FR2972561A1 - ELECTRICAL CABLE WITH MEDIUM OR HIGH VOLTAGE - Google Patents

Abstract

The present invention relates to a cable (1) comprising an elongate conductive element (2) surrounded by at least one polymeric layer (3, 4, 5), characterized in that said polymeric layer (3, 4, 5) is a non-conductive layer crosslinked material obtained from a composition comprising at least one polyolefin-type thermoplastic polymer having a capillary viscosity (η) of between 11000 Pa.s at 170 ° C. and 5000 Pa.s at 230 ° C., with a shear of 0 , 1 s-1.

Description

The present invention relates to a cable comprising an elongate conductive element surrounded by at least one polymeric layer.

It applies typically, but not exclusively, to the fields of medium-voltage (in particular 6 to 45-60 kV) or high-voltage (in particular greater than 60 kV, and up to 800 kV) energy cables. , whether DC or AC. The medium or high voltage energy cables comprise at least typically a central electrical conductor and, successively and coaxially around this electrical conductor, a semiconducting inner layer, an electrically insulating intermediate layer, a semiconducting outer layer. In operational configuration, the power cables have a normal operating temperature related to the maximum temperature of the electrical conductor that composes them. According to the IEC 60840 standard of 2004, Table 1 on page 62, the maximum temperatures of the electrical conductor can range from 70 ° C to 90 ° C. At 70 ° C., the insulating materials recommended are non-crosslinked insulators of the low-density thermoplastic polyethylene type. At 80 ° C., the insulating materials recommended are non-crosslinked insulators of the high-density thermoplastic polyethylene type. Finally, at 90 ° C, the recommended insulators are insulators of the crosslinked polyethylene type, or elastomer of ethylene and propylene. An improperly used insulator, such as a low or high density thermoplastic polyethylene used as an insulating layer in cables with maximum temperatures of 90 ° C, would induce problems of mechanical deformation of the insulation material and therefore risk of electrical breakdown of the cable in question. To date, no existing polyolefin type insulation makes it possible to have a holding at 90 ° C in operational configuration, while being easy to implement and recyclable. The object of the present invention is to overcome the drawbacks of the prior art techniques by providing a polymer cable layer ensuring good mechanical properties at high temperature (e.g. at least 90 ° C) while being easy to implement. The present invention relates to a cable comprising an elongated conductive element surrounded by at least one polymeric layer, characterized in that said polymeric layer is a non-crosslinked layer obtained from a composition comprising at least one thermoplastic polymer of polyolefin type having a capillary viscosity (n) of between 11000 Pa.s at 170 ° C. and 5000 Pa.s at 230 ° C., with a shear of 0.1 s -1, preferably a capillary viscosity (n) of between 10800 Pa at 170 ° C. and 5300 Pa.s at 230 ° C., with a shear of 0.1 s -1, and particularly preferably a capillary viscosity (n) of between 10300 Pa.s at 170 ° C. and 5700 Pa. Pa.s at 230 ° C, with a shear of 0.1 s-1 According to one particular embodiment, the capillary viscosity may furthermore be at most 0.80 Pa.s at 170 ° C. and at 230 ° C. C, with a shear of 106 s-1 and a capillary viscosity of between 0.60 and 170 ° C and 0.50 at 230 ° C, with a shear of 106 s-1. According to another particular embodiment, the capillary viscosity may also be between 280 Pa.s at 170 ° C. and 210 Pa.s at 230 ° C., with a shear of 103 s-1, and preferably the capillary viscosity. is between 260 Pa.s at 170 ° C and 220 Pa.s at 230 ° C, with a shear of 103 s-1. The Applicant has surprisingly found that the polyolefin thermoplastic polymer of the invention, used as a non-crosslinked cable layer, advantageously enables the requirements of the 130 ° C hot pressure test to be met, according to the IEC standard. 60811-3-1 paragraph 8. The polymeric layer of the invention thus has the advantage of ensuring good mechanical properties at high temperatures, especially at temperatures of 90 ° C or more. It can therefore be applied to power cables that have an operating temperature of 90 ° C, in operational configuration. In addition, the polymeric layer of the invention is easy to implement, especially by conventional extrusion techniques well known to those skilled in the art.

The polymeric layer of the invention is a thermoplastic layer, or in other words a so-called "non-crosslinked" layer: it is therefore easily recyclable at the end of its life. In the context of the invention, capillary viscosity measurements (n), corresponding to the flow resistance, are carried out in accordance with ISO 11443: 2005 or ASTM D3835-08. For applications in the field of cabling, where the shear is generally between 0.1 and 106 s -1 in the tools, the capillary viscosity is conventionally determined using a capillary rheometer. The thermoplastic polyolefin of the invention of the invention may be an olefin homopolymer or an olefin copolymer. Polyethylene will preferably be used as the polyolefin. By way of example of polyethylene, mention may be made of linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE) and ethylene copolymers. and vinyl acetate (EVA), copolymers of ethylene and butyl acrylate (EBA), methyl acrylate (EMA), 2-hexylethylacrylate (2HEA), copolymers of ethylene and alpha-olefins such as, for example, polyethylene octene (PEO), or terpolymers of ethylene propylene diene (EPDM), and a mixture thereof. It will be preferred to use a homopolymer of ethylene, and especially a high density ethylene homopolymer, which is preferably connected. According to a first feature, the density of the thermoplastic polymer is at least 941 kg / m3 at 23 ° C, and preferably at least 950 kg / m3 at 23 ° C (according to ISO 1183 / A). We speak conventionally of high density polymer. According to a second characteristic, the melting temperature of the thermoplastic polymer may be at least 130 ° C, and preferably at least 134 ° C. The melting temperature of said polymer can typically be determined by differential scanning calorimetry (DSC) according to ISO 11357-3, with a temperature ramp of 10 ° C / min under inert atmosphere, after a second heating cycle, well known of the skilled person, in order to obtain the most accurate melting temperature possible.

According to a third characteristic, the ratio of the weight-average molecular weight (Mw) of the thermoplastic polymer to the number-average molecular weight (Mn) of the thermoplastic polymer may range from 3 to 30, and preferably from 5 to 7.

According to a fourth characteristic, the weight-average molecular weight (Mw) can range from 142,000 to 152,000 daltons (Da). According to a fifth characteristic, the number-average molecular mass (Mn) can range from 24800 to 26700 daltons (Da). According to a sixth characteristic, the melt flow index (MFI) of the thermoplastic polymer may range from 0.1 to 2.0 g / 10 min (190 ° C./2.16 kg according to ISO 1133), and preferably from 0.7 and 1.1 g / 10 min (190 ° C / 2.16 kg according to ISO 1133). According to a seventh characteristic, the thermoplastic polymer is a monomodal polyolefin. A monomodal polyolefin is a polyolefin the distribution of its molecular weight is monomodal, that is to say that said polyolefin comprises only one type of polyolefin fraction. Each of the seven features mentioned above, taken alone or in combination, can be combined with the characteristic of capillary viscosity specific to the thermoplastic polymer of the invention.

More particularly, the characteristic of capillary viscosity specific to the thermoplastic polymer of the invention can be combined with at least one of said seven characteristics, preferably at least two of said seven characteristics, preferably at least three of said seven characteristics, preferably at least at least four of said seven features, preferably at least five of said seven features, preferably at least six of said seven features, and particularly preferably said seven features. The composition of the invention is a thermoplastic composition, and may comprise more than 50.0 parts by weight of thermoplastic polymer per 100 parts by weight of polymer (s) (ie polymer matrix) in the composition, preferably at least 70 parts by weight of thermoplastic polymer per 100 parts by weight of polymer (s) in said composition, and particularly preferably at least 90 parts by weight of thermoplastic polymer per 100 parts by weight of polymer (s) in said composition. Particularly advantageously, the composition of the invention comprises a polymer matrix which is composed only of the thermoplastic polymer of the invention or a mixture of thermoplastic polymers including the thermoplastic polymer of the invention. In a particularly preferred manner, all the polymers used in the composition of the invention are one or more thermoplastic polymers of polyolefin type as defined in the invention.

The composition according to the invention may further comprise at least one protective agent such as an antioxidant. Antioxidants help to protect the composition of the heat stress generated during cable manufacturing or cable operation.

The antioxidants are preferably chosen from: hindered phenolic antioxidants such as tetrakismethylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate) methane, octadecyl 3- (3,5-di-t) -butyl-4-hydroxyphenyl) propionate, 2,2'-thiodiethylene bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,2'-thiobis (6-t- butyl-4-methylphenol), 2,2'-methylenebis (6-t-butyl-4-methylphenol), 1,2-bis (3,5-di-t-butyl-4-hydroxyhydrocinnamoyl) hydrazine, [2,2'-oxamido-bis (ethyl 3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate), and 2,2'-oxamido-bis [ethyl 3- (t-butyl) -4 hydroxyphenyl) propionate]; thioethers such as 4,6-bis (octylthiomethyl) -o-cresol, bis [2-methyl-4- {3-n-alkyl (C 12 or C 14) thiopropionyloxy} -5-t-butylphenyl] sulfide and Thiobis- [2-t-butyl-5-methyl-4,1-phenylene] bis [3- (dodecylthio) propionate]; sulfur-based antioxidants such as Dioctadecyl-3,3'-thiodipropionate or Didodecyl-3,3'-thiodipropionate; phosphorus-based antioxidants such as phosphites or phosphonates, for example Tris (2,4-di-t-butyl-phenyl) phosphite or bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite; and amine antioxidants such as polymerized 2,2,4-trimethyl-1,2 dihydroquinoline (TMQ), the latter type of antioxidant being particularly preferred in the composition of the invention. The TMQ can have different grades, namely: a "standard" grade with a low degree of polymerization, that is to say with a residual monomer level greater than 1% by weight and having a residual NaCl content ranging from 100 ppm to more than 800 ppm (parts per million by mass); a so-called "high degree of polymerization" grade with a high degree of polymerization, that is to say with a residual monomer content of less than 1% by weight and having a residual NaCl content ranging from 100 ppm to more than 800 ppm; a so-called "low residual salt" grade with a residual NaCl content of less than 100 ppm.

The type of stabilizer and its level in the composition of the invention are conventionally chosen as a function of the maximum temperature experienced by the polymers during the production of the mixture and during the extrusion operation on the cable as well as according to the maximum duration of exposure to this temperature.

The composition may typically comprise from 0.1% to 2% by weight of antioxidant (s). Preferably, it may comprise at most 0.7% by weight of antioxidant (s), especially when the antioxidant is TMQ. Other additives and / or other fillers well known to those skilled in the art may also be added to the composition of the invention such as scorch retarders; agents promoting implementation such as lubricants or waxes; compatibilizing agents; coupling agents; UV stabilizers; non-conductive charges; electrically conductive charges; semiconductor charges; and / or halogen-free inorganic fillers for improving the fire behavior of the composition. In order to guarantee an electric cable called "HFFR" for the anglicism "Ha / ogen Free Delayed Rame", the cable of the invention preferably does not include halogenated compounds. These halogenated compounds can be of any kind, such as, for example, fluorinated polymers or chlorinated polymers such as polyvinyl chloride (PVC), halogenated plasticizers, halogenated mineral fillers, etc.

The cable of the invention may be an energy and / or telecommunication cable, such as an electrical and / or optical cable, intended for the transmission of energy and / or the transmission of data. Thus, the elongated conductive element may be one or more electrical conductor (s) and / or optical (s).

The polymeric layer may be a layer in direct physical contact or not with the electrical conductor (s) and / or optical (s). It can also be a protective sheath surrounding one or more electrically isolated conductor (s) and / or optic (s). The polymeric layer of the invention is preferably an extruded layer by techniques well known to those skilled in the art. In a particularly preferred embodiment, the cable of the invention is an electric cable type energy cable. In this case, the cable of the invention may comprise in particular a first semiconductor layer surrounding the elongated conductive element, a second electrically insulating layer surrounding the first layer, and a third semiconductor layer surrounding the second layer, a of these three layers being the non-crosslinked layer of the invention. Preferably, the non-crosslinked layer of the invention is the electrically insulating layer (i.e. second layer). In the case of the electrically insulating layer, the composition of the invention does not comprise an (electrically) conductive filler and / or does not comprise a semiconductor filler. More particularly, at least two of the three layers of the cable are uncrosslinked layers, and preferably the three layers of the cable are uncrosslinked layers. When the composition of the invention is used for the manufacture of the semiconductor layers (first layer and / or third layer), the composition further comprises at least one (electrically) conductive filler or a semiconductor filler, in an amount necessary and sufficient to render the semiconductor composition. It is more particularly considered that a layer is semiconductive when its electrical conductivity is at least 0.001 s.m-1 (siemens per 5 meters). The composition used to obtain a semiconductor layer may comprise from 4 to 40% by weight of (electrically) conductive filler, preferably at least 15% by weight of conductive filler, and even more preferably at least 25% by weight of filler. conductive. The conductive filler may be advantageously selected from carbon blacks, and graphites, or a mixture thereof. Whether it is the first semiconductor layer, the second electrically insulating layer and / or the third semiconductor layer, at least one of these three layers is an extruded layer, preferably two of these three layers are extruded layers, and even more preferably these three layers are extruded layers. In a particular embodiment, generally in accordance with the energy cable-type electrical cable of the invention, the first semiconductor layer, the second electrically insulating layer and the third semiconductor layer constitute a three-layer insulation. In other words, the second electrically insulating layer is directly in physical contact with the first semiconductor layer, and the third semiconductor layer is directly in physical contact with the second electrically insulating layer. The electrical cable of the invention may further comprise a metal screen surrounding the third semiconductor layer. This metal screen may be a "wired" screen, consisting of a set of copper or aluminum conductors arranged around and along the third semiconductor layer, a so-called "ribbon" screen composed of one or more conductive metal ribbons laid helically around the second semiconductor layer, or a so-called "sealed" screen of metal tube type surrounding the second semiconductor layer. This last type of screen makes it possible in particular to provide a moisture barrier that tends to penetrate the electrical cable radially. All types of metal screens can act as grounding of the electric cable and can thus carry fault currents, for example in the event of a short circuit in the network concerned. In addition, the electrical cable of the invention may comprise an outer protective sheath surrounding the third semiconductor layer, or more particularly surrounding said metal screen when it exists. This outer protective sheath can be conventionally made from suitable thermoplastic materials such as HDPE, MDPE or LLDPE; or else materials retarding the propagation of the flame or resistant to the propagation of the flame. In particular, if the latter materials do not contain halogen, it is called cladding type HFFR (for Anglicism "Ha / ogen Free Rame Retardant"). Other layers, such as swelling layers in the presence of moisture, may be added between the third semiconductor layer and the metal screen when it exists, and / or between the metal screen and the outer sheath when they exist, these layers making it possible to ensure the longitudinal sealing of the electric cable with water. The electrical conductor of the cable of the invention may also include swelling materials in the presence of moisture to provide a "sealed core". Other features and advantages of the present invention will emerge in the light of the description of a non-limiting example of an electric cable according to the invention with reference to FIG. 1, showing a diagrammatic view in perspective and in section of FIG. an electric cable according to a preferred embodiment 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 or high voltage power cable 1, illustrated in FIG. 1, comprises an elongate central conducting element 2, in particular made of copper or aluminum, and, successively and coaxially, comprises around this element 2, a first layer 3 semiconductor so-called "internal semiconductor layer", a second electrically insulating second layer 4, a third semiconductor layer 5 called "external semiconductor layer", a metal screen 6 of the cylindrical tube type, and an outer protective sheath 7, the layers 3, 4 and 5 can be obtained from a composition according to the invention. Layers 3, 4 and 5 are extruded and uncrosslinked layers. The presence of the metal screen 6 and the outer protective sheath 7 is preferred, but not essential, this cable structure being as such well known to those skilled in the art.

Example Thermoplastic Composition Cl Eltex 99.7 Antioxidants 0.3 Table 1 The amounts of the constituents of the composition C1 according to the invention, detailed in Table 1, are expressed as a percentage (%) by weight in the composition of the invention. The composition C1 comprises only: a thermoplastic polymer of ethylene homopolymer type, sold by INEOS Polyolefins under the reference ELTEX® A4009MFN1325, and antioxidants. This thermoplastic polymer is characterized by the properties gathered in the following tables 2a and 2b. Property: Capillary Viscosity Shear Shear Shear 0.1s1 1035-1 10651 10223 Pa.s 254 Pa.s 0.57 Pa.s 5732 Pa.s 228 Pa.s 0.53 Pa.s Temperature 170 ° C 230 ° C Table 2b Capillary viscosity was determined using a capillary rheometer marketed by Porpoise Ltd. under the reference P9-A, and in accordance with ISO 11443: 2005 or ASTM D3835-08.

The measurements were carried out at atmospheric pressure and the temperatures measured during the measurements vary between + 1.7 ° C and -0.2 ° C relative to the control temperature. Properties Values Methods of determination Density at 23 ° C 959 kg / m3 ISO 1183 / A Mn 25779 Da ISO 16014 by steric exclusion chromatography Mw 146799 Da ISO 16014 by MFI steric exclusion chromatography (190 ° C / 2.16 kg ) 0.9 g / 10 min ISO 1133 Melting temperature 136 ° C ISO 11357-3 Table 2b Hot pressure test according to IEC 60811-3-1 paraaraphe 8.1 In order to carry out the hot pressure test, an energy cable with an extruded and uncrosslinked three-layer insulation. This cable comprises an aluminum conductor successively surrounded and coaxially by a first semiconductor layer, a second electrically insulating layer, and a third semiconductor layer. The first and third layers are layers obtained by materials well known to those skilled in the art. The second layer is obtained from the thermoplastic composition Cl. Two sections of 50 to 100 mm are taken from the cable thus formed. From each section, the third semiconductor layer is mechanically removed to obtain a specimen (i.e. energy cable comprising the aluminum conductor surrounded solely by the first semiconductor layer and the second electrically insulating layer). The impression device used for the test consists of a rectangular blade with an edge 0.70 mm wide, which can be pressed against the specimen. The pressure test is carried out at a temperature of 130 ° C. (specimen and impression device). The results of the 130 ° C. hot pressure test according to IEC 60811-3-1, paragraph 8, are summarized in Table 3 below. Cylinders C1-1 C1-2 Weight 875 g 875 g Thickness 3.7 mm 3.7 mm Outer diameter 21.9 mm 21.9 mm Deformation 10% 9% Table 3

In Table 3, the "Weight" refers to the weight of the impression device used on the specimens to perform the pressure test; "Thickness" is that of the second electrically insulating layer according to the invention; and the "Outside Diameter" is that of the specimen. To meet the requirements of IEC 60811-3-1 clause 8, the deformation value at 130 ° C (or the median value of the 20 measured finger depths) must not exceed 500/0, which is effectively the case for specimens C1-1 and C1-2.

Claims (13)

REVENDICATIONS1. Cable (1) comprising an elongate conductive element (2) surrounded by at least one polymeric layer (3, 4, 5), characterized in that said polymeric layer (3, 4, 5) is a non-crosslinked layer obtained from a composition comprising at least one thermoplastic polymer of the polyolefin type having a capillary viscosity (n) of between 11000 Pa.s at 170 ° C. and 5000 Pa.s at 230 ° C., with a shear of 0.1 s-1. 2. Cable according to claim 1, characterized in that the capillary viscosity may further be at most 0.80 Pa.s at 170 ° C and 230 ° C, with a shear of 106 s-1. 3. Cable according to claim 1 or 2, characterized in that the density of the thermoplastic polymer at 23 ° C is at least 941 kg / m3. 4. Cable according to any one of the preceding claims, characterized in that the melting temperature of the thermoplastic polymer is at least 130 ° C. 5. Cable according to any one of the preceding claims, characterized in that the ratio of the molecular weight (Mw) of the thermoplastic polymer to the number-average molecular weight (Mn) of the thermoplastic polymer is between 5 and 7. 6. Cable according to any one of the preceding claims, characterized in that the melt flow index (MFI) of the thermoplastic polymer is from 0.1 to 2.0 g / 10min. 7. Cable according to any one of the preceding claims, characterized in that the thermoplastic polymer is a monomodal polyolefin. 8. Cable according to any one of the preceding claims, characterized in that the thermoplastic polymer is a polyethylene 9. Cable according to claim 8, characterized in that the thermoplastic polymer is a homopolymer of ethylene. 10. Cable according to any one of the preceding claims, characterized in that the composition comprises more than 50.0 parts by weight of thermoplastic polymer per 100 parts by weight of polymer in the composition. 11.Cable according to any one of the preceding claims, characterized in that it comprises a first semiconductor layer (3) surrounding the elongated conductive element (2), a second electrically insulating second layer (4) surrounding the first layer (3), and a third semiconductor layer (5) surrounding the second layer (4), one of these three layers (3, 4, 5) being said non-crosslinked layer. 12.Cable according to claim 11, characterized in that the non-crosslinked layer is the electrically insulating layer (4). 13.Cable according to claim 11 or 12, characterized in that the three layers (3, 4, 5) of the cable are non-crosslinked layers.