GB1585683A - Electric power cable conductors - Google Patents

Description

(54) ELECTRIC POWER CABLE CONDUCTORS (71) We, KABEL- UND METALL WERKE GUTEHOFFNUNGSHUTTE AKTIENGESELLSCHAFT, a body corporate organised under the laws of Germany of 271, Vahrenwalder Strasse, Hannover, Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - The present invention relates to electric power cable conductors. The conductors with which the invention is concerned include gas-insulated cable conductors consisting of a plurality of individual conductor elements. The invention also includes a conductor according to the invention when installed within a gasinsulated cable.

For power transmission, electric cables are used which have relatively large conductor cross-sections, appropriate to the purpose for which they are intended.

According to requirements, the insulation in these cables may be a solid material or gas insulation. Cables insulated with solid materials can have an insulation in the form of a layered dielectric, as is usual for example in the case of oil cables, or they may instead have an extruded insulation. These cables are commercially available for example as polyethylene insulated cables, the polyethylene being un-crosslinked or crosslinked. In the case of gas-insulated cables, one conductor, for example, can be disposed coaxially within a sheath, the space between the conductor and the sheath being filled with a high voltage resistant gas, e.g. sulphur hexafluoride, SFG.

Although these cables vary widely in construction, their conductors are in all cases heated under load, and so tend to expand in the longitudinal direction. This tendency to expand in the longitudinal direction becomes all the more pronounced as the working temperature of the cable rises, and the forces coming into play increase with the conductor thickness. The longitudinal expansion which tends to take place as a result of the heating of the conductor is liable to affect the sealing sleeves or other terminations of the cable, and may result in damage to or even destruction of the components of these terminations. However, it is not only the cable terminations which are in jeopardy, but also the non-rectilinear portions of a cable laid in a curved path, or at least not in a straight path, because here the forces coming into play have a transverse component.Thus in the case of gasinsulated cables having a conductor which is secured in a central position within the sheath by spacing components which are provided only at intervals, it is possible, when there is a rise in working temperature, that the spacing components, which may be composed for example of a synthetic resin material, may become excessively loaded, and be deformed or otherwise damaged by the forces coming into play as a result of longitudinal expansion being prevented, unless this effect of these expansion forces can be prevented or at least diminished.

It is an object of this invention to enable the above-mentioned forces occurring in certain cables to be reduced so that the risk of damage to the cable when it is in use can be substantially avoided.

The basis of the present invention is the proposition that the above-mentioned thermal expansion effects should be accommodated by providing for the conductors to accentuate an initial undulating configuration, when heated.

The invention will be explained in greater detail with reference to the accompanying diagrammatic drawings in which: Figure 1 is a fragmentary side view of a conductor assembly of a cable, of a construction in accordance with the invention.

Figure 2 is a cross-sectional view of an assembly similar to that of Figure 1, showing a plurality of conductor elements, however, instead of only a single conductor element, Figure 3 is a fragmentary side view of a conductor assembly of a cable, of another construction in accordance with the invention, having a plurality of conductor layers, and Figure 4 is a cross-sectional view of an assembly similar to that of Figure 3.

According to the invention, we provide an electric power cable conductor wherein one or more conductor elements, which are not wound around one another, are applied to an inner carrier in an undulating configuration, the conductor being of a layered construction employing corrugated tubes, and the one or more conductor elements applied in an undulating configuration being disposed in the annular space between two coaxial corrugated tubes, in one layer or a plurality of layers.

In the event of thermal expansion, the amplitude of the undulations of these elements is increased in a circumferential direction; no undesirable mechanical forces come into play in a longitudinal direction.

Despite the expansion of the conductor elements at operating temperatures or higher temperatures, therefore, damage to the cable itself, which may be a gasinsulated cable, or to its termination assemblies is avoided. It is particularly advantageous for the conductor elements to be meander-shaped, i.e. undulating, when, for example, the cable is of a construction wherein multiple-wire or solid conductor elements, which may have a rectangular cross-section, are applied on to the outer surface of a corrugated tube at a slight separation from one another in a peripheral direction, this providing an adequate distance for expansion accommodating purposes. A further corrugated tube can then be formed around the conductor elements to secure them in position.In the annular space between these two corrugated tubes, a deviation of the conductor elements in a sense corresponding to an accentuation of their undulating configuration at increased temperatures is then both possible and acceptable.

The present undulating configuration of the conductor elements does not necessarily require them to be disposed in only a single layer; thus it may be of advantage to dispose these conductor elements in a plurality of layers. The layers of the conductor elements, which may be ordinary round wires or elements of other crosssections, e.g. rectangular cross-section, are then preferably separated from one another by encircling strips, e.g. of synthetic resin material or of metal. Should this be particularly desirable, however, the layers can instead be separated from one another by longitudinally applied strips bent round into an encircling tubular configuration.

In order to produce a cable incorporating conductors according to the present invention, conductor elements preformed with the desired undulating configuration can be applied to the inner carrier, e.g.

by being pulled from storage drums and longitudinally fed to and laid on the inner carrier, which may be an inner tube, provided for example for a cooling medium. Instead, however, it is possible to provide the conductor elements with their undulating configuration while they are being applied to the inner carrier.

The inner carriers employed in the present invention may be tubular, or may instead be in the form of flexible spirals or coils, or other flexible carrier structures already familiar in cable technology.

In the conductor assembly of Figure 1, a corrugated tube 12, which is of metal, and which can be used to convey a cooling medium, serves as a carrier for a conductor element 11. The conductor element 11 is preformed with an undulating configuration so that the mechanical forces occurring at elevated working temperatures can, as indicated by the arrows, result only in a change in the amplitude of its undulations. The corrugated tube 12 is surrounded by a corrugated sheath 13, which is also of metal, and which, as clearly shown in Figure 2, can be used to provide a smooth outer surface of the conductor assembly.

Whereas only one conductor element 11 is shown in Figure 1, Figure 2 shows a plurality of solid cross-sectionally approximately rectangular conductor elements 11 which are distributed around the periphery of the corrugated tube 12, a gap 14 being provided between adjacent conductor elements 11 to allow the necessary freedom of movement of these conductor elements in a space between the two coaxial corrugated tubes 12 and 13.

If a conductor assembly constructed according to Figures 1 and 2 is to be used as an inner conductor, for example for a gas-insulated high-voltage cable, then around the outer corrugated sheath 13, insulating spacers can be provided, at predetermined intervals, which serve to centre the inner conductor assembly coaxially within an outermost sheath (not shown in Figures 1 and 2). The space between the outermost sheath and the sheath 13 is then filled with an insulating gas.

Also as an alternative to the embodiment shown in Figures 1 and 2, the inner conductor assembly can be constructed in a plurality of layers, as indicated in Figures 3 and 4. In this case, around an inner corrugated sheath 15, conductor elements 16 are applied in several layers, four in the case illustrated, the individual layers being separated by separating strips 17 of synthetic resin material, e.g. polyterephthalate-based material, or even of metal.

In the case illustrated, the strips 17 are wound helically with the high pitch shown in Figure 3 on to the underlying layer.

If necessary, this winding can instead be applied as a closed layer. For this purpose, the strips may either be wound with a helical overlap, or may be laid longitudinally around the underlying layer before the next layer of the undulatingly preformed conductor elements is applied.

The conductor elements 16 may have any desired cross-section, but in the case of a multi-layer structure, the cross-section is advantageously circular. Also in the conductor assembly shown in Figures 3 and 4, the inner corrugated sheath 15 may be used to convey a cooling medium if this should be needed to attain the desired performance of the cable.

A further possibility of improving the ability of the conductor elements to deviate, in the case of a multi-layer construction, is that of making the amplitude of the undulation of the conductor elements 16 vary according to the distance from the centre of the cable.

An outer corrugated sheath is shown at 18.

If the conductor elements should be too tightly held on to their support by an outer corrugated sheath, then it may also be advantageous to provide between the outermost layer of conductor elements and the outer corrugated sheath, or, in the case of a single-layer construction, between the single layer of conductor elements and the outer corrugated sheath, a conductive film or a conductive strip which will facilitate sliding between the adjacent layers.

WHAT WE CLAIM IS: 1. An electric power cable conductor wherein one or more conductor elements, which are not wound around one another, are applied to an inner carrier in an undulating configuration, the conductor being of a layered construction employing corrugated tubes, and the one or more conductor elements applied in an undulating configuration being disposed in the annular space between two coaxial corrugated tubes, in one layer or a plurality of layers.

2. A conductor according to claim 1, when installed within a gas-insulated cable.

3. A conductor according to claim 1 or 2, in which the one or more conductor elements applied in an undulating configuration are disposed in a plurality of layers.

4. A conductor according to claim 3, in which the said layers are separated from one another by encircling strips.

5. A conductor according to claim 1, substantially as described with reference to Figures 1, 2, 3 or 4 of the accompanying drawings.

6. A method of producing a conductor according to any of claims 1 to 5, wherein the conductor elements are given their undulating configuration while being applied to the inner carrier.

7. A method of producing a conductor according to any of claims 1 to 5, wherein the conductor elements are preformed with the desired undulating configuration before being applied to the inner carrier.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. between the outermost sheath and the sheath 13 is then filled with an insulating gas. Also as an alternative to the embodiment shown in Figures 1 and 2, the inner conductor assembly can be constructed in a plurality of layers, as indicated in Figures 3 and 4. In this case, around an inner corrugated sheath 15, conductor elements 16 are applied in several layers, four in the case illustrated, the individual layers being separated by separating strips 17 of synthetic resin material, e.g. polyterephthalate-based material, or even of metal. In the case illustrated, the strips 17 are wound helically with the high pitch shown in Figure 3 on to the underlying layer. If necessary, this winding can instead be applied as a closed layer. For this purpose, the strips may either be wound with a helical overlap, or may be laid longitudinally around the underlying layer before the next layer of the undulatingly preformed conductor elements is applied. The conductor elements 16 may have any desired cross-section, but in the case of a multi-layer structure, the cross-section is advantageously circular. Also in the conductor assembly shown in Figures 3 and 4, the inner corrugated sheath 15 may be used to convey a cooling medium if this should be needed to attain the desired performance of the cable. A further possibility of improving the ability of the conductor elements to deviate, in the case of a multi-layer construction, is that of making the amplitude of the undulation of the conductor elements 16 vary according to the distance from the centre of the cable. An outer corrugated sheath is shown at 18. If the conductor elements should be too tightly held on to their support by an outer corrugated sheath, then it may also be advantageous to provide between the outermost layer of conductor elements and the outer corrugated sheath, or, in the case of a single-layer construction, between the single layer of conductor elements and the outer corrugated sheath, a conductive film or a conductive strip which will facilitate sliding between the adjacent layers. WHAT WE CLAIM IS:

1. An electric power cable conductor wherein one or more conductor elements, which are not wound around one another, are applied to an inner carrier in an undulating configuration, the conductor being of a layered construction employing corrugated tubes, and the one or more conductor elements applied in an undulating configuration being disposed in the annular space between two coaxial corrugated tubes, in one layer or a plurality of layers.

2. A conductor according to claim 1, when installed within a gas-insulated cable.

3. A conductor according to claim 1 or 2, in which the one or more conductor elements applied in an undulating configuration are disposed in a plurality of layers.

4. A conductor according to claim 3, in which the said layers are separated from one another by encircling strips.

5. A conductor according to claim 1, substantially as described with reference to Figures 1, 2, 3 or 4 of the accompanying drawings.

6. A method of producing a conductor according to any of claims 1 to 5, wherein the conductor elements are given their undulating configuration while being applied to the inner carrier.

7. A method of producing a conductor according to any of claims 1 to 5, wherein the conductor elements are preformed with the desired undulating configuration before being applied to the inner carrier.