JPH0620772A - Power supply method to arc electrode in ac arc heating furnace - Google Patents

Abstract

PURPOSE:To supply electric power uniformly to arc electrodes in three phases when from a transformer for a heating furnace. CONSTITUTION:Through cables 14, electric power is supplied from a transformer for heating furnace to arc electrodes 4 in three phases, which are supported by respective arms 7, in the condition that the spacing of cables in connection with those of the three arms which are positioned on the outsides is made larger than the spacing of cables in connection with the arms 7 positioned in the middle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying electric power from a furnace transformer to a plurality of arc electrodes provided in a furnace in a three-phase AC arc heating furnace.

[0002]

2. Description of the Related Art In an arc heating furnace of this type, three electrode supporting arms are arranged in parallel above the furnace, and the arc electrodes inserted toward the inside of the furnace are respectively supported at the front ends of the electrode supporting arms. Along with being provided, a cable terminal that is electrically connected to the arc electrode of each front end is provided on the rear side of each electrode support arm,
Each of the cable terminals is connected to a furnace transformer via a cable.

[0003]

When power is supplied from the furnace transformer to the above arc electrodes in such an arc heating furnace, the reactance from the cable terminal in each electrode support arm to each arc electrode is It is small in the phase of the electrode support arm located in the middle of the electrode support arms, and large in the phase located on both outer sides. Therefore, the electric power supplied to the arc electrodes related to the intermediate phase becomes larger than the electric power supplied to the arc electrodes related to other phases, and in the furnace, refractory materials in the furnace near the former arc electrode There have been problems that hot spots are generated and are locally damaged, or that the melting of raw materials in the furnace is not uniform.

The present invention has been made to solve the above-mentioned problems (technical problems) of the prior art. When power is supplied from a furnace transformer to a plurality of arc electrodes, the power is evenly distributed to the arc electrodes. The method for supplying electric power to the arc electrode in the AC arc heating furnace, which is capable of uniformly melting the molten raw material in the furnace without causing local damage to the furnace, It is intended to be provided.

[0005]

In order to achieve the above object, a method of supplying power to an arc electrode in an AC arc heating furnace according to the present invention is such that three electrode support arms are arranged in parallel above the furnace and each electrode is At the front end of the supporting arm, the arc electrodes inserted toward the inside of the furnace are respectively supported, and at the rear side of each electrode supporting arm, there is a cable terminal electrically connected to the arc electrode at each front end. In each of the AC arc heating furnaces, each of the cable terminals is connected to the furnace transformer via a plurality of cables, and power is supplied from the furnace transformer to the arc electrode via the cable. In doing so, in order to equalize the electric power applied to each arc electrode, the intervals between the plurality of cables connected to the electrode support arms respectively located on both outer sides of the above three electrode support arms are set to the intermediate value. On top While wider than the plurality of cables mutual spacing are continuous to the electrode support arm which is intended to power at.

[0006]

The electric power from the furnace transformer is supplied to the cable terminals of the respective electrode supporting arms via a plurality of cables, and further supplied from the cable terminals to the arc electrodes. The reactance of each of the plurality of cables connected to the electrode support arms located on both outer sides is smaller than the reactance of the plurality of cables connected to the electrode support arms located in the middle of the above cables.
On the other hand, the reactance from the cable terminal of the electrode support arm located in the middle to the arc electrode supported by the electrode support arm is the arc electrode supported by the electrode support arm from the cable terminals of the electrode support arms located on both outer sides. Is smaller than the reactance up to. Therefore, the reactance from the furnace transformer to each arc electrode can be made equal for all arc electrodes. As a result, the power supplied to each arc electrode can be equalized.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 to 14 represent respective members of a normal arc melting apparatus, 1 is an arc furnace shown as an example of an arc heating furnace, 2 is its body, 3 is a furnace lid, 4 is an arc electrode,
5 is a furnace lid rising and turning device, 6 is an electrode column, 7 is an electrode supporting arm,
Reference numeral 8 is an electrode gripper provided at the front end of the support arm 7, 9 is a cable terminal provided at the rear side of the support arm 7, 11 is a transformer chamber, and a transformer for a furnace is housed therein. Reference numeral 12 denotes a secondary busbar of the transformer protruding from the transformer room 11, 13 denotes a cable terminal provided on the secondary busbar, and 14 denotes a cable connecting the cable terminals 9 and 13, respectively. The arc furnace 1 is a three-phase AC arc furnace, and includes three electrodes 4, 4, as shown in FIG.
4, and three supporting arms 7 supporting them are arranged side by side as shown in the figure. As the supporting arm 7, what is called a conductor supporting arm is used as an example, and electric power for arc generation can be supplied from the cable terminal 9 at the rear end toward the electrode 4 through the supporting arm 7. Since this conductive support arm has a small reactance, there is little power loss, and it is used because of the advantage that a large amount of power can be input to the arc electrode 4 by the same furnace transformer. Similarly to the support arm 7, three secondary bus bars 12 are provided side by side, and each of them has a cable terminal 13. Similarly, three sets of cables 14 are arranged side by side, and each set has two cables, each of which has a cable terminal 9,
13 are connected. In this specification, the three phases in the aligned state are A phase, B phase in order from one side thereof.
Phases and C phases are referred to as reference numerals A, B and C, respectively.
Therefore, the B phase is the phase located in the middle, and the A phase and the C phase are the phases located outside.

Next, the cable terminal 9 in the electrode supporting arm 7 will be described with reference to FIGS. 2 and 3. 15 and 15 are supporting arms 7
A pair of terminal plates attached to the rear ends of the terminal plates, 16 are cable connecting portions defined on one surface side of each terminal plate 15, and are on the outer surface side of the pair of terminal plates 15 in the A phase and C phase, and in the B phase. They are defined on the inner surfaces of the pair of terminal plates 15, respectively. As shown in the drawing, the end portion 17 of the cable 14 is firmly connected to the connecting portion 16 with a large number of bolts 18. As a result of the connection part 16 being defined as described above, in the A phase and the C phase located outside, the distance between the cable ends connected to the connection part 16 is larger than that in the B phase located in the middle. It is getting bigger. To give an example of the dimensions, the dimensions Da and Dc of the A and C phases are 580 mm.
And the dimension Db of the B phase is 340 mm. The distance D between each phase is 800 mm.

Next, the cable terminal 13 on the transformer side will be described with reference to FIG. The cable terminal 13 is configured to be substantially equal to the cable terminal 9 on the supporting arm 7 side. That is, a pair of terminal plates 21 and 21 are attached to each secondary busbar 12, and a cable connecting portion 22 in each terminal plate 21 has a cable terminal 9 on the supporting arm 7 side for each phase A, B and C. The same as in the case of. The end portion 23 of the cable 14 is firmly connected to the connecting portion 22 with a bolt 24.

Next, the cable 14 will be described. A flexible water-cooled cable is used as the cable 14, and two cables are used for each phase. As shown in FIG. 4A for the B phase, the cable 14 in each phase has a space holding plate 26 made of an insulating material such as rubber interposed between the pair of cables 14 and 14. It is tied together with wire 27. Further, in the C-phase, as shown in FIG. 4B, the wide spacing plate 28 has a pair of cables.
It is placed between 14 and 14 and is tied together by a wire 27. Phase A has the same structure. With such a structure, in the phase B, the distance between the pair of cables 14 and 14 is such that the distance between the ends connected to the cable terminal 9 is large.
It is the same as Db, and the intervals between the pair of cables 14 and 14 for the A phase and the C phase are the same as the intervals Da and Dc, respectively. Further, as a result of such a configuration, even if a large current flows through each cable, it is possible to prevent the cables from approaching each other due to electromagnetic force.

When the arc furnace is operated in the above-described structure, the electric power for arc generation output from the transformer in the transformer room 11 is supplied from the secondary bus bar 12 to the cable terminal.
It is sent to the cable 14 through 13 and further reaches the cable terminal 9 of the electrode supporting arm 7 through the cable 14. Then, it is supplied to each electrode 4 from the cable terminal 9 through the supporting arm 7 and the electrode gripper 8. By such power supply, an arc is generated from the electrode 4 in the arc furnace 1, and the melting raw material charged inside is melted.

When the electric power is supplied as described above, the electrode support arms 7 of the three phases are arranged side by side, so that the reactance of the B phase electrode support arm 7 located in the middle is small (for example, 0.375). mΩ), and the reactances of the A and C phases located outside are large (eg, 0.613 mΩ). On the other hand, regarding the cable 14, since the distance between the pair of B-phase cables 14 located in the middle is small and the distance between the pair of A-phase and C-phase cables 14 located outside is large, their reactances are large. The former is large (eg 1.413 mΩ) and the latter is small (eg 1.264 mΩ). Therefore, the total reactance from the cable terminal 13 to the electrode 4 is substantially the same for the B phase located in the middle and the A phase and C phase located outside (for example, B phase is 2.421 mΩ, A Phase and C are 2.
51 mΩ). As a result, the electric power output to the secondary side of the transformer is evenly supplied to the electrodes 4, 4, 4 of each phase, and inside the arc furnace 1, no local hot spots are generated and The entire raw material for melting is dissolved uniformly. The distance between the pair of A-phase and C-phase cables 14 located outside is larger than the distance between the pair of B-phase cables 14 located in the middle, from the transformer to the arc electrode of each phase. It is preferable to set so that the reactances of are balanced, that is, the reactances of the respective phases are equal.

Next, the power supply by the above method may be carried out in a facility called a ladle furnace, that is, a ladle refining furnace as another example of the arc heating furnace.

Next, FIG. 6 shows a different embodiment of the present application, and shows an example in which each electrode supporting arm 7e is provided with a supporting arm busbar 31, respectively. When such a supporting arm bus bar 31 is provided, in the cable terminal 9e on the rear side of the supporting arm bus in phase B, the distance between the rear ends of the supporting arm bus bars 31 is narrowed as shown in the drawing, and a terminal board 15e is provided on each bus bar. In the cable terminals 9e on the rear side of the supporting arm in the A phase and the C phase, the supporting arm bus bar 31
The distance between the rear end portions is widened as shown in the figure, and each bus bar is provided with a terminal plate 15e. Then, the cables of the respective phases are connected to the respective terminal plates 15e. Then, similar to the above-mentioned embodiment, the mutual spacing between the cables becomes narrower in the B phase and becomes wider between the cables in the A phase and the C phase. In addition, parts that are considered to be the same or equivalent in configuration to those in the previous figure in terms of function are denoted by the same reference numerals as those in the previous figure with the letter e added to omit redundant description.

[0015]

As described above, according to the present invention, when electric power is supplied from the furnace transformer to the arc electrodes 4 respectively supported by the three electrode supporting arms 7, the arc electrodes 4 are supported. Of the three electrode support arms 7, a plurality of cables 14 and 14 connected to the electrode support arms located on both outer sides, respectively.
Electric power is supplied in a state in which the mutual distances Da and Dc are made wider than the mutual distance Db between the plurality of cables 14 and 14 connected to the electrode support arm 7 located in the middle, so that each arc electrode 4 is supplied from the furnace transformer. It is possible to equalize the reactance up to any of the arc electrodes 4 and to supply electric power to each arc electrode 4 evenly. This solves the above-mentioned problems of the prior art, and exerts the advantage of enabling uniform melting of the molten raw material in the furnace without causing local damage to the furnace refractory in the furnace. effective.

[Brief description of drawings]

FIG. 1 is a side view schematically showing an arc melting device.

FIG. 2 is a plan view showing a state where electrode support arms are arranged side by side.

FIG. 3A is an enlarged plan view of a cable terminal on an electrode supporting arm, and FIG. 3B is a front view of the cable terminal.

FIG. 4A is a cross-sectional view showing a coupling state of a pair of cables in the intermediate phase (IV-IV in FIG. 1).
(Cross-sectional view at line position), (B) is a cross-sectional view showing a similar state in a phase positioned outside.

5A is a plan view of a cable terminal in a transformer, FIG. 5B is an enlarged plan view of FIG. 5C, and FIG.

FIG. 6 is a plan view showing an example in which the electrode support arm includes a support arm busbar.

[Explanation of symbols]

 1 arc furnace 4 arc electrode 7 electrode support arm 9,13 cable terminal 14 cable A, C outside phase B intermediate phase

Claims (1)

[Claims] 1. The three electrode support arms are arranged side by side above the furnace,
At the front end of each electrode support arm, an arc electrode inserted toward the inside of the furnace is supported, and on the rear side of each electrode support arm, a cable electrically connected to the arc electrode at each front end is provided. In an AC arc heating furnace in which a terminal is provided and each of the cable terminals is connected to a furnace transformer via a plurality of cables, power is supplied from the furnace transformer to the arc electrode via the cable. In order to supply the electric power to each arc electrode evenly, the distance between the plurality of cables connected to the electrode support arms located on both outer sides of the three electrode support arms is set to be equal to each other. , A method for supplying power to an arc electrode in an AC arc heating furnace, characterized in that power is supplied in a state in which it is wider than a distance between a plurality of cables connected to an electrode supporting arm located in the middle.