Cable

Abstract

Use of a cable, for example for transmitting electrical power in a saline environment such as in or under the sea; the cable comprising a conductor surrounded in sequence at least by an internal semiconductor layer, an insulating layer and an external semiconductor layer; wherein the insulating layer comprises (i) at least 60% by weight of a low density polyethylene homopolymer or a low density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and, (ii) 10 - 35% by weight of a low density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate or vinyl acetate.

Description

Technical Field

[0001] The present invention relates to a wet-designed cable for a brine environment, particularly a wet-designed power cable for a brine environment, including an insulating layer in which a polymer water tree retarder is used to achieve water tree retardation. In particular, the insulating layer of the cable of the present invention comprises a combination of LDPE homopolymer or LDPE copolymer and a polymer water tree retarder. The present invention also relates to a method for manufacturing such a cable and the use of such a cable in a brine environment. Background Art

[0002] A standard power cable includes a conductor surrounded successively by an inner semiconductor layer (also referred to as a conductor shield layer), an insulating layer, and an outer semiconductor layer (also referred to as an insulation shield layer). The cable may also be provided with additional layers, such as a jacket layer, as is well known in the art.

[0003] In cases where the cable will be used underwater or buried underground, it is known to wrap the cable with a waterproof layer (moisture barrier layer), which is typically a metal waterproof layer, to protect the cable from problems caused by water ingress.

[0004] We refer to this as a dry cable design. Thus, a dry cable structure or dry cable design refers to a cable design in which there is a moisture barrier layer around the cable core (defining the core as the conductor, inner semiconductor layer, insulating layer, outer semiconductor layer). Optionally, other layers may also be present outside the cable core, such as a shielding layer. The moisture barrier layer is a layer that cannot be penetrated by water.

[0005] Long-term on-site experience has shown that an extruded metal sheath, such as an extruded lead / lead alloy sheath, serves as a moisture barrier layer. When the cable design includes a waterproof layer different from an extruded metal sheath, tests for evaluating whether the structure is dry can be found in Cigre TB722. Thus, the moisture barrier layer is preferably metal.

[0006] A so-called wet design or wet structure is defined as a cable structure in which there is no moisture barrier layer. Thus, such a design does not have a moisture barrier layer such as an extruded metal moisture barrier layer.

[0007] Thus, in a dry cable design, the moisture barrier layer can prevent water from entering the cable, but it significantly increases the raw material cost of the cable and is also expensive to use. In addition, traditional moisture barrier layers are typically made of lead, which may have a significant impact on the environment.

[0008] It is necessary to determine a cable material system (i.e., the materials of the cable insulation layer and the semiconductor layer) that can be used for "wet" designed cables. In wet design, the outer semiconductor layer may not have a covering layer, or may have a shielding layer or a jacket layer as the outermost layer. Such cables are advantageous in terms of raw material costs and manufacturing expenses, but cables without a waterproof layer (moisture barrier) must be strictly tested to prove that the cables have sufficient water resistance.

[0009] Therefore, in wet designed cables, attention must be paid to maximizing the water tree retardant (WTR) performance of the cable insulation layer.

[0010] One limitation of polyethylene is that they are prone to forming shrub-like defects, namely so-called water trees, in the presence of water and an electric field, which will lead to a reduction in breakdown strength and may cause electrical failures. This tendency is affected by the inhomogeneities, microcavities, and impurities present in the material.

[0011] In electro-strain polymer materials affected by water, a process characterized by "water trees" occurs. It is well known that when insulated cables are installed in an environment where the polymer contacts water, for example, underground or in a high humidity area, the service life of the insulated cables will be shortened.

[0012] Theoretically, water trees can be divided into two types:

[0013] "Vent trees" starting from the semiconductor shielding surface and extending into the cable insulation layer and "bow-tie trees" originating within the cable insulation layer.

[0014] The water tree structure constitutes local damage, resulting in a reduction in dielectric strength.

[0015] Various water tree retardants are well known in the art. There are many literatures disclosing the addition of water tree retardants in cables to minimize water trees. In EP1731566, the combination of an unsaturated polyolefin with a specific vinyl content and a polar copolymer is taught to improve wet aging performance.

[0016] WO2010 / 112333 describes a cable comprising a conductor surrounded by a semiconductor layer and an insulation layer, wherein the semiconductor layer is composed of a composition (A) containing a polar copolymer (a) and carbon black, and the insulation layer is composed of a composition (B) containing a polar copolymer, and the difference between the melting temperature of the polar copolymer (a) and the melting temperature Tm(b2) of the polar copolymer (b2) is less than 25 °C.

[0017] WO 85 / 05216 describes an insulating composition composed of polyethylene and 10 - 40 wt% of a (meth)acrylate polymer such as ethylene butyl acrylate.

[0018] JP H08 319381 illustrates some blends based on ethylene methyl acrylate and LDPE and test sheets made therefrom, and the above blends and test sheets were subjected to a water tree test in very strong brine (2 mol / L).

[0019] The present inventors have paid particular attention to wet aging in brine, especially seawater. Brine tends to exacerbate the water tree problem in cables, so designing cables that may be exposed to brine is challenging.

[0020] In addition to sodium chloride, brine can also contain magnesium, calcium, potassium, and sulfate ions, etc. These dissolved salts can have an impact on water trees in wet-designed cables. Brine, such as seawater, is a more corrosive environment compared to, for example, fresh water. This does not mean that materials that can operate in a fresh water environment can withstand exposure to seawater.

[0021] The present inventors have now found that the insulating layer of a wet-designed cable suitable for a brine environment can comprise a combination of an LDPE homopolymer or an LDPE copolymer having a polyunsaturated comonomer and an LDPE copolymer having a polar comonomer. The LDPE copolymer having a polar comonomer acts as a polymer water tree retarder.

[0022] Johansson et al. discussed wet-designed cables, the influence of subsea conditions on the long-term performance of AC XLPE cables, at the 8th International Conference on Insulated Power Cables, Jicable'11 - 19 - 23 June 2011, Versailles - France (Influence of subsea conditions on the long term performance of AC XLPE cables, Jicable’11–19–23 June 2011, Versailles–France). A variety of cables tested used a high-performance water tree retardant, namely copolymer XLPE.

[0023] Featherstone et al. reported the brine testing of wet-designed XLPE cables in "Full scale wet age testing of XLPE insulated power cables in salt water", Jicable’19, Paris 23 - 27 June 2019 (Jicable’19, Paris 23 - 27 June 2019, Featherstone et al.).

[0024] However, the combination of specific polymers in the insulating layer and the semiconductor layer as defined herein and the ability of this combination to resist dielectric breakdown in a saline environment are novel. Summary of the Invention

[0025] In one aspect, the present invention provides a use of a cable, for example, for transmitting electric power in a saline environment such as in the sea or under the sea;

[0026] The cable includes a conductor, which is at least sequentially surrounded by an internal semiconductor layer, an insulating layer, and an external semiconductor layer;

[0027] Wherein, the insulating layer includes

[0028] (i) at least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and,

[0029] (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, or vinyl acetate.

[0030] In another aspect, the present invention provides a use of a cable, for example, for transmitting electric power in a saline environment such as in the sea or under the sea;

[0031] The cable includes a conductor, which is at least sequentially surrounded by an internal semiconductor layer, an insulating layer, and an external semiconductor layer;

[0032] Wherein, the insulating layer includes

[0033] (i) at least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and,

[0034] (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, or vinyl acetate; and

[0035] Wherein, each of the internal semiconductor layer and the external semiconductor layer includes:

[0036] (a) a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, or vinyl acetate; and

[0037] (b) carbon black.

[0038] In one aspect, the present invention provides a cable, which comprises a conductor surrounded in sequence by at least an inner semiconductor layer, an insulating layer, and an outer semiconductor layer;

[0039] wherein the insulating layer comprises

[0040] (i) at least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and,

[0041] (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and

[0042] wherein each of the inner semiconductor layer and the outer semiconductor layer comprises:

[0043] (c) a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and

[0044] (d) carbon black.

[0045] The cable of the present invention is desirably a wet design cable.

[0046] The cable of the present invention is crosslinkable or crosslinked. Thus, in another embodiment, the insulating layer contains peroxide and is crosslinkable. In another embodiment, the inner semiconductor layer and / or the outer semiconductor layer contains peroxide and is crosslinkable. In another embodiment, the insulating layer, the inner semiconductor layer, and the outer semiconductor layer contain peroxide and are crosslinkable. When under crosslinking conditions, the crosslinkable cable can be crosslinked. The peroxide decomposes and generates free radicals, which initiate the crosslinking reaction in the composition.

[0047] In another aspect, the present invention provides a crosslinked cable, which can be obtained by crosslinking the crosslinkable cable as defined above. In another aspect, the present invention provides the use of the crosslinked cable as defined above, for example, for transmitting electricity in a saline environment such as in the sea or under the sea.

[0048] In another aspect, the present invention provides a method for producing a cable, which comprises a conductor surrounded in sequence by at least an inner semiconductor layer, an insulating layer, and an outer semiconductor layer, wherein the method comprises the following steps:

[0049] - extruding, for example, co-extruding, the inner semiconductor layer, the insulating layer, and the outer semiconductor layer onto the conductor; and

[0050] - crosslink one or more of the internal semiconductor layer, the insulating layer, and the external semiconductor layer;

[0051] wherein the insulating layer comprises

[0052] (i) at least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and,

[0053] (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and

[0054] wherein each of the internal semiconductor layer and the external semiconductor layer comprises:

[0055] (a) a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and

[0056] (b) carbon black. Detailed Description

[0057] The present invention provides a cable for use in a brine environment, such as a crosslinkable cable or a crosslinked cable, for example, a crosslinkable or crosslinked power cable, the cable comprising a conductor surrounded by at least an internal semiconductor layer, an insulating layer, and an external semiconductor layer. The present invention also relates to a crosslinked cable comprising a conductor surrounded by at least an internal semiconductor layer, an insulating layer, and an external semiconductor layer.

[0058] As used herein, the term "brine" or "brine environment" means a solution containing dissolved sodium chloride (NaCl) and having an NaCl content of 1.0% by weight or more, preferably 2.0% by weight or more, more preferably 3.0% by weight or more, and an NaCl content of 10% by weight or less, preferably 8% by weight or less, more preferably 6% by weight or less, relative to the total amount of water.

[0059] The cables of the present invention preferably have a wet design as defined above. Ideally, the cables do not include a moisture barrier, such as a metal water barrier, to prevent water ingress. Despite the wet design of the cables of the present invention, they provide excellent resistance to water treeing in a brine environment. This is demonstrated by the analysis of the electrical breakdown strength after wet aging in brine. Thus, in other words, the present invention provides cables having improved electrical breakdown strength in a brine environment.

[0060] Some experts consider the presence of a polymer jacket on the outer semiconductor layer as a "semi-wet" design because the jacket layer restricts the rate of water vapor ingress. In this article, we consider this solution as a wet design because water or moisture can permeate the jacket layer.

[0061] Insulating layer

[0062] The cable of the present invention comprises an insulating layer comprising at least 60% by weight of a low density polyethylene homopolymer or a low density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and

[0063] 10 - 35% by weight of a low density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates or vinyl acetate.

[0064] Low density polyethylene homopolymer or low density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers

[0065] Component (i) of the insulating layer is an LDPE homopolymer or an LDPE copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers. This is referred to herein as the LDPE polymer component (i).

[0066] Although the term LDPE is an abbreviation for Low Density Polyethylene, it should be understood that this term does not limit the density range but encompasses high pressure (HP) polyethylene similar to LDPE. Compared with polyethylene produced in the presence of an olefin polymerization catalyst, the term LDPE only describes and differentiates the properties of HP polyethylene having typical characteristics, such as different branching structures.

[0067] It should be understood that the term "LDPE homopolymer" generally refers to a low density polyethylene polymer consisting essentially of ethylene monomers. Thus, ideally, the LDPE homopolymer does not contain comonomers. However, a small amount of comonomers different from ethylene will not have a substantial impact on the properties of LDPE and this is tolerable because this material remains essentially a homopolymer. In this regard, a small amount of comonomers can be understood as less than 3% by weight, such as less than 1% by weight, less than 0.5% by weight or less than 0.1% by weight of non-polar or polar comonomers different from ethylene.

[0068] Preferably, the LDPE polymer component (i) is an LDPE copolymer having at least one polyunsaturated comonomer.

[0069] In one embodiment, the low-density polyethylene copolymer in the insulating layer having at least one polyunsaturated comonomer and optionally one or more other comonomers comprises less than 5 wt% of a polar comonomer selected from alkyl acrylates, alkyl methacrylates or vinyl acetate. In one embodiment, the LDPE copolymer component (i) of the insulating layer comprises less than 3.0 wt%, preferably less than 2.0 wt%, especially less than 1.0 wt% of such polar comonomers.

[0070] Preferably, the LDPE copolymer component (i) is a binary copolymer of ethylene and only one polyunsaturated comonomer.

[0071] The polyunsaturated comonomer preferably consists of a straight carbon chain having at least 8 carbon atoms and having at least 4 carbon atoms between non-conjugated double bonds, with at least one double bond at the end. The polyunsaturated comonomer is preferably a diene, such as a diene containing at least eight carbon atoms, with the first carbon-carbon double bond at the end and the second carbon-carbon double bond non-conjugated with the first double bond, such as selected from C8 to C 14 non-conjugated dienes or mixtures thereof, such as selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene or mixtures thereof, such as from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene or any mixture thereof.

[0072] If another comonomer is present, it may be a C3 to C 10 alpha-olefin.

[0073] The LDPE copolymer component (i) preferably comprises 0.001 to 40 wt%, preferably 0.05 to 40 wt%, more preferably 0.05 to 30 wt%, still more preferably 1.0 to 30 wt%, still more preferably 1.0 to 20 wt% of one or more total comonomers (i.e., all comonomers). In one embodiment, the LDPE copolymer comprises 0.05 to 20 wt%, preferably 0.05 to 15 wt%, such as 1.0 to 10 wt%, particularly 0.05 to 5.0 wt%, such as 1.0 to 5.0 wt%, more particularly 0.05 to 3.0 wt%, such as 1.0 to 3.0 wt% of total comonomers.

[0074] The content of the polyunsaturated comonomer is preferably from 0.001 to 10% by weight, preferably from 0.01 to 10% by weight, more preferably from 0.01 to 5.0% by weight, even more preferably from 0.01 to 3.0% by weight, particularly from 0.01 to 2.0% by weight, and more particularly from 0.1 to 2.0% by weight. In some embodiments, the only comonomer present is the polyunsaturated comonomer.

[0075] The LDPE polymer component (i) is preferably unsaturated. It preferably has a total number of carbon-carbon double bonds more than 0.4 / 1000 carbon atoms, preferably more than 0.5 / 1000 carbon atoms, such as more than 0.6 / 1000 carbon atoms, particularly more than 0.7 / 1000 carbon atoms, for example, more than 0.8 / 1000 carbon atoms. There is no limit to the upper limit of the number of carbon-carbon double bonds present in the polyolefin and it can preferably have a total number of carbon-carbon double bonds less than 5.0 / 1000 carbon atoms, preferably less than 3.0 / 1000 carbon atoms.

[0076] In some embodiments, in the LDPE polymer component (i), the total number of carbon-carbon double bonds derived from vinyl, vinylidene and trans-vinylidene (if present) is more than 0.40 / 1000 carbon atoms, preferably more than 0.50 / 1000 carbon atoms, more preferably more than 0.60 / 1000 carbon atoms, even more preferably more than 0.70 / 1000 carbon atoms, still even more preferably 0.75 / 1000 carbon atoms, particularly 0.8 / 1000 carbon atoms. Preferably, the total number of carbon-carbon double bonds derived from vinyl, vinylidene and trans-vinylidene is less than 5.0 / 1000 carbon atoms, preferably less than 3.0 / 1000 carbon atoms.

[0077] In some embodiments, the LDPE polymer component (i) contains at least vinyl and the total number of vinyl is preferably more than 0.05 / 1000 carbon atoms, even more preferably more than 0.08 / 1000 carbon atoms, and most preferably more than 0.11 / 1000 carbon atoms.

[0078] In some embodiments, the LDPE polymer component (i) contains at least vinyl and the total number of vinyl is preferably more than 0.15 / 1000 carbon atoms, such as more than 0.20 / 1000 carbon atoms, more preferably more than 0.25 / 1000 carbon atoms, particularly more than 0.3 / 1000 carbon atoms, more particularly more than 0.35 / 1000 carbon atoms, most particularly more than 0.40 / 1000 carbon atoms, such as more than 0.45 / 1000 carbon atoms or 0.50 / 1000 carbon atoms.

[0079] Preferably, the total amount of vinyl groups is less than 4.0 / 1000 carbon atoms. More preferably, the LDPE polymer component (i) contains vinyl groups in a total amount of more than 0.20 / 1000 carbon atoms before crosslinking, even more preferably more than 0.30 vinyl groups / 1000 carbon atoms, most preferably more than 0.40 vinyl groups / 1000 carbon atoms, such as more than 0.45 vinyl groups / 1000 carbon atoms, especially more than 0.50 vinyl groups / 1000 carbon atoms.

[0080] Preferably, the melt flow rate MFR 2.16 / 190 °C of the LDPE polymer component (i) is from 0.1 to 50 g / 10 min, preferably from 0.3 to 20 g / 10 min, more preferably from 0.3 to 15 g / 10 min, even more preferably from 0.50 to 15 g / 10 min, or from 0.60 to 10 g / 10 min. In some embodiments, MFR 2 is from 0.50 to 8.0 g / 10 min, such as from 0.60 to 6.0 g / 10 min, preferably from 0.70 to 5.5 g / 10 min, such as from 0.80 to 5.0 g / 10 min, more preferably from 0.90 to 4.75 g / 10 min, even more preferably from 1.0 to 4.5 g / 10 min, even more preferably from 1.1 to 4.25 g / 10 min, most preferably from 1.2 to 4.0 g / 10 min, such as from 1.2 to 3.0 g / 10 min.

[0081] The density of any LDPE polymer component (i) can be from 905 to 935 kg / m 3 , preferably from 910 to 935 kg / m 3 , such as from 910 to 928 kg / m 3 .

[0082] The insulating layer preferably does not contain carbon black.

[0083] The insulating layer may comprise at least 60 wt% of the LDPE polymer component (i), such as at least 60 to 90 wt% of the LDPE polymer component (i), especially 70 to 85 wt% of the LDPE polymer component (i). A mixture of LDPE polymers can be used as component (i). In the case of using a mixture of LDPE polymers, the percentage refers to the sum of the LDPE polymers present.

[0084] Once the other components have been calculated, the LDPE polymer component (i) generally constitutes the remainder of the layer.

[0085] Polymer water tree retarder: low density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates or vinyl acetate

[0086] The insulating layer further contains a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate (Component ii). This component is referred to as a polymer water tree retardant. Mixtures of these compounds can be used.

[0087] The low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate used as a polymer water tree retardant can be the same as or different from the low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate used in the inner semiconductor layer and the outer semiconductor layer. Generally, the definition of the low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate provided in the following context for the inner semiconductor layer and the outer semiconductor layer applies to the polymer water tree retardant component (ii) of the insulating layer.

[0088] The polar comonomer in the low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate is preferably selected from C1-C6 alkyl acrylates, C1-C6 alkyl methacrylates, or vinyl acetate. Further more preferably, the LDPE copolymer used is a copolymer of ethylene and a C1-C6 alkyl acrylate, such as ethylene and methyl acrylate, ethyl acrylate, propyl acrylate, or butyl acrylate, or vinyl acetate.

[0089] The use of ethylene methyl acrylate (EMA) copolymer, ethylene methyl methacrylate (EMMA) copolymer, ethylene ethyl acrylate (EEA) copolymer, ethylene ethyl methacrylate (EEMA) copolymer, ethylene butyl methacrylate (EBMA) copolymer, ethylene butyl acrylate (EBA) copolymer, or ethylene vinyl acetate (EVA) copolymer is preferred.

[0090] Particularly preferably, ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), or ethylene ethyl acrylate (EEA) is used.

[0091] The low-density polyethylene copolymer of ethylene and at least one polar comonomer in the insulating layer preferably comprises 0.001 to 40% by weight, more preferably 0.05 to 40% by weight, even more preferably 1 to 30% by weight of one or more comonomers. The content of the polar comonomer is more preferably 5 to 30% by weight, 5 to 25% by weight, 5 to 20% by weight, such as 7 to 25% by weight, especially 7 to 20% by weight, 10 to 25% by weight or 10 to 30% by weight.

[0092] Preferably, the melt flow rate MFR2.16 / 190 °C of the low-density polyethylene copolymer of ethylene and at least one polar comonomer in the insulating layer is 0.1 to 50 g / 10 min, more preferably 1.0 to 30 g / 10 min, even more preferably 2.0 to 25 g / 10 min, and most preferably 2.0 to 22 g / 10 min. In some embodiments, the melt flow rate MFR2.16 / 190 °C of the low-density polyethylene copolymer of ethylene and at least one polar comonomer in the insulating layer is 0.1 to 20 g / 10 min, more preferably 0.5 to 12 g / 10 min. In a further preferred option, the low-density polyethylene copolymer of ethylene and at least one polar comonomer in the insulating layer has an MFR2.16 / 190 °C of 2.0 to 20.0 g / 10 min, such as 2.0 to 17.0 g / 10 min, preferably 2.0 to 15 g / 10 min, such as 2.0 to 13.5 g / 10 min, 2.0 to 13.0 g / 10 min, 2.5 to 12.5 g / 10 min or 2.5 to 12.0 g / 10 min.

[0093] The density of the LDPE copolymer can be 910 to 940 kg / m 3 preferably 915 to 940 kg / m 3 such as 920 to 940 kg / m 3 .

[0094] The insulating layer may comprise 10 to 35% by weight of the low-density polyethylene copolymer (ii) of ethylene and at least one polar comonomer, such as 10 to 30% by weight or 12 to 35% by weight, especially 15 to 30% by weight. In the case of using a blend of these polymers in component (ii), this percentage refers to the sum of the low-density polyethylene copolymer of ethylene and at least one polar comonomer present.

[0095] Peroxide - Insulating layer

[0096] The insulating layer can be crosslinkable or crosslinked. In such crosslinkable embodiments, the crosslinkable insulating layer preferably comprises a peroxide. Once the cable core structure has been formed, the crosslinkable insulating layer preferably comprises a peroxide. A mixture of peroxides can be used.

[0097] Preferred crosslinking agents are organic peroxides. Non-limiting examples are organic peroxides such as di-tert-amyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumyl peroxide, di(tert-butyl) peroxide, dicumyl peroxide, butyl-4,4-bis(tert-butylperoxy)valerate, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl perbenzoate, benzoyl peroxide, di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-amylperoxy)cyclohexane, or any mixture thereof. Preferably, the peroxide is selected from 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, tert-butylcumyl peroxide, or a mixture thereof. Most preferably, the peroxide is dicumyl peroxide.

[0098] Based on the weight of the insulating layer, the peroxide is preferably present in the insulating layer in an amount of less than 3.0 wt%, more preferably 0.1 - 2.5 wt%, and even more preferably 0.3 - 2.5 wt%. In the case of using a mixture of peroxides, the percentage refers to the sum of the peroxides present.

[0099] Inner semiconductor layer and outer semiconductor layer

[0100] The inner semiconductor layer and the outer semiconductor layer can be the same or different, preferably the same. Here, "the same" means that the chemical compositions of the inner semiconductor layer and the outer semiconductor layer are the same before crosslinking. The inner semiconductor layer and the outer semiconductor layer are different from the insulating layer.

[0101] The semiconductor properties of the semiconductor layer are generated by the conductive component, i.e., carbon black, contained in the semiconductor layer.

[0102] Preferably, both the inner semiconductor layer and the outer semiconductor layer contain an LDPE copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate, and carbon black. Preferably, both the inner semiconductor layer and the outer semiconductor layer contain an LDPE copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate, carbon black, peroxide, and optionally an antioxidant. The following discussion is applicable to either or both semiconductor layers.

[0103] Low density polyethylene copolymer (LDPE) of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate

[0104] The LDPE copolymer of the inner semiconductor layer and the outer semiconductor layer comprises a polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates or vinyl acetate or mixtures thereof. Mixtures of such LDPE copolymers can also be used.

[0105] Further preferably, the polar comonomer is selected from C1-C6 alkyl acrylates, C1-C6 alkyl methacrylates or vinyl acetate. Even more preferably, the LDPE copolymer for the inner semiconductor layer and / or the outer semiconductor layer is a copolymer of ethylene and a C1-C6 alkyl acrylate, such as methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate, or vinyl acetate.

[0106] The use of ethylene methyl acrylate (EMA) copolymer, ethylene methyl methacrylate (EMMA) copolymer, ethylene ethyl acrylate (EEMA) copolymer, ethylene butyl methacrylate (EBMA) copolymer, ethylene ethyl acrylate (EEA) copolymer, ethylene butyl acrylate (EBA) copolymer or ethylene vinyl acetate (EVA) copolymer is preferred.

[0107] Particularly preferably, ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA) or ethylene ethyl acrylate (EEA) is used.

[0108] The LDPE copolymer of the inner semiconductor layer and / or the outer semiconductor layer preferably contains 0.001 to 40% by weight, more preferably 0.05 to 40% by weight, even more preferably 1 to 30% by weight of one or more comonomers. The content of the polar comonomer is more preferably 5 to 30% by weight, 5 to 25% by weight, 5 to 20% by weight, such as 7 to 20% by weight.

[0109] Preferably, the melt flow rate MFR2.16 / 190 °C of the LDPE copolymer of the inner semiconductor layer and / or the outer semiconductor layer is 0.1 to 50 g / 10 min, more preferably 1.0 to 30 g / 10 min, even more preferably 2.0 to 25 g / 10 min, such as 3.0 to 20 g / 10 min or 4.0 to 20 g / 10 min, and most preferably 4.0 to 22 g / 10 min, such as 5.0 to 20 g / 10 min.

[0110] The density of the LDPE copolymer can be 910 to 940 kg / m 3 , preferably 915 to 940 kg / m 3 , such as 920 to 940 kg / m 3 .

[0111] The internal semiconductor layer and / or the external semiconductor layer may comprise at least 50% by weight of an LDPE copolymer, such as at least 55% by weight. In the case of using a mixture of LDPE copolymers, the percentage refers to the sum of the LDPE copolymers present.

[0112] In some embodiments, there is at least 60% by weight of an LDPE copolymer in the internal semiconductor layer and / or the external semiconductor layer. Once the other components of the semiconductor layer are selected, the LDPE generally forms the remainder of the layer. The internal semiconductor layer and / or the external semiconductor layer preferably comprise no more than 90% by weight of an LDPE copolymer.

[0113] Any LDPE homopolymer or copolymer described in the present invention can be produced by any conventional polymerization method. Preferably, it is produced by free radical polymerization, such as high-pressure free radical polymerization. The high-pressure polymerization can be carried out in a tubular reactor or an autoclave reactor. Preferably, it is a tubular reactor. Generally, the pressure can be in the range of 1200 - 3500 bar and the temperature can be in the range of 150 °C - 350 °C. For more details on high-pressure free radical polymerization, see Encyclopedia of Polymer Science and Engineering, Volume 6 (1986), pp. 383 - 410 and Encyclopedia of Materials: Science and Technology by Elsevier Science & Technology Ltd.: "Polyethylene: High-pressure, R. Klimesch, D. Littmann and F.-O. pp. 7181 - 7184, 2001", which is incorporated herein by reference.

[0114] As is well known, for example, propylene can be used as a comonomer or as a chain transfer agent (CTA), or both, whereby it can contribute to the total number of C-C double bonds, preferably to the total number of vinyl groups. For the purposes of the present invention, when a compound that can also be used as a comonomer is used as a CTA during the polymerization to provide double bonds, the copolymerizable comonomer is not counted as part of the comonomer content.

[0115] Carbon black

[0116] According to the present invention, the internal semiconductor layer and the external semiconductor layer further comprise carbon black.

[0117] The semiconductor properties result from the added carbon black. Thus, the amount of carbon black is at least such that a semiconductor layer is obtainable. Preferably, the inner semiconductor layer and / or the outer semiconductor layer comprise 10 to 60% by weight, preferably 15 - 48% by weight, of carbon black. In other preferred embodiments, based on the weight of the semiconductor layer, the amount of carbon black is 10 - 45% by weight, such as 20 - 45% by weight, preferably 25 - 45% by weight, more preferably 25 - 40% by weight, or particularly 30 - 41% by weight.

[0118] Any electrically conductive carbon black can be used. Examples of suitable carbon blacks include furnace black and acetylene black. Mixtures can also be used. In the case of using a carbon black mixture, the percentage refers to the sum of the carbon black present.

[0119] When measured according to ASTM D3037 - 93, the carbon black can have a nitrogen adsorption surface area (BET) of 5 to 400 m 2 / g, such as 10 to 300 m 2 / g, and again such as 30 to 200 m 2 / g. In addition, the carbon black can have one or more of the following properties:

[0120] i) Defining the number - average particle size as at least 5 nm according to ASTM D3849 - 95a,

[0121] ii) When measured according to ASTM D - 1510, the iodine adsorption value (IAN) is at least 10 mg / g, such as 10 to 300 mg / g, such as 30 to 200 mg / g; and / or

[0122] iii) When measured according to ASTM D 2414, the DBP (dibutyl phthalate) adsorption value ( = oil value) is at least 30 cm 3 / 100 g, such as 60 to 300 cm 3 / 100 g, such as 70 to 250 cm 3 / 100 g, such as 80 to 200 cm 3 / 100 g, such as 90 to 180 cm 3 / 100 g.

[0123] In addition, the carbon black can have one or more of the following properties:

[0124] a) Defining the number - average particle size as at least 5 nm according to ASTM D3849 - 95a.

[0125] b) According to ASTM D1510, the iodine value is at least 30 mg / g;

[0126] c) When measured according to ASTM D2414, the oil absorption value is at least 30 ml / 100 g.

[0127] A suitable group of furnace blacks has an average initial particle size of 28 nm or less. The average initial particle size is defined as the number average particle size measured according to ASTM D3849-95a. According to ASTM D1510, such particularly suitable furnace blacks can have an iodine value between 60 and 300 mg / g. Further suitable are those having an oil absorption value between 50 and 225 ml / 100 g, such as between 50 and 200 ml / 100 g and this is measured according to ASTM D2414.

[0128] Another equally suitable group of furnace blacks has an average initial particle size greater than 28 nm. The average initial particle size is defined as the number average particle size according to ASTM D3849-95a. According to ASTM D1510, such suitable furnace blacks can have an iodine value between 30 and 200 mg / g. In addition, the oil absorption value (of such) measured according to ASTM D2414 is, for example, between 80 and 300 mL / 100 g.

[0129] Other suitable carbon blacks can be prepared by any other method or can be further processed.

[0130] The carbon blacks suitable for the semiconductor cable layer are characterized by their cleanliness. Thus, the suitable carbon blacks have an ash content of less than 0.2 wt% measured according to ASTM D1506, a 325 mesh sieve residue of less than 30 ppm measured according to ASTM D1514, and a total sulfur content of less than 1 wt% according to ASTM D1619.

[0131] Furnace black is a well-known and accepted term for a type of carbon black produced in a furnace reactor. As examples of carbon blacks, their preparation methods, and reactors, reference can be made, for example, to Cabot's EP-A-0629222, US 4,391,789, US 3,922,335, and US 3,401,020. Examples of commercial furnace black grades described in ASTM D 1765-98b can be mentioned, such as N351, N293, and N550. Furnace black is generally different from acetylene black, which is another type of carbon black suitable for the semiconductor layer. Acetylene black is produced by the reaction of acetylene and unsaturated hydrocarbons in the acetylene black process, as described, for example, in US 4,340,577.

[0132] In particular, acetylene black may have an average particle size greater than 20 nm, for example, 20 to 80 nm. The average initial particle size is defined as the number average particle size according to ASTM D3849-95a. Such suitable acetylene black may have an iodine value between 30 and 300 mg / g, for example, 30 to 150 mg / g according to ASTM D1510. In addition, the oil absorption value (such) is, for example, between 80 and 300 mL / 100 g, for example, 100 to 280 mL / 100 g, and this is measured according to ASTM D2414. Acetylene black is a recognized term and is well known, such as acetylene black provided by Denka.

[0133] According to another embodiment of the present invention, a semiconductor layer is disclosed, wherein the conductive component comprises or consists of conductive carbon black, for example, carbon black having one or more, and for example, all of the following characteristics:

[0134] The initial particle size of at least 5 nm is defined as the number average particle size according to ASTM D3849-95a;

[0135] When measured according to ASTM D-1510, the iodine adsorption value (IAN) is at least 10 mg / g, for example, 10 to 300 mg / g; or

[0136] When measured according to ASTM D 2414, the DBP (dibutyl phthalate) adsorption value (= oil absorption value) is at least 30 cm 3 / 100 g, for example, 60 to 300 cm 3 / 100 g.

[0137] Peroxide

[0138] The inner semiconductor layer and / or the outer semiconductor layer is crosslinkable or crosslinked. Based on the weight of the semiconductor layer, peroxide is preferably present in the crosslinkable inner semiconductor layer and / or outer semiconductor layer in an amount less than 3.0 wt%, more preferably 0.1 - 2.5 wt%, even more preferably 0.3 - 2.5 wt%. In some embodiments, based on the weight of the semiconductor layer, peroxide is present in an amount of 0.4 to 2.5 wt%, preferably 0.4 to 2.0 wt%. In the case of using a mixture of peroxides, this percentage refers to the total amount of peroxides present.

[0139] Preferred crosslinking agents are organic peroxides. Non-limiting examples are organic peroxides such as di-tert-amyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumyl peroxide, di(tert-butyl) peroxide, dicumyl peroxide, butyl-4,4-bis(tert-butylperoxy)valerate, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl perbenzoate, benzoyl peroxide, di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-bis(peroxybenzoyl)hexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-amylperoxy)cyclohexane, or any mixture thereof. Preferably, the peroxide is selected from 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, tert-butylcumyl peroxide, or a mixture thereof. Most preferably, the peroxide is di(tert-butylperoxyisopropyl)benzene.

[0140] Antioxidant

[0141] Any layer of the cable may include an antioxidant. As antioxidants, mention may be made of hindered phenols or semi-hindered phenols, aromatic amines, aliphatic hindered amines, organic phosphates, sulfur compounds, polymeric 2,2,4-trimethyl-1,2-dihydroquinoline, and mixtures thereof.

[0142] More preferably, the antioxidant is selected from the group consisting of 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-styryldiphenylamine, 4,4'-thiobis(2-tert-butyl-5-methylphenol), polymeric 2,2,4-trimethyl-1,2-dihydroquinoline or its derivatives.

[0143] More preferably, the antioxidant is selected from (but not limited to) the group consisting of 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-styryldiphenylamine, 4,4'-thiobis(2-tert-butyl-5-methylphenol), 2,2'-thiobis(6-tert-butyl-4-methylphenol), distearyl thiodipropionate, 2,2'-thio-diethyl-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), polymeric 2,2,4-trimethyl-1,2-dihydroquinoline or its derivatives. Of course, not only one of the above antioxidants can be used, but also any mixture thereof.

[0144] Based on the weight of the semiconductor layer, the amount of antioxidant (optionally a mixture of two or more antioxidants) can be from 0.005 to 2.5 wt%, such as from 0.01 to 2.5 wt%, preferably from 0.01 to 2.0 wt%, more preferably from 0.03 to 2.0 wt%, especially from 0.03 to 1.5 wt%, more particularly from 0.05 to 1.5 wt%, or from 0.1 to 1.5 wt%.

[0145] In some embodiments, based on the weight of the insulating layer, the amount of antioxidant is from 0.05 to 1.5 wt%, preferably from 0.05 to 1.0 wt%, more preferably from 0.05 to 0.8 wt%, especially from 0.05 to 0.6 wt%, more particularly from 0.05 to 0.5 wt%.

[0146] Other components

[0147] The internal semiconductor layer and / or the external semiconductor layer or the insulating layer may include additional additives. As possible additives, mention may be made of scorch retardants, crosslinking accelerators, stabilizers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage regulators or mixtures thereof.

[0148] A "scorch retardant" is defined as a compound that reduces premature crosslinking, i.e., the formation of coking during the extrusion process. In addition to its scorch prevention properties, a scorch retardant can also have other effects simultaneously, such as a promoting effect, i.e., enhancing the crosslinking performance. The use of a scorch retardant in the insulating layer is particularly preferred.

[0149] Useful scorch retardants may be selected from substituted or unsubstituted diphenylethylene, quinone derivatives, hydroquinone derivatives such as 2,5-di-tert-butylhydroquinone, esters and ethers containing a monofunctional vinyl group, or mixtures thereof. More preferably, the scorch retardant is selected from substituted or unsubstituted diphenylethylene or mixtures thereof. A highly preferred choice is 2,4-diphenyl-4-methyl-1-pentene.

[0150] Preferably, based on the weight of the layer, the amount of scorch retardant is in the range of 0.005 to 1.0 wt%, more preferably in the range of 0.01 to 0.8 wt%. Based on the weight of the layer, further preferred ranges are 0.03 to 0.75 wt%, 0.05 to 0.50 wt%, 0.05 to 0.70 wt% and 0.10 to 0.50 wt%.

[0151] The crosslinking promoter can be a compound containing at least 2 unsaturated groups, such as an aliphatic or aromatic compound, an ester, an ether, an amine or a ketone, which contains at least 2 unsaturated groups, such as a cyanurate, an isocyanurate, a phosphate ester, an orthoformate, an aliphatic or aromatic ether or an allyl ester of benzene - tricarboxylic acid. Examples of esters, ethers, amines and ketones are compounds of the general group selected from diacrylate, triacrylate, tetraacrylate, triallyl cyanurate, triallyl isocyanurate, 3,9 - divinyl - 2,4,8,10 - tetra - oxa - spiro[5,5] - undecane (DVS), triallyl trimellitate (TATM) or N,N,N',N',N",N" - hexaallyl - 1,3,5 - triazine - 2,4,6 - triamine (HATATA) or any mixture thereof. Based on the weight of the polymer composition or based on the weight of the layer in question, the amount of such a crosslinking promoter added can be less than 2.0 wt%, such as less than 1.5 wt%, such as less than 1.0 wt%, such as less than 0.75 wt%, such as less than 0.5 wt%, and its lower limit is, for example, at least 0.05 wt%, such as at least 0.1 wt%.

[0152] In another embodiment of the present invention, the insulating layer does not contain a water - tree retarder in addition to the polymer water - tree retarder discussed herein.

[0153] Conductor

[0154] The cable of the present invention includes a conductor. The conductor can be made of any suitable conductive metal, such as copper or aluminum.

[0155] Cable

[0156] A power cable is defined as a cable that transmits energy at any voltage, typically operating at a voltage higher than 1 kV. The voltage applied to the power cable can be alternating current (AC), direct current (DC) or transient (pulse). Additionally, the cable is very advantageously an AC power cable, such as a power cable operating at 1 - 525 kV, 6 - 525 kV, 6 - 275 kV, 6 - 220 kV, 6 - 150 kV, 6 - 72 kV or 6 to 60 kV (root - mean - square voltage, voltage between any two conductors in a three - phase cable). In some embodiments, the cable is an AC power cable operating at a voltage higher than 1 kV, preferably higher than 6 kV. In some embodiments, the cable is an AC power cable operating at a voltage lower than 525 kV, preferably lower than 400 kV, more preferably lower than 380 kV, particularly lower than 275 kV, lower than 220 kV or even lower than 150 kV.

[0157] It is well - known that the cable can optionally include other layers, such as a layer surrounding an outer semiconductor layer, such as a jacket layer. Preferably, a moisture - proof layer that prevents water from entering is avoided, i.e., the cable is a wet - design cable.

[0158] The cable can be produced by a method including step (a).

[0159] - Provide and mix, for example, by melt mixing in an extruder, a crosslinkable first semiconductor composition for the inner semiconductor layer.

[0160] - Provide and mix, for example, by melt mixing in an extruder, a crosslinkable insulating composition for the insulating layer.

[0161] - Provide and mix, for example, by melt mixing in an extruder, a second semiconductor composition for the outer semiconductor layer.

[0162] (b) Apply to a conductor, for example, by coextrusion.

[0163] - The molten mixture of the first semiconductor composition obtained in step (a) to form the inner semiconductor layer.

[0164] - The molten mixture of the insulating layer composition obtained in step (a) to form the insulating layer, and

[0165] - The molten mixture of the second semiconductor composition obtained in step (a) to form the outer semiconductor layer, and

[0166] (c) Optionally crosslink one or more of the insulating layer, inner semiconductor layer, and outer semiconductor layer of the resulting cable under crosslinking conditions.

[0167] Preferably, if a peroxide is used in the manufacture of a cable layer, that layer is crosslinked. Thus the cable is crosslinkable.

[0168] The first semiconductor composition for the inner semiconductor layer, the crosslinkable insulating composition for the insulating layer, and the second semiconductor composition for the outer semiconductor layer include the components necessary to form the inner semiconductor layer, insulating layer, and outer semiconductor layer of the cable, respectively.

[0169] The required polymer composition can be obtained in several ways using several different production techniques, for example, such as Banbury or Bolling internal mixers, such as BUSS continuous single screws, or such as Farrel or Werner & Pfleiderer continuous twin screws. The type of mixer and the operating conditions selected for preparing the semiconductor compound will have a direct impact on the melt quality and will affect the final compound properties, such as melt flow rate, volume resistivity, and surface smoothness. Particularly useful is the co-kneader technology (BUSS, X-compounds). In the preparation of the semiconductor layer, the conductive filler can be added to the polymer in a molten state under full control of the production temperature. Using this technology, those skilled in the art can achieve blends with fully improved dispersion and distributive mixing.

[0170] Preferably, all layers are crosslinked. Accordingly, the present invention also provides a crosslinked cable obtained by crosslinking the cable defined herein.

[0171] The crosslinking process can be carried out at an elevated temperature, for example, above 150 °C, for example, 160 to 350 °C.

[0172] Melt mixing refers to mixing above the melting point of at least the major polymer component of the resulting mixture, typically at a temperature at least 10 - 15 °C higher than the melting point or softening point of the polymer component.

[0173] The term "coextrusion" as used herein refers to the simultaneous formation of all or part of the layers using one or more extrusion dies. For example, triple extrusion can be used to form three layers.

[0174] In a further embodiment of the present invention, as described in the determination method section below, the crosslinked cable of the present invention has a Weibull Eb of at least 55 kV / mm, for example, 55 to 75 kV / mm, measured on a 20 kV cable (5.5 mm nominal insulation thickness) after 1 year of wet aging in salt water.

[0175] In addition, the first semiconductor composition and the second semiconductor composition can be the same, for example.

[0176] When measured from the cross-section of the insulation layer of the cable, the thickness of the insulation layer of a power cable (such as an AC cable) is generally 2 mm or greater, for example, at least 2.5 mm, at least 3 mm, for example, at least 3.5 to 50 mm, for example, from 4 to 50 mm, preferably at least 4.5 to 35 mm, for example, from 5 to 30 mm.

[0177] When measured from the cross-section of the layer, the thickness of the internal semiconductor layer and / or the external semiconductor layer of the power cable can generally be in the range of 0.5 mm or greater, for example, from 0.7 mm to 5.0 mm.

[0178] From another aspect, the present invention provides a cable comprising a conductor surrounded in sequence by at least an internal semiconductor layer, an insulating layer, and an external semiconductor layer;

[0179] wherein, each of the internal semiconductor layer and the external semiconductor layer comprises:

[0180] at least 50 wt% of an LDPE copolymer having a polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate;

[0181] 25 - 48 wt% of carbon black; and

[0182] 0.1 - 2.5 wt% of a peroxide; and

[0183] wherein, the insulating layer comprises

[0184] (i) at least 60 wt% of a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers;

[0185] (ii) 10 - 35 wt% of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate, preferably an alkyl acrylate; and

[0186] (iii) 0.1 - 2.5 wt% of a peroxide.

[0187] Use

[0188] The cable of the present invention is a cable particularly suitable for a brine environment. Thus, the cable can be buried under the seabed or can be located in or on the seabed. Cables buried on land but close to the coast may also experience a brine environment underground. Cables used in tidal estuaries are also affected by brine. There are also brine lakes and brine seas where the cable of the present invention has practical applications, such as in or under such water bodies. The cable of the present invention is applicable to any brine environment.

[0189] In one embodiment, the present invention relates to a method comprising burying the cable as defined above under the seabed.

[0190] In one embodiment, the present invention relates to a method comprising laying the cable as defined herein on the seabed. Thus, such a cable can be dispensed from a reel. Such a process may involve a cable laying vessel.

[0191] In one embodiment, the cable of the present invention can be used to connect an offshore power generation system to the shore, and thus the cable is located on the seabed. Thus, from another aspect, the present invention provides a power generation system, comprising:

[0192] (A) An offshore generator, such as a wind turbine;

[0193] (B) A cable as claimed herein, which connects the offshore generator to a substation located on land and / or offshore via the seabed.

[0194] Offshore wind turbines are usually located on offshore platforms and are connected to an offshore substation and / or an onshore substation located on a separate platform by cables. These cables are submarine cables, so the cable of the present invention performs excellently in the presence of seawater and is very suitable for this purpose.

[0195] Thus, generally speaking, the cable of the present invention can connect offshore equipment to onshore equipment or other offshore equipment. Therefore, the cable of the present invention can connect these equipment through the seabed.

[0196] In one embodiment, the cable of the present invention can be used to distribute the power generated in an offshore power generation system and connect the system to a substation or a collection system located on land and / or offshore through the seabed.

[0197] The present invention will now be described with reference to the following non-limiting examples.

[0198] Measurement methods

[0199] Unless otherwise specified in the specification or the experimental section, the following methods are used for property determination.

[0200] wt%: weight percentage %

[0201] Melt flow rate

[0202] The melt flow rate (MFR) is determined according to ISO 1133 and is expressed in g / 10 min. MFR is an indicator of fluidity and thus also an indicator of the polymer processing performance. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR of polyethylene is measured at 190 °C, and this MFR can be measured under different loads, such as 2.16 kg (MFR2) or 21.6 kg (MFR 21 )

[0203] Density

[0204] The density is measured according to ISO 1183-1 / Method A. The sample preparation is completed by compression molding according to ISO 17855-2:2016.

[0205] Comonomer content

[0206] a) Quantitative analysis of the α-olefin content in low-density polyethylene by NMR spectroscopy:

[0207] After basic assignment (J. Randall JMS-Rev. Macromol. Chem. Phys., C29(2&3), 201-317(1989)), the comonomer content is determined by quantitative 13C nuclear magnetic resonance (NMR) spectroscopy. The experimental parameters are adjusted to ensure the measurement of quantitative spectra for this specific task.

[0208] Specifically, solution-state NMR spectra are measured using a Bruker AvanceIII 400 spectrometer. A homogeneous sample is prepared by dissolving approximately 0.200 g of the polymer in 2.5 ml of deuterated tetrachloroethylene in a 10 mm sample tube at 140 °C using a heating block and a spinning tube furnace. The proton-decoupled 13C single-pulse NMR spectra with NOE (power-gated) are recorded using the following acquisition parameters: 90° flip angle, 4 dummy scans, 4096 transient collection time of 1.6 s, spectral width of 20 kHz, temperature of 125 °C, binary WALTZ proton decoupling scheme, and relaxation delay of 3.0 s. The resulting FID is processed using the following processing parameters: zero filling to 32k data points and apodisation using a Gaussian window function; automatic zero-order and first-order phase correction and automatic baseline correction using a fifth-order polynomial restricted to the region of interest.

[0209] Based on methods well-known in the art, the quantity is calculated using a simple correction ratio of the signal integrals at representative sites.

[0210] b) Determination of the comonomer content of polar comonomers in low-density polyethylene

[0211] The comonomer content (wt%) is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) measurements calibrated using quantitative nuclear magnetic resonance (NMR) spectroscopy.

[0212] At 150 °C, the film is pressed for 1 - 2 minutes at approximately 5 tons using a Specac film press and then cooled using cold water in a non-controlled manner. The exact thickness of the resulting film sample is measured.

[0213] After analysis using FTIR, a baseline is drawn in the absorbance mode for the peaks to be analyzed. The absorption peaks of the comonomer are normalized with respect to the absorption peaks of polyethylene. For reference materials determined by NMR, the FTIR peak height ratio is correlated with the polar comonomer content. The NMR spectroscopy calibration method is carried out in a conventional manner detailed in the literature.

[0214] Quantitative Analysis of Polar Comonomer Content in Polymers by NMR Spectroscopy

[0215] After basic assignment, the polar comonomer content is determined by quantitative nuclear magnetic resonance (NMR) spectroscopy (e.g., “NMR Spectra of Polymers and Polymer Additives”, A.J. Brandolini and D.D. Hills, 2000, Marcel Dekker, Inc. New York). The experimental parameters are adjusted to ensure the measurement of quantitative spectra for this specific task (e.g., “200 and More NMR Experiments: A Practical Course”, S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). The quantity is calculated using a simple correction ratio of the signal integrals at representative sites in a method known in the art.

[0216] The following are exemplary determinations of the polar comonomer content of ethylene ethyl acrylate, ethylene butyl acrylate, and ethylene methyl acrylate.

[0217] The weight % can be converted to mol % by calculation. It is described in more detail in the literature.

[0218] (1) Ethylene Copolymer Containing Butyl Acrylate

[0219] Film samples of the polymer were prepared for FTIR measurement: 0.5 - 0.7 mm thickness for ethylene butyl acrylate with an amount of >6 wt% of butyl acrylate and 0.05 - 0.12 mm thickness for ethylene butyl acrylate with an amount of <6 wt% of butyl acrylate.

[0220] After analysis by FTIR, the maximum absorbance peak at 3450 cm -1 for >6 wt% of butyl acrylate was subtracted by the absorbance value of the baseline at 3510 cm -1 (A 丙烯酸丁酯 –A 3510 ). Then the maximum absorbance peak of the polyethylene peak at 2020 cm -1 was subtracted by the absorbance value of the baseline at 2120 cm -1 (A 2020 –A 2120 ). Then the ratio between (A 丙烯酸甲酯 -A 3510 ) and (A 2020 -A 2120 ) was calculated in a conventional manner described in detail in the literature.

[0221] Subtract the absorbance value of the baseline at 1865 cm -1 from the maximum absorbance peak of the butyl acrylate comonomer at <6 wt% at 1165 cm -1 (A 丙烯酸丁酯 –A 1865 ). Then subtract the absorbance value of the baseline at 1865 cm -1 from the maximum absorbance peak of the polyethylene peak at 2660 cm -1 (A 2660 -A 1865 ). Then calculate the ratio between (A 丙烯酸丁酯 -A 1865 ) and (A 2660 -A 1865 ).

[0222] (2) Ethylene copolymer containing ethyl acrylate

[0223] A film sample of the polymer was prepared for FTIR measurement: 0.5 mm thickness for ethylene ethyl acrylate.

[0224] After analysis using FTIR, the maximum absorbance of the ethyl acrylate peak at 3450 cm -1 was determined, and a linear baseline correction was applied between approximately 3205 and 3295 cm -1 (A 丙烯酸乙酯 ). Then the maximum absorbance of the polyethylene peak at 2020 cm -1 was determined, and a linear baseline correction was applied between approximately 1975 and 2120 cm -1 (A 2020 ). Then the ratio between (A 丙烯酸乙酯 ) and (A 2020 ) was calculated in a conventional manner detailed in the literature.

[0225] (3) Ethylene copolymer containing methyl acrylate

[0226] A film sample of the polymer was prepared for FTIR measurement: 0.1 mm thickness for ethylene methyl acrylate with an amount of >8 wt% of methyl acrylate and 0.05 mm thickness for ethylene methyl acrylate with an amount of <8 wt% of methyl acrylate.

[0227] After analysis using FTIR, subtract the absorbance value of the baseline at 3510 cm -1 from the maximum absorbance peak of the >8 wt% of methyl acrylate at 3455 cm -1 (A 丙烯酸甲酯 –A 3510 ). Then subtract the absorbance value of the baseline at 1865 cm -1The maximum absorbance peak of the polyethylene peak at [location] minus 2450 cm -1 The absorbance value of the baseline at [location] (A 2675 –A 2450 ). Then calculate the ratio between (A 丙烯酸甲酯 -A 3510 ) and (A 2675 -A 2450 ) in the conventional manner detailed in the literature.

[0228] Subtract the absorbance value of the baseline at 1850 cm -1 from the maximum absorbance peak of the <8 wt% methyl acrylate comonomer at 1164 cm -1 (A 丙烯酸甲酯 –A 1850 ). Then subtract the absorbance value of the baseline at 1850 cm -1 from the maximum absorbance peak of the polyethylene peak at 2665 cm -1 (A 2665 -A 1850 ). Then calculate the ratio between (A 丙烯酸甲酯 -A 1850 ) and (A 2665 -A 1850 ).

[0229] The methods of ASTM D3124-98 and ASTM D6248-98 are used to determine the number of double bonds in the polymer (i.e., polyethylene)

[0230] The methods of ASTM D3124-98 and ASTM D6248-98 are applicable to the determination of double bonds in the LDPE component (i). In the description of this method, the LDPE component (i) is simply referred to as "polymer".

[0231] The methods of ASTM D3124-98 and ASTM D6248-98 include, on the one hand, procedures for determining the amount of double bonds per 1000 carbon atoms based on the method of ASTM D3124-98. In the method of ASTM D3124-98, the determination of vinylidene per 1000 carbon atoms based on 2,3-dimethyl-1,3-butadiene is described in detail. In the method of ASTM D6248-98, the determination of vinyl and trans-vinylidene per 1000 carbon atoms is given based on 1-octene and trans-3-hexene, respectively. The sample preparation procedures described therein have been applied to the determination of vinyl per 1000 carbon atoms, vinylidene per 1000 carbon atoms, and trans-vinylidene per 1000 carbon atoms in the present invention. The method of ASTM D6248-98 gives a suggestion that the bromination procedure in the method of ASTM D3124-98 may be included, but the samples of the present invention are not brominated. To determine the extinction coefficients of these three double bonds, the following three compounds are used: 1-decene corresponds to vinyl, 2-methyl-1-heptene corresponds to vinylidene, and trans-4-decene corresponds to trans-vinylidene, and the procedures described in ASTM D3124-98 and ASTM-D6248-98 are followed with the above exceptions.

[0232] The total amounts of vinyl bonds, vinylidene bonds, and trans-vinylidene double bonds in the "polymer" are analyzed by IR spectroscopy, and the amounts of vinyl bonds, vinylidene bonds, and trans-vinylidene double bonds per 1000 carbon atoms are given.

[0233] The polymer to be analyzed is compressed into a film with a thickness of 0.5 - 1.0 mm. The actual thickness is measured. FT-IR analysis is carried out on a Perkin Elmer near-infrared spectrometer (Perkin Elmer Spectrum One). Two scans are recorded at a resolution of 4 cm -1 .

[0234] 1) A polymer composition comprising a polyethylene homopolymer and a polyethylene copolymer, or a polymer composition comprising a polyethylene homopolymer and a copolymer, with the exception that the polyethylene copolymer has a polar comonomer content of > 0.4 wt% 2) A polymer composition comprising a polyethylene copolymer, or a polymer composition comprising a polyethylene copolymer having a polar comonomer content of > 0.4 wt%

[0235] The three types of C═C-containing functional groups in polyethylene are quantified, each having a characteristic absorption, and each is calibrated for a different model compound, thus generating their respective extinction coefficients:

[0236] · Based on 1-decene [dec-1-ene], the vinyl (R-CH═CH2) at 910 cm -1 gives E = 13.13 l·mol -1 ·mm -1

[0237] · Based on 2-methyl-1-heptene [2-methylhept-1-ene], at 888 cm-1 For vinylidene (RR’C=CH2), E = 18.24 l·mol -1 ·mm -1

[0238] ·Based on trans-4-decene [(E)-dec-4-ene], for the trans vinylidene (R-CH=CH-R'), E = 15.14 l·mol -1 ·mm -1 ·mm -1

[0239] For polyethylene homopolymers or copolymers with a polar comonomer content < 0.4 wt%, a linear baseline correction is applied between approximately 980 cm -1 and 840 cm -1

[0240] 3) ​

[0241] Two types of C=C-containing functional groups in polyethylene copolymers with > 0.4 wt% polar comonomer were quantified, each having a characteristic absorption and each calibrated against a different model compound, resulting in their respective extinction coefficients:

[0242] ·Based on 1-decene [dec-1-ene], for the vinyl (R-CH=CH2) at 910 cm -1 E = 13.13 l·mol -1 ·mm -1

[0243] ·Based on 2-methyl-1-heptene [2-methylhept-1-ene], for the vinylidene (RR’C=CH2) at 888 cm -1 E = 18.24 l·mol -1 ·mm -1

[0244] EBA:

[0245] For the poly(ethylene-butyl acrylate copolymer) (EBA) system, a linear baseline correction is applied between approximately 920 cm -1 and 870 cm -1

[0246] EEA:

[0247] For the poly(ethylene-ethyl acrylate copolymer) (EEA) system, a linear baseline correction is applied between approximately 920 cm -1 and 825 cm -1 ​​​

[0248] EMA:

[0249] For the poly(ethylene-methyl acrylate copolymer) (EMA) system, a linear baseline correction is applied between approximately 930 cm -1 and 870 cm -1 The amount of vinyl groups derived from polyunsaturated comonomers per 1000 carbon atoms is determined and calculated as follows:

[0250] On the other hand, the methods of ASTM D3124-98 and ASTM D6248-98 also include procedures for determining the molar extinction coefficient. At least three 0.18 mol·l -1 solutions of carbon disulfide (CS2) are used, and the average value of the molar extinction coefficient is used.

[0251] The polymer to be analyzed and the reference polymer are produced on the same reactor under substantially the same conditions, i.e., at similar peak temperatures, pressures, and production rates, but the only difference is that the polyunsaturated comonomer is added to the polymer to be analyzed and not to the reference polymer. As described herein, the total amount of vinyl groups in each polymer is determined by FT-IR. Then, assuming that the baseline level of vinyl groups is the same for the reference polymer and the polymer to be analyzed, i.e., those vinyl groups formed by the process and by the chain transfer agent (if any) that generates vinyl groups, the only exception being that the polyunsaturated comonomer in the polymer to be analyzed is also added to the reactor. Then, this baseline level is subtracted from the measured amount of vinyl groups in the polymer to be analyzed, thus obtaining the amount of vinyl groups / 1000 carbon atoms, which is generated by the polyunsaturated comonomer.

[0252] The polymer to be analyzed and the reference polymer are produced on the same reactor under substantially the same conditions, i.e., at similar peak temperatures, pressures, and production rates, but the only difference is that the polyunsaturated comonomer is added to the polymer to be analyzed and not to the reference polymer. As described herein, the total amount of vinyl groups in each polymer is determined by FT-IR. Then, assuming that the baseline level of vinyl groups is the same for the reference polymer and the polymer to be analyzed, i.e., those vinyl groups formed by the process and by the chain transfer agent (if any) that generates vinyl groups, the only exception being that the polyunsaturated comonomer in the polymer to be analyzed is also added to the reactor. Then, this baseline level is subtracted from the measured amount of vinyl groups in the polymer to be analyzed, thus obtaining the amount of vinyl groups / 1000 carbon atoms, which is generated by the polyunsaturated comonomer.

[0253] Brine wet aging test

[0254] The wet aging characteristics of the cable in brine are evaluated using the Regime A procedure described in the Cigré Technical Brochure 722 "Additional Test Recommendations for Submarine Cables from 6 kV (Um = 7.2 kV) to 60 kV (Um = 72.5 kV)", published in April 2018.

[0255] Pretreatment:

[0256] At 55 °C, the cable is immersed in a water tank for 500 hours. The NaCl content in the water is 3.5 wt%.

[0257] Aging:

[0258] The cable is electro-aged in a water tank. The water temperature is 40 °C, and the applied 50 Hz voltage is 38.5 kV, which is equivalent to a conductor stress of 9.1 kV / mm. The NaCl content in the water is 3.5 wt%.

[0259] AC breakdown test:

[0260] The AC breakdown test after 1 year of aging time is carried out in accordance with Section 3.6.4.1 of Cigré Technical Brochure 722 and HD 6055.4.15.3.4(b). Therefore, the cable is cut into six test samples with an effective length of 10 m (excluding the length at the ends). According to the following procedure, within 72 hours after being removed from the aging tank, the breakdown test of the samples is carried out using a 50 Hz AC step test:

[0261] · Start at 36 kV for 5 minutes

[0262] · Increase the voltage in steps of 12 kV every 5 minutes until breakdown occurs

[0263] The calculation of the Weibull parameters for the six datasets of breakdown values follows the least squares regression procedure described in IEC 62539 (2007).

[0264] Experimental section

[0265] The following materials are used in these examples:

[0266] EEA1 is an LDPE copolymer produced by copolymerizing ethylene and 15 wt% ethyl acrylate comonomer (i.e., polar comonomer) in a high-pressure process. The MFR2 is about 7 g / 10 min.

[0267] LDPE1 is an LDPE copolymer of ethylene and 1,7-octadiene comonomer (i.e., polyunsaturated comonomer), the vinyl content of this LDPE copolymer is about 0.55 vinyl / 1000 carbon atoms, the MFR2 is about 2 g / 10 min, and it is produced by a high-pressure process.

[0268] DCP: Dicumyl peroxide

[0269] Using a linear velocity of 2.79 m / min and the following temperatures in the heating zone, two 20 kV cables with the following dimensions (described below) are extruded on the test CCV line: the temperature in the vulcanization tube is 460 / 400 / 385 / 375 °C, and then the cable core is water-cooled. The same semiconductor layer has been used for the two 20 kV cables (the insulation thickness is about 5.5 mm), and the above cables are all used for the inventive examples as comparative examples.

[0270] The inner semiconductor layer and the outer semiconductor layer include LE0595 provided by Borealis (containing carbon black and peroxide). The cable has the following dimensions:

[0271] 150 mm 2 Aluminum conductor

[0272] Inner semiconductor layer: thickness is about 1 mm

[0273] Insulating layer: thickness is 5.5 - 5.6 mm

[0274] Outer semiconductor layer: thickness is about 0.8 mm

[0275] Table 1 – Insulating composition (weight %) of the embodiments of the present invention

[0276]

[0277] The insulating layer in the comparative example is LE4212, which is a crosslinkable WTR retardant additive material provided by Borealis. As described above, after 1 year of wet aging in salt water, the electrical breakdown strength of the cable of the present invention and the comparative 20 kV cable was measured.

[0278] In the test results 1 year after the Eb test, it can be seen that the use of a polymer composition containing polymer WTR has significant advantages compared to a polymer composition containing additive WTR. The Weibull Eb (63.2%) value of the insulated cable with polymer WTR is 64.1 kV / mm after 1 year of wet aging.

[0279] The Weibull Eb (63.2%) value of the insulated cable with additive WTR is 51.2 kV / mm after 1 year of wet aging. These breakdown strength values refer to the electrical stress at the conductor stress when breakdown occurs. This clearly shows the advantages of the polymer WTR component during long-term wet aging tests in a salt water environment. Table 2 below summarizes the measured Eb values.

[0280] Table 2 AC breakdown strength after 1 year of wet aging in salt water according to Cigre TB722

[0281]

Claims

1. Use of a cable for transmitting electricity in a saline environment in the sea or on the seabed; The cable includes a conductor, which is at least surrounded by an inner semiconductor layer, an insulating layer, and an outer semiconductor layer in sequence; Among them, The insulating layer includes (i) at least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and, (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate.

2. Use of the cable according to claim 1, Among them, The inner semiconductor layer and the outer semiconductor layer each include: (a) a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and (b) carbon black.

3. Use of the cable according to claim 2, wherein the inner semiconductor layer has the same chemical composition as the outer semiconductor layer.

4. Use of the cable according to claim 2, wherein the inner semiconductor layer and / or the outer semiconductor layer includes an ethylene alkyl acrylate or an ethylene-vinyl acetate copolymer.

5. Use of the cable according to claim 2, wherein the component (ii) of the insulating layer is an ethylene alkyl acrylate copolymer.

6. Use of the cable according to claim 4, wherein the ethylene alkyl acrylate copolymer is ethylene methyl acrylate, ethylene ethyl acrylate, or ethylene butyl acrylate.

7. Use of the cable according to claim 2, wherein the polyunsaturated comonomer of the LDPE copolymer component (i) has a straight carbon chain with at least 8 carbon atoms and at least 4 carbon atoms between non-conjugated double bonds, and at least one double bond is at the end.

8. Use of the cable according to claim 2, wherein the polyunsaturated comonomer of the LDPE copolymer component (i) is a C8 to C 14 non-conjugated diene.

9. Use of the cable according to claim 2, wherein the polyunsaturated comonomer of the LDPE copolymer component (i) is selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or a mixture thereof.

10. Use of the cable as claimed in claim 2, wherein the insulating layer, the inner semiconductor layer, and the outer semiconductor layer contain peroxides.

11. Use of the cable as claimed in claim 2, wherein the conductor includes aluminum.

12. Use of the cable as claimed in claim 2, the cable is a wet design cable.

13. Use of the cable according to claim 2, wherein, The inner semiconductor layer and the outer semiconductor layer each include: (a) at least 50% by weight of an LDPE copolymer having a polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate, (b) 25 - 48% by weight of carbon black; and (c) 0.1 - 2.5% by weight of peroxide; and wherein, the insulating layer includes (i) At least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and (iii) 0.1 - 2.5% by weight of a peroxide.

14. Use of a cross-linked cable for transmitting electric power in a saline water environment in the sea or under the sea; Wherein the crosslinked cable is obtained by crosslinking a cable comprising a conductor surrounded at least sequentially by an inner semiconductive layer, an insulating layer, and an outer semiconductive layer; Wherein, The insulating layer comprises (i) At least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; and, (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; And Wherein each of the inner semiconductive layer and the outer semiconductive layer comprises: (a) A low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; And (b) Carbon black.

15. Use of the crosslinked cable according to claim 14, wherein the crosslinked cable is an alternating current power cable.

16. A power generation system, comprising: (A) An offshore generator; (B) A cable that connects the offshore generator to a substation located on land and / or offshore via the seabed, The cable comprising a conductor surrounded at least sequentially by an inner semiconductive layer, an insulating layer, and an outer semiconductive layer; Wherein each of the inner semiconductive layer and the outer semiconductive layer comprises: (a) At least 50% by weight of an LDPE copolymer having a polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate, (b) 25 - 48% by weight of carbon black; and (c) 0.1 - 2.5% by weight of a peroxide; and Wherein the insulating layer comprises (i) At least 60% by weight of a low-density polyethylene homopolymer or a low-density polyethylene copolymer having at least one polyunsaturated comonomer and optionally one or more other comonomers; (ii) 10 - 35% by weight of a low-density polyethylene copolymer of ethylene and at least one polar comonomer selected from the group consisting of alkyl acrylates, alkyl methacrylates, or vinyl acetate; and (iii) 0.1 - 2.5% by weight of a peroxide.

17. The power generation system according to claim 16, wherein, The offshore generator is a wind turbine.

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