Improved Process for Manufacturing a Medium or High Voltage Electric Cable

Abstract

The invention relates to a method for manufacturing a medium or high voltage electrical cable, of the type comprising:- a core formed from an elongated electrically conductive element and an insulating system comprising at least one layer comprising at least one crosslinked polyethylene, said at least one layer being arranged coaxially around the elongated electrically conductive element, and- a tape enveloping the core, the tape being formed from a semiconducting polymer material, characterized in that the method comprises at least one step of extracting at least one chemical species from the tape, said chemical species being a chemical species capable of reaching the insulating system by migration from the tape and of reducing the dielectric performance of the insulating system. Figure for abstract: None

Description

Title of the invention: Improved Method for Manufacturing a Medium or High Voltage Electric Cable Technical field

[0001] The invention relates to the technical field of manufacturing energy cables.

[0002] The invention relates to a method for manufacturing a medium or high voltage electrical cable and extends to an electrical cable capable of being obtained by this method. The invention therefore relates to and applies to the manufacture of medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular greater than 60 kV, and up to 800 kV) power cables, whether they are direct current (HVDC) or alternating current (HVAC).

[0003] The invention relates to and applies in particular to the manufacture of medium or high voltage electrical cables of the type comprising an insulating system comprising at least one layer comprising at least one crosslinked polyolefin, in particular comprising at least one layer comprising at least one crosslinked polyethylene (cables of the “HVDC XLPE” type for “High Voltage Direct Current Crosslinked PolyEthylene” or of the “HVAC XLPE” type for “High Voltage Alternating Current Crosslinked PolyEthylene”).

[0004] The invention thus finds applications in the fields of aerial, underwater, terrestrial electricity transport, or even aeronautics.

[0005] The invention relates to and applies to the manufacture of medium and high voltage electrical cables and connections for such cables for terrestrial applications but also extends to the manufacture of connections for underwater medium and high voltage electrical cables.

[0006] The invention relates to and applies more particularly to the manufacture of a medium or high voltage electric cable, of the type comprising: - a central core formed of at least one elongated electrically conductive element, in particular made of copper or aluminum, and at least one insulating system, each insulating system being arranged coaxially around an elongated electrically conductive element, at least one layer of the insulating system comprising crosslinked polyethylene (XLPE), and - a tape surrounding and enveloping the central core, in contact or not with said central core, and participating in the formation of a sheath surrounding the core of the electric cable.

[0007] The invention relates to and applies to the manufacture of a medium or high voltage electric cable in which the insulating system comprises at least one layer (semiconductor or electrically insulating) comprising at least one polyethylene reticle.

[0008] Throughout the text, the expression “cross-linked polyethylene” means any cross-linked polyethylene (“cross-linked” in English or XLPE) by any cross-linking process known to those skilled in the art, such as for example peroxide (and / or organic peroxide) cross-linking, electron beam cross-linking, silane cross-linking, cross-linking by ultraviolet radiation, and others.

[0009] Throughout the text, the following terms are understood to mean: - "electrically insulating layer", a layer whose electrical conductivity may be very low, or even zero, and in particular at most 106 S / m (Siemens per meter), or at most 1.108 S / m (Siemens per meter), or at most 1.109 S / m, or at most 1.10 10 S / m or at most 10 13 S / m (measured at 25°C in direct current), and by - “semiconductor layer” a layer whose electrical conductivity may be strictly greater than 1.108 S / m (Siemens per meter), preferably at least 1.10 3 S / m, and preferably may be less than 1.103 S / m (measured at 25°C in direct current).

[0010] The semiconductor layer has an electrical conductivity greater than that of the electrically insulating layer. More particularly, the electrical conductivity of the electrically insulating layer may be at least 10 times lower than the electrical conductivity of the semiconductor layer, preferably at least 100 times lower than the electrical conductivity of the semiconductor layer, and particularly preferably at least 1000 times lower than the electrical conductivity of the semiconductor layer.

[0011] The level of electrical conductivity of the insulating system of such electrical cables influences the dielectric strength of the insulating system and consequently the dielectric performance of the electrical cable. In other words, the lower the electrical conductivity of the insulating system, the higher the performance of the electrical cable and the insulating system. Electrical conductivity is an intrinsic property of the material. In the case of electrical cables comprising an insulating system comprising crosslinked polyethylene, the electrical conductivity of this insulating system is likely to increase due to the addition of exogenous chemical species into the insulating system.

[0012] Such an increase in the electrical conductivity of the insulating system constitutes a considerable threat to the reliability of the energy transmission network with economic consequences caused by the failure of the electrical energy distribution network.

[0013] The invention aims to overcome this drawback. Prior art

[0014] EP3699931 discloses a method for immobilizing crosslinking by-products of an insulating system based on crosslinked polyethylene (XLPE, "Crosslinked poly-ethylene") of an electric cable intended for the transmission of medium voltage or high voltage energy. The electric cable of EP3699931 is produced by extrusion of the insulating system onto the electrical conductor, the insulating system also comprising a carrier layer of a zeolite system comprising a first CBV 600 zeolite intended to absorb the crosslinking by-products of the insulating system and an A3 zeolite intended to absorb the water formed due to oligomerization and decomposition reactions of said crosslinking by-products of the insulating system during or after their absorption by the first zeolite, the oligomerization and decomposition reactions being accompanied by in situ water formation.

[0015] The electrical cable of EP3699931 requires incorporating two types of zeolite particles, including one type of particles intended for the absorption of crosslinking by-products and one type of particles intended for the irreversible absorption of water molecules formed due to said absorption of by-products.

[0016] The manufacture of the electric cable of EP3699931 is complex and the zeolite system is likely to affect the electrical and / or mechanical properties of the electric cable.

[0017] The invention aims in particular to propose a method for manufacturing a medium or high voltage electrical cable making it possible to limit the loss of dielectric performance of the insulating system, or even to maintain or preserve the dielectric performance of the insulating system of an HVDC-XLPE or HVAC-XLPE type electrical cable.

[0018] The invention also aims to propose such a method for manufacturing a medium or high voltage electric cable making it possible to maintain the dielectric performance of the insulating system and, preferably, preserving good mechanical properties of the electric cable. Statement of the invention

[0019] To this end, the invention relates to a method for manufacturing a medium or high voltage electric cable, of the type comprising: - a core formed from an elongated electrically conductive element and an insulating system comprising at least one - in particular a plurality of - layer(s) comprising at least one crosslinked polyethylene, said at least one layer being arranged coaxially around the elongated electrically conductive element, and - a ribbon wrapping the core and extending in contact or not (or at a distance) from the core, characterized in that the method comprises at least one step of extracting at least at least one chemical species - in particular at least one undesirable chemical species - from the tape, said chemical species being a chemical species capable of reaching the insulating system by migration from the tape during use of the cable and of reducing the dielectric performance of the insulating system.

[0020] The inventors have observed that semiconducting tapes of the prior art, applied around and wrapping layer(s) of the insulating system comprising crosslinked polyethylene, in particular but not exclusively semiconducting layers comprising XLPE polyethylene, are in reality likely to contribute to a modification over time of the electrical conductivity properties of the insulating system of electrical cables in use, in particular medium and high voltage direct current (HVDC) electrical cables. Without being supported by a scientific approach, the inventors assume that the semiconducting tapes of the prior art incorporate chemical species which are likely to migrate into the insulating system comprising at least one crosslinked polyethylene, during the lifetime of the electrical cable and to modify its properties and have proven to be undesirable.These chemical species are referred to throughout this text as undesirable chemical species. The inventors have further determined that a step likely to lead to an extraction of all or part of these undesirable chemical species actually makes it possible to limit the loss of dielectric performance of the insulating system, or even to maintain this dielectric performance of the insulating system of HVDC cables. However, maintaining the electrical conductivity of the crosslinked polyethylene insulating material at as low a level as possible is an essential objective to be achieved during the manufacture of medium or high voltage electrical cables comprising at least one crosslinked polyethylene (XLPE).

[0021] But the inventors have also observed that these undesirable chemical species, in particular water, constitute(s) a problem for alternating current (HVAC) electrical cables because they can cause a degradation of the dielectric performance of the insulating system by treeing. The method according to the invention makes it possible to extend the service life of alternating current cables, in particular of a cable of wet design (without a metallic barrier against water) for which the time necessary to reach humidity conditions likely to initiate the degradation of the dielectric performance can be considerably prolonged.

[0022] The insulating system of the electrical cable may be formed of at least one layer(s) arranged coaxially around the central elongated electrically conductive element. In some of these known embodiments, the insulating system is formed of a plurality of layers arranged coaxially around the elongated electrically conductive element, including at least one semiconducting layer and at least one electrically insulating layer.

[0023] In some of these embodiments, the insulating system is formed from a plurality of layers arranged coaxially around the central elongated electrically conductive element, including a first semiconducting layer called the “inner semiconducting layer” extending in contact with the elongated electrically conductive element, an electrically insulating layer extending in contact with said inner semiconducting layer and a second semiconducting layer called the “outer semiconducting layer” extending in contact with the electrically insulating layer.

[0024] These three layers are typically layers comprising at least one polymer - in particular at least one polyethylene - crosslinked and obtained by techniques well known to those skilled in the art, by crosslinking a precursor composition comprising at least one polymer - in particular at least one polyethylene - not crosslinked. The crosslinked polymers of the different layers may be distinct or identical. The crosslinked polyethylenes of the different layers may be distinct or identical.

[0025] According to the invention, the tape is adapted to prevent migration and progression of water in the longitudinal direction of the electric cable in the event of damage to the electric cable in service. The tape is adapted to form a barrier preventing direct contact between the layers between which it is interposed, in particular between the external stranded layers and the insulating system of the electric cable.

[0026] According to the invention, the tape is a strip of great length and of substantially constant width and much less than its length. According to the invention, the tape is formed from at least one solid material capable of containing at least one undesirable chemical species and capable of reaching the insulating system by migration from the tape during use of the electric cable comprising the tape.

[0027] According to the invention, the ribbon is formed from at least one flexible material chosen according to the expected functionalities of the ribbon. By "ribbon formed from at least one flexible material" or "flexible ribbon" is meant a ribbon whose material and dimensions, in particular the thickness, are adapted to be able to allow the ribbon to be wound around an axis orthogonal to the largest dimension (length) of the ribbon for the purpose of storing the ribbon and to be able to allow the ribbon to be unwound when it is placed around - in contact or not - the core of the electric cable driven in movement along a longitudinal axis of the electric cable during manufacture.

[0028] According to certain embodiments, the tape is a protective tape. It may be a protective tape against chemical and / or physical attacks. According to certain embodiments, the tape is a protective tape for the core of the electrical cable. According to certain embodiments of a method according to the invention, the tape is applied by helically winding onto the external face of the insulating system of the cable. with or without overlapping areas. According to certain other embodiments, alone or in combination, the tape can be applied to the surface of a more external layer of the electric cable by helically winding it around said more external layer of the electric cable with or without overlapping areas. Any other application method is possible. Nothing prevents provision being made, according to certain embodiments, for applying the tape by folding / winding the tape along its longitudinal axis around the core of the electric cable or around a more external layer of the electric cable surrounding the core of the electric cable. According to these embodiments, the two longitudinal edges of each section of tape are folded facing each other.

[0029] According to certain embodiments, the ribbon is formed from at least one material selected from the group consisting of polymeric materials. According to certain embodiments, the ribbon is formed from at least one material selected from the group consisting of woven materials and non-woven materials. According to certain embodiments, the ribbon is formed from at least one woven material. According to certain embodiments, the ribbon formed from at least one woven material has better tensile strength compared to a ribbon formed from at least one non-woven material. According to certain embodiments, the ribbon formed from at least one material, in particular a woven material, has a tensile strength value of between 10 N / cm and 200 N / cm. According to certain embodiments, the ribbon is formed from a non-woven and swelling material.

[0030] By "swellable material" is meant a material capable of swelling on contact with water, for example by absorption of water. Advantageously, a ribbon made of at least one swelling material is adapted to act as a water-blocking material by opposing the axial propagation of water blocked between the layers - in particular polymeric (plastic) and metallic layers - framing the ribbon on its two main faces.

[0031] According to certain embodiments, the ribbon may be formed from at least one swelling material. According to these embodiments, the ribbon made of swelling material may make it possible to protect the core of the electrical cable from water, for example by capturing / absorbing water. But the swelling material may also allow reciprocal physical protection between two layers made of distinct materials, in particular between a layer made of at least one polymer material and a layer made of a metallic material.

[0032] According to certain embodiments, the ribbon may be formed from at least one non-swelling material. Such a ribbon made from at least one non-swelling material may provide mutual physical protection between two layers made from distinct materials, in particular between a layer made from at least one polymer material and a layer made from a metallic material.

[0033] According to certain embodiments, the ribbon is formed from a polymer material. According to certain embodiments, the ribbon is formed from at least one semiconducting polymer material. The ribbon formed from at least one semiconducting polymer material promotes electrical contact between the layers surrounding the ribbon, in particular a semiconducting polymer layer and a metal layer.

[0034] According to some embodiments, the tape is formed from a plurality of layers sandwiched together and each having at least one of the properties mentioned. According to these embodiments, the layers of the plurality of layers can be formed from similar or distinct materials.

[0035] According to certain embodiments, the ribbon is formed from at least one material selected from the group of textile fibers. According to certain embodiments, the ribbon is formed from at least one material selected from the group of polymeric materials including nylons, polyesters, rayon, etc. for example. According to certain embodiments, the material forming the ribbon may comprise at least one additive such as a corrosion inhibitor and / or an absorbent powder. The material(s) forming the ribbon are chosen to obtain the properties required for the ribbon, such as mechanical properties, swelling properties. The material(s) forming the ribbon are chosen to obtain the required dimensions.

[0036] According to some embodiments, the ribbon may have a width of between 20 mm and 200 mm. The ribbon may have a thickness of between 0.1 mm and 1 mm. The ribbon may have a density of between 10 g / m2 and 300 g / m2.

[0037] The tape may be arranged directly in contact with a face forming the outer face of the insulating system of the cable. However, the tape may be arranged without direct contact with the face forming the outer face of the insulating system of the cable, functional or non-functional layers being able to be interposed between the core of the cable and the tape.

[0038] According to certain embodiments, the tape is subjected to said extraction step prior to the application of the tape around the core of the electric cable.

[0039] According to these embodiments, the ribbon being packaged in the form of a roll or a wafer, said roll of ribbon is placed in an extraction enclosure for a sufficient time to allow said extraction. According to these embodiments, the ribbon being packaged in the form of a roll or wafer, said roll of ribbon is placed in said extraction enclosure for a sufficient time and under conditions (in particular temperature and / or pressure and / or ventilation) suitable for allowing said extraction.

[0040] According to these embodiments, a roll of tape is subjected to preconditioning in an extraction enclosure for a sufficient time to allow said extraction, prior to its placement around the core of the cable. electrical at the finishing stage. Pre-conditioning of the tape in the extraction chamber and extraction of undesirable chemical species can be achieved remotely from the electrical cable manufacturing and production site and independently of the electrical cable manufacturing. The tape, substantially free of undesirable chemical species, can be retained and / or stored before being placed around the electrical cable core.

[0041] According to other embodiments, alone or in combination with a previous embodiment, nothing prevents the provision of placing the electric cable provided with the tape and packaged in a roll or pancake in an extraction enclosure for a sufficient time to allow said extraction. According to some of these other embodiments, the electric cable may be a section of terrestrial electric cable having a length of between around 1000 m and around 2000 m.

[0042] That being said, nothing prevents providing, according to other embodiments, alone or in combination with at least one previous embodiment, that the tape is subjected to said extraction step during (concomitantly with) the application of the tape around the core of the electric cable, that is to say in contact with the core of the electric cable or in contact with a more external layer of the electric cable. According to these other embodiments, the electric cable may be a section of underwater electric cable having a length of the order of 10,000 m or more.

[0043] According to some of these other embodiments, it is possible to form the core of the electric cable by extrusion / crosslinking of the insulating system on the surface of the central elongated electrically conductive element according to a technique known per se, then to apply the tape to the surface of the core of the electric cable and to carry out the step of extracting at least one undesirable chemical species from the material constituting the tape, said tape extending on the surface of the core of the electric cable.

[0044] According to certain embodiments, said extraction step is a step of heating the ribbon, at a temperature chosen to allow said extraction.

[0045] According to these embodiments, said extraction step is a step of heating the ribbon, carried out by means of a radiative heating member - in particular a Joule effect heating member or a heat pipe - or an inductive heating member. According to these embodiments, said extraction step is a step of heating the ribbon, at a temperature chosen according to the nature of these chemical species, to allow said extraction. Of course, according to the invention, the temperature and the duration of heating of the ribbon are controlled so as not to degrade the physical properties of the ribbon. According to these embodiments, said step of heating the ribbon is carried out in an extraction enclosure comprising means for heating an interior space of said extraction enclosure, and the extraction of the undesirable chemical species from the ribbon can be obtained remotely from the manufacturing site and production of the electric cable and independently of the manufacture of the cable.

[0046] According to some of these other embodiments, alone or in combination with one of the preceding embodiments, said extraction step comprises at least one step of blowing a flow of a gaseous composition into contact with the ribbon, said ribbon extending on the external surface - in particular on the external surface of the core - of the electrical cable being manufactured. According to some of these embodiments, the flow of gaseous composition is at ambient temperature. According to some of these embodiments, the flow of gaseous composition is a flow of atmospheric air. According to some of these embodiments, the flow of gaseous composition may be a flow of atmospheric air at ambient temperature or at a temperature above ambient temperature.

[0047] According to certain embodiments, the blowing of a flow of gaseous composition in contact with the ribbon is carried out in a tubular space open at its two longitudinal ends and in which the electric cable being manufactured - in particular the core of the electric cable being manufactured - and said ribbon extending on the surface of the electric cable being manufactured are jointly driven in movement.

[0048] Any other means of extraction is possible, alone or in combination.

[0049] According to certain embodiments, said undesirable chemical species may be water. It may be water formed during the manufacture of the tape and capable of subsequently reaching at least one layer of the insulating system, by migration from the tape during use of the electric cable and of reducing the dielectric performance of this layer and of the insulating system. For example, it may be water formed due to oligomerization reactions and decomposition of by-products of crosslinking of the tape into crosslinked polymer material.

[0050] In these embodiments, at least one undesirable chemical species of the ribbon being water, the heating temperature of the ribbon is chosen to allow extraction of at least a portion of this water.

[0051] In other embodiments, said undesirable chemical species may be a by-product of manufacturing at least one material forming the ribbon.

[0052] According to certain embodiments, the heating temperature of the tape is between ambient temperature and a temperature preserving the physical properties of the tape. According to certain embodiments, the heating temperature of the tape is between 50°C and 100°C. The heating temperature of the tape applied to the electrical cable (on the core of the electrical cable or on a more external layer of the electrical cable) is chosen so as not to modify the performance of the electrical cable and in particular the performance of the core of the electrical cable. According to certain embodiments, it is possible to choose a heating temperature of the tape which is high and an exposure time of the tape which is short. According to certain other embodiments, it is possible to choose a lower ribbon heating temperature and an increased ribbon exposure time.

[0053] According to certain embodiments, the electrical cable is a medium or high voltage electrical cable in which at least one layer, in particular each layer, of the insulating system comprises at least one crosslinked polyethylene.

[0054] According to certain embodiments, the electrical cable being an underwater cable comprising fittings, portions of ribbon extending opposite the fittings are subjected to said at least one extraction step.

[0055] According to some embodiments, the electrical cable is a medium or high voltage direct current (HVDC) electrical cable.

[0056] According to certain embodiments, the electrical cable is a medium or high voltage alternating current (HVAC) electrical cable. The presence of undesirable chemical species—particularly water—in the ribbon poses a problem for alternating current cables. In particular, the presence of water can lead to degradation by treeing. The method according to the invention therefore makes it possible to maintain the service life of such alternating current electrical cables and in particular factory fittings. The method according to the invention therefore makes it possible to manufacture such electrical cables and to maintain the service life of such alternating current electrical cables for use in a humid environment, in particular alternating current electrical cables free of a protective metal barrier against water.The method according to the invention therefore makes it possible to manufacture such alternating current electric cables for which the time required to reach humid conditions marking the start of degradation, by diffusion of water through the tape, can be considerably extended.

[0057] In a method according to the invention, said extraction step is limited to an extraction of undesirable chemical species, in particular water, from the ribbon.

[0058] The invention also extends to a medium or high voltage electrical cable capable of being obtained - in particular obtained - by a method according to the invention. A medium or high voltage electrical cable according to the invention comprises an insulating system whose dielectric properties are at least substantially maintained over time. Brief description of the drawings

[0059] Other characteristics and advantages of the invention will become apparent from reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings in which:

[0060] [Fig.l]] [Fig.l] is a schematic representation of a cross-section of an electric cable according to a particular embodiment of the invention, and;

[0061] [Fig.2] [Fig.2] is a graphical representation of comparative results provided by the method according to the invention on the breakdown resistance of a medium voltage electric cable. Description of the embodiments

[0062] Power cables or electrical cables typically comprise an elongated central electrically conductive element and an insulating system extending in contact with the outer face of the elongated central electrically conductive element and comprising at least one electrically insulating layer crosslinked by techniques well known to those skilled in the art, for example by peroxide or other means. The crosslinked electrically insulating layer may be a layer of crosslinked polyethylene (XLPE).But the insulating system may also comprise a plurality of layers superimposed and coaxial with respect to the elongated central electrically conductive element, including a first semiconducting layer called "internal semiconducting layer" extending in contact with an external surface of the elongated central conductive element, an electrically insulating layer extending in contact with an external surface of said internal semiconducting layer and a second semiconducting layer called "external semiconducting layer" extending in contact with an external surface of the electrically insulating layer. Each of the layers of the insulating system may comprise a polymer material such as a crosslinked polyethylene, in particular the same crosslinked polyethylene. Each of said internal semiconducting layer and external semiconducting layer comprises a semiconducting filler in sufficient quantity to make the corresponding layer semiconducting.

[0063] For reasons of clarity, only the essential elements for understanding the embodiments set out below have been shown schematically, and this without necessarily respecting the relative dimensions of the constituent elements of the electric cable.

[0064] A cross-section of a medium or high voltage electrical cable 1 shown in [Fig.l] as an illustrative but non-limiting example of the invention, comprises an elongated central conductive core 1. The elongated central conductive core 1 may be of any type. It may be in particular but not exclusively of the type comprising at least one elongated electrically conductive element, for example in the form of at least one electrically conductive metal wire, in particular made of copper or aluminum, and at least one insulating system, each insulating system being arranged coaxially around an elongated electrically conductive element.

[0065] The insulating system of the elongated central conductive core 1 may comprise a plurality of layers, including at least one layer made of at least one crosslinked polymer material, arranged coaxially and successively around this elongated electrically conductive element, enveloping the electrically conductive element lying down, including for example: - a first semi-conductor layer called “internal semi-conductor layer” extending in contact with an external surface of the elongated electrically conductive element, - an electrically insulating layer extending in contact with an external surface of said internal semiconducting layer, - a second semiconducting layer called the “external semiconducting layer” extending in contact with an external surface of the electrically insulating layer. Other insulating systems are possible.

[0066] The electric cable of [Fig. 1] has a ribbon 2 extending to the contact and surrounding the elongated central conductive core 1. The ribbon 2 is a ribbon obtained by a method according to the invention, and surrounding the elongated central conductive core 1. The ribbon 2 can be wound in a helix around the elongated central conductive core 1 with or without overlapping zones or be folded radially over the core of the electric cable.

[0067] The electric cable shown in [Fig.l] also successively comprises: - a conductor screen 3 extending in contact with the external face of the strip 2 and surrounding the elongated central conductive core 1 and the strip 2, - an insulating layer 4 placed in contact with the external face of the screen 3 and covering said screen 3, - a screen 5 of the insulating layer 4 arranged in contact with the external face of the insulating layer 4 and surrounding the underlying elements 1,2,3,4, -a longitudinal water blocking element 6 arranged in contact with the screen 5. The longitudinal water blocking element 6 is a ribbon 6 obtained by a method according to the invention, and surrounding the underlying elements 1, 2, 3, 4, 5, -an external assembly comprising a plurality of successive layers, in particular a protective lead layer 7 forming a metal barrier arranged in contact with the external face of the longitudinal water-blocking element 6, an internal sheath 8 of the external assembly, a padding 9 accommodating reinforcement wires 10 and a layer 11 forming an interface of the electric cable with its environment. In the embodiment shown, certain reinforcement wires 10 are replaced by elements 12 of optical fibers contained in metal tubes (FIMD, for “Fiber In Metallic Tube”).

[0068] The tape 2 makes it possible to oppose and prevent water migration along the longitudinal axis of the cable in the event of damage to the latter during operation. But the tape 2 also makes it possible to prevent direct contact of the materials (“stranding materials”) of the peripheral layers with the insulation system.

[0069] The ribbon 6 surrounding the underlying elements 1,2,3,4,5 extends under the layer 7 lead protective layer forming a metal barrier against water. Tape 6 provides contact between the metal barrier 7 and the underlying cross-linked polyethylene. Tape 6 also prevents water from spreading in the event of infiltration into the electrical cable.

[0070] According to certain embodiments, the invention relates to a method for manufacturing a medium or high voltage electric cable comprising: - a core based on crosslinked polyethylene (HVDC XLPE or HVAC XLPE type cables), of the type comprising a central elongated electrically conductive element, in particular made of copper or aluminum, and an insulating system comprising or formed of a plurality of layers arranged coaxially around this central elongated electrically conductive element, including a first semi-conductive layer called the "internal semi-conductive layer" extending in contact with the elongated electrically conductive element, an electrically insulating layer extending in contact with said internal semi-conductive layer and a second semi-conductive layer called “outer semiconducting layer” extending in contact with the electrically insulating layer, and - a tape enveloping the core and formed from a flexible semiconducting material. The three layers forming the insulating system are typically layers of polymer(s) - in particular polyethylene - crosslinked by techniques known to those skilled in the art.

[0071] At least one of the insulating and / or semiconducting layers - in particular each of the insulating and semiconducting layers - comprises at least one crosslinked polyethylene.

[0072] The soul of the electric cable

[0073] The core of the electric cable can be obtained by any method known to those skilled in the art, for example by extrusion / crosslinking (in particular by co-extrusion / crosslinking) of the insulating system around a central elongated electrically conductive element, according to any technique known per se.

[0074] The precursor compositions of the insulating and semiconducting layers of the insulating system may be coextruded around the elongated electrically conductive element and the crosslinking of the precursor compositions coextruded around the elongated electrically conductive element is induced by activation of the corresponding crosslinking agent.

[0075] For example, the crosslinked semiconducting and insulating layers of the insulating system are obtained from precursor compositions based on a polyethylene polymer matrix associated with organic peroxides. The crosslinking of these precursor compositions is typically induced by a heat treatment during the extrusion of the insulating and semiconducting layer(s) around the elongated electrically conductive element.

[0076] The crosslinked polymer materials of the different layers of the insulating system can be obtained from the same polyethylene precursor matrix. However, nothing prevents provision being made for at least two of the layers of the insulating system to be obtained from separate polyethylene precursor matrices.

[0077] Ribbon

[0078] At least one material constituting the ribbon may be a polymer material, in particular a semiconducting polymer material. At least one material constituting the ribbon may be a non-woven material, in particular a swelling non-woven material. The ribbon may be formed from at least one material chosen from the group of polymer materials. The ribbon may be formed from at least one material chosen from the group of textile fibers. The ribbon may be textile fibers including nylons, polyesters, rayon, in particular.

[0079] Extraction step

[0080] The method according to the invention for manufacturing an electric cable provides at least one step of extracting at least one chemical species from the tape, said chemical species being a chemical species capable of reaching the insulating system by migration from the tape and of reducing the dielectric performance of the insulating system.

[0081] According to a first embodiment, a roll of ribbon is subjected to a heating step in an oven. The dimensions of the oven are chosen to allow the heating of the number of rolls required. An air circulation between the outside and the inside of the oven is established so as to carry away the undesirable chemical species - in particular humidity - extracted from the ribbons. The temperature in the oven is between 50°C and 100°C.

[0082] According to a second embodiment, the ribbon wound on the central core of the electric cable is subjected to a heating step by blowing hot air at a temperature between 50°C and 100°C onto the ribbon. In this second embodiment, the hot air blown is dry air. Preferably, the hot air is dried using a dehumidifying agent, such as for example silica before being blown onto the ribbon. This second embodiment has the advantage of being able to be implemented on a cable production line in a continuous system.

[0083] According to another embodiment, nothing prevents the provision of subjecting the electric cable, that is to say the electric cable provided with the tape, to the heating step in a ventilated oven heated to a temperature between 50°C and 100°C.

[0084] In a particular embodiment, a step of extracting at least one undesirable chemical species from the tape is carried out by subjecting the tape to said extraction step prior to placing the tape around the core of the electric cable.

[0085] According to this embodiment, the tape substantially freed from undesirable chemical species can be preserved until its application to the core of the cable.

[0086] It is possible to carry out said extraction step by placing the protective cable in a heating enclosure and heating said material to a temperature chosen to allow extraction of at least one undesirable chemical species from the tape. For example, the tape may be packaged in a form wound on a reel adapted to allow subsequent application to the surface of the electric cable being manufactured - in particular to the surface of the core of the electric cable being manufactured - of a tape at least partially freed from undesirable chemical species as obtained after subjection to said extraction step. In this particular embodiment, said extraction step is a step of heating the tape and at least partial vaporization of at least one of the undesirable chemical species.In this particular embodiment, said extraction step is carried out so as to extract from the extraction enclosure, at least one of the vaporized undesirable chemical species.

[0087] In this embodiment, nothing prevents the provision of forming a flow of gaseous composition passing through said extraction enclosure, so as to entrain at least one of the undesirable chemical species vaporized at a distance from the ribbon.

[0088] According to some of these embodiments, the tape obtained by the method according to the invention can be applied to the surface of factory joints for electric cables intended for underwater use, for which the risk of migration of undesirable chemical species is the same as for an electric cable.

[0089] In another embodiment of a method according to the invention, a step of extracting at least one undesirable chemical species from the tape is carried out by subjecting the tape to said extraction step when the tape is placed around the core of the electric cable or after said placement of the tape around the core of the electric cable. In these embodiments, the core of the cable is moved along its longitudinal axis and the tape is applied and made integral with the core of the cable moved. In these embodiments, the electric cable formed by applying and wrapping the tape around the core of the electric cable is subjected to said extraction step by blowing a flow of gaseous composition - in particular a flow of atmospheric air - directed and applied to the external face of the tape.In certain embodiments, said blowing extraction step is carried out in an extraction enclosure formed by a tube crossed by the electric cable driven in movement, the flow of gaseous composition being directed and applied to the external face of the ribbon of the protective cable driven in movement in the tube. According to certain embodiments, the flow of gaseous composition and / or the internal space of the tube is(are) heated to a temperature suitable for allowing. a vaporization of at least one undesirable chemical species from the tape applied to the core of the electrical cable.

[0090] Due to this extraction of undesirable chemical species from the ribbon of the electric cable, the loss of dielectric performance of said electric cable obtained by a method according to the invention is limited, in particular the dielectric performance of said electric cable is maintained during use of the electric cable. Examples

[0091] [Fig. 2] is an illustration of the results obtained by a method according to the invention. Water-swellable non-woven material tapes were preconditioned and then wound around a medium voltage cable. The preconditionings include: A- tape dried for 24 hours at a temperature of 100°C in an oven, B- tape placed for 24 hours in an enclosure with a humidity level of 30% at 25°C, C- tape placed for 24 hours in an enclosure with a humidity level of 50% at 25°C, and C- tape placed for 24 hours in an enclosure with a humidity level of 80% at 25°C.

[0092] The ribbons thus obtained are each wound around the outer semiconducting layer of crosslinked polyethylene (XLPE) of a medium voltage electrical cable comprising an elongated electrically conductive element and an insulating system arranged coaxially around the elongated electrically conductive element. The insulating system comprises an inner semiconducting layer extending in contact with an outer surface of the elongated electrically conductive element, an electrically insulating layer extending in contact with an outer surface of said inner semiconducting layer, and an outer semiconducting layer extending in contact with an outer surface of the electrically insulating layer.Each cable equipped with one of the ribbons A, B, C or D is subjected to successive high voltage cycles, each cycle lasting 12 hours, the high voltage increasing between two successive cycles and by applying to the cable a temperature at most equal to +90°C for 4 hours and cooling the cable to room temperature. The increase in high voltage during the cycles continues until the breakdown voltage is reached. The breakdown resistance given in [Fig.2] corresponds to the high voltage value which led to the breakdown.

[0093] The results presented in [Fig.2] were obtained by heating the ribbons to a temperature of 100°C, but tests carried out at a lower temperature (70°C) led to very similar results.

[0094] Due to said step of extracting undesirable chemical species from the ribbon, the re the breakdown resistance of said electric cable obtained by the method according to the invention is increased and the loss of dielectric performance of said electric cable obtained by a method according to the invention can be limited.

Claims

Claims

1. A method of manufacturing a medium or high voltage electrical cable, of the type comprising: - a core formed from an elongated electrically conductive element and an insulating system comprising at least one layer comprising at least one crosslinked polyethylene, said at least one layer being arranged coaxially around the elongated electrically conductive element, and - a tape enveloping the core and extending in contact or not with the core, characterized in that the method comprises at least one step of extracting at least one chemical species from the tape, said chemical species being a chemical species capable of reaching the insulating system by migration from the tape and of reducing the dielectric performance of the insulating system.

2. Method according to claim 1, characterized in that the ribbon is formed from at least one material chosen from the group formed of non-woven materials and polymeric materials.

3. Method according to one of claims 1 or 2, characterized in that the tape is subjected to said at least one extraction step prior to the application of the tape around the core of the electric cable.

4. Method according to claim 3, characterized in that, the ribbon being packaged in the form of a roll, said roll is placed in an extraction enclosure for a time sufficient to allow said extraction.

5. Method according to one of claims 1 to 4, characterized in that the electric cable provided with the tape and packaged in a roll is placed in an extraction enclosure for a sufficient time to allow said extraction.

6. Method according to one of claims 1 to 5, characterized in that the tape is subjected to at least one extraction step, during the application of the tape to the core of the electric cable.

7. Method according to one of claims 1 to 6, characterized in that at least one extraction step is a step of heating the ribbon, at a temperature chosen to allow said extraction.

8. A method according to claim 7, characterized in that said step of heating the ribbon is carried out by means of a radiative heating member or an inductive heating member.

9. Method according to one of claims 7 or 8, characterized in that at least one extraction step comprises at least one step of blowing a flow of a gaseous composition into contact with the ribbon, said ribbon extending on the external surface of the electric cable being manufactured.

10. Method according to claim 9, characterized in that the blowing of a flow of a gaseous composition in contact with the ribbon is carried out in a tubular space open at its two longitudinal ends and in which the electric cable being manufactured and said ribbon extending on the surface of said electric cable being manufactured are jointly driven in movement.

11. Method according to one of claims 7 to 10, characterized in that at least one chemical species of the ribbon being water, the heating temperature of the ribbon is chosen to allow extraction of at least part of this water.

12. Method according to one of claims 7 to 11, characterized in that the heating temperature of the ribbon is between 50°C and 100°C.

13. Method according to one of claims 1 to 12, characterized in that the electric cable is a high voltage electric cable in which each layer of the insulating system comprises - in particular consists of - at least one crosslinked polyethylene.

14. Method according to one of claims 1 to 13, characterized in that the electric cable being an underwater cable comprising fittings, portions of ribbon extending opposite the fittings are subjected to said at least one extraction step.

15. Method according to one of claims 1 to 14, characterized in that the electric cable is a direct current (DCV) electric cable.

16. Method according to one of claims 1 to 14, characterized in that the electric cable is an alternating current electric cable (ACHT).

17. Medium or high voltage electric cable capable of being obtained - in particular obtained - by a method according to one of claims 1 to 16.

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