FR3048812A1 - ELECTRIC CABLE INTENDED FOR BURNING - Google Patents

Abstract

The present invention relates to an electrical cable comprising: - at least one elongated electrical conductor (1) surrounded by an electrically insulating layer (3), - a first polymeric protective sheath (6) surrounding the electrically insulating layer, characterized in that the electric cable further comprises a second polymeric protective sheath (7) surrounding the first polymeric protective sheath (6).

Description

Electric cable intended to be buried

The present invention relates to an electric cable to be buried.

It is typically, but not exclusively, applied to the fields of low-voltage (especially less than 6kV), medium-voltage (in particular 6 to 45-60 kV) or high-voltage (especially higher than 60) power cables. kV, and up to 800 kV), whether DC or AC.

The medium voltage power cables of the prior art typically comprise at least one elongate electrical conductor surrounded by the succession of following layers: a first semiconductor layer, an electrically insulating layer, a second semiconductor layer, a screen metal, and a polymeric protective sheath.

They can be classically buried, and as such different precautions must be taken not to damage this type of cable. As such, the burial of these cables of the prior art must follow a very restrictive burial method including burial to a minimum depth, a type of very specific covering material to not damage the cable with too much pressure important, such as sand.

In addition, it is well known that this type of cable also has a relatively high level of electrical loss. In particular, the maximum permissible intensity loss of the cable can be up to 10%.

The object of the present invention is to overcome the drawbacks of the prior art techniques by proposing an electric cable with a structure allowing it to be buried easily, in particular avoiding the constraints related to the current burial method, while limiting in a manner significant electrical losses.

The subject of the present invention is an electrical cable comprising: at least one elongated electrical conductor surrounded by an electrically insulating layer; a first protective polymeric sheath surrounding the electrically insulating layer, characterized in that the electric cable further comprises a second polymeric protective sheath surrounding the first polymeric protective sheath.

Thanks to the invention, the second polymeric protective sheath of the invention advantageously makes it possible to significantly limit the electrical losses in the cable of the invention, while facilitating its installation in the ground so as to be buried. The installation of the electric cable of the invention in a trench can be done in a very simple way, using directly the backfill material that has been output to dig the trench, without in particular needing sand to cover the electric cable.

In the present invention, the term "polymeric sheath" or "polymeric layer" means a sheath or layer comprising at least one polymer.

The second sheath

The second protective sheath of the invention may comprise at least two layers, and more particularly a first polymeric layer, called an "inner layer" surrounded by a second polymeric layer, called "outer layer", the first layer being different from the second layer.

Preferably, said first layer may be a non-crosslinked layer, or in other words a thermoplastic layer. More particularly, said first layer may be obtained from at least one thermoplastic polymer.

Said second layer may be a non-crosslinked layer, or in other words a thermoplastic layer. More particularly, said second layer may be obtained from at least one thermoplastic polymer.

In the present invention, the term "non-crosslinked layer" means a layer whose gel level according to ASTM D2765-01 (xylene extraction) is at most 20%, preferably at most 10%, preferably at most 5%, and particularly preferably 0%.

In a particular embodiment, the second layer of the second protective sheath is in direct physical contact with the first layer of the second protective sheath.

More particularly, the first and second layers of the second protective sheath can be manufactured by a conventional extrusion process, whether concomitantly (then referred to as coextrusion), successively (this is called tandem extrusion). , or in recovery (we speak then of extrusion in two distinct stages).

The first layer

The first polymeric layer of the second cladding may comprise at least a first olefin polymer.

In the present invention, the term "olefin polymer" means any type of polymer well known to those skilled in the art such as homopolymer or copolymer of olefin (e.g., block copolymer, random copolymer, terpolymer, etc.).

Preferably, the olefin polymer is a polymer of the thermoplastic type.

An olefin polymer is conventionally a polymer obtained from at least one olefin monomer.

Preferably, the olefin polymer may be an ethylene polymer, or in other words a polymer obtained from at least one ethylene monomer.

Said first olefin polymer may advantageously have a density strictly less than 0.935 g / cm 2, and preferably less than or equal to 0.925 g / cm 2. Preferably, the density of the first polymer is at least 0.910 g / cm 2.

In the present invention, the density of a polymer can be conventionally measured according to ISO 1183 (at a temperature of 23 ° C.).

The first olefin polymer may advantageously have a melt index (MFI) ranging from 0.1 to 5.0 g / 10 min, and preferably from 0.5 to 2.5 g / 10 min.

In the present invention, the melt index, known in English as MFI for "Melt Flow Index" or MFR for "Melt Flow Rate", is expressed in grams / 10 minutes ASTM D 1238 at 190 ° C / 2.16 kg.

The temperature (ie 190 ° C.) and the weight (ie 2.16 kg) mentioned in accordance with ASTM D 1238 respectively refer to the temperature of the sleeve and the die of the measuring apparatus, and to the total mass of the piston with load which presses the material to be measured to push it through the die of said apparatus.

According to a particular embodiment of the invention, the first layer may comprise more than 50% by weight of the first olefin polymer, preferably at least 70% by weight of the first olefin polymer, relative to the total weight of the the first layer. By way of example, the first olefin polymer may be chosen from linear low density polyethylene (LLDPE); a very low density polyethylene (VLDPE); low density polyethylene (LDPE); and one of their mixtures.

In a particular embodiment, the first polymeric layer may further comprise at least one lubricating agent. The lubricating agent advantageously allows the second protective sheath to limit its adhesion around the layer on which it is deposited (ie to limit the stickiness of the first layer of the second protective sheath), and in particular on the outer surface of the sheath. the first protective sheath, in order to be easily peelable during the installation of the electric cable. By way of example, the lubricating agent may be chosen from a polysiloxane, a fatty acid or a derivative thereof, and a mixture thereof.

The polysiloxane may be more particularly a polyorganosiloxane, such as polydimethylsiloxane (PDMS).

The fatty acid derivative may be more particularly a fatty amide acid, such as stearyl erucamide, ethylene bisolamide or ethylene bis-stearamide.

The first layer of the second protective sheath may comprise between 0.1% and 10.0% by weight of lubricating agent, and preferably between 1.0 and 5.0% by weight of lubricating agent, relative to total weight of the first layer.

The first layer of the second protective sheath may further comprise one or more charges.

The filler of the first layer may be a mineral or organic filler. It can be a fire-retardant filler and / or an inert filler (or non-combustible filler). By way of example, the flame retardant filler may be a filler selected from hydrated fillers, halogenated fillers, metalloid oxides, and a mixture thereof.

The hydrated fillers may be metal hydroxides, such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH).

The halogenated fillers can be, for example, chlorinated and brominated compounds.

The metalloid oxides may be, for example, antimony trioxide.

The inert filler can be, for its part, chalk, talc, clay (e.g., kaolin), carbon black, or carbon nanotubes.

The first layer may comprise at least 1% by weight filler (s), preferably at least 10% by weight filler (s), and preferably at most 50% by weight filler (s), relative to the weight total of the first layer.

The first layer of the second protective sheath may further comprise one or more additives.

The first layer may comprise an amount of additive (s) ranging from 0.1 to 20% by weight relative to the total weight of the first layer.

The additives are well known to those skilled in the art and may be chosen, for example, from: protective agents, such as antioxidants, anti-UV, anti-copper agents, water anti-tree agents, processing agents, such as plasticizers, lubricants, oils, compatibilizers, coupling agents, pigments, dyes, crosslinking catalysts, and a mixture thereof.

In a particular embodiment, the first layer may have a thickness of 0.1 to 2 millimeters (mm), and preferably 0.2 to 1.5 mm.

The second layer

The second polymeric layer of the second cladding may comprise at least one second olefin polymer, different from the first olefin polymer.

Said second olefin polymer may advantageously have a density greater than or equal to 0.935 g / cm 2, and preferably greater than or equal to 0.940 g / cm 3. Preferably, the density of the second polymer is at most 0.960 g / cm 2.

The second olefin polymer may advantageously have a melt index (MFI) ranging from 0.1 to 5.0 g / 10 min, and preferably from 0.6 to 1.4 g / 10 min.

According to a particular embodiment of the invention, the second layer may comprise more than 50% by weight of the second olefin polymer, preferably at least 70% by weight of the second olefin polymer, relative to the total weight of the second layer. By way of example, the second olefin polymer may be chosen from a medium-density polyethylene (MDPE); high density polyethylene (HDPE); and one of their mixtures.

The second layer of the second protective sheath may further comprise one or more charges.

The charge of the second layer may be a mineral or organic filler. It can be a fire-retardant filler and / or an inert filler (or non-combustible filler). By way of example, the flame retardant filler may be a filler selected from hydrated fillers, halogenated fillers, metalloid oxides, and a mixture thereof.

The hydrated fillers may be, for example, metal hydroxides, such as magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH).

The halogenated fillers can be, for example, chlorinated and brominated compounds.

The metalloid oxides may be, for example, antimony trioxide.

The inert filler can be, for its part, chalk, talc, clay (e.g., kaolin), carbon black, or carbon nanotubes.

The second layer may comprise at least 1% by weight of filler (s), preferably at least 10% by weight of filler (s), and preferably at most 50% by weight of filler (s), relative to the weight total of the second layer.

The second layer of the second protective sheath may further comprise one or more additives.

The second layer may comprise an amount of additive (s) ranging from 0.1 to 20% by weight relative to the total weight of the second layer.

The additives are well known to those skilled in the art and may be chosen, for example, from: protective agents, such as antioxidants, anti-UV, anti-copper agents, water anti-tree agents, processing agents, such as plasticizers, lubricants, oils, compatibilizers, coupling agents, pigments, dyes, crosslinking catalysts, and a mixture thereof.

In a particular embodiment, the second layer may have a thickness at least 1.5 times greater, preferably at least 2 times larger, and preferably at least 3 times greater, than the thickness of the first layer . By way of example, the thickness of the second layer may range from 0.3 to 6 millimeters (mm), and preferably from 0.5 to 2 mm.

The electric cable The invention finds a particularly advantageous, but not exclusive, application in the field of energy or telecommunication cables intended to be buried in the ground.

In a particularly preferred embodiment, the electrical cable of the invention may further comprise: - a first semiconductor layer surrounding the elongate electrical conductor, and being surrounded by the electrically insulating layer, - a second semiconductor layer surrounding the electrically insulating layer; - a metal screen surrounding the second semiconductor layer, the first protective sheath surrounding the metal screen.

More particularly, the assembly consisting of the first semiconductor layer, the electrically insulating layer and the second semiconductor layer form a so-called "three-layer" insulation, particularly typical of medium voltage and high voltage electrical cables.

The electric cable of the invention may comprise one or more elongated electric conductors.

The electrical conductor of the cable of the invention may be a single conductor such as for example a wire, or a multiconductor such as a plurality of metal son, twisted or not.

The elongated electrical conductor may be made from a metallic material chosen in particular from aluminum, an aluminum alloy, copper, a copper alloy, and one of their combinations.

The nominal cross-section of the electrical conductor may range from 0.5 mm to more than 1200 mm, and preferably from 50 mm to 240 mm. The nominal section of the electrical conductor can in particular be defined according to IEC 60228 (2004),

Preferably, all the layers of the electrical cable of the invention which are arranged around the elongate electrical conductor, are positioned coaxially with said electrical conductor.

The second protective sheath of the invention surrounds a set of layers well known to those skilled in the art, such as in particular the first semiconductor layer when it exists, the electrically insulating layer, the second semiconductor layer when it exists, the metal screen when it exists, and the first protective sheath.

In the present invention, the term "electrically insulating layer" or "electrically insulating composition" means a layer or a composition whose electrical conductivity may be less than or equal to 1.10® S / m (Siemens per meter), and preferably not more than 1.10 "'S / m (at 25 ° C).

In the present invention, the term "semiconductor layer" or "semiconductor composition" means a layer or composition whose electrical conductivity may be at least 1.10 S S / m (Siemens per meter), preferably at least 1.10% S / m, and preferably may be less than 1.10% S / m (at 25 ° C).

In a particular embodiment, the first and second semiconductor layers (where they exist) and the electrically insulating layer are polymeric layers, and preferably crosslinked polymeric layers by techniques well known to those skilled in the art.

In the present invention, a so-called "crosslinked" layer can easily be characterized by determining its gel level according to ASTM D2765-01. More particularly, said crosslinked layer may advantageously have a gel level, according to ASTM D2765-01 (xylene extraction), of at least 50%, preferably at least 70%, preferably at least 80% by weight. %, and particularly preferably at least 90%.

The first and second semiconductor layers (where they exist) and the electrically insulating layer may be obtained from at least one olefin polymer, in particular from at least one ethylene polymer. The metallic screen (when it exists) may be a conventional metal layer for connecting the electrical cable to the earth and / or protecting it.

The first protective sheath is a polymeric layer, and preferably a non-crosslinked layer.

The first protective sheath can be obtained from at least one olefin polymer, in particular from at least one ethylene polymer. By way of example, said olefin polymer may be chosen from a medium-density polyethylene (MDPE); high density polyethylene (HDPE); and one of their mixtures.

The first protective sheath may comprise fillers and / or additives as described in the second protective sheath.

In a particular embodiment, the first protective sheath may comprise at least two layers, in particular at least two non-crosslinked layers.

The first and second semiconductor layers (where present), the electrically insulating layer, and the first protective sheath may be extruded layers by techniques well known to those skilled in the art.

Another object of the invention relates to an electrical device, intended in particular to be buried, comprising at least two electric cables according to the invention, and preferably at least three electric cables according to the invention. The constituent cables of said electrical device may advantageously be twisted together. This is called a twist assembly. The assembly by twist is performed around the longitudinal axis of the electrical device formed by all the electrical cables of the invention. Other features and advantages of the present invention will become apparent in the light of the description of non-limiting examples of an electric cable according to the invention, with reference to the figures.

Figure 1 shows a schematic cross-sectional view of an electric cable according to the invention.

For the sake of clarity, only the essential elements for understanding the invention have been shown schematically, and this without respect of the scale.

The medium-voltage electrical cable, illustrated in FIG. 1, comprises an elongate central conducting element 1, in particular made of copper or aluminum, comprising a plurality of metal wires, with a nominal cross-section of 240 mm 2.

The electric cable further comprises several layers arranged successively and coaxially around this conductive element 1, namely: a first semiconductor layer 2 called an "internal semiconducting layer", obtained from a marketed semiconducting composition by the company Dow Chemicals under the reference HFDK-0586BK, - an electrically insulating layer 3, obtained from an electrically insulating composition marketed by Borealis under the reference LS4201S, - a second semiconductor layer 4 called "semi-layer - external conductor ", obtained from a semiconductor composition marketed by Dow Chemicals under the reference HFDA-0792BK, - a metal screen 5 grounding, the type of aluminum strip marketed by the company Amcor under the reference Aluthene 150V, a first protective sheath 6, obtained from a polymer of high density ethylene marketed by Dow Chemicals under the reference DGDK-6862NT in which additives and fillers have been conventionally added, and a second protective sheath 7 according to the invention.

The second protective sheath 7 comprises: a first layer 7a of which an exemplary composition is given in Table 1 below, and a second layer 7b of which an example of composition is given in Table 2 below, the first layer 7a being directly in physical contact with the second layer 7b.

The layers 2, 3, 4 are conventional layers, extruded and crosslinked by techniques well known to those skilled in the art.

The first protective sheath is a conventional non-crosslinked layer and extruded by techniques well known to those skilled in the art.

The layers 7a and 7b according to the invention are non-crosslinked layers (i.e. thermoplastic layers), extruded by techniques well known to those skilled in the art.

Example of realization

Table 1

Table 2

The first and second layers forming the second protective sheath detailed in Tables 1 and 2 respectively are extruded using a single-screw extruder (Diameter (D) / Single-screw length: 100 / 24D), with a standard temperature profile. ranging from 180 ° C to 240 ° C. The extrusion of the first and second layers forming the second sheath can be carried out around an electric cable comprising for example the elements 1 to 6 as described in FIG. 1. It can be done by extraditing concomitantly (ie by coextrusion) layers 7a and 7b.

The thicknesses formed in this embodiment are as follows: 0.6 mm thick for the first layer of the second sheath, and 1.8 mm for the second layer of the second sheath.

Claims (15)

An electric cable comprising: at least one elongated electrical conductor (1) surrounded by an electrically insulating layer (3), a first polymeric protective sheath (6) surrounding the electrically insulating layer, characterized in that the electrical cable comprises in addition, a second polymeric protective sheath (7) surrounding the first polymeric protective sheath (6). 2. Cable according to claim 1, characterized in that the second protective sheath (7) comprises a first polymeric layer (7a) surrounded by a second polymeric layer (7b). 3. Cable according to claim 2, characterized in that the first layer (7a) comprises at least a first olefin polymer. 4. Cable according to claim 3, characterized in that the first olefin polymer has a density strictly less than 0.935 g / cm ^. 5. Cable according to claim 3 or 4, characterized in that the first olefin polymer has an MFI ranging from 0.1 to 5.0 g / 10min. Cable according to any one of claims 3 to 5, characterized in that the first layer (7a) comprises more than 50% by weight of the first olefin polymer, preferably at least 70% by weight of the first polymer of Oiefine, based on the total weight of the first layer. 7. Cable according to any one of claims 2 to 6, characterized in that the first layer (7a) further comprises at least one lubricating agent. 8. Cable according to claim 7, characterized in that the lubricant is selected from a polysiloxane, a fatty acid or a derivative thereof, and a mixture thereof. 9. Cable according to any one of claims 3 to 8, characterized in that the second layer (7b) comprises at least a second olefin polymer, different from the first olefin polymer. 10. Cable according to claim 9, characterized in that the second olefin polymer has a density greater than or equal to 0.935 g / cm 2. Cable according to claim 9 or 10, characterized in that the second olefin polymer has an MFI ranging from 0.1 to 5.0 g / 10 min. Cable according to any one of claims 9 to 11, characterized in that the second layer (7b) comprises more than 50% by weight of the second olefin polymer, preferably at least 70% by weight of the second polymer of Oiefine, based on the total weight of the second layer. 13. Cable according to any one of the preceding claims, characterized in that the first protective sheath (6) comprises at least two layers. 14. Cable according to any one of the preceding claims, characterized in that the electric cable further comprises: - a first semiconductor layer (2) surrounding the elongate electrical conductor (1), and being surrounded by the electrically insulating layer (3), - a second semiconductor layer (4) surrounding the electrically insulating layer (3), - a metal screen (5) surrounding the second semiconductor layer (4), the first protective sheath (6) surrounding the metal screen (5). 15. Electrical device comprising at least two electrical cables according to any one of the preceding claims, the electrical cables of the electrical device being twisted together.