Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
  • H01B13/06—Insulating conductors or cables
  • H01B13/14—Insulating conductors or cables by extrusion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
  • H01B13/22—Sheathing; Armouring; Screening; Applying other protective layers
  • H01B13/24—Sheathing; Armouring; Screening; Applying other protective layers by extrusion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/02—Disposition of insulation
  • H01B7/0275—Disposition of insulation comprising one or more extruded layers of insulation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/14—Peroxides
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49117—Conductor or circuit manufacturing

Definitions

• a method of manufacturing an electric power cable and cable manufactured by such a method is a method of manufacturing an electric power cable and cable manufactured by such a method.
• the present invention relates to a method for manufacturing an electric power transmission cable and more particularly to a cable dedicated to the transmission of medium voltage electrical energy and a cable dedicated to the transmission of high voltage electrical energy. .
• the invention also relates to such cables.
• the energy transport cables generally consist of at least one central electrical conductor, surrounded by an intermediate electrical insulator, itself protected from the external environment by an external protective sheath.
• the conductor is generally made of metal strands, aluminum or copper, assembled in strands.
• the outer sheath is usually made of electrically insulating thermoplastic material.
• the intermediate electrical insulation was formed from a thermoplastic material. More recently, the thermoplastic material has been replaced by crosslinked materials, essentially to raise the operating temperature of the cables to 90 ° C, with the possibility of overload temperature above 100 ° C. This has made it possible to increase the transmission capacity of the electrical networks, a capacity limited by Joule heating of the conductors, which depends on the properties of the metals used to constitute said conductors.
• the cable When the cable is intended to be subjected to a voltage greater than one thousand volts, the cable further comprises conductive layers that are extruded or ribboned. These conductive layers have the function of regularly distributing the electric field at the interfaces of the intermediate electrical insulators to avoid peak effects and, consequently, limit the risks of electrical breakdown.
• the cables of this type generally comprise a first internal semiconductor screen in contact with the conductor and a second external semiconductor screen in contact with a metal screen which is intended to collect the leakage currents, or the current of short circuit in the event of an incident, and which is itself in contact with the outer sheath.
• the metal screen is earthed via a protection system that will open the circuit if the intensity passing through the screen becomes too high.
• the complex formed by the intermediate electrical insulation surrounded by the two semiconductor screens is called a tri-layer.
• intermediate electrical insulators and / or semiconductor screens whose material is composed mainly of low-density polyethylene to which additives, in particular peroxides, are added.
• additives in particular peroxides
• peroxides whose decomposition will lead to the formation of radicals, will allow to create, in polyethylene, a three-dimensional network that will ensure thermal stability and prevent the mechanical deformation of the cable at operating temperatures that is to say 90 ° C to 110 ° C.
• the material intended to form the intermediate electrical insulator is introduced, at ambient temperature, in the form of granules into the hopper of an extruder and then melted in the screw of the extruder between 120 and 140 °. C in general, to be brought to a plastic state and a sufficiently low viscosity to be shaped around the conductor. It is the same for the two semiconductor screens which are generally coextruded, so that one finds at the output of the triple extrusion head of the extruder a complex that must still be crosslinked.
• This operation takes place in a tube of a few tens, or even a few hundred meters, which is directly connected to the extrusion head by a telescopic part.
• the cable is heated so as to allow the decomposition of the peroxide (s) used and thus the crosslinking of the polyethylene.
• This heating can be obtained by heat transfer fluid, such as water vapor or oil. It is also possible that the complex is heated by radiation from the tube in a neutral atmosphere such as nitrogen gas.
• a neutral atmosphere such as nitrogen gas.
• systems are also used which will heat the central conductor, for example by induction.
• the temperatures encountered in this first part of the tube may be between 200 and 400 ° C, depending on the nature of the materials involved, the heating method used, the geometry of the cable, and the speed of manufacture.
• the tube Following the first heating part, the tube comprises a second part which is dedicated to the cooling of the complex.
• this cooling is obtained by passing the cable in cold water, which circulates continuously in the second part of the tube by means of pumps, so as to maintain a relatively constant low temperature.
• the cooling can also be obtained by passing in an atmosphere of neutral gas, generally nitrogen, which circulates continuously in the second part of the tube.
• the resulting cable has a fully crosslinked insulating tri-layer and is at a sufficiently low temperature to be able to be wound on a receiving drum without the cable being permanently deformed by the drum.
• the peroxides decompose to form the radicals necessary for the crosslinking of the polyethylene.
• the decomposition of peroxides causes the formation of by-products which are in fact molecules of lower molecular weight than those of the radicals and which are trapped at the heart of the three-dimensional network created in the polyethylene by the radicals of peroxides.
• the formation of these by-products is particularly important in the case of the material for forming the intermediate electrical insulation.
• Some of the by-products are gaseous at the cross-linking temperatures encountered in the first part of the tube. It is to avoid the formation of bubbles in the intermediate electrical insulation and the semiconductor screens that the first part of the tube is kept under pressure between 8 and 25 bar. Indeed, such bubbles are particularly damaging to the electrical quality of the intermediate electrical insulation and semiconductor screens. After passing through the second part of the tube, these by-products are always present in the dissolved state in the intermediate electrical insulation and the semiconductor screens, the crystallinity of the material thereof preventing the formation of bubbles.
• this degassing step generally takes a few days in general and is carried out at room temperature. Above a thickness of intermediate electrical insulation of 6 millimeters, it is however necessary to condition the cables for ten days at a temperature between 50 and 90 degrees Celcius.
• the degassing step proves to be particularly long and considerably slows the process for manufacturing the cables, in particular cables dedicated to the transport of high voltage electrical energy, the thickness of the intermediate electrical insulator being greater.
• the degassing step requires having a large space for storing the cables.
• the degassing step is energy intensive and requires the availability of appropriate ovens.
• An object of the invention is to provide a method of manufacturing an electric power transmission cable whose implementation is further accelerated.
• an electric power transmission cable comprising at least, from the inside to the outside, a central electrical conductor, a first semiconductor screen , an intermediate electrical insulator, a second semiconductor screen, a metal screen and an outer sheath, the method comprising a step of extruding a composition comprising at least one polyolefin to form at least one layer constituting the first half screen. conductor, intermediate electrical insulation or second screen semiconductor and a step of crosslinking said layer.
• the method comprises the step of injecting into the composition a liquid solution which contains at least one peroxide and at least one so-called co-crosslinking agent during the manufacture of said layer.
• Crosslinking co-agents are unsaturated and polyfunctional organic compounds that can form free radicals.
• the co-agents by bridging between two polymer chains, make it possible to crosslink the polyolefin.
• the co-crosslinking agent thus greatly contributes to the crosslinking of the polyolefin. It is therefore possible to limit the proportion of peroxide in the liquid solution while maintaining a very good crosslinking of the polyolefin. As the peroxide gives rise to the formation of unwanted volatile by-products, limiting the proportion of peroxide makes it possible to reduce the level of volatile by-products produced during the crosslinking step. The degassing step is thus shortened, which ultimately makes it possible to accelerate the cable manufacturing process.
• the table below indicates the values of the rheometric couples Mh of different structures of the layer of the intermediate electrical insulation 3 once the crosslinking step is complete when the layer has been manufactured according to the invention. It is recalled that a rheometric torque makes it possible to evaluate the degree of crosslinking of a material. The higher the rheometric torque, the better the degree of crosslinking.
• the rheometric torque is here measured at 200 degrees Celsius with an Alpha-Technologies RPA 2000 Analyzer type rheometer.
• compositions studied are:
• composition No. 1 comprises by weight substantially 99.03% of linear low density polyethylene, 0.27% of antioxidant, 0.35% of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (also known as DBPH) as peroxide and 0.35% Triallyl Isocyanurate (also called TAIC) as a Type II crosslinking co-agent;
• Composition No. 2 comprises by weight substantially 98.73% linear low density polyethylene, 0.27% antioxidant, 0.35% DBPH and 0.65% TAIC;
• composition No. 3 comprises by weight substantially 98.58% linear low density polyethylene, 0.27% antioxidant, 0.35% DBPH and 0.8% TAIC.
• composition 1 9,105
• Composition 2 3.5 70
• the invention thus makes it possible to manufacture the layer making up the first semiconductor screen and / or the second semiconductor screen and / or the intermediate electrical insulation with few undesirable by-products.
• the liquid solution is chosen so that the material of said layer comprises, after the extrusion step, a lower percentage by weight of peroxide relative to the polyolefin than the percentage by weight of the co-crosslinking agent. relative to the polyolefin.
• the co-crosslinking agent it is possible to significantly reduce the proportion of peroxide without degrading the crosslinking of the polyolefin: the method of the invention thus allows to have a lower peroxide content of the co-agent.
• Table 1 it is clear that the compositions . 2 and 3 more concentrated in co-crosslinking agent than in peroxide allow to obtain a better density of crosslinking of polyethylene despite their low levels of peroxide.
• the inventors have also found that the rates of gaseous by-products and non-gaseous by-products can thus be particularly low, which makes it possible to reduce, or even eliminate, the degassing step.
• the step of injecting the liquid solution into the composition is carried out during the extrusion step.
• the liquid solution is thus mixed with the composition directly during the extrusion step. It is therefore not necessary to disperse the peroxide and the crosslinking agent in the composition before the extrusion step. This makes it possible to further accelerate the cable manufacturing process.
• the screw of the extruder which implements the extrusion step makes it possible to ensure that the composition and the solution are correctly mixed in addition to advancing the composition-solution mixture in the heated portion of the extruder.
• injecting the solution and not mixing it with the composition before the extrusion step has the advantage that the liquid solution, during the injection, can be filtered very easily.
• the final composition that is extruded is therefore of much better quality.
• the peroxide is dispersed in the composition prior to the extrusion step.
• the peroxide tends to move in the polyolefin of the composition resulting in peroxide exudation phenomena.
• injecting the solution directly during the extrusion step one thus obviates said problems of exudation.
• the final composition that is extruded is therefore of much better quality.
• a co-agent of type II is chosen.
• a type II crosslinking co-agent is a compound which comprises molecules carrying unsaturated bonds intended to cooperate with free radicals of the polyolefin during the formation of the intermediate electrical insulator, said molecules being derivatives vinyl or allylic or polybutadienes.
• the use of the type II crosslinking co-agent greatly promotes the crosslinking of the polyolefin.
• type II crosslinking co-agents also form free radicals that are more stable than type I crosslinking co-agents.
• type II crosslinking co-agents are less "grilling" than type I co-agents, i.e. type II co-agents are less reactive than co-agents of type II. type I agents.
• the molecules carrying unsaturated bonds of the co-agent of type II cooperate less rapidly with the free radicals of the polyolefin, which limits a beginning of crosslinking in the extruder that is not desired.
• the table below shows the values of the rheometric couples Mh of different structures of the layer of the intermediate electrical insulation 3 once. the crosslinking step completed when the layer has been manufactured according to the invention. It is recalled that a rheometric torque makes it possible to evaluate the degree of crosslinking of a material. The higher the rheometric torque, the better the degree of crosslinking.
• the rheometric torque is here measured at 200 degrees Celsius with an Alpha-Technologies RPA 2000 Analyzer type rheometer.
• compositions studied are:
• composition No. 1 comprises by weight substantially 99.03% of linear low density polyethylene, 0.27% of antioxidant, 0.35% of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (also known as DBPH) as peroxide and 0.35% Triallyl Isocyanurate (also called TAIC) as a Type II crosslinking co-agent;
• Composition No. 2 comprises by weight substantially 98.73% linear low density polyethylene, 0.27% antioxidant, 0.35% DBPH and 0.65% TAIC;
• composition No. 3 comprises by weight substantially 98.58% linear low density polyethylene, 0.27% antioxidant, 0.35% DBPH and 0.8% TAIC.
• composition 1 2.9 105
• Composition 2 3.5 70
• the invention also relates to an electric power transmission cable, comprising at least, from the inside towards the outside, a central electrical conductor, a first semiconductor screen, an intermediate electrical insulator, a second semiconductor screen , a metal screen and an outer sheath.
• the material of the intermediate electrical insulator and / or the first semiconductor screen and / or the second semiconductor screen comprises at least one polyolefin in which a liquid solution comprising at least one peroxide and at least one less a compound called co-crosslinking agent.
• the electric power transmission cable comprises, from the inside towards the outside, a central electrical conductor 1, a first semi ⁇ conductor screen 2, an intermediate electrical insulator 3, a second semiconducting shield 4, a metal screen 5 and an outer sheath 6.
• the central conductor 1 is for example aluminum.
• the materials of the first semiconductor screen 2 and the second semiconductor screen 4 are here based on copolymer and carbon black.
• the second semiconductor screen 4 can be "peelable” that is to say it can easily separate from the intermediate electrical insulation 3.
• the central electrical conductor 1, the first semiconductor screen 2, the second semiconductor screen 4, the metal screen 5 and the sheath 6 are known per se and will not be detailed here.
• the material of the intermediate electrical insulation 3 comprises at least one polyolefin in which has been injected, during the manufacture of the cable, a liquid solution comprising at least one peroxide and at least one compound known as co-agent. crosslinking.
• a composition comprising at least one polyolefin is extruded by an extruder.
• the extruder comprises a hopper opening into a heated cylindrical sleeve in which a worm rotates, the screw allowing the circulation of the composition of the hopper to the outlet port of the sleeve.
• Granules of the composition are introduced into the hopper and the screw continuously pushes the granules which gradually soften in the sleeve until melting.
• the composition is thus brought to a plastic state and to a sufficiently low viscosity to be shaped around the central conductor 1 in the form of a continuous tube at the output of the extruder so as to constitute the intermediate electrical insulation 3.
• the manufacturing method according to the invention comprises the step of crosslinking the intermediate electrical insulation 3 to improve the mechanical characteristics of the intermediate electrical insulation 3.
• the liquid solution is injected into the composition during the extrusion step.
• the solution is here added to the granules of the composition by a drip injection device which is arranged substantially at the inlet of the extruder at the hopper.
• the screw in addition to pushing the granules into the extruder, the screw makes it possible to ensure that the composition and the liquid solution which are intended to form the material of the intermediate electrical insulation 3 mix correctly.
• the mixture of the composition and the solution is therefore carried out directly during the extrusion step. It is no longer necessary to disperse the peroxide and the crosslinking agent in the composition prior to the extrusion step.
• the crosslinking co-agent is a type II crosslinking coagent.
• the polyolefin is a polyethylene and the liquid solution is chosen so that the material of the intermediate electrical insulation 3 comprises at the output of the extruder before the crosslinking step between 0.01% and 1.2% by peroxide weight relative to polyethylene and between 0.3% and 4% by weight of type II crosslinking co-agent with respect to polyethylene.
• the liquid solution is chosen here so that said material comprises between 0.01% and 1% by weight of peroxide relative to polyethylene.
• the liquid solution is chosen so that said material comprises, after the extrusion step, a lower percentage by weight of peroxide relative to the polyethylene than the percentage by weight of the co-crosslinking agent. compared to polyethylene.
• the polyethylene chosen is linear low density polyethylene.
• Such linear low density polyethylene crosslinks much more effectively than a radical polyethylene.
• the liquid solution may comprise less peroxide without affecting the crosslinking of the composition.
• linear low density polyethylene has a much more ordered structure than a radical polyethylene. Its melting temperature is thus higher, which makes it possible to use the cable according to the invention at higher temperatures and thus to pass a larger amount of current through the central conductor 1.
• the cable according to the invention is thus particularly suitable for transporting medium and high voltage electrical energy.
• the linear low density polyethylene is for example selected from the following references: Index of
• the fluidity index (or IF) is better known by its English name MFI
• composition No. 1 comprises by weight substantially 98.1% of radical type polyethylene BP 2000 (Ineos trademark), 0.3% antioxidant and 1.6% Tert-Butyl Cumuyl Peroxide (also called TBCP) in as peroxide;
• composition No. 2 comprises by weight substantially 98.1% linear low polyethylene density of BP 3220 (Ineos trademark), 0.3% antioxidant and 1.6% TBCP.
• the rheometric torque must be order of 3.3 for linear low density polyethylene.
• the rheometric torque must be of the order of 2.2 for a radical polyethylene.
• the liquid solution may comprise less peroxide, which limits the formation of undesirable products without affecting the crosslinking of the composition.
• the peroxide is a non-aromatic peroxide.
• the nonaromatic peroxide allows the by-products from the decomposition of said peroxide during the crosslinking step to have relatively low molecular weights. Said by-products are then much easier to evacuate the intermediate electrical insulation 3. The degassing step is thus accelerated.
• the degassing step is not always performed at room temperature (which is substantially around 20 degrees Celsius).
• room temperature which is substantially around 20 degrees Celsius.
• the liquid solution is obtained by mixing a liquid non-aromatic peroxide and a solid type II crosslinking co-agent with a liquid antioxidant compound.
• the type II crosslinking co-agent is obviously chosen to be soluble in the liquid antioxidant compound and the non-aromatic peroxide is obviously chosen to be miscible with the liquid antioxidant compound.
• the aging of the material of the intermediate electrical insulation 3 that is to say the degradation of said material over time, is generally due to the effects of temperature, oxygen and possibly light and is manifested by the formation of very reactive free radicals inside the intermediate electrical insulation 3.
• the antioxidant compound By adding the antioxidant compound to the liquid solution, the molecules of said compound react with these free radicals so as to neutralize them. This makes it possible to avoid degradation reactions within the intermediate electrical insulation 3 due to the presence of said free radicals. The life period of the cable is thus lengthened.
• the liquid antioxidant compound is for example Irgastab Cable KV 10 (registered trademark BASF).
• the liquid solution further comprises at least one anti-grilling compound.
• Such a compound is intended to neutralize at least the first undesirable by-products from the decomposition of peroxide during the crosslinking of the intermediate electrical insulation 3.
• the quality of the material of the intermediate electrical insulation 3 is improved.
• the screw of the extruder has a diameter of 45 millimeters and a length of 1080 millimeters.
• the screw has a square head and four separate heating zones. The screw rotates at 30 rpm.
• the liquid solution is prepared by mixing triallyl isocyanurate (also called TAIC) as a crosslinking co-agent of type II, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (also called DBPH) in as non-aromatic peroxide and Irgastab Cable KV 10 as an antioxidant. Then the solution is filtered on a sieve of 25 micrometers before being injected at the entrance of the extruder into the granules.
• triallyl isocyanurate also called TAIC
• DBPH 2,5-dimethyl-2,5-di (t-butylperoxy) hexane
• Irgastab Cable KV 10 as an antioxidant
• the temperature profile of the screw used for the extrusion of the mixture is as follows:
• the material of the intermediate electrical insulation 3 comprises by weight substantially 98.75% of Flexirene CL 10 F, substantially 0.25% of Irgastab Cable KV 10, substantially 0 , 35% of DBPH and substantially 0.65% of TAIC.
• liquid solution is thus chosen here so that said material comprises, after the extrusion step, a lower percentage by weight of peroxide relative to the polyolefin than the percentage by weight of the co-crosslinking agent with respect to polyolefin.
• specimens are created. Said specimens are press-cured for 15 minutes at 190 ° C. Different properties are then measured on said crosslinked specimens.
• the material of the intermediate electrical insulation 3 thus has very satisfactory mechanical, thermal and electrical properties.
• the material also has good aging resistance.
• the crosslinked specimens have a methane content of 98 parts per million (ppm), an ethane level of 45 ppm or a total gas content of 143 ppm.
• BP 2000 which is a radical polyethylene, 0.3% antioxidant and 1.5% Tert-Butyl Cumuyl Peroxide (also called TBCP) as aromatic peroxide
• the cable of the invention comprises an intermediate electrical insulation 3 comprising a much lower gas rate than that of a cable of the prior art once the crosslinking step completed.
• the degassing step will thus be much shorter or nonexistent with the cable of the invention so that the method of manufacturing such a cable is accelerated.
• the process according to the invention makes it possible to select, as peroxide and as co-crosslinking agent, already existing commercial products. It is therefore not necessary to synthesize, by long and tedious steps, a peroxide or a "laboratory" crosslinking co-agent, specifically adapted to the intended application, before forming the liquid solution.
• the thicknesses of the various layers forming the cable will of course be determined depending in particular on the current and voltage to which the cable is intended to be subjected.
• the described cable is dedicated to the transmission of electrical energy of DC or AC direct voltage or of high DC or AC voltage, the cable may also be arranged for the transport of electrical power of small voltage.
• high voltage means a voltage of between 30 and 500 kV, by average voltage a voltage between 1 and 30 kV and a voltage of less than 1 kV.
• a composition of the material of the semiconductor screens once the crosslinking step has been completed comprises, for example, by weight substantially 63.5% of a polyolefin (such as a polar polymer of the ethylene acrylate or ethylene vinyl acetate type) loaded with 35% of carbon black, 0.5% peroxide and 1% co-crosslinking agent.
• a polyolefin such as a polar polymer of the ethylene acrylate or ethylene vinyl acetate type
• liquid solution is chosen so that said material comprises, after the extrusion step, a lower percentage by weight of peroxide relative to the polyolefin than the percentage by weight of the co-crosslinking agent with respect to polyolefin.
• the method comprises the successive steps of:
• the method according to the invention may be implemented for the manufacture of both the component layer of the intermediate electrical insulation and the layers making up the semiconductor screens.
• the layers will then be coextruded: the layers will be extruded in separate sleeves by separate extrusion screws, the three sleeves being connected by a triple extrusion head. At the output of the extruder is thus obtained a tri-layer that should be crosslinked.
• the injection step may be implemented by another device.
• the injection step may be performed by means of a continuous spraying device all along the screw or by injection into the extruder barrel via a pump.
• the liquid solution may have a composition different from what has been described provided that the solution is sufficiently liquid to be easily injected into the extruder.
• the different ingredients of the liquid solution will therefore be liquid and miscible with each other and / or solid and soluble with the other ingredients.
• the liquid solution may comprise a solid peroxide and a co-liquid curing agent or a liquid peroxide and a co-solid curing agent.
• the peroxide and crosslinking agent can both be solid and mixed with a liquid solvent.
• the liquid peroxide can then be chosen from the following commercial references: LUPEROX 801 (comprising the t-butyl cumyl peroxide molecule), LUPEROX 130 (comprising the 5- molecule dimethyl-2, 5-di (t-butylperoxy) hexyne-3), LUPEROX 233 (comprising the molecule Ethyl-3,3 ⁇ di (t-butylperoxy) butyrate), LUPEROX 533 (comprising the molecule Ethyl-3,3 - di (t-amylperoxy) butyrate), TRIGONOX B (comprising the di-t-butyl peroxide molecule), TRIGONOX 101 (comprising the 2,5-dimethyl-2,5-di (t-butylperoxy) hexane molecule) or else TRIGONOX 201 (comprising the molecule Di (t-amyl) peroxide).
• the liquid solution may comprise other compounds in addition to the peroxide and the co-crosslinking agent such as anti-tree water additives and / or anti-UV additives and / or acid-sensing compounds and / or anti-grilling compounds and / or antioxidant compounds ... Some compounds may also play the dual role of antioxidant and anti-grilling or the dual role of antioxidant and anti-UV.
• the peroxide is chosen as non-aromatic, the peroxide may be selected as aromatic or semi-aromatic.
• crosslinking co-agent is a type II cross-linking agent
• the co-agent may be of another type such as a type I crosslinking co-agent such as di-methacrylate. ethylene glycol.
• the antioxidant compound may be solid and non-liquid.
• the antioxidant compound will be, for example, Irganox 1081 which is soluble in liquid peroxides or Lowinox TBP6.
• the composition may be different from what has been described.
• the composition may comprise one or more polyolefins and optionally another polyolefin such as ethylene-ethyl acrylate (EEA) or ethylene-butyl acrylate (EBA) ... or include other ingredients in addition to a first polyolefin such as a second polyolefin, one or more copolymers, anti-water tree additives, anti-UV additives, acid-scavenging compounds, anti-grilling compounds, antioxidant compounds, peroxides, mineral or organic fillers ...
• ESA ethylene-ethyl acrylate
• EBA ethylene-butyl acrylate
• polyethylene chosen is a linear polyethylene
• polyethylene chosen may be a radical polyethylene.
• Linear polyethylenes in general and linear low density polyethylenes in particular will be preferred.
• a radical polyethylene may thus be chosen, for example, from the following commercial references:
• the composition comprises a radical polyethylene
• BP 2000 is chosen as radical polyethylene and the liquid solution is chosen so that the material of the intermediate electrical insulation comprises, after the crosslinking step 0.3 % by weight of antioxidant relative to BP 2000, 1.7% of Triallyl cyanurate (TAC) as co-crosslinking agent and 0.5% of DBPH.
• TAC Triallyl cyanurate
• Such an intermediate electrical insulation has in fact a low level of undesirable by-products.
• the liquid solution is chosen so that said material comprises, after the extrusion step, a lower percentage by weight of peroxide relative to the polyolefin than the percentage by weight of the co-crosslinking agent with respect to polyolefin.
• the term "at least one layer making up the first semiconductor screen, the intermediate electrical insulation or the second semiconductor screen” means either the layer constituting the first semiconductor screen, the intermediate electrical insulation or the second semiconductor screen. conductor when the screen or insulation in question has only one layer; or at least one of the layers constituting the first semiconductor screen, the intermediate electrical insulation or the second semiconductor screen when the screen or the insulation in question comprises several layers.
• the composition may be incorporated in one or the other of the screens, or to the two screens, and / or to the insulator.

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