EP0184140B2 - Arc furnace - Google Patents

Description

The invention relates to an arc furnace with at least one electrode support arm according to the preamble of claim 1 or according to the preamble of claim 15.

In arc furnaces of this type, the current is supplied to the electrodes via power cables and high-current tubes or solid busbars attached to the electrode support arm of the relevant electrode.

The object of the invention is to simplify the construction required for the current supply in an arc furnace of the type mentioned above. With a box profile or tubular profile made of steel, i.e. Electrode support arm formed from a ferromagnetic material may be possible to make the high-current tubes or busbars attached to it unnecessary and still keep the magnetic losses low. At the same time, fault current paths are to be avoided and the electrode current is to be fed to the contact jaw of the electrode via a defined path. In the case of an arc furnace with three electrode support arms arranged approximately parallel to one another (claim 15), the symmetry of the three phases should also be substantially maintained, i.e. the impedance of the power supply for the three electrodes must be matched to one another. A simple measure is to avoid reactance asymmetry of the live parts.

The solution to this problem is specified in claim 1. Claim 15 specifically defines an arc furnace with three electrode support arms arranged approximately parallel to one another in approximately one plane, with at least one phase being formed with at least one loop to avoid a reactance asymmetry of the high-current conductor.

In the arc furnace according to the invention, the electrode support arm is provided on the outside with at least part of its length with an electrically highly conductive layer, such as copper or aluminum. The area in which the preferably plated-on layer with good electrical conductivity is present serves as a high-current conductor for the electrode current. Since the electrically highly conductive layer is electrically connected to the box or tubular profile made of steel and an actuating device and an actuating rod for the electrode clamping device are present within the supporting arm, it is necessary to electrically isolate the electrode clamping bracket from the electrode supporting arm in order to avoid fault current paths. For this purpose, the actuating rod at the end on the electrode side should also be insulated from the electrode support arm. In the case of an arc furnace with three electrode support arms arranged approximately parallel to one another, it is expedient to conduct the current over a current tube over part of the length of the support arm and only to pass it on from a central region over the electrode support arm to the contact jaw in order to increase the reactance of the central support arm and to adjust to the reactance of the two outer support arms, ie largely eliminate the reactance asymmetry.

The loop provided according to the invention is located between the transformer of the arc furnace and the relevant electrode support arm, in particular the middle electrode support arm. This measure makes it possible to dispense with the additional busbar of the middle electrode support arm and the arrangement of this busbar in the sense of an equilateral triangle with respect to the other two electrode support arms.

Advantageous developments of the invention are specified in the subclaims.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing.

• die Fig. 1 und 2 in einer Seitenansicht, teilweise im Schnitt und in einer Draufsicht, die für das Verständnis der Erfindung wesentlichen Teile eines Lichtbogenofens mit drei etwa parallel zueinander angeordneten Elektrodentragarmen;
• Fig. 3 die Ausbildung eines Elektrodentragarms im Längsschnitt;
• Fig. 4 die Elektrodeneinspannvorrichtung in einer Draufsicht;
• Fig. 5 eine Ansicht einer Reaktanzschleife für die Stromführung eines Lichtbogenofens. wobei die Darstellungsebene senkrecht zur Längsachse der Hochstromleiterabschnitte zwischen Transformator und Elektrodentragarm des Lichtbogenofens verläuft;
• Fig. 6 eine Ansicht der in Fig. 5 gezeigten Reaktanz Schleife von rechts und
• Fig. 7 eine Ansicht der in Fig. 5 gezeigten Reaktanzschleife von oben.

Show it

• Figures 1 and 2 in a side view, partly in section and in a plan view, the parts of an arc furnace essential for understanding the invention with three electrode support arms arranged approximately parallel to one another;
• Figure 3 shows the formation of an electrode support arm in longitudinal section.
• 4 shows the electrode clamping device in a top view;
• Fig. 5 is a view of a reactance loop for the current supply of an arc furnace. wherein the plane of representation runs perpendicular to the longitudinal axis of the high-current conductor sections between the transformer and the electrode support arm of the arc furnace;
• Fig. 6 is a right and right view of the reactance loop shown in Fig. 5
• Fig. 7 is a top view of the reactance loop shown in Fig. 5.

1 and 2 show an arc furnace 1 with three electrode support arms 2, 3, 4 arranged approximately parallel to one another, of which only the electrode support arms 3 and 4 are shown in the sectional view according to FIG. 1. The electrode support arms can be raised and lowered in a known manner by the lifting column 5 and can be pivoted to the side about an axis 7 by means of a portal 6 in which the lifting columns 5 are guided. Each electrode support arm is provided with an electrode clamping device 8 which contains a contact jaw 9 which is supported on the electrode support arm and through which an electrode 10 on the electrode support arm is clamped and is supplied with current. The electrodes 10 are so-called combination electrodes with a metallic upper part and a screwable one. the lower part subject to erosion.

The two outer support arms 2 and 4 are over their entire length, the middle support arm 3 only over part of its length from the electrode-side end with an electrically highly conductive layer 11 or 12 made of copper or aluminum provided, which is shown hatched in FIGS. 1 and 2 in each case only at the end of the relevant layer. A high-current tube 14 is fastened on the middle electrode support arm 3 by means of support arms 13 and is electrically connected to the electrode support arm 3 in the area of the electrode support arm 3 which is provided with the highly conductive layer 12. At the end of the support arms 2 and 4 and the high-current tube 14 facing away from the respective electrode, connecting terminals 15 for high-current cables 16 are provided, which are connected to a transformer (not shown) and supply the current for the electrodes 10. The electrode support arms 2 to 4 are each electrically insulated from the associated lifting column 5. The insulation is indicated in Fig. 1 by an insulating plate 17.

The support arms have a box-shaped profile and, in addition to cooling channels for a cooling liquid, such as water, contain a device for actuating the electrode clamping device. Details of the structure of the electrode arm 4 and the clamping device 8 will now be explained with reference to FIGS. 3 and 4.

The electrode support arm 4 is formed by a box profile made of, for example, 20 mm thick steel sheet 18, which is provided on the outside of the electrode support arm with an electrically highly conductive layer 11. In the support 4 shown, the layer 11 is applied over the entire length around the support arm, in the electrode support arm 3 it is limited to the area at the electrode end shown in FIG. 2. In a practical embodiment, a copper layer 11 with a thickness of 4 mm was plated onto a steel layer 18 with a thickness of 20 mm. In the area of the mechanical connection with the lifting column assigned to the electrode support arm, the copper plating is left out.

3 is closed on the left side by a connecting plate 20 and on the right side by contact plates 21, each made of an electrically highly conductive material, preferably copper. The two contact plates 21 delimit a receiving space 22, which extends over the entire width of the support arm, for a holding piece 23 of a clamping bracket 24 of the electrode clamping device 8. As shown in FIG. 4, the holding piece 23 connects the ends of the electrode clamping bracket 24, through which the electrode 10 can be clamped is. The electrode is clamped in that the clamping bracket 24 is pulled to the left by means of the holding piece 23 in the illustration according to FIG. 3 and the electrode is pressed against a contact piece 25 made of electrically highly conductive material, preferably copper, which is fastened to the contact plates 21. By moving the electrode clamp 24 to the right, the clamping device is released and the electrode 10 is released. The displacement movement of the electrode clamping bracket 24 takes place by means of an actuating rod 26 arranged centrally in the electrode supporting arm with the aid of an actuating device comprising a spring assembly 27 and a hydraulic cylinder 28, which are arranged together with the actuating rod within a central tube 29 of the electrode supporting arm. The actuating rod 26 is pulled to the left by the spring assembly 27, i.e. the electrode clamping device is held in the clamping position, the actuating rod is pressed to the right against the spring force of the spring assembly 27 by the hydraulic cylinder 28 and thus the electrode clamping device is brought into the release position. Within the central tube 29 there are guides 30 and 31 for the axially displaceable actuating rod 26. In the space between the central tube 29 and the steel sheet 18 there are channels 32 for a cooling liquid for cooling the electrode support arm.

The electrode clamp 24 is electrically insulated from the electrode support arm. For this purpose, as shown in FIG. 4, two insulating sliding blocks 33 and 34, preferably made of ceramic material, are inserted in the top and in the bottom of the holding piece 23, which protrude above the relevant surface of the holding piece and on the upper and lower Bearing side of the receiving space 22. The sliding blocks 33 and 34 are offset in the axial direction of the electrode support arm in order to be able to absorb the moment exerted by the weight of the electrode on the clamping bracket. In addition to this insulation, there is also an electrical insulation between the holding piece 23 and the actuating rod 26, which is designated by 35, and an insulation between the electrode clamping bracket 24 and a clamping jaw 36 which bears against the electrode 10 and is designated by 37. The electrode clamp 24 is therefore also electrically insulated from the electrode 10. Finally, electrical insulation 38 is also provided between the electrode-side guide 31 of the actuating rod 26 and the latter. This prevents that fault currents can form inside the electrode support arm and in particular in the electrode-side end region of this support arm via the electrode clamp and the actuating rod 26, which can lead to local overheating and damage. The current introduced via the connection plate 20 is thus forced to take a defined path via the outer wall of the box section to the contact plates 21 and from here via the contact piece 25 into the electrode 10.

In the case of the middle electrode support arm 3, the power supply line to compensate for the different reactances between the different support arms first takes place via the current tube 14 and only from a central region in analogy to the route described with the aid of the electrode support arm 4. The location of the current introduction from the high-current tube 14 into the electrode support arm is determined by the requirement to adjust the reactance of the middle electrode support arm of the two outer electrode support arms, ie to eliminate the reactance asymmetry. With a view to eliminating the reactance asymmetry, the axis of the high-current tube 14 is offset so far upwards relative to the central support arm that it forms an equilateral triangle with the axes of the outer support arms when the support arms 2, 3 and 4 are in one plane. In the described embodiment it is assumed that the arc furnace is operated with a three-phase alternating current.

The electrically highly conductive layer 11 does not have to extend over the entire circumference of the support arms. Good results have also been achieved with an embodiment in which the two outer support arms had only one plated copper layer on the top, the bottom and the two facing inner sides. Local recesses in the cladding are of course also permissible if it is ensured that a sufficient cross-section is available for the current transport.

In the following, a simple measure is described as a special embodiment of the invention, by means of which a reactance asymmetry can be avoided. This exemplary embodiment relates specifically to an arc furnace operated with three-phase alternating current, which has three electrodes, each with an associated electrode support arm. The three electrode support arms are arranged parallel to one another in a plane above the furnace vessel. For the supply of current to the individual electrodes, the electrode support arms have on their outside a layer of electrically good conductive material, e.g. B. copper, as described in detail above.

To avoid reactance losses, it is necessary to adapt the impedance in the current paths of the three phases to one another. The loop described below (reactance loop) serves this purpose. In the exemplary embodiment specifically described here, a single loop is formed in that high-current conductor. which is connected to the central electrode support arm, that is to the electrode support arm 3 shown in FIG. 2.

The loop 101 shown in FIGS. 5 to 7 is located, for example, at a location of the high-current cable assigned to the central electrode support arm 3, where it runs approximately horizontally.

The high-current cables provided with the reference symbol 16 in FIG. 2 form two ends where they run approximately horizontally, so that the cables are actually divided into two high-current conductor sections. A high-current conductor section 102 connected to the transformer has an end piece. which is shaped such that it forms two straight sections 102a and 102b which run at right angles to one another and to the incoming high-current conductor section 102. In the end region of section 102b, a clamping connection 105, for example made of copper, is fastened by means of screws 107. The clamp connection 105 is part of a cross member 104, which is also made, for example, of copper or a similarly highly conductive material, and at the other end of which a clamp connection 106 is formed which is similar to the clamp connection 105.

The screws 107 are shown in FIG. 7 and only indicated by dash-dotted lines in FIGS. 5 and 6. The clamp connection 106 holds an end section 103 b of a high-current conductor section 103 leading to the furnace. The sections 102 and 103 thus together form the high-current conductor cable 16 partially shown in FIG. 2. The end of the high-current conductor 103 facing away from the loop 101 is on the central electrode support arm of the arc furnace fixed. In the area of the loop, the high-current conductor section 103 is shaped such that it forms two end sections 103a and 103b which form a right angle with respect to one another and with respect to the high-current conductor section 103.

As can be seen from FIG. 7, the loop 101 is located in a plane that runs perpendicular to the central axis L1, L2 of the two high-current conductor sections 102 and 103. The current direction from the transformer to the furnace is indicated in Fig. 5.

In the present embodiment, the two high current conductor sections 102 and 103 are individual cable sections, i.e. the cable sections each have an open end, as shown in FIG. 5. Deviating from this embodiment, it is fundamentally also possible to provide a through-going high-current cable, e.g. B. in the middle high current conductor 16 shown in FIG. 2 to form the loop. In Fig. 5 the two open cut surfaces of the cables would then be connected to one another.

In order to adjust the reactance formed by the loop 101 for the purpose of matching the impedances in the three current guides, the position of the crossbar 104 with respect to the other parts of the loop is changed. By loosening the screws 107, the traverse can be changed up and down in the direction of the arrow P shown in FIG. 5, as a result of which the reactance of the loops can be increased or decreased.

Like the high-current cables, the reactance loop is cooled with cooling water.

Claims (15)

1. An electric arc furnace (1) comprising at least one electrode support arm (2, 3, 4) which is provided with an electrode holding means (8) including a contact jaw (9) which is supported on the electrode support arm and which is connected to a heavy-current conductor, and also an electrode clamping stirrup (24) which is displaceable by an actuating rod (26) which is arranged within the electrode support arm (2, 3, 4) and which is longitudinally displaceable by means of an actuating device (27, 28), between a clamping position in which the electrode clamping stirrup (24) presses the electrode (10) against the contact jaw (9) and a release position in which the electrode clamping stirrup (24) releases the electrode (10), characterised in that, at least over a part of its length, on the outside, the electrode support am (2, 3, 4) is provided with a layer (11, 12) of copper or the like, which is a good conductor of electricity, and in that region forms the heavy-current conductor for the supply of power to the contact jaw, and the electrode clamping stirrup (24) is electrically insulated with respect to the electrode support arm (2, 3, 4).
2. An electric arc furnace comprising three electrode support arms (2, 3, 4) which are disposed in substantially parallel relationship with each other, according to claim 1, characterised in that the two outer electrode support arms (2 and 4) form the heavy-current conductor over a larger part of their length than the middle electrode support arm, in the region adjacent to the electrode (10).
3. An electric arc furnace according to claim 2 characterised in that the middle electrode support arm (3), in the region which is remote from the electrode (10), carries a heavy-current tube (14) or a bus bar, the heavy-current tube or the bus bar forming the heavy-current conductor in that region of the electrode support arm (3).
4. An electric arc furnace according to one of claims 1 to 3 characterised in that, in the region forming the heavy-rent conductor, the electrode support arm (2, 3, 4) has a plating of material such as copper which is a good conductor of electricity.
5. An electric arc furnace according to one of claims 1 to 4 characterised in that, in the region of the electrode support arm (2, 3, 4) forming the heavy-current conductor, the layer (11, 12) which is a good conductor of electricity extends over the entire periphery of the electrode support arm.
6. An electric arc furnace according to claim 5 characterised in that the layer (11) which is a good conductor of electricity on the electrode support arm is omitted in the region of the junction between the electrode support arm (2, 4) and the associated lift column.
7. An electric arc furnace according to one of claims 1 to 6 characterised in that the electrode clamping stirrup (24) carries on its inside a clamping jaw (36) which is insulatedly set in position.
8. An electric arc furnace according to one of claims 1 to 7 characterised in that the electrode clamping stirrup (24) is secured to a holding portion (23) which is connected to the actuating rod (26) and which is displaceable in the end portion, which is towards the electrode, of the electrode support arm (2, 3, 4) and is bunted in such a way as to electrically insulated with respect to said arm.
9. An electric arc furnace according to claim 8 characterised in that the holding portion (23) has projecting insulating sliding members (33, 34) on its top and on its underside, the sliding members (33, 34) bearing against sliding surfaces on the support arm.
10. An electric arc furnace according to one of claims 1 to 9 characterised in that the end portion of the actuating rod (26), which is towards the electrode, is electrically insulatedly mounted in a sliding guide (31).
11. An electric arc furnace according to one of claims 1 to 10 characterised in that the heavycurrent conductor (102, 103) at least of one phase comprises at least one loop (101).
12. An electric arc furnace according to claim 11 characterised in that the loop (101) is disposed in a plane which extends normal to the centre line (L1, L2) of the heavy-current conductor portion (102, 103) upstream and downstream of the loop (101).
13. An electric arc furnace according to claim 11 characterised in that the size of the loop is variable.
14. An electric arc furnace according to claim 13 characterised in that the end portion (102a. 102b) of a heavy-current conductor section (102) connected to the transformer and the end portion (103a, 103b) of a heavy-current conductor section connected to the electrode support arm respectively form parts of the loop (101) and that the end portions are mechanically and electrically connected by way of a transverse member (104), by means of releasable clamping connections (105, 106).
15. An electric arc furnace comprising a transformer, three electrode support arms which are disposed substantially in parallel relationship with each other in substantially one plane and which have on their outside at least over a portion of their length a layer of material which is a good conductor of electricity, for the supply of power to the respective electrode, and heavy-current conductors which electrically connect the transformer to said layers on the electrode support arms, characterised in that the heavy-current conductor (102, 103) of the middle phase has a single almost closed reactance loop (101) which symmetrises the reactance asymmetry.

Images