Medium-voltage or high-voltage electrical device

Abstract

The invention relates to an electrical device (1, 20, 30) comprising a semi-conductive cross-linked layer (3, 4, 5, 21, 22, 23, 31, 32) produced from a polymer composition comprising: at least one polymer A comprising at least one epoxy function, and a cross-linking agent B comprising at least one reactive function that can react with the epoxy function of said polymer A in order to allow the cross-linking of said polymer A, characterised in that the polymer composition also comprises an electrically conductive filler having a specific surface area BET of at least 100 m2/g according to the ASTM standard D 6556.

Claims

1. An electrical device (1, 20, 30) comprising a semiconductive crosslinked layer (3, 5, 21, 22, 31) obtained from a polymer composition comprising: at least one polymer A comprising at least one epoxy functional group; and a crosslinking agent B comprising at least one reactive functional group capable of reacting with the epoxy functional group of said polymer A in order to allow the crosslinking of said polymer A, characterized in that the polymer composition additionally comprises an electrically conductive filler having a BET specific surface area of at least 100 m.sup.2/g according to ASTM standard D 6556 (2014).

2. The electrical device as claimed in claim 1, characterized in that the electrical conductivity of the polymer composition is lower than the electrical conductivity of the crosslinked layer, and the electrical conductivity of the polymer composition is preferably at least 10 times lower than the electrical conductivity of the crosslinked layer.

3. The electrical device as claimed in claim 1 or 2, characterized in that the amount of said electrically conductive filler is sufficient to allow the polymer composition to undergo a dynamic percolation transition.

4. The electrical device as claimed in any one of the preceding claims, characterized in that the electrical conductivity of the crosslinked layer is at least 1.10.sup.−3 S/m measured at 25° C. under a direct current.

5. The electrical device as claimed in any one of the preceding claims, characterized that the polymer A is obtained from at least one olefin polymer.

6. The electrical device as claimed in any one of the preceding claims, characterized in that the polymer composition comprises more than 50 parts by weight of polymer A per 100 parts by weight of polymer(s) in the polymer composition.

7. The electrical device as claimed in any one of the preceding claims, characterized in that the gel content of the crosslinked layer, according to ASTM standard D 2765-01, is at least 50%.

8. The device as claimed in any one of the preceding claims, characterized in that the aspect ratio of the electrically conductive filler is at least 10.

9. The device as claimed in any one of the preceding claims, characterized in that the electrically conductive filler is a carbon filler.

10. The device as claimed in any one of the preceding claims, characterized in that the electrically conductive filler is chosen from among carbon blacks, carbon fibers, graphites, graphemes, fullerenes, carbon nanotubes, and a mixture thereof.

11. The device as claimed in any one of the preceding claims, characterized in that the polymer composition comprises at most 20.0 parts by weight of electrically conductive filler per 100 parts by weight of polymer A.

12. The device as claimed in any one of the preceding claims, characterized in that the polymer composition is an electrical insulator.

13. The device as claimed in any one of the preceding claims, the polymer composition additionally comprises a compound C comprising: at least one aromatic group; and a reactive group capable of interacting physically with the hydroxy functional group formed by the opening of said epoxy functional group during the crosslinking of polymer A.

14. The device as claimed in claim 13, characterized in that the reactive group of the compound C comprises a hydrogen atom.

15. The device as claimed in claim 13 or 14, characterized in that the reactive group of the compound C takes the form of a hydroxy group (OH) and/or an amine group (NH).

16. The device as claimed in any one of the preceding claims, characterized in that the polymer A comprises at least one compound chosen from among the glycidyl esters.

17. The device as claimed in any one of the preceding claims, characterized in that the polymer A comprises at most 10% by weight of epoxy functional group.

18. The electrical device as claimed in any one of the preceding claims, characterized in that the crosslinking agent B is a non-polymeric compound.

19. The device as claimed in any one of the preceding claims, characterized in that the reactive functional group of the crosslinking agent B is chosen from among an anhydride functional group, a carboxyl functional group and an amine functional group.

20. The device as claimed in any one of the preceding claims, characterized in that the crosslinking agent comprises an amine functional group and a carboxyl functional group.

21. The device as claimed in any one of the preceding claims, characterized in that the device is an electrical cable comprising an elongated electrically conductive element surrounded by said semiconductive crosslinked layer.

22. The device as claimed in claim 21, characterized in that the electrical cable comprises a first semiconductive layer (3) surrounding the elongated electrically conductive element (2), an electrically insulating layer (4) surrounding the first semiconductive layer (3), and a second semiconductive layer (5) surrounding the electrically insulating layer (4), the crosslinked layer being the first and/or the second semiconductive layer(s).

23. The device as claimed in any one of claims 1 to 20, characterized in that it is an accessory (20, 30) for an electrical cable, said accessory comprising said crosslinked layer (21, 22, 31).

24. The device as claimed in claim 23, characterized in that the accessory is a junction (20) or a termination (30) for an electrical cable.

Description

[0174] Other features and advantages of the present invention will become apparent in the light of the description of a non-limiting example of an electrical cable according to the invention, provided with reference to the figures.

[0175] FIG. 1 shows a schematic view in cross section of an electrical cable according to one preferred embodiment in accordance with the invention.

[0176] FIG. 2 shows a schematic view of an electrical device according to the invention, comprising a junction in longitudinal cross section, this junction surrounding the ends of two electrical cables.

[0177] FIG. 3 shows a schematic view of an electrical device according to a first variant of the invention, comprising a termination in longitudinal cross section, this termination surrounding the end of a single electrical cable.

[0178] For the sake of clarity, only those elements essential for the understanding of the invention have been represented schematically, this being done without observing a scale.

[0179] The medium- or high-voltage power cable 1, illustrated in FIG. 1, comprises an elongated central conductive element 2, in particular made of copper or of aluminum. The power cable 1 additionally comprises several layers positioned successively and coaxially around this conductive element 2, namely: a first semiconductive layer 3, referred to as the “inner semiconductive layer”, an electrically insulating layer 4, a second semiconductive layer 5, referred to as the “outer semiconductive layer”, an earthing and/or protective metal shield 6 and an external protective sheath 7.

[0180] The semiconductive layer 3 and/or the semiconductive layer 5 may be extruded and crosslinked layers obtained from the polymer composition according to the invention.

[0181] The electrically insulating layer 4 is also an extruded and crosslinked layer.

[0182] The presence of the metal shield 6 and of the external protective sheath 7 is preferential but not essential, this cable structure being as such well known to a person skilled in the art.

[0183] FIG. 2 shows a device 101 comprising a junction 20 surrounding, in part, two electrical cables 10a and 10b.

[0184] More particularly, the electrical cables 10a and 10b comprise an end 10′a and 10′b, respectively, which are intended to be surrounded by the junction 20.

[0185] The body of the junction 20 comprises a first semiconductive element 21 and a second semiconductive element 22 separated by an electrically insulating element 23, said semiconductive elements 21, 22 and said electrically insulating element 23 surround the ends 10′a and 10′b of the electrical cables 10a and 10b, respectively.

[0186] This junction 20 makes it possible to electrically connect the first cable 10a to the second cable 10b, in particular by virtue of an electrical connector 24 positioned at the center of the junction 20.

[0187] The first semiconductive element 21 and/or the second semiconductive element 22 may be molded and crosslinked layers obtained from the polymer composition according to the invention.

[0188] The first electrical cable 10a comprises an electrical conductor 2a surrounded by a first semiconductive layer 3a, an electrically insulating layer 4a surrounding the first semiconductive layer 3a, and a second semiconductive layer 5a surrounding the electrically insulating layer 4a.

[0189] The second electrical cable 10b comprises an electrical conductor 2b surrounded by at least one first semiconductive layer 3b, an electrically insulating layer 4b surrounding the first semiconductive layer 3b, and a second semiconductive layer 5b surrounding the electrically insulating layer 4b.

[0190] These electrical cables 10a and 10b may be those described in the present invention.

[0191] At said end 10′a, 10′b of each electrical cable 10a, 10b, the second semiconductive layer 5a, 5b is at least partially denuded in order for the electrically insulating layer 4a, 4b to be at least partially positioned inside the junction 20, without being covered with the second semiconductive layer 5a, 5b of the cable.

[0192] Inside the junction 20, the electrically insulating layers 4a, 4b are in direct physical contact with the electrically insulating element 23 and the first semiconductive element 21 of the junction 20. The second semiconductive layers 5a, 5b are in direct physical contact with the second semiconductive element 22 of the junction 20.

[0193] FIG. 3 shows a device 102 comprising a termination 30 surrounding a single electrical cable 10c.

[0194] More particularly, the electrical cable 10c comprises an end 10′c intended to be surrounded by the termination 30.

[0195] The body of the termination 30 comprises a semiconductive element 31 and an electrically insulating element 32, said semiconductive element 31 and said electrically insulating element 32 surrounding the end 10′c of the electrical cable 10c.

[0196] The semiconductive element 31 may be a molded and crosslinked layer obtained from the polymer composition according to the invention.

[0197] The electrical cable 10c comprises an electrical conductor 11c surrounded by a first semiconductive layer 3c, an electrically insulating layer 4c surrounding the first semiconductive layer 3c, and a second semiconductive layer 5c surrounding the electrically insulating layer 4c.

[0198] This electrical cable 10c may be that described in the present invention.

[0199] At said end 10′c of the electrical cable 10c, the second semiconductive layer 5c is at least partially denuded in order for the electrically insulating layer 4c to be at least partially positioned inside the termination 30, without being covered with the second semiconductive layer 5c of the cable.

[0200] Inside the termination 30, the electrically insulating layer 4c is in direct physical contact with the electrically insulating element 32 of the termination 30. The second semiconductive layer 5c is in direct physical contact with the semiconductive element 31 of the junction 30.

EXAMPLES

1. Crosslinkable Compositions

[0201] A comparative polymer composition C1, and comparative compositions I1 and I2 in accordance with the present invention, the amounts of the compounds of which are expressed as parts by weight per 100 parts by weight of the polymer(s), are collated in table 1 below, the colymer here being solely colymer/ecoxy.

TABLE-US-00001 TABLE 1 Polymer composition C1 I1 I2 Polymer/epoxy 100 100 100 Amino acid 0.75 0.75 0.75 Carbon black 43 0 0 Carbon nanotube 1 0 21.8 0 Carbon nanotube 2 0 0 41.5 Composition type Semiconductive Electrically Electrically composition insulating insulating composition composition

[0202] The percentage by weight of electrically conductive filler in the compositions C1, I1 and 12 is given in table 2 below.

TABLE-US-00002 TABLE 2 Polymer composition C1 I1 I2 Electrically 29.9 5.3 5.0 conductive filler (% by weight) Composition type Semiconductive Electrically Electrically composition insulating insulating composition composition

[0203] The compounds of table 1 have the following origins: [0204] polymer/epoxy is a copolymer of ethylene and glycidyl methacrylate (GMA) sold by Arkema under the reference Lotader AX8840, this copolymer comprising 8% by weight of GMA; [0205] amino acid is 11-aminoundecanoic acid sold by Sigma-Aldrich under the reference 11-Aminoundecanoic acid; [0206] carbon black is carbon black sold by Cabot under the reference Carbon Black VXC500, and has a BET specific surface area of 56 m.sup.2/g according to ASTM standard D 6556 (2014); [0207] carbon nanotube 1 is a masterbatch comprising approximately 30% by weight of multi-walled carbon nanotubes in a polyethene matrix, sold by Arkema under the reference Graphistrength CM4-30; these carbon nanotubes have the following characteristics: [0208] a BET specific surface area of approximately 250m.sup.2/g according to ASTM standard D 6556 (2014); [0209] a mean external diameter of 10 to 15 nanometers, measured by TEM; [0210] a length of 0.1 to 10 micrometers, measured by TEM; and [0211] an aspect ratio of the order of 100 to 1000. [0212] carbon nanotube 2 is a masterbatch comprising 17% by weight of multi-walled carbon nanotubes in an ethylene vinyl acetate (EVA) copolymer matrix, sold by Nanocyl under the reference Plasticyl EVA 2001; these carbon nanotubes have the following characteristics: [0213] a BET specific surface area of between 250 and 300 m.sup.2/g according to ASTM standard D 6556 (2014); [0214] a mean external diameter of approximately 10 nanometers, measured by TEM; [0215] a mean length of approximately 1 micrometer, measured by TEM; and [0216] an aspect ratio of the order of 100.

[0217] The compositions collated in table 1 are processed as follows.

In a first step: [0218] For the composition C1, the carbon black is first of all mixed with the molten polymer in an internal mixer of twin-screw or Buss type, then the crosslinking agent is incorporated. The addition of the crosslinking agent in a separate step subsequent to the addition of the carbon black makes it possible to prevent any premature crosslinking of the polymer composition which may occur subsequent to the increase in temperature brought about by the addition of the carbon black. The crosslinking agent is thus added to the filler-comprising mixture once the mixture has cooled to a temperature of less than 130° C. The homogeneous mixture thus obtained is subsequently granulated. [0219] For the compositions I1 and I2, the crosslinking agent and the masterbatch containing the carbon nanotubes are mixed together with the polymer in the molten state in an internal mixer of twin-screw or Buss type, the temperature within the mixer not exceeding 130° C. in order to prevent the opening of the epoxy functional group of the polymer and thus to prevent the crosslinking of the polymer. The homogeneous mixture thus obtained is subsequently granulated.

[0220] In a second step, the granules are subsequently introduced into a single-screw extruder and extruded at a maximum temperature of 130° C., in order to prevent any crosslinking of the polymer in the extruder.

[0221] The extrusion is carried out around a copper conductive wire with a cross section of 1.5 mm.sup.2. An electrical cable comprising an extruded and non-crosslinked layer in direct contact with the conductive wire is obtained.

[0222] In a third step, the extruded layer is crosslinked by heating at a temperature of 200° C., said electrical cable being passed inside a steam tube under a steam pressure of 15 bar.

3. Characterization of the Semiconductive Crosslinked Materials

[0223] Various properties of the materials obtained from the compositions of table 1 have been measured and collated in table 3 below.

[0224] These properties relate to: [0225] electrical conductivity, measured according to standard ISO 3915 under a direct current and at 25° C. before and after heat treatment at 200° C. (i.e. crosslinking), determined using a sourcemeter (source of current and voltage measurement) sold under the tradename 2611A by Keithley; [0226] the hot set test (HST), determined using an oven at 200° C. according to standard BS EN 608 11-2-1, and more particularly to elongation under load and set; and [0227] stress at break and elongation at break, determined using a dynamometer according to standard IEC 60811-1-1.

TABLE-US-00003 TABLE 3 C1 I1 I2 Electrical 2.0 * 10.sup.−1 9.0 * 10.sup.−12 6.8 * 10.sup.−9 conductivity (S/cm) before heat treatment at 200° C. Electrical 1.1 * 10.sup.−1 2.1 * 10.sup.−2  1.9 * 10.sup.−2 conductivity (S/cm) after heat treatment at 200° C. HST: elongation 30-40% 30-35% 15-30% under load (%) HST: set (%) 0-5% 0-5% 5% Stress at break 17.3 ± 0.6 14.3 ± 0.5 13.9 ± 0.3 (MPa) Elongation at 184 ± 19 309 ± 13 284 ± 12 break (%)