US2731510A - Overhead electric lines and conductors therefor - Google Patents

Description

Jan. 17, 1956 a. BRAZIER ET AL OVERHEAD ELECTRIC LINES AND CONDUCTORS THEREFOR Filed Aug. 8, 1951 2 Sheets-Sheet 1 JA Attorneys Jan. 17, 1956 L. G. BRAZIER E'T AL 2,731,510

OVERHEAD ELECTRIC LINES AND CONDUCTORS THEREFOR Filed Aug. 8, 1951 2 Sheets-Sheet 2 Inventors lea/[e fife/dens Braz/Pr- 2F Attorneys 2,731,510 Patented Jan. 17, 1956 OVERHEAD Enters-ac MINES AND rrmnnnon Leslie Giddens Brazier, Hatchet, and VVilliam George Hawley, Hinchley Wood, Esher, England, assignors to British Insulated Callenders Cables Limited, London, England, a British company Application August 8, 1951, Serial No. Claims priority, application Great Eritain Aug-M1129, 1956i 4 Claims. (Cl. 174 114) This invention relates to overhead electric transmission lines working at high voltages. The conductors of such lines have to provide mechanical strength, conveyance of current and suitable conditions for electric stress in the surrounding air. For the high voltages with which the invention is concerned the last mentioned requirement determines the outside diameter of the conductor. This is made such that the loss by electric discharge through the air is not excessive.

For this purpose conductors havebeen designed consisting of two co-axial metal parts separated by a layer of non-metallic material serving for spacing them apart. In this construction the tensile stress is taken mainly by the central part while both metal parts share in conducting the current. The intermediate layer does not carry tensile stress or take part in the conduction.

The present invention provides an improved conductor of the kind just referred to and an overhead transmission system embodying it. In this improved conductor, the central member is a strand of wires of steel or other metal of high tensile strength with an outer part of wires. of a metal of good electrical conductivity, for example, aluminium wires. On this central. member is applied a continuous covering of paper, hemp or other filling material of suitable properties, as indicated hereinafter. The outer member of the conductor is a lhinavalled tube of metal of low density and goon electrical conductivity, such as aluminium or an aluminium rich alloy, having a smooth circular continuous outer surface and fitting closely on the filling material and forming a complete enclosure for the rest of the conductor structure.

The invention will now be more fully described with reference to the accompanying drawings wherein Figure l is a perspective view of a short length of overhead line conductor made in accordance with the invention and from which component layers have been cut back to show more clearly the construction of the conductor,

Figure 2 is a perspective view of a short length of a second example of overhead line conductor made in accordance with the invention and from which parts have been cutback to expose certain features of its construction,

Figure 3 is an isometric view of a joint between two lengths of one form of our improved conductor, a central part of this figure being in section to show the construction of the conductor joint.

On referring to Figures 1 and 2 of the drawings, it Will be seen that the examples of overhead line conductor shown therein comprise a central member which comprises a central core 1 consisting of seven wires of which six are laid up helically around a seventh to form a sevenwire strand. These seven wires are of steel or other metal of high tensile strength. Surrounding this central core 1 is a layer 2 of twelve wires of metal of good electrical conductivity, preferably a light metal such as aluminium. These twelve wires are laid up helically about the central core with a direction of lay opposite to that of the core wires. Around this layer 2 of conductor Wires is a second layer 3 of eighteen similar wires which are laid up helically about and preferably in the opposite direction to the wires of the underlying layer 2. The core 1 and its surrounding layers 2 and 3 of conductor wires constitute the central member of our overhead conductor. It will of course be understood that the particular description that has been given above of the central member has been given by way of example and that central members of other forms may be used. For instance, the core may con" se more than seven wires of high tensile metal and the set rounding part (if any) of the central member may consist of a single layer of wires of .a metal of good conductivity or of more than two layers. The number of wires in each layer may also vary from that shown when the diameter of the wires in one layer differs from that of the wires in an adjacent lever. Surrounding the metallic central member (3, 2 and 3) of our improved overhead electric conductor is a continuous covering 4 of nonmetallic material. Closely fitting the covering 4 and forming complete enclosure for the rest of the conductor structure is a thin-walled tube 5 of a light metal or" good electrical conductivity, such as aluminium or an aluminium rich alloy. This tube has a smooth circular continuous outer surface.

The covering lof non-rnetallic material between the metallic central member and the metal tube should be of relatively low density and capable of undergoing the required bending without either offering great resistance or suffering disintegration and should yet be sufficiently strong to maintain the spacing of the two metal parts of the conductor and transmit the necessary mechanical forces between them, during manufacture, installation and service. This intermediate layer may, for instance, be formed of helical lappings of paper tape, as shown for example in Figure l where they are designated 6. It is preferred to use paper or" substantial thickness, say 10 mils, to facilitate the operation of building up the required thickness. The turns of each layer of paper may be applied with a substantial gap between them, say 25% of the width of the tape, care being taken that these gaps do not line up in adjacent layers of paper. In the example of conductor shown in Figure 2, the layer 4 of filling material is formed by cords 7 of paper, hemp, or other material applied with a long lay side by side over the metallic central member and held in position with a binder 8 of tape applied with a short lay. It is emphasised that these two forms of intermediate layer are given only as examples of appropriate forms of construction, materials of other compositions and/or form and other methods of application are available and will be recognised as suitable from the information given.

Several methods of forming the tubular outer member 5 are available. It may be extruded directly on the layer 4 of filling material so as to fit closely thereon. It may be formed round the layer 4 by transversely bending to shape a strip of sheet metal and then welding the edges to complete the tube. In another method the tube may be formed separately, by extrusion or by bending and welding, or otherwise, so as to have an internal diameter somewhat larger than the external diameter of the body on which it is to fit, namely, the covered central member.

This body can then be drawn into the tube and the latter then reduced by drawing through a die to become a tight fit on the enclosed body.

In constructing the overhead line system, the conductor will be supported in the usual manner by clamps applied to its outer surface, that is, to the thin walled metal tube. In making joints, the inner and outer metal parts of the conductor will be joined separately by metal joint sleeves applied over the adjacent ends and connected thereto. To ensure that the inner and outer metal parts of our improved conductor are put in good electric conductive connection at sufiiciently frequent intervals in the length of the line that appreciable potential difierences between them will not occur at intermediate points, conductive filling material, such as an intermediate tube or tubes of metal, will be placed between the inner and outer metal joint sleeves at each conductor joint.

An example of a joint made between two lengths of our improved overhead conductor is shown in Figure 3. it

is made as follows: From the adjacent ends of the conductors short lengths of the outer tubular parts 5 and 5 and of the layers 4 and 4 of filling material are removed and where, as shown, the metallic inner member includes an outer layer, or layers, of wires of a light metal of good electrical conductivity, parts of such layers are cut back in the manner shown in Figure l to expose short lengths of the cores 1 and l and each of the layers 2 and 2' and 3 and 3. A sleeve 9 of suitable metal, that is metal of high tensile strength such as steel, is slipped as a good fit over the two projecting ends 1 and 1' of the stranded member and is compressed thereon in known manner so as to make effective connection. If, as is shown, this sleeve 9 has when compressed on the core, an external diameter approximating to that of the first layer of wires 2, an opened split metallic tubular member 10 is laterally inserted on the sleeve 9 and the adjacent exposed ends of the layers 2 and 2 and closed down again. This split sleeve serves electrically to connect the wires of layer 2 of one conductor length to those of the layer 2 of the other conductor and to build up the diameter of the joint to that of the outer layers 3 and 3'. Over this split sleeve 10 is laterally applied a second split sleeve 11 serving to connect the wires of the layers 3 and 3' electrically and to build up the joint to the external diameter of the outer tubular conductors 5 and 5. These are then joined and the split sleeves compressed on to the wire conductors and the core tube 9 by a sleeve 12 which was slipped over one of the ends before the inner joint was made. This is now brought into position over that joint so as to cover it and appropriate lengths of the adjacent parts of the tubes. It is then compressed in known manner to make a good mechanical connection with these tubular ends. To facilitate this connection the filling material 4 and 4' may be removed, as by a trepanning tool, from between the metallic inner member and the tube 5 or 5' for a short distance and replaced by metal sleeves 13 and 13', as shown in Figure 3. This is preferably done before jointing the cores 1 and l to avoid having to use a split sleeve. The sleeves 13, 13 may be grooved as at 14, 14 or otherwise formed to permit slight local inward compression of the tubular parts 5 and 5' and jointing sleeve 12 over it.

Instead of two separate sleeves 1t and 11 a single sleeve having a stepped bore may be used. Where the inner joint sleeve 9 has an external diameter greater than the external diameter of the inner layer of conductor wires this layer may be built up to the diameter of the sleeve 9 and a single split sleeve be used to connect the conductor wires of both layers of one length to those of the other length and to build up the inner joint diameter to that of the tubular conductor of each length. In place of one or more or the split tubes it) and 11, which are preferably of aluminum, a wrapping of sheet metal or a binding of wire may be used to effect a good electrical connection between the conductor wires surrounding the steel cores of the two lengths of overhead conductor and to build up the diameter of the core joint to the diameter of the tubular outer conductors.

The improved conductor, which has been found to be sufficiently flexible for the requirements of erection and service, has the advantage of providing a smooth circular form so as to avoid local electric stress concentrations. This form also minimises wind resistance. The improved construction also has the important advantage that the tubular outer part forms a complete enclosure which is continuous over the joints between lengths. This provides complete protection against the entry of moisture or gas which may corrode the internal strand or produce deterioration in the filling material. By appropriate choice of materials the construction will provide a conductor of light weight for a given diameter and conductivity. Corrosion of the tubular outer part may be retarded and its smooth surface maintained by the application of a cor rosion resistant coating to its external surface.

What we claim as our invention is:

1. An overhead line conductor for high voltage electric power transmission lines, comprising a steel cored aluminum wire strand having a continuous covering layer of fibrous filling material surrounding said strand, and a tube having a thin, gas-impervious wall of metal selected from the group consisting of aluminum and aluminum rich alloys of good electrical conductivity, said tube having a circumferentially continuous wall with a smooth circular continuous outer surface and fitting closely on and being supported in spaced co-axial relationship to said strand by said fibrous covering layer and forming a complete gas-tight and water-tight envelope for said fibrous covering layer and said strand.

2. An overhead line conductor for high voltage electric transmission lines, comprising a steel cored aluminum wire strand, helical lappings of paper tape disposed about said strand to form a supporting layer, and a thin walled tube of a metal selected from the group consisting of aluminum and aluminum rich alloys of good electrical conductivity, said tube having a circumferentially continuous wall with a smooth circular continuous surface and fitting closely on and being supported by said supporting layer in spaced co-axial relationship to said strand and forming a complete gas-tight and water-tight envelope for said supporting layer and said strand.

3. An overhead line conductor for high voltage electric transmission lines, comprising a steel cored aluminum wire strand, a continuous covering layer enclosing said strand and comprising cords of low density flexible, strong, nonmetallic material applied side by side over said strand with a long lay, a binder of short lay disposed about and securing said cords applied with a long lay, and a thin walled tube of a metal selected from the group consisting of aluminum and aluminum rich alloys of good electrical conductivity, said tube having a circumferentially continuous wall with a smooth circular continuous outer surface and fitting closely on and being supported by said covering layer in spaced co-axial relationship to said strand and forming a complete gas-tight and water-tight envelope for said covering layer and said strand.

4. An overhead line conductor for high voltage electric transmission lines, comprising a central metallic member comprising a steel cored aluminum wire strand a continuous covering layer comprising non-metallic filling material and surrounding said continuous covering layer a thin-walled tube of sheet metal of low density and good electrical conductivity and having a single longitudinally extending seam weld uniting the longitudinal edges of the sheet metal, said covering layer supporting said seam welded tube in spaced co-axial relationship to said central member and said tube having a smooth circular continuous outer surface and fitting closely on the covering layer and forming a complete gas-tight and Water-tight envelope for said covering layer and said central member.

(References on following page) 5 6 References Cited in the file of this patent FOREIGN PATENTS UNITED STATES PATENTS 503,044 Germany July 25, 1930 1,664,100 Austin Mar. 27, 1928 243,209 Switzerland Dec. 2, 1946 1,981,890 Zapf Nov. 27, 1934 5 959,407 France Sept. 26, 1949 1,992,656 Fletcher Feb. 26, 1935 3 Daniels Dec. 17, 1940 OTHER REFERENCES 2,342,736 Herzog et 29, 1944 Ser. No. 193,918, Schmitt (A. P. 0. published May 2,534,935 Wagner Dec. 19, 1950 18,1943.

2,589,507 Noyes 1952 10 Electrical Engineering, July 1948, pg. 645.

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