High voltage electric transmission cable

Abstract

An electric cable (10) includes at least one composite reinforcement element (1) including one or more reinforcement element(s) at least partially embedded in an organic matrix. A coating (2) surrounds the composite reinforcing element(s) (1). The coating (2) is sealed all around the composite reinforcing element(s) (1). At least one conducting element (3) surrounds the coating (2), where the thickness of the sealed coating (2) does not exceed 3000 m.

Claims

1. An over head cable comprising: at least one composite strength member having one or more reinforcing elements at least partly embedded in an organic matrix; a metal coating surrounding said at least one composite strength member, said metal coating welded directly to itself along its seams so as to be completely sealed tube all around the at least one composite strength member so that the sealed metal coating prevents thermal oxidation of the organic matrix of the at least one composite strength member along the cable; and at least one conducting element surrounding said sealed metal coating, said conducting element having an assembly of metal wires; wherein the electrical cable further comprises at least one electrically insulating layer positioned between the sealed metal coating and the composite strength member or members, and wherein the thickness of the sealed metal coating is between 150 and 3000 m so as to be sufficient to protect said composite strength member from environmental degradation and also thin enough to remain flexible enough such that said cable can operate as said over head cable.

2. The cable as claimed in claim 1, wherein the sealed metal coating is at least one metallic layer obtained by heat treatment of a metallic material.

3. The cable as claimed in claim 2, wherein the metallic layer is obtained by welding along the metallic material in the form of a strip.

4. The cable as claimed in claim 2, wherein the metallic layer is obtained by helical welding of the metallic material in the form of a tape.

5. The electrical cable as claimed in claim 2, wherein the metallic layer is annulate.

6. The cable as claimed in claim 2, wherein the metallic material is selected from the group consisting of steel, steel alloys, aluminum, aluminum alloys, copper and copper alloys.

7. The cable as claimed in claim 1, wherein the sealed metal coating is in the form of a tube.

8. The cable as claimed in claim 1, wherein the matrix of the composite strength member is chosen from a thermoplastic matrix and a thermosetting matrix, or a blend thereof.

9. The cable as claimed in claim 1, wherein the reinforcing elements of the composite strength member are selected from the group consisting of fibers, nanofibers and nanotubes, or a mixture thereof.

10. The cable as claimed in claim 1, wherein the electrically insulating layer surrounds the assembly formed by the at least one composite strength member.

11. The cable as claimed in claim 1, wherein the conducting element is based on aluminum.

12. The cable as claimed in claim 1, wherein the electrical cable comprises no external layer surrounding the at least one conducting element.

13. The cable as claimed in claim 1, wherein the welding of the metal coating is carried out by either one of laser welding or gas shielded arc welding.

14. The cable as claimed in claim 1, wherein said cable does not have an adhesive layer positioned between the composite strength member or members and the conducting element.

15. The cable as claimed in claim 1, wherein the conductive element is made of aluminum and zirconium alloy.

16. An over head cable comprising: at least one composite strength member having one or more reinforcing elements at least partly embedded in an organic matrix; a metal coating surrounding said at least one composite strength member, said metal coating is a sealed tube welded along all of its seams directly to itself all around the at least one composite strength member so that the coating has no openings along its length; and at least one conducting element surrounding said coating, said conducting element having an assembly of metal wires; wherein the electrical cable further comprises at least one electrically insulating layer positioned between the sealed metal coating and the composite strength member or members, and wherein the thickness of the sealed coating is between 150-3000 m so as to be sufficient to protect said composite strength member from environmental degradation and also thin enough to remain flexible enough such that said cable can operate as said over head cable.

17. The cable as claimed in claim 16, wherein the welding of the metal coating is carried out by either one of laser welding or gas shielded arc welding.

18. The cable as claimed in claim 16, wherein said cable does not have an adhesive layer positioned between the composite strength member or members and the conducting element.

19. The cable as claimed in claim 16, wherein the conductive element is made of aluminum and zirconium alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will become apparent in the light of the following examples with reference to the annotated figures, said examples and figures being given by way of illustration but implying no limitation.

(2) FIG. 1 shows, schematically and in perspective, an electrical cable according to the present invention.

(3) FIG. 2 shows, schematically and in perspective, the electrical cable of FIG. 1 to which an electrically insulating layer according to the invention has been added.

DETAILED DESCRIPTION

(4) For the sake of clarity, only the essential elements for understanding the invention have been shown schematically and have not been drawn to scale.

(5) The electrical cable 10 illustrated in FIG. 1 corresponds to a high-voltage electrical transmission cable of the OHL type.

(6) This cable 10 comprises a central composite strength member 1 and, in succession and coaxially around this composite member 1, a metal tube 2 made of aluminum and an electrical conducting element 3. The conducting element 3 is in direct contact with the metal tube 2, the latter being in direct contact with the composite strength member 1.

(7) The composite strength member 1 comprises a plurality of carbon fiber strands embedded in an epoxy thermosetting matrix.

(8) In this example, the conducting element 3 is an assembly of strands made of an aluminum-zirconium alloy, the cross section of each strand of which has a trapezoidal shape, these strands being twisted together. Said conducting element is therefore not in any way sealed from the external environment, and the strands that constitute it also move apart under the heat due to the thermal expansion of the conducting element.

(9) The metal tube 2 may be obtained from a metal strip converted into a tube with a longitudinal slit using a forming tool. The longitudinal slit is then welded, especially using a laser welding device or a gas-shielded arc welding device, after the edges of said strip are brought into contact with each other and held in place in order to be welded. During the welding step, the composite strength member may be on the inside of the metal strip converted into a tube. The diameter of the tube formed is then shrunk (reduction in cross section of the tube) around the composite strength member using techniques well known to those skilled in the art.

(10) As indicated above, other embodiments of this metal tube are possible. The metal tube 2 may be obtained from a metal tape helically wound around the composite strength member or a substitute. The helical slit of this metal tape is then welded, especially using a laser welding device or a gas-shielded arc welding device, after the edges of said tape have been brought into contact with each other and held in place in order to be welded. The abovementioned shrinkage step is also conceivable.

(11) The cable of FIG. 1 does not also include an outer jacket: the conducting element 3 is thus left directly in contact with its external environment (i.e. the ambient air). In the operational configuration of the cable (i.e. once the cable has been suspended between two pylons), the absence of an outer jacket advantageously enables the span of said cable between two pylons to be increased.

(12) FIG. 2 shows an electrical cable 20 according to the present invention, which is identical to the electrical cable 10 of FIG. 1 except for the fact that the cable 20 further includes a single electrically insulating layer 4 surrounding the composite strength member (i.e. all the composite strength members). This electrically insulating layer 4 is positioned between the metal tube 2 and the composite strength member 1. The cable 20 again does not include an outer jacket around the conducting element 3.

EXAMPLE

(13) To show the advantages of the electrical cable according to the invention, comparative aging and porosity tests were carried out on electrical cable specimens.

(14) A first electrical cable, called cable I1, was produced as follows. A composite strength member comprising an assembly of carbon fibers embedded in an epoxy resin thermosetting matrix was coated with an electrically insulating layer of PEEK followed by a sealed aluminum layer. The sealed aluminum layer was produced from an aluminum strip welded along its length so as to create a tube around the composite strength member. This aluminum tube was then shrunk around said composite member so as to form said sealed aluminum layer.

(15) A second electrical cable, called cable C1, corresponded to the cable I1 except that it did not include the sealed aluminum layer.

(16) The aging test was carried out on cables I1 and C1 respectively. This aging test consisted in leaving the cables I1 and C1 to age in ovens at various temperatures. The cable specimens were between about 65 cm and 85 cm in length.

(17) To prevent oxygen from propagating between the sealed aluminum layer and the composite strength member, the two ends of the specimen of cable I1 were covered with metal caps fixed using a Kapton cape and a Teflon tape so as to ensure that the ends of said specimen were sealed.

(18) These specimens were then isothermally aged at various temperatures (160, 180, 200 and 220 C.) for variable lengths of time (10, 18, 32, 60, 180 and 600 days).

(19) The aged specimens were weighed so as to monitor the weight loss associated with degradation of the thermosetting matrix. The porosity of the thermosetting matrix was also measured.

(20) Three cable portions about 2 cm in length were cut from the aged specimens one portion of each side of the ends about 2-3 cm from the edge and one portion in the center of the cable specimen.

(21) The cable portions were then potted in a resin, to make the polishing process easier, and then polished so as to obtain a very flat surface.

(22) This surface was then examined under an optical microscope, photographed and analyzed using image analysis software, making it possible to measure the area of the pores relative to the area of the specimen. The degree of porosity of the specimen was thus deduced therefrom.

(23) In view of the results obtained, the electrical cable according to the invention has significantly improved aging properties owing to the presence of the sealed metallic coating.