FR3086791A1 - CARBON-METAL MULTIBRIN CONDUCTIVE CORE FOR ELECTRIC CABLE - Google Patents

Abstract

The invention relates to an electric cable comprising a multi-strand conductive core and an insulating electric layer surrounding said multi-strand conductive core, said multi-strand conductive core comprising at least one metallic strand, and at least one non-composite carbon strand and / or having a conductivity. at least 0.1% IACS, its manufacturing process, and the use of said multi-strand conductive core in various types of cables

Description

CARBON-METAL MULTIBRIN CONDUCTIVE CORE FOR ELECTRIC CABLE

The invention relates to an electric cable comprising a multi-strand conductive core and an insulating electric layer surrounding said multi-strand conductive core, said multi-strand conductive core comprising at least one metal strand, and at least one non-composite carbon strand and / or having a conductivity at least 0.1% IACS, its manufacturing process, and the use of said multi-strand conductive core in various types of cables.

The invention typically applies, but not exclusively, to the field of low voltage (less than 6 kV) and / or medium voltage (especially from 6 to 45-60 kV) energy cables, whether they are direct current or alternative. The invention also applies to cables used in the field of transport, such as, for example, the automobile, railway, aeronautics or navigation; or in the field of automation or servo motors (industrial automation cables such as sensor cables on production lines, robot arm cables, etc.); electrical control cables, or heating cables.

In particular, the invention relates to a cable having a good compromise in terms of flexibility, mechanical strength, and electrical conductivity.

An electric cable generally comprises a conductive core, the role of which is to conduct the electric current, and one or more layers of insulating and / or protective materials surrounding said conductive core. Depending on the type of cable envisaged, the conductive core can be rigid or flexible.

Transport cables or cables for industrial automation conventionally comprise a flexible conductive core containing a plurality of metallic strands of copper or tinned copper, generally twisted to form a strand, and an insulating sheath surrounding said flexible conductive core, so as to increase the flexibility of said cables. In fact, the use of a flexible conductive core makes it possible to obtain a cable which is sufficiently flexible to be able to be easily installed in narrow places and / or corner spaces, which is particularly advantageous for transport cables. In addition, it makes it possible to better resist mechanical stresses (e.g. bending or fatigue stresses) which are particularly numerous in cables for industrial automation. However, such a conductive core has a high production cost, it is subject to corrosion problems induced by contact between the different metal strands, thus affecting its service life, and it does not have an optimized weight in a context. where we are always looking for lighter materials.

From EP1926108B1 is known an electrical control cable comprising a plurality of strands extending in the longitudinal direction of the cable, said strands being twisted to form a strand, only some of the strands of the strand being of electrically conductive material such as copper or copper clad aluminum, the rest of the strands being of a non-conductive material such as a polymer material chosen from a polyamide, a high tenacity polyester, and a polyetherimide. However, the electrical conductivity of such a cable is not sufficient. It is also known that conductors comprising aluminum strands and copper strands are particularly sensitive to galvanic corrosion in the presence of solutes.

The object of the present invention is therefore to provide an electrical cable having an improved electrical conductivity, while guaranteeing a reduction in weight, significantly reduced or even avoided galvanic corrosion, good mechanical strength, and good flexibility.

The first object of the invention is an electric cable comprising a multi-strand conductive core, and a polymer layer surrounding said multi-strand conductive core, said multi-strand conductive core comprising at least one elongated electrically conductive element, at least a first layer of electrically conductive strands surrounding said elongated electrically conductive element, and at least a second layer of electrically conductive strands surrounding said first layer, characterized in that said multi-strand conductive core comprises:

* at least one metallic strand, and * at least one non-composite carbon strand and / or having an electrical conductivity of at least 0.1% IACS approximately in direct current.

Indeed, the combination of at least one metallic strand and at least one non-composite carbon strand and / or having an electrical conductivity of at least about 0.1% IACS, within the multi-strand conductive core, allows to obtain a cable having an improved electrical conductivity, while guaranteeing a reduction in weight, reduced or even avoided galvanic corrosion, good mechanical strength and good flexibility, in particular allowing its use as a transport, electrical control cable or for industrial automation.

Carbonized strand (s)

The expression “carbon strand” means that the strand comprises carbon, preferably from 85 to 99.5% by weight approximately of carbon element, and more preferably from 90% to 99% by weight approximately of carbon element, relative to the total weight of said strand.

The carbon strand may include carbon fibers, carbon nanofibers, carbon nanotubes and / or graphene, or a mixture thereof.

The carbon strand preferably comprises carbon fibers, in particular continuous fibers. This thus optimizes the electrical conductivity of the electrical cable. Thanks to all of the carbon fibers, a carbon strand is obtained in which the orientation of the carbon fibers promotes electrical conduction. In particular, good electrical conductivity and good mechanical properties are maintained over the entire length of the strand, and thus of the electrical cable.

According to a preferred embodiment of the invention, the carbon strand consists of carbon fibers.

A carbon fiber is mainly composed of crystalline carbon atoms aligned more or less parallel to the axis of the carbon fiber. A carbon fiber generally comprises from 85 to 99.5% by weight approximately of carbon element, and preferably from 90% to 99% by weight approximately of carbon element, relative to the total weight of said carbon fiber. The carbon element content of the carbon fiber essentially depends on the stages of the process for manufacturing said fiber.

The carbon strand may comprise several thousand carbon fibers, in particular from 1000 to 96000 carbon fibers approximately, and preferably from 3000 to 24000 carbon fibers approximately.

The carbon strand may be in the form of a wick of carbon fibers. Indeed, several carbon fibers can be organized into carbon threads commonly known as "wicks". As examples of carbon fiber yarns or wicks, mention may be made of a 12000 carbon fiber yarn, called "12K".

Carbon fibers can be organized parallel to each other.

According to a preferred variant, the carbon fibers can be twisted or braided. The use of twisted fibers facilitates their handling, and improves their mechanical strength. The use of braided fibers allows better covering power, and increased mechanical resistance in several directions. Twisted fibers are preferred.

The carbon fibers may have a length ranging from approximately 100 m to 200 km, preferably ranging from approximately 100 m to 10 km, and more preferably ranging from approximately 100 m to 3 km.

The carbon fibers can have a diameter ranging from 0.5 μm to 100 μm, preferably ranging from 1 μm to approximately 50 μm, and more preferably ranging from 2 μm to approximately 10 μm.

The carbon strand may have a section ranging from 10 pm ² to 10 mm ² , preferably ranging from 0.1 mm ² to 5 mm ² approximately, and more preferably ranging from 0.2 mm ² to 3 mm ² approximately.

The carbon fibers of a carbon strand may include metallized and / or bare carbon fibers.

A metallized carbon fiber is a carbon fiber surrounded by one or more metallic layer (s). Metallized carbon fibers are carbon fibers surrounded (individually) by one or more metallic layer (s).

For example, some of the carbon fibers or all of the carbon fibers contained in the carbon strand are metallized. The presence of metallized fibers can increase the electrical conductivity of the carbon strand.

The metallic layer (s) of metallized carbon fibers can (at least) comprise at least one metal chosen from copper, nickel, zinc, tin, silver, aluminum, and one of their alloys.

By “alloy” is meant the combination or mixture of at least two metals, in particular chosen from those listed above.

Preferably, the metallic layer is of the same nature as the metallic strand (s), in particular in order to limit the risk of galvanic corrosion.

The metal layer can be directly in physical contact with the carbon fiber of the metallized carbon fiber.

The metal layer can be linked by physical and / or chemical interactions, preferably by covalent bonding, to the carbon fiber to allow good adhesion of the metal layer to the carbon fiber.

An intermediate layer called "adhesion" can be placed between the carbon fiber and the metal layer of the metallized carbon fiber, in particular in order to improve the adhesion of the metal layer around the carbon fiber. The intermediate layer may be a metallic layer, which may include one or more metals chosen from tin, nickel, copper, aluminum, silver, and one of their mixtures.

In the invention, the metal layer may have an average thickness of at least about 100 nm, and preferably at least about 500 nm. The metal layer may have an average thickness of at most 5 µm, and preferably at most about 1 µm. These thickness values given for the metal layer are not included in the carbon fiber diameter values indicated in the invention.

Preferably, the metal layer can have a constant thickness over the entire length of the carbon fiber. A constant thickness means that the thickness of the metallic layer can vary by approximately ± 30% relative to the average thickness of the metallic layer, preferably by ± 20% relative to the average thickness of the metallic layer, and more preferably ± 10% relative to the average thickness of the metal layer.

In the invention, the thickness of the metal layer can be adapted according to the nature of the metal or metals which it comprises and according to the desired conductivity. In particular, a metal layer comprising a metal having a low conductivity may be thicker than a metal layer comprising a metal having a higher conductivity.

The metallization of the carbon fiber can be carried out by a process chosen from electroplating, electroplating (known under Anglicism "electroplating"), electroplating without electric current (known under Anglicism "electroless plating") , vacuum thermal evaporation ("heated evaporation"), electron beam evaporation, sputtering, ion assisted deposition "). According to a preferred embodiment, the metallization of the carbon fiber (s) is carried out by electrodeposition.

The carbon strand preferably has a diameter ranging from 0.01 to 3 mm approximately, and more preferably ranging from 0.1 to 1.5 mm approximately.

The carbon strand preferably has a circular or substantially circular section (e.g. oval).

In the invention, the electrical conductivity of a material, expressed in% IACS (IACS corresponding to Anglicism "International Annealed Copper Standard"), is determined relative to the electrical conductivity at 20 ° C of pure annealed copper which is 5.8001xl0 ⁷ S / m. The electrical conductivity (S / m) characterizes the ability of a material to let the electrons it contains move freely under the effect of an electric field and therefore allow the passage of an electric current. The electrical conductivity in% IACS is a conductivity determined in direct current.

The carbon strand may have an electrical conductivity of up to approximately 2% IACS, preferably up to approximately 10% IACS, and preferably up to approximately 15% IACS, in particular when the carbon fibers comprise fibers of carbon metallic.

According to a preferred embodiment of the invention, the multi-strand conductive core comprises several carbon strands as defined in the invention.

When the multistrand conductive core comprises several carbon strands, each of the strands may comprise metallized and / or bare carbon fibers. Each carbon strand may then comprise a different number of metallized and / or bare carbon fibers, a different metal constituting the metallic layer of metallized carbon fibers, etc.

Carbon strand before an electrical conductivity of at least 0.1% IACS and / or non-composite

The carbon strand has an electrical conductivity of at least 0.1% IACS approximately in direct current, either it is a non-composite strand, or it has an electrical conductivity of at least 0.1% IACS in direct current and it is a non-composite strand.

According to a preferred embodiment of the invention, the carbon strand is non-composite and has an electrical conductivity of at least 0.1% IACS in direct current.

In the invention, the expression “non-composite” relating to the carbon strand means that the carbon strand does not comprise an organic polymer. In other words, a non-composite carbon strand is different from a carbon strand in which the carbon is mixed with (or impregnated with) at least one organic polymer. Indeed, the composite carbon strands as described in the prior art are non-conductive strands or strands having an insufficient electrical conductivity (i.e. electrical conductivity less than 0.1% IACS in direct current).

The carbon strand having an electrical conductivity of at least 0.1% IACS (and optionally non-composite) preferably has an electrical conductivity of at least 0.6% IACS approximately, preferably of at least 0.8% IACS approximately, and particularly preferably at least about 1% IACS, in direct current.

Metallic strands

In the inventive term, the expression "metallic strand" means that the strand comprises from 85 to 100% by weight of metal approximately, and preferably from 90 to 99% by weight of metal, compared to the total pcids of the metallic strand.

The metal strand may include at least one metal selected from copper, aluminum, silver, a copper alloy, an aluminum alloy, a silver alloy, and a mixture thereof.

The metal strand preferably has an electrical conductivity greater than or equal to 55% IACS, and more preferably ranging from 58 to 110% IACS approximately.

According to a preferred embodiment of the invention, the multi-strand conductive core comprises several metal strands as defined in the invention.

When the multi-strand conductive core comprises several metal strands, each of the strands may comprise a different metal or mixture of metals.

A metal strand preferably has a diameter ranging from 50 μm to approximately 3 mm, and more preferably ranging from 200 μm to approximately 1.5 mm.

The metal strand may have a cross section ranging from 2 μm ² to 10 mm ² , preferably ranging from 0.1 mm ² to 5 mm ² approximately, and more preferably ranging from 0.2 mm ² to 3 mm ² approximately.

Each of the metal strand (s) of the multi-strand conductive core may include one or more metal wires. This thus makes it possible to soften the multi-strand conductive core.

The metal strands are preferably of circular or substantially circular section (e.g. oval).

Multistrand conductive core

The multistrand conductive core preferably has an electrical conductivity of at least 30% IACS, preferably at least 70% IACS, and more preferably at least 95% IACS.

According to the invention, the multi-strand conductive core can have an electrical conductivity of at most 104% IACS.

The multi-strand conductive core includes uninsulated strands.

In the invention, the expression “non-insulated strands” means that each of said strands is free from an electrically insulating layer, in particular from an electrically insulating layer based on polymer (s) and / or ceramic (s).

Advantageously, all the strands of the multi-strand conductive core are uninsulated strands.

A strand of the multi-strand conductive core preferably has at least one surface of direct physical contact with another strand of the multi-strand conductive core which is adjacent to it.

The multi-strand conductive core preferably comprises twisted strands.

Advantageously, all the strands of the multi-strand conductive core are twisted, in particular to form a strand or a twist.

The multi-strand conductive core preferably has the shape of a strand, in particular comprising the elongated electrically conductive element, and the electrically conductive strands of the first and second layers.

The multi-strand conductive core in the form of a strand is preferably manufactured in a twisted configuration.

Furthermore, the strands twisted within the multistrand conductive core can be in a concentric ("concentric stranding"), random ("bunched stranding"), or corded ("rope stranding") configuration.

Several types of concentric constructions or configurations are appropriate such as the true concentric configuration (known under Anglicism "true concentric stranding"), the concentric configuration of constant pitch (known under Anglicism "equilay concentric stranding"), the concentric configuration unidirectional (known as “unidirectional concentric stranding”), and the unidirectional concentric configuration of constant pitch (known as “unilay concentric stranding”).

In the true concentric configuration, the central elongated electrically conductive element is surrounded by at least said first and second layers of electrically conductive strands laid helically in a geometric arrangement, with an alternating direction of pitch and an increasing length of step.

In the concentric configuration of constant pitch, the central elongate electrically conductive element is surrounded by at least said first and second layers of electrically conductive strands laid helically in a geometric arrangement, with an alternate pitch direction and a constant pitch length .

In the unidirectional concentric configuration, the central elongated electrically conductive element is surrounded by at least said first and second layers of electrically conductive strands laid helically in a geometric arrangement, with the same pitch direction and an increasing pitch length.

In the unidirectional concentric configuration and constant pitch, the elongated central electrically conductive element is surrounded by at least said first and second layers of electrically conductive strands laid helically in a geometric arrangement, with the same direction of pitch and the same length to not.

In the random configuration, the elongated electrically conductive member and the electrically conductive strands are more randomly arranged. Twisted in one operation, all strands have the same pitch direction and the same pitch length.

In the corded configuration, single strands are formed by an assembly of strands in a concentric or random configuration. The core is formed by assembling the strands into a concentric or random final configuration.

The multi-strand conductive core comprises at least two layers of electrically conductive strands.

The conductive core may further comprise one or more additional layers of electrically conductive strands. Thus, the electrically conductive strands (metallic strands and carbon strands) are distributed in the first and second layers, and in the additional layer or layers of electrically conductive strands.

The conductive core can comprise from 4 to 50 electrically conductive strands, and preferably from 10 to 40 electrically conductive strands.

According to a preferred embodiment of the invention, the multi-strand conductive core comprises only metal strands as defined in the invention, and non-composite carbon strands and / or having a conductivity of at least 0.1% IACS as defined in the invention.

The strands constituting the first layer (respectively of the second layer) are preferably of a shape such that said first layer (respectively said second layer) has an irregular surface. In other words, the strands constituting the first layer (respectively of the second layer) do not fit together to form a continuous envelope, or each of the strands constituting the first layer (respectively of the second layer) does not have a cross section of shape complementary to that of the constituent strands of the first layer (respectively of the second layer) which are adjacent thereto.

Thus, the multi-strand conductive core advantageously comprises interstices between the strands.

The elongated electrically conductive element of the multi-strand conductive core can be positioned in the center of the cable (i.e. central position).

The elongated electrically conductive element of the multi-strand conductive core can be a metallic strand as defined in the invention or a carbon strand as defined in the invention.

The elongated electrically conductive element of the conductive core is traversed like all the strands of the multi-strand conductive core (in particular of the first and second layers), by an electric current. In other words, it is different from a mechanical reinforcement element such as traditionally used in particular in OHL cables which is not traversed by an electric current.

According to a preferred embodiment of the invention, the multi-strand conductive core comprises a plurality of metal strands as defined in the invention, and a plurality of non-composite carbon strands and / or having a conductivity of at least 0, 1% IACS as defined in the invention.

The number of metallic strand (s) within the multi-strand conductive core is advantageously greater than or equal to the number of carbon strand (s). This ensures good electrical conductivity of the multi-strand conductive core.

According to a preferred embodiment of the invention, at least one of the first and second layers comprises x metallic strands and x 'carbon strands; and at least the other of the first and second layers comprises y carbon strands and y 'metal strands, so that:

* x> x ', and preferably x> x', * y> y ', and preferably y> y', and * x> 1, x '> 0, y> 1, and y'> 0, * x, x ', y and y' being whole numbers.

When x = x ′, the metal strands and the carbon strands are advantageously alternated within the layer.

When y = y ', the metal strands and the carbon strands are advantageously alternated within the layer.

When x> x 'and x' ψ 0, the carbon strands are uniformly distributed within the layer between the metal strands.

When y> y 'and y' has 0, the metal strands are uniformly distributed within the layer between the carbon strands.

The metal strands of the multi-strand conductive core preferably have a pitch length ranging from 2 to 32D, and more preferably from 8 to 16D, where D corresponds to the diameter of the layer.

The carbon strands of the multi-strand conductive core preferably have a pitch length ranging from 2 to 32D, and more preferably from 8 to 16D, where D corresponds to the diameter of the layer.

The pitch length corresponds to the distance required by a strand to complete a complete revolution around the diameter of the multi-strand conductive core.

The metallic and carbon strands may have sections of different sizes within the conductive core.

Polymer layer

In the invention, the multi-strand conductive core is surrounded by at least one polymer layer. The polymer layer therefore surrounds the first and second layers of electrically conductive strands. If other layer (s) of electrically conductive strands are present, the polymer layer surrounds the outermost layer of electrically conductive strands.

Preferably, the polymer layer is an electrically insulating layer. The term “electrically insulating layer” means a layer generally having an electrical conductivity of at most 1.10 ' ⁹ S / m (siemens per meter) (at 25 ° C).

The term “polymer layer” is understood to mean a layer comprising at least one polymer, the term “polymer” as such meaning generally homopolymer or copolymer (e.g. block copolymer, random copolymer, terpolymer, etc.).

In the invention, the polymer of the polymer layer is advantageously an olefin polymer (polyolefin) or, in other words, an olefin homo- or copolymer.

The polymer can be a thermoplastic or crosslinked polymer.

Preferably, the olefin polymer is a polymer of ethylene or propylene.

In a particular embodiment, the polymer layer comprises at least one polymer chosen from a linear low density polyethylene (LLDPE), a very low density polyethylene (VLDPE), a low density polyethylene (LDPE), a medium density polyethylene (MDPE) , a high density polyethylene (HDPE), a copolymer of ethylene and vinyl acetate (EVA), a copolymer of ethylene and butyl acrylate (EBA), methyl acrylate (EMA), of 2 -hexylethyl acrylate (2HEA), a copolymer of ethylene and alphaolefin, a copolymer of ethylene and propylene (EPR.), a polyurethane, a fluorinated polymer, a chlorinated polymer such as a polyvinyl chloride (PVC) , a polyphenylene oxide (PPO), a technical polymer, and a mixture thereof.

As an example of a copolymer of ethylene and of alpha-olefin, mention may, for example, be made of poly (ethylene-octene) (PEO).

As an example of copolymers of ethylene and propylene (EPR), mention may be made of terpolymers of ethylene propylene diene (EPDM).

The term “technical polymer” is intended to mean a polymer having improved properties, in particular chosen from a polyphenylethylene ether, a polyamide, a polyetheretherketone (PEEK), a polyimide, a fluorinated ethylene copolymer (FEP), a polyethylene furanoate (PEF), and one of their mixtures.

The polymer layer may also comprise at least one additive chosen from antioxidants, stabilizers, crosslinking agents, toasting retarders, crosslinking co-agents, processing-promoting agents such as lubricants or waxes , compatibilizers, coupling agents, charge stabilizers, and a mixture thereof.

Preferably, the polymer layer is a so-called “HFFR” layer. for anglicism "Halogen-Free Flame Retardant" according to standard IEC 60754 Parts 1 and 2 (2011).

The polymer layer may further comprise at least one filler. The filler of the invention can be a mineral or organic filler. It can be chosen from a flame retardant filler, an inert filler and one of their mixtures.

For example, the flame retardant filler is a hydrated filler, chosen in particular from metal hydroxides such as for example magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH). These flame retardant charges act mainly by physical means, decomposing in an endothermic manner (e.g. release of water), which has the consequence of lowering the temperature of the polymer layer and limiting the propagation of flames along the cable. We speak in particular of flame retardant properties, well known under Anglicism "flame retardant".

The inert filler can be chalk, talc, or clay (e.g. kaolin).

The polymer layer can be extruded.

The polymer layer can be crosslinked or uncrosslinked. Crosslinking can be carried out by conventional crosslinking techniques well known to those skilled in the art such as, for example, peroxide crosslinking and / or hydrosilylation under the action of heat; silane crosslinking in the presence of a crosslinking agent; crosslinking by electron beams, gamma rays, X-rays, or microwaves; crosslinking by photochemical means such as irradiation under beta radiation, or irradiation under ultraviolet radiation in the presence of a photoinitiator. The crosslinking is preferably carried out according to the silane crosslinking technique.

The polymer layer can have a thickness ranging from 10 μm to 2 mm, preferably from 100 μm to 1 mm, and more preferably from 100 μm to 700 μm.

The polymer layer surrounds the multi-strand conductive core.

According to a preferred embodiment of the invention, the polymer layer is in direct physical contact with the second layer of the multi-strand conductive core, and when the multi-strand conductive core comprises one or more layers of electrically conductive strands, the polymer layer is advantageously in direct physical contact with the outermost layer of electrically conductive strands of the multi-strand conductive core.

Electric cable

The electric cable can be a cable of the energy cable type, in particular low voltage or medium voltage, and preferably low voltage.

The electric cable of the invention may also comprise a mechanical armor, preferably in the form of a sheet or a ribbon of aluminum or steel, or in the form of a metallic or carbon braid.

The mechanical armor preferably surrounds the polymer layer.

Process

The second object of the invention is a method of manufacturing an electric cable in accordance with the first object of the invention, characterized in that it comprises at least the following steps:

i) manufacturing at least one non-composite carbon strand and / or having a conductivity of at least 0.1% IACS, ii) manufacturing at least one metallic strand, iii) assembling several strands obtained according to steps i) and ii), in order to form the first layer, and the second layer, around the elongated electrically conductive element, to obtain the multi-strand conductive core, and iv) extrude the polymer layer around the multi-strand conductive core formed in step iii) .

Step iii) is advantageously carried out by stranding or twisting.

Uses

The third object of the invention is the use of a multi-strand conductive core as defined in the first object of the invention, in a low voltage or medium voltage energy cable, in particular in the field of transport, industrial automation, electrical control cables, or heating cables.

More particularly, the multi-strand conductive core comprises at least one elongated electrically conductive element, at least a first layer of electrically conductive strands surrounding said elongated electrically conductive element, and at least a second layer of electrically conductive strands surrounding said first layer, characterized in what she understands:

* at least one metallic strand, and * at least one non-composite carbon strand and / or having an electrical conductivity of at least 0.1% IACS approximately in direct current.

The metallic strand, the non-composite carbon strand and / or having an electrical conductivity of at least 0.1% IACS approximately in direct current, and the elongated electrically conductive element are preferably as defined in the first object of the invention.

In particular, the multi-strand conductive core can be used in heating cables, in particular for heated seats, de-icing of roads or heating the floor of dwellings, in cables for articulated machine arms or other robotic solutions.

Other characteristics and advantages of the present invention will appear in the light of the description of nonlimiting examples of electric cables according to the invention, made with reference to FIG. 1 and FIG. 2.

FIG. 1 represents a cross-sectional view of a cable according to the state of the prior art and of three cables according to three embodiments of the invention.

FIG. 2 represents a cross-sectional view of four cables according to four other embodiments of the invention.

For reasons of clarity, only the essential elements for the understanding of the invention have been represented schematically, and this without respecting the scale.

Figure 1 shows a cross-sectional view of a cable 1 according to the prior art (Figure la), and according to three distinct embodiments of the invention (Figures lb, le, and ld).

In FIG. 1a, the electric cable 1a comprises a multi-strand conductive core comprising a central elongated electrically conductive element 2a in the form of a metal strand, a first layer comprising six metal strands 3a surrounding said central elongate electrically conductive element 2a, and a second layer comprising twelve metal strands 4a surrounding said first layer. The multi-strand conductive core is surrounded by a polymer layer 5a.

In FIG. 1b, the electric cable 1b comprises a multi-strand conductive core comprising an electrically conductive elongated central element 2b in the form of a non-composite carbon strand or having a conductivity of at least 0.1% IACS, a first layer comprising six metallic strands 3b surrounding said central elongated electrically conductive element 2b, and a second layer comprising twelve metallic strands 4b surrounding said first layer. The multi-strand conductive core is surrounded by a polymer layer 5b.

In FIG. 1c, the electric cable 1c comprises a conductive multi-strand core comprising an electrically conductive elongated central element 2c in the form of a non-composite carbon strand or having a conductivity of at least 0.1% IACS, a first layer comprising six metallic strands 3c surrounding said central elongated electrically conductive element 2c, and a second layer comprising six metallic strands 4c and six non-composite carbon strands or having a conductivity of at least 0.1% IACS 4c 'surrounding said first layer, said strands 4c and 4c 'being in alternate configuration. The multi-strand conductive core is surrounded by a polymer layer 5c.

In FIG. 1d, the electric cable 1d comprises a conductive multi-strand core comprising an electrically conductive elongated central element 2d in the form of a non-composite carbon strand or having a conductivity of at least 0.1% IACS, a first layer comprising six 3d metallic strands surrounding said central elongated electrically conductive element 2d, and a second layer comprising twelve non-composite carbon strands or having a conductivity of at least 0.1% IACS 4d surrounding said first layer. The multi-strand conductive core is surrounded by a polymer layer 5d.

Figure 2 shows a cross-sectional view of a cable 10 according to four separate embodiments of the invention (Figures 2a, 2b, 2c, and 2d).

In FIG. 2a, the electric cable 10a comprises a multi-strand conductive core comprising a central elongated electrically conductive element 20a in the form of a metal strand, a first layer comprising six carbon strands which are non-composite or have a conductivity of at least 0, 1% IACS 30a surrounding said central elongated electrically conductive element 20a, and a second layer comprising twelve metallic strands 40a surrounding said first layer. The multi-strand conductive core is surrounded by a polymer layer 50a.

In FIG. 2b, the electric cable 10b comprises a multi-strand conductive core comprising a central elongated electrically conductive element 20b in the form of a metal strand, a first layer comprising six carbon strands which are non-composite or have a conductivity of at least 0, 1% IACS 30b surrounding said central elongated electrically conductive element 20b, and a second layer comprising nine metallic strands 40b and three non-composite carbon strands or having a conductivity of at least 0.1% IACS 40b 'surrounding said first layer, each of carbon strands 40b 'being alternated with three metal strands 40b. The multi-strand conductive core is surrounded by a polymer layer 50b.

In FIG. 2c, the electric cable 10c comprises a conductive multi-strand core comprising an elongated central electrically conductive element 20c in the form of a non-composite carbon strand or having a conductivity of at least 0.1% IACS, a first layer comprising six non-composite carbon strands or having a conductivity of at least 0.1% IACS 30c surrounding said central elongated electrically conductive element 20c, and a second layer comprising nine metallic strands 40c and three non-composite carbon strands or having a conductivity of minus 0.1% IACS 40c 'surrounding said first layer, each of the carbon strands 40c' being alternated with three metal strands 40c. The multi-strand conductive core is surrounded by a polymer layer 50c.

In FIG. 2d, the electric cable 10d comprises a conductive multi-strand core comprising an electrically conductive elongated central element 20d in the form of a non-composite carbon strand or having a conductivity of at least 0.1% IACS, a first layer comprising three metallic strands 30d and three non-composite carbon strands or having a conductivity of at least 0.1% IACS 30d 'surrounding said elongated central electrically conductive element 20d, said strands 30d and 30d' being in alternating configuration, and a second layer comprising nine metallic strands 40d and three non-composite carbon strands or having a conductivity of at least 0.1% IACS 40d 'surrounding said first layer, each of the carbon strands 40d' being alternated with three metallic strands 40d. The multi-strand conductive core is surrounded by a polymer layer 50d.

Examples

In order to show the technical effects of the present invention, tests were carried out.

Formation of the conductive core

The example consists in preparing a multi-strand conductive core A1 comprising:

- an electrically conductive elongated central copper element 0.408 mm in diameter,

a first layer of electrically conductive strands surrounding said elongated electrically conductive element, and consisting of 3 metallic copper strands of 0.408 mm in diameter, and 3 strands of carbon fibers of 0.38 mm in diameter (3K fibers not metallized); and

a second layer of electrically conductive strands surrounding said first layer and consisting of 9 metallic copper strands of 0.408 mm in diameter, and 3 strands of carbon fibers of 0.38 mm in diameter (3K fibers not metallized), said strands being distributed according to the configuration as described in Figure 3 and explained below.

In FIG. 3, the electric cable 100 comprises a multi-strand conductive core comprising a central elongated electrically conductive element 200 in the form of a metal strand, a first layer comprising three metal strands 300 and three non-composite carbon strands or having a conductivity d 'at least 0.1% IACS 300' surrounding said central elongated electrically conductive element 200, said strands 300 and 300 'being in alternating configuration, and a second layer comprising nine metallic strands 400 and three non-composite carbon strands or having a conductivity 'at least 0.1% IACS 400' surrounding said first layer, each of the carbon strands 400 'being alternated with three metal strands 400. The multi-strand conductive core is surrounded by a polymer layer 500.

The multi-strand conductive core A1 according to the invention has been compared with a conductive core AO in which all the strands (19 strands: 1 + 6 + 12) are metallic copper strands of 0.408 mm in diameter, AO not making part of the invention.

The table below shows the mechanical and electrical performance of the two multi-strand conductive cores AO and Al.

Conductive soul Resistivity (Ω.ιτι) Conductivity (% IACS) Tensile strength (MPa) Linear mass (Kg / m) AO 1.702 x 10 ' ⁸ 101.3% 235 0.0191 Al 2,462 x 10 ' ⁸ 70.0% 277 0.0163

BOARD

The multistrand conductive core of the invention has better mechanical properties than a pure copper core, while guaranteeing a good conductivity of 70% IACS and a lower weight.

Claims (17)

1. Electric cable comprising a multi-strand conductive core, and a polymer layer surrounding said multi-strand conductive core, said multi-strand conductive core comprising at least one elongated electrically conductive element, at least one first layer of electrically conductive strands surrounding said elongate electrically conductive element, and at least a second layer of electrically conductive strands surrounding said first layer, characterized in that said conductive core comprises: * at least one metallic strand, and * at least one non-composite carbon strand and / or having an electrical conductivity in direct current of at least 0.1% IACS approximately. 2. Electric cable according to claim 1, characterized in that the carbon strand comprises carbon fibers. 3. Electric cable according to claim 1 or 2, characterized in that the carbon strand is in the form of a wick of carbon fibers. 4. Electric cable according to claim 2 or 3, characterized in that the carbon fibers comprise metallized and / or bare carbon fibers. 5. Electric cable according to claim 4, characterized in that the metallized carbon fibers are carbon fibers surrounded by one or more metallic layer (s), the metallic layer (s) of the fibers metallized carbon comprising at least one metal chosen from copper, nickel, zinc, tin, silver, aluminum, and one of their alloys. 6. Electric cable according to any one of the preceding claims, characterized in that the carbon strand has a diameter ranging from 0.01 to 3 mm. 7. Electric cable according to any one of the preceding claims, characterized in that the carbon strand is non-composite and has an electrical conductivity of at least 0.1% IACS. 8. Electric cable according to any one of the preceding claims, characterized in that the metal strand comprises at least one metal chosen from copper, aluminum, silver, a copper alloy, an aluminum alloy, a silver alloy, and one of their mixtures. 9. Electric cable according to any one of the preceding claims, characterized in that the metal strand has a diameter ranging from 50 μm to 3 mm. 10. Electric cable according to any one of the preceding claims, characterized in that the carbon strand and the metal strand have a circular section. 11. Electric cable according to any one of the preceding claims, characterized in that the multi-strand conductive core comprises non-insulated strands. 12. Electric cable according to any one of the preceding claims, characterized in that the multi-strand conductive core comprises twisted strands. 13. Electric cable according to any one of the preceding claims, characterized in that the multi-strand conductive core comprises a plurality of metal strands, and a plurality of non-composite carbon strands and / or having a conductivity of at least 0.1 % IACS. 14. Electric cable according to any one of the preceding claims, characterized in that the number of metal strand (s) within the conductive multi-strand core is greater than or equal to the number of carbon strand (s) ). 15. Electric cable according to any one of the preceding claims, characterized in that at least one of the first and second layers comprises x metal strands and x 'carbon strands; and at least the other of the first and second layers comprises y carbon strands and y 'metal strands, so that: * x> x ', and preferably x> x', * y> y ', and preferably y> y', * x> 1, x '> 0, y> 1, and y'> 0, and * x, x ', y and y' being whole numbers. 16. Method for manufacturing an electric cable as defined in any one of the preceding claims, characterized in that it comprises at least the following steps: i) manufacturing at least one non-composite carbon strand and / or having a conductivity of at least 0.1% IACS, ii) manufacturing at least one metallic strand, iii) assembling several strands obtained according to steps i) and ii), in order to form the first layer, and the second layer, around the elongated electrically conductive element, to obtain the multi-strand conductive core, and iv) extrude the polymer layer around the multi-strand conductive core formed in step iii) . 17. Use of a multi-strand conductive core as defined in any one of claims 1 to 15, in a low voltage or medium voltage energy cable, in particular in the field of transport, industrial automation, cables electrical control, or heating cables.