US2752409A - Low voltage connections for electrode furnace - Google Patents

Description

June 26, 1956 M. EATON LOW VOLTAGE CONNECTIONS FOR ELECTRODE FURNACE 2 Sheets-Sheet 2 Filed April 1, 1955 ELECTRODE HEADTH LEVEL flue/d2? Mu ro/v [470M United States Patent LOW VOLTAGE CONNECTIONS FOR ELECTRODE URNACE Milton Eaton, Shawinigan Falls, Quebec, Canada, assignor to Shawinigan Chemicals Limited, Montreal, Quebec, Canada, a corporation of Canada Application April 1, 1955, Serial No. 498,686

2 Claims. (Cl. 13-9) This invention relates to improvements in the low-voltage connections between the transformer terminals and the electrode contact shoes of three-phase electric furnaces designed for low reactance. The invention pertains particularly to closed electric furnaces having the contact shoe connections above the furnace cover and three electrodes spaced triangularly.

Certain electric furnaces, such as calcium carbide furnaces, operate with a low electrical resistance. A satisfactory power factor is therefore obtained only if the reactance of the electric circuits is correspondingly low. Since the reactance is directly proportional to the frequency of the power supply the advantages gained by this invention are greater for 60-cycle furnaces than they are for furnaces operated with a power supply of a lower frequency.

The reactance of the furnace depends mainly on the length, diameter, and spacing of the electrodes. These dimensions are largely governed by the capacity of the furnace and little can be done about them to limit the reactance except to locate the electrode contact shoes just high enough on the electrodes to clear the cover when the electrodes are in their lower operating position.

Transformers for large electric furnaces are preferably made with multiple secondary windings having terminal risers made of closely interlaced thin rectangular bars or straps; alternate straps are plus and minus, i. e., they carry current in opposite directions.

The reactance of the connections between the transformer and the electrodes can be minimized by appropriatelayout and it is the object of this invention to provide such connections of very low reactance.

Detailed description The invention will be understood from the following detailed description of preferred embodiments of it, reference being made to the accompanying drawings in which:

Fig. 1 shows schematically the electrical connections,

Fig. 2. is a developed View in elevation showing the arrangement of connections in greater detail, and

Fig. 3 is an enlarged detailed cross-sectional view of part of the connections at the line A--A of Figure 2.

Figs. 4 and 5 show alternate arrangements of details of connections shown in Fig. 2.

Referring to Figure 1, the delta-connected transformer 123 may have its three phases mounted in one case or in three separate cases. For each phase, six secondary windings, in parallel, with interlaced terminals are shown. The number of parallel windings is optional, but preferably there are from six to twelve such windings. The delta connections of the secondary windings are made at the electrodes, 1, 2, and 3.

Groups of interlaced bars (preferably of copper) 10, 20, 30, are connected to the transformer terminals, one bar to each terminal. The reactance of these groups of bars is much less than that of separated conductors and they therefore terminate at a location such that the total 2,752,409 Patented June 26, 1956 length of the separated conductors (distributor bars, connectors, and flexible leads) is a minimum. The longitudinal axis of the furnace end of each group is symmetrical with respect to the two electrodes to which the bars are connected.

For minimum reactance these bars must be thin in proportion to their width and they must be arranged side by side with separation suflicient only for the required insulation. Each of the bars may consist of a single wide bar or of a divided bar, one part vertically above the other as shown in Figures 2 and 3. The two parts, for example, 21 and 22, are joined together at the furnace end by tie-bar 23, preferably by welding. The advantage of using a divided bar is that the lighter parts are easier to erect and a space may be left between them for clamping bolts.

Figure 3 shows more detail. Adjoining bars carry current in opposite directions and are separated with suitable insulating material, such as asbestos board, only at the clamps which are spaced two or three feet apart depending on the rigidity of the bars. Figure 3 indicates that the clamping is done by means of lengths of angle iron 26 and insulated bolts 27, one of which is shown in crosssection. The groups of interlaced bars are preferably enclosed in ducts 25 made with heat-resisting material, such as asbestos board, and angle iron framing. To dissipate the heat corresponding to the power loss in these bars, air is blown through the ducts by fans 37. The groups of interlaced bars may be supported from an overhead structure 39 by rods 38 attached to the structure and the clamps.

Distributor bars 40 to 45 (41 to 44, located between 40 and 45, are not numbered in the drawing) extend horizontally from the upper part of each of the plus bars of the interlaced group 20 toward electrode 1, while 70 to (71 to 74 are not numbered in the drawing) extend horizontally from the lower part of each of the minus bars toward electrode 3. Each of the distributor bars projects outside enclosure 25. The plus and minus groups of distributor bars are thus separated vertically to permit them to cross each other. The distributor bars for groups 10 and 30 are similarly arranged. Connector 56, on the end of a distribtor bar, has a lug, 56A, for attachment to the distributor bar, suitably by welding, and a head 56B for attachment to the succeeding currentcarrying part and to a connection to a source of cooling water or a drain. In Figure 2 the lug 56A of connector 56 is connected to an upper distributor bar, and the head 56B is below the lug; for connection to a lower distribu tor bar, the connector is reversed and the head is above the lug, the design of the connector suitably being such that the elevation of the head is the same in the two cases.

Electrode contact shoes are arranged symmetrically around each electrode, their number being equal to the number of pairs of interlaced bars and the number of parallel-connected windings in the transformer, or a multiple thereof. To compensate for the variable distance between the shoes 100 and the ends of the distributor bars, some of the connectors 56 can be equipped with extensions consisting of tubes 50 of appropriate length between elbow 58 and 59 (Figure 2). Where the connector lacks this extension, the lugs 56D of those connectors 56E which are attached to upper distributor bars 43 can be made longer so that the tops of the heads 56F (instead of the tops of elbows 58) are at the same elevation as the top of the shoes 100 at mid-travel as shown in Fig. 4; the lugs 56A of those connectors 56 which are attached to lower distributor bars 73 can remain unchanged in size but the connectors are then suitably mounted with their heads 56B below the lugs, as shown in Fig. 5, so that again the tops of the heads are at the same elevation as the tops of the shoes 100, when the latter are in their mid-travel positions.

In order to permitverticalmovement of the electrodes as required during the operation of 'the furnace, 'flexible leads 6t), 63, 9th, 93 etc., must be used in the electrical connection between the electrode contactshoes .100 and the connector heads 56B or the extension of the.connectors, elbows 58. Leads .63 and 93 are examples of those connected .direct to the connector heads 563. These flexible leads are preferably of the type described in copending application .Serial Number 337,841 filed February 19, 1953, and are mounted in a vertical archsas shown in Figure 2. This arrangementpermits the vertical clearance above the operating floor, required .by the furnace operators, to be obtained with connections of minimum lengthand therefore minimum reactance.

Some large .electric furnaces, .e. .g., carbide furnaces, have flames rising from the charge; in the case of covered furnaces the flames rise through the'feed hoppers around the electrodes. In the illustrated embodiment of the invention all the electrical connections from the connectors 56 to the electrode contact shoes 100 are therefore provided with channels for a cooling fluid, usually water. The cooling fluid, usually water. The cooling fluid suitablyenters at 57, flows through the head 56B, elbow 59, tube 50, and elbow 58 of the connector 56, then through flexible lead 60 to the electrode contact shoe 100, suitably returning through the adjacent flexible lead .61 (not numbered in the drawing), the .connector extension attached thereto, and emerging through the connector head.

Where connector 56 has no extension (e. g. for connection to leads 63 or 93), the lead-is suitably connected to the top of the connector head and the cooling fluid enters (or leaves) the bottom. In the embodiment of the invention shown in Figure 1, there are two flexible leads connected to each contact shoe. When the number of contact shoes is double the number of windings in the transformer and the number of pairs of interlaced bars, there is, of course, only one flexible lead connected to each contact shoe and a connection for the cooling fluid is required between adjoining shoes.

In the preferred embodiment of the invention, the bottoms of the interlaced bars are preferably at the same level as the terminals of the flexible leads on the electrode contact shoes when the electrodes are in their mid-travel position.

From the foregoing detailed description of an embodiment of the invention, it will be seen that a system of furnace connections has been provided which includes simultaneously (a) flexible connection between the electrodes of a furnace and the transformer supplying power to the furnace, permitting necessary electrode movement, (b) cooling facilities for'those parts of the connections exposed to heat and flame from the furnace, and (0) minimum reactance between the transformer and the electrodes, providing maximum power factor. It will be apparent that numerous modifications may be made in the specific expedients described, and the invention includes all such modifications as are claimed ,in the following claims.

What is claimed is:

1. Low-voltage connections between a transformer, having a plurality of secondary windings in parallel, and the electrode contact shoes of a three-phase covered electric furnace having three electrodesin triangular spacing, comprising elements connected in sequence as follows: (a) interlaced transformer terminals ,made of thin bars, (11) three groups of interlaced plus and minus bars (one bar for each transformer terminal, andone group for each phase), (0) distributor bars (one for each of the interlaced bars) extended horizontally from the interlaced bars, those from the plus bars being directed toward the contact shoes of one electrode, and those from the minus bars being .directed toward the contact shoes of another electrode, (d) water-cooled connectors, (e) water-cooled flexible leads, and (f) water-cooled contact shoes symmetrically arranged around each electrode; the longitudinal axis of the furnace end of eachgroup of interlaced ,bars being symmetrical with respect'to the two electrodes to which the bars are connected and each group of interlaced bars being terminated at :a location such that the total length of the series-connected distributor bars, Water-cooled connectors, and water-cooled flexible cables is a minimum.

2. Low-voltage connections as claimed in claim 1 wherein the bottom of the furnace end of .each group of interlaced bars is at the same elevation asthe terminals of the flexible leads on the electrode contact shoes when the electrodes are in their mid-travel position.

Marshall Feb. 9, 1915 vNissirn Feb. 6,.1945

Images