As already mentioned, the illustrated embodiment relates to the arrangement of six solid pipe rails, as can be seen from FIGS. 4 and 5, for example. The outer diameter of the tubular rails is in each case 12.7 cm hei an inner diameter of 9 _t 5 cm. The length of the four longest pipe rails, ie leading to the outer electrode holders 18 and 20, is 8.5 m. The three electrode arms have an outer diameter of 40.7 cm and an inner diameter of 35.6 cm 3 shows, the pipe rail pairs connected to an electrode holder are held at a distance above the associated electrode arms by means of brackets 26 made of stainless steel. The tabs 26 are electrically insulated from the pipe rails and dimensioned so that they can withstand the greatest possible electromagnetic attraction between two adjacent pipe rails. 109883/0467

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From! Ig. 5 shows the arrangement of the tubular rails 6 to 11 with respect to the three electrode arms 12, 13 »14, which are at the same height. The two pipe rails 6 and 7 lie in a common vertical plane, while the two pipe rails 10 and 11 are spaced apart of which also Tertikai extending plane are arranged, the middle pipe rails 8 and 9 are in a common Horizontal plane, symmetrically with respect to the four outer tube rails 6, 7 and 10, 11. All Pipe rails 6 to 11 run horizontally parallel to one another. The pipe rail spacings according to FIG. 5 result as follows:

a 91 , u cm b 28 , 5 cm C. 106 , 0 cm d 61 ,8th cm e 114 , 0 cm f , 0 cm

6 illustrates the arrangement of the six pipe rails in the area of their connections with the flexible lines 4, the distance g being 28.0 cm. The inductance per meter of pipe rail can be calculated using the usual physical formulas. Judging from the vorbe β MODEL SPEEDLIMITS arrangement of the pipes rails, then the average inductance per meter is all the pipe rails 0.335 ^ iH. The inductance of the middle pipe rails 8 and 9 is somewhat higher at 0.374 4 H / m. As already mentioned,

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are in furnaces with flexible cable bundles, for example according to Pig · 2a, with low inductance of the middle Phase the pipe rails are preferably arranged in such a way that the * The inductance of the middle pipe rails 8 and 9 is greater than that of the outer pipe rails 6, 7> 10 and 11 to counteract the influence of the flexible lines 4 and to bring about a phase balance

An increase in the distance between the two middle pipe rails 8 and 9 while maintaining their symmetrical position in relation to the outer pipe rails has an effect corresponding to the position in Mg. 7 * There the inductance 1 is in μ H / m against the distance d between the pipe rails 8 and 9 applied in cm. The other pipe rails and the electrode arms are arranged as shown in Figures 5 and 6. The curve marked with m illustrates the dependency for the lines of the middle phase, the curve marked with ρ the dependency for the lines of the outer phase and the curve marked with η the resulting mean value.The mutual distance between the two middle pipe rails 8 and 9 is chosen so that the inductance is unbalanced equal and opposite to that of the flexible lines 4.

The effect of increasing the distance between the tubes 6 and 7 or 10 and 11 is to reduce their

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additive common inductance without reducing their subtractive common inductance with the tube rails of the center phase greatly reducing it. The balanced state, in which all phases are the same, lies roughly at the intersection of the three curves m, n, p. The pipe rails 6 and 10 and the pipe rails 7 and 11 should be close to each other, but their smallest distance is determined by the heat of the current flowing in them on the central electrode arm 13 when these pipe rails are at the same height _c

It has already been mentioned that the average inductance in the illustrated embodiment is 0.335 / t H / a. In comparison, the average inductance of a comparable conventional arrangement of six pipe rails in the same horizontal plane is 0.485 ^ i H / m. In addition, the central pipe rails have a lower inductance than the outer pipe rails, so that with a similar effect on the flexible lines, there is a considerable unbalance between the phases. Another comparable arrangement of a conventional type consists of three pipe rails, the longitudinal axes of which lie on the eoks of an equilateral triangle. The pipe rails are as close to one another as the given electrode arm spacing allows. Although the inductance of this Rohrsohienen substantially equal, the inductance per meter is in the order of 0.508 u H. 109883/0467

Claims (1)

3.1 * Hai ... lSÜ5fi.an "! Draiphaaen arc furnace" sheet * f. The United Steel Companies Limited, The Mount »Broomhill, Sheffield, Yorkshire, England Claims ι A three-phase arc furnace with a transformer, three of Electrodes held by an electrode holder each, about three parallel, horizontally extending and vertically adjustable electrode arms with horizontally at a distance from the Electrode arms running and on the electrode holders leading rigid lines and flexible lines connecting the rigid lines to the transformer, characterized in that at least two rigid lines (6, 7; 10, 11) held in parallel from each of the two continuous electrode holders (18, 20) and in pairs (6, 10; 7i 11) in one of two vertical, parallel and spaced-apart lines Levels lie and that at least two of the parallel-connected and leading to the central electrode holder (19) rigid lines (8, 9) lie in a common horizontal plane running symmetrically between the two vertical planes. 2. Pulp-phase arc furnace according to claim 1, characterized in that the transformer (1) 109883/0467 ι 51. Mal-1968 to gI) r.e1phag «n ~ Llch, 1; bQ.geiiQ. £ eji! ^t . Βία « three old six secondary windings (3) has secondary windings and the flexible lines (4-) the terminals (a., ä ₂ j "b ^, b ₂ ; Cg ₉ C ₂ ) of each pair of terminals (3) with different electrodes (21 , 22, 23) connect leading rigid line pairs (6 fcis 11). 3. Three-phase arc furnace according to claim 1, characterized in that the secondary windings of the transformer β (1) are connected in series and each secondary terminal (a ₂ , b ₂ , C ₂ ) via a flexible line (4) with one of the rigid line pairs (6 to 11) is connected. 109883/0467 Blank page