Peroxide cross-linked polyethylene insulating material for medium-voltage direct-current cable, preparation method of peroxide cross-linked polyethylene insulating material and medium-voltage direct-current cable

Abstract

The invention discloses a peroxide crosslinked polyethylene insulation material for a medium-voltage direct-current cable and a preparation method thereof, and the medium-voltage direct-current cable. The raw material formula of the insulation material comprises the following components in percentage by mass: 87-95% of low-density polyethylene; 1.8%-2.2% of a cross-linking agent; 0.6%-0.8% of an assistant cross-linking agent; 0.1%-0.2% of a main antioxidant; 0.2%-0.4% of a voltage stabilizer; 0.4%-0.6% of a space charge inhibitor; 1.5%-2.0% of a polar compatilizer; 0.3%-0.5% of a synergistic charge inhibitor; 0.1%-0.2% of a lubricant; and 0.5%-0.8% of an acid trapping agent. The insulation material adopted by the medium-voltage direct-current cable is added into a charge inhibition system, polarity interface regulation and thermal stability cooperation (an antioxidant and an acid trapping agent), breakthrough improvement of the direct-current insulation performance is achieved, and the space charge inhibition capacity of the cable is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of cables, and in particular relates to a peroxide cross-linked polyethylene insulating material for a medium-voltage direct current cable and a preparation method thereof, and a medium-voltage direct current cable. Background Art

[0002] With the rapid development of renewable energy generation, smart grids, and other fields, the application of medium-voltage DC transmission technology will become increasingly widespread. As a key component of medium-voltage DC transmission systems, the performance of the insulation material used in medium-voltage DC cables directly affects the cable's service life and operational reliability. However, traditional cross-linked polyethylene insulated medium-voltage cables are prone to space charge accumulation in DC environments, leading to local electric field distortion and reduced insulation life. Furthermore, current research on DC cables focuses on high-voltage applications, and there are currently no mature products available for the medium-voltage sector. Therefore, developing a medium-voltage DC cable that can operate stably in long-term DC environments is particularly important. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art and provide a peroxide cross-linked polyethylene insulation material for a medium-voltage DC cable and a preparation method thereof, as well as a medium-voltage DC cable. The cable can meet the long-term stable operation of the cable in a medium-voltage DC environment without the problem of cable electrical performance degradation and shortened service life caused by space charge accumulation and migration.

[0004] The technical solution adopted to solve the technical problem of the present invention is to provide a peroxide cross-linked polyethylene insulation material for medium voltage DC cables, the raw material formula of which includes the following components in percentage by mass:

[0005] Low-density polyethylene 87% to 94.5%;

[0006] Cross-linking agent 1.8% to 2.2%;

[0007] Cross-linking agent 0.6% to 0.8%;

[0008] Main antioxidant 0.1% to 0.2%;

[0009] Voltage stabilizer 0.2% to 0.4%;

[0010] Space charge inhibitor 0.4% to 0.6%;

[0011] Polar compatibilizer 1.5% to 2.0%;

[0012] Synergistic charge inhibitor 0.3% to 0.5%;

[0013] Lubricant 0.1% to 0.2%;

[0014] Acid scavenger 0.5%-0.8%.

[0015] Preferably, the polyethylene has an ash content of ≤10 ppm, a surface residue content of ≤1000 ppm, a moisture content of ≤200 ppm, and a molecular weight distribution of 4.5 to 5.8.

[0016] Preferably, the cross-linking agent is dicumyl peroxide (DCP).

[0017] Preferably, the cross-linking agent is trimethylolpropane trimethacrylate (TMPTMA) or pentaerythritol tetraacrylate (PET4A).

[0018] The auxiliary cross-linking agent and the cross-linking agent synergistically form a high cross-linking density (gel content ≥ 85%) to reduce the mobility of the molecular chain and lower the conductivity.

[0019] Preferably, the primary antioxidant is one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, and 4,4'-thiobis(6-tert-butyl-3-methylphenol).

[0020] Preferably, the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0021] Preferably, the voltage stabilizer is 5-oleoyloxy-p-naphthoquinone or 2,5-di-tert-butyl-p-benzoquinone, whose molecular structure can efficiently capture high-energy electrons and has low mobility.

[0022] Preferably, the space charge inhibitor is hydroxylated molybdenum disulfide or fluorinated graphene (F / C≈0.3),

[0023] The space charge inhibitor forms deep and shallow traps through surface hydroxyl groups and interlayer defects to capture carriers.

[0024] Preferably, the polar compatibilizer is MAH-g-PE (maleic anhydride grafted polyethylene) or GMA-g-PE (glycidyl methacrylate grafted polyethylene).

[0025] The polar groups of the polar compatibilizer enhance filler dispersion, optimize interfacial bonding, and reduce the risk of agglomeration.

[0026] Preferably, the synergistic charge inhibitor is nano-hydroxylated SiO2 or hydroxylated boron nitride nanosheets.

[0027] The surface hydroxyl groups of the cooperative charge inhibitor provide additional traps, which synergistically homogenize the electric field distribution with MoS2.

[0028] Preferably, the lubricant is zinc stearate or ethylene bisstearamide (EBS).

[0029] Preferably, the acid scavenger is calcium oxide or nano-flaky magnesium hydroxide.

[0030] The present invention also provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cables, comprising the following steps:

[0031] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 60-70°C to enhance compatibility with the matrix;

[0032] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and the polar compatibilizer into an internal mixer, mix at 120°C to 140°C for 6 to 12 minutes to form a pre-dispersed masterbatch;

[0033] (3) Melt blending: melt blending and granulating the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 120°C to 175°C;

[0034] (4) Drying: Drying the mixture obtained in step (3) at a temperature of 70-80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0035] The present invention also provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulating layer, an insulating shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, which are arranged in sequence from the inside to the outside. The insulating layer is made by extruding the above-mentioned medium-voltage DC cable with peroxide cross-linked polyethylene insulation material.

[0036] Preferably, the conductive core is formed by twisting at least two strands of copper wire, tinned copper wire, aluminum wire, or aluminum alloy wire.

[0037] Preferably, the conductor shield is formed by extruding a peroxide cross-linked semi-conductive shielding material, or wrapping a semi-conductive tape and then extruding a peroxide cross-linked semi-conductive shielding material.

[0038] Preferably, the insulation shield is composed of an extruded peroxide cross-linked semi-conductive shielding material or an extruded peroxide cross-linked semi-conductive shielding material plus a semi-conductive tape wrapped around the material.

[0039] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0040] Preferably, the semi-conductive tape is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0041] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0042] Preferably, the metal shield is a copper tape shield or a copper wire plus copper tape composite shield.

[0043] Preferably, the isolation layer is made of extruded polyvinyl chloride or polyethylene material, or a combination of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon to improve the overall waterproof performance of the cable.

[0044] Preferably, the armor layer is composed of a double layer of wrapped steel tape or sparsely wound steel wire, which improves the compression and tensile strength of the cable.

[0045] Preferably, the outer sheath is made of extruded polyvinyl chloride or polyethylene material.

[0046] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in the present invention, adopt a unique formula to add a charge suppression system, polar interface regulation and thermal stability synergy (antioxidant + acid scavenger) to the insulation material used in the DC cable to achieve a breakthrough improvement in DC insulation performance, which can significantly improve the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the cross-sectional structure of the cross-linked polyethylene insulated medium-voltage DC cable in Example 2 of the present invention;

[0048] Figure 2 The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 2 was tested at a field strength of 30 kV / mm and 23°C.

[0049] Figure 3 The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 3 was tested at a field strength of 30 kV / mm and 23°C.

[0050] Figure 4 The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 4 was tested at a field strength of 30 kV / mm and 23°C.

[0051] Figure 5 The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 5 was tested at a field strength of 30 kV / mm and 23°C.

[0052] Figure 6The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 6 was tested at a field strength of 30 kV / mm and 23°C.

[0053] Figure 7 The electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 7 was tested at a field strength of 30 kV / mm and 23°C.

[0054] Figure 8 This is the result of testing the electric field distortion rate of the cross-linked polyethylene insulation material used in the medium voltage DC cable in Example 8 at a field strength of 30 kV / mm and 23°C.

[0055] In the figure, 1-wire core; 2-conductor shield; 3-insulation layer; 4-insulation shield; 5-semi-conductive tape; 6-metal shield; 7-water-blocking tape; 8-isolation layer; 9-armor layer; 10-outer sheath. DETAILED DESCRIPTION

[0056] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0057] Example 1

[0058] This embodiment provides a peroxide cross-linked polyethylene insulation material for a medium-voltage DC cable. The raw material formula includes the following components in percentage by mass:

[0059] Low-density polyethylene 87% to 94.5%;

[0060] Cross-linking agent 1.8% to 2.2%;

[0061] Cross-linking agent 0.6% to 0.8%;

[0062] Main antioxidant 0.1% to 0.2%;

[0063] Voltage stabilizer 0.2% to 0.4%;

[0064] Space charge inhibitor 0.4% to 0.6%;

[0065] Polar compatibilizer 1.5% to 2.0%;

[0066] Synergistic charge inhibitor 0.3% to 0.5%;

[0067] Lubricant 0.1% to 0.2%;

[0068] Acid scavenger 0.5%-0.8%.

[0069] This embodiment also provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cable, comprising the following steps:

[0070] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 60-70°C to enhance compatibility with the matrix;

[0071] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and the polar compatibilizer into an internal mixer, mix at 120°C to 140°C for 6 to 12 minutes to form a pre-dispersed masterbatch;

[0072] (3) Melt blending: melt blending and granulating the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 120°C to 175°C;

[0073] (4) Drying: Drying the mixture obtained in step (3) at a temperature of 70-80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0074] This embodiment also provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside to the outside. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used for the medium-voltage DC cable.

[0075] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0076] Example 2

[0077] This embodiment provides a peroxide cross-linked polyethylene insulation material for a medium-voltage DC cable. The raw material formula includes the following components in percentage by mass:

[0078] Low-density polyethylene 87% to 94.5%;

[0079] Cross-linking agent 1.8% to 2.2%;

[0080] Cross-linking agent 0.6% to 0.8%;

[0081] Main antioxidant 0.1% to 0.2%;

[0082] Voltage stabilizer 0.2% to 0.4%;

[0083] Space charge inhibitor 0.4% to 0.6%;

[0084] Polar compatibilizer 1.5% to 2.0%;

[0085] Synergistic charge inhibitor 0.3% to 0.5%;

[0086] Lubricant 0.1% to 0.2%;

[0087] Acid scavenger 0.5%-0.8%.

[0088] Preferably, the polyethylene has an ash content of ≤10 ppm, a surface residue content of ≤1000 ppm, a moisture content of ≤200 ppm, and a molecular weight distribution of 4.5 to 5.8.

[0089] Preferably, the cross-linking agent is dicumyl peroxide (DCP).

[0090] Preferably, the auxiliary cross-linking agent is trimethylolpropane trimethacrylate (TMPTMA) or pentaerythritol tetraacrylate (PET4A).

[0091] The auxiliary cross-linking agent and the cross-linking agent synergistically form a high cross-linking density (gel content ≥ 85%) to reduce the mobility of the molecular chain and lower the conductivity.

[0092] Preferably, the primary antioxidant is one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, and 4,4'-thiobis(6-tert-butyl-3-methylphenol).

[0093] Preferably, the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0094] Preferably, the voltage stabilizer is 5-oleoyloxy-p-naphthoquinone or 2,5-di-tert-butyl-p-benzoquinone.

[0095] The molecular structure of the voltage stabilizer can efficiently capture high-energy electrons with low mobility.

[0096] Preferably, the space charge inhibitor is hydroxylated molybdenum disulfide or fluorinated graphene (F / C≈0.3).

[0097] Deep and shallow traps are formed by surface hydroxyl groups and interlayer defects to capture carriers.

[0098] Preferably, the polar compatibilizer is MAH-g-PE (maleic anhydride grafted polyethylene) or GMA-g-PE (glycidyl methacrylate grafted polyethylene).

[0099] The polar groups of the polar compatibilizer enhance filler dispersion, optimize interfacial bonding, and reduce the risk of agglomeration.

[0100] Preferably, the synergistic charge inhibitor is nano-hydroxylated SiO2 or hydroxylated boron nitride nanosheets.

[0101] The surface hydroxyl groups of the cooperative charge inhibitor provide additional traps, which synergistically homogenize the electric field distribution with MoS2.

[0102] Preferably, the lubricant is zinc stearate or ethylene bisstearamide (EBS).

[0103] Preferably, the acid scavenger is calcium oxide or nano-flaky magnesium hydroxide.

[0104] This embodiment also provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cable, comprising the following steps:

[0105] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 60-70°C to enhance compatibility with the matrix;

[0106] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and the polar compatibilizer into an internal mixer, mix at 120°C to 140°C for 6 to 12 minutes to form a pre-dispersed masterbatch;

[0107] (3) Melt blending: melt blending and granulating the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 120°C to 175°C;

[0108] (4) Drying: Drying the mixture obtained in step (3) at a temperature of 70-80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0109] like Figure 1 As shown, this embodiment also provides a medium-voltage DC cable, comprising a conductive core 1, a conductor shield 2, an insulating layer 3, an insulating shield 4, a metal shield 6, an isolation layer 8, an armor layer 9, and an outer sheath 10, which are arranged in sequence from the inside to the outside. The insulating layer 3 is made by extruding the above-mentioned peroxide cross-linked polyethylene insulation material for the medium-voltage DC cable.

[0110] Preferably, the conductive core 1 is formed by twisting at least two strands of copper wire, tinned copper wire, aluminum wire, or aluminum alloy wire.

[0111] Preferably, the conductor shield 2 is formed by extruding a peroxide cross-linked semi-conductive shielding material, or wrapping a semi-conductive tape and then extruding a peroxide cross-linked semi-conductive shielding material.

[0112] Preferably, the insulating shield 4 is composed of an extruded peroxide cross-linked semi-conductive shielding material or an extruded peroxide cross-linked semi-conductive shielding material plus a semi-conductive tape wrapped around the material.

[0113] The conductor shield 2, the insulating layer 3, the insulating shield 4 and the conductive core constitute an insulated core.

[0114] Preferably, the semi-conductive tape is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape 7;

[0115] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0116] Preferably, the metal shield 6 is a copper tape shield or a copper wire and copper tape composite shield.

[0117] Preferably, the isolation layer 8 is made of extruded polyvinyl chloride or polyethylene material, or a combination of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon to improve the overall waterproof performance of the cable.

[0118] Preferably, the armor layer 9 is composed of a double layer of wrapped steel tape or sparsely wound steel wire to improve the compression and tensile strength of the cable.

[0119] Preferably, the outer sheath 10 is made of extruded polyvinyl chloride or polyethylene material.

[0120] Specifically, this embodiment provides a cross-linked polyethylene insulated medium-voltage DC cable, comprising a conductive core 1 and a conductor shield 2 disposed outside the conductive core 1, an insulating layer 3 disposed outside the conductor shield 2, an insulating shield 4 disposed outside the insulating layer 3, a semi-conductive tape 5 disposed outside the insulating shield 4, a metal shield 6 disposed outside the semi-conductive tape 5, a water-blocking tape 7 disposed outside the copper wire shield 6, an isolation layer 8 disposed outside the water-blocking tape 7, an armor layer 9 disposed outside the isolation layer 8, and an outer sheath 10 disposed outside the armor layer 9. The conductive core 1 is a Class 2 copper or aluminum (aluminum alloy) conductor in accordance with GB / T 3956, with a cross-section of 25-800mm. 2, the conductor shield 2 is an extruded peroxide cross-linked semi-conductive shielding material or a wrapped semi-conductive tape plus an extruded peroxide cross-linked semi-conductive shielding material, with a thickness of 0.4-1.0mm, the insulation layer 3 is an extruded peroxide cross-linked polyethylene insulation material for medium voltage DC cables, with a thickness of 2.5-10.5mm, the insulation shield 4 is an extruded peroxide cross-linked semi-conductive shielding material, with a thickness of 0.4-1.0mm, the semi-conductive tape 5 is a semi-conductive nylon tape, with a thickness of 0.14mm, and the metal shield 6 is copper Wire winding or copper tape wrapping shielding, the copper tape thickness is 0.09-0.12mm, the copper wire diameter is 0.8-1.2mm, the water blocking tape 7 thickness is 0.1-0.5mm, the isolation layer 8 is made of polyethylene or polyvinyl chloride extrusion, with a thickness of 1.2-5.0mm, the armor layer 9 is steel tape or steel wire armor, the steel tape thickness is 0.5-0.8mm, the steel wire diameter is 0.8-4.0mm, and the outer sheath 10 is made of polyethylene or polyvinyl chloride extrusion, with a thickness of 1.2-5.0mm.

[0121] Specifically, the insulating layer 3 in this embodiment is made of extruded peroxide cross-linked polyethylene insulation material for medium voltage DC cables. The raw material formula of the insulating material includes the following components in percentage by mass:

[0122] - Low-density polyethylene 92.7%;

[0123] - Cross-linking agent dicumyl peroxide (DCP) 2.2%;

[0124] - Cross-linking agent trimethylolpropane trimethacrylate (TMPTMA) 0.8%;

[0125] - Primary antioxidant: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] 0.2%;

[0126] - Voltage stabilizer 5-oleoyloxy-naphthoquinone 0.2%;

[0127] - Space charge inhibitor hydroxylated molybdenum disulfide 0.6%;

[0128] -Polar compatibilizer MAH-g-PE (maleic anhydride grafted polyethylene) 2.0%;

[0129] - Synergistic charge inhibitor nano-SiO2 (hydroxylated) 0.3%;

[0130] - Lubricant zinc stearate 0.2%;

[0131] -Acid scavenger calcium oxide 0.8%.

[0132] The method for preparing the cross-linked polyethylene insulation material for the medium voltage DC cable comprises the following steps:

[0133] (1) Filler pretreatment: MoS2-OH and nano-hydroxylated SiO2 were pretreated with KH550 silane coupling agent (1-2mas%) in a fluidized bed reactor at a temperature of 60°C to enhance compatibility with the matrix.

[0134] (2) Premixing: KH550-MoS2-OH and KH550-SiO2 were added to the internal mixer with MAH-g-PE respectively, and mixed at 120 °C for 10 minutes to form a pre-dispersed masterbatch.

[0135] (3) Melt blending: The pre-dispersed masterbatch, polyethylene, DCP and other components were melt blended and granulated using a twin-screw extruder at 175°C.

[0136] (4) Drying: Dry the mixture obtained in step (3) at a drying temperature of 70° C., and then cool it to room temperature to obtain a cross-linked polyethylene insulation material.

[0137] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0138] Example 3

[0139] The insulating layer 3 in this embodiment is a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that the raw material formula of the peroxide cross-linked polyethylene insulation material for medium-voltage DC cables includes the following components in percentage by mass:

[0140] It includes the following ingredients in percentage by mass:

[0141] - Low-density polyethylene 93.65%;

[0142] - Cross-linking agent dicumyl peroxide (DCP) 2.0%;

[0143] - Cross-linking agent trimethylolpropane trimethacrylate (TMPTMA) 0.6%;

[0144] - Primary antioxidant tris[2,4-di-tert-butylphenyl]phosphite 0.15%;

[0145] - Voltage stabilizer 5-oleoyloxy-naphthoquinone 0.4%;

[0146] - Space charge inhibitor hydroxylated molybdenum disulfide 0.5%;

[0147] -Polar compatibilizer MAH-g-PE (maleic anhydride grafted polyethylene) 1.5%;

[0148] - Synergistic charge inhibitor nano-SiO2 (hydroxylated) 0.5%;

[0149] - Lubricant zinc stearate 0.2%;

[0150] -Acid scavenger calcium oxide 0.5%.

[0151] The method for preparing the cross-linked polyethylene insulation material for the medium voltage DC cable comprises the following steps:

[0152] (1) Filler pretreatment: MoS2-OH and nano-hydroxylated SiO2 were pretreated with KH550 silane coupling agent (1-2mas%) in a fluidized bed reactor at a temperature of 70°C to enhance compatibility with the matrix.

[0153] (2) Premixing: KH550-MoS2-OH and KH550-SiO2 were added to the internal mixer with MAH-g-PE respectively, and mixed at 130 °C for 10 minutes to form a pre-dispersed masterbatch.

[0154] (3) Melt blending: The pre-dispersed masterbatch, polyethylene, DCP and other components were melt blended and granulated using a twin-screw extruder at 120°C.

[0155] (4) Drying: Drying the mixture obtained in step (3) at a drying temperature of 75° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0156] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0157] Specifically, the conductive core in this embodiment is formed by twisting at least two copper wires.

[0158] Specifically, the conductor shielding in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0159] Specifically, the insulation shield in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0160] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0161] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0162] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0163] Specifically, the metal shielding in this embodiment is a copper tape shielding.

[0164] Specifically, the isolation layer in this embodiment is composed of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon to improve the overall waterproof performance of the cable.

[0165] Specifically, the armor layer in this embodiment is a double-layer wrapped steel tape to improve the compression and tensile strength of the cable.

[0166] Specifically, the outer sheath in this embodiment is made of extruded polyvinyl chloride material.

[0167] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0168] Example 4

[0169] The insulating layer 3 in this embodiment is a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that the raw material formula of the peroxide cross-linked polyethylene insulation material for medium-voltage DC cables includes the following components in percentage by mass:

[0170] - Low-density polyethylene 93.3%;

[0171] - Cross-linking agent dicumyl peroxide (DCP) 1.8%;

[0172] - Cross-linking agent trimethylolpropane trimethacrylate (TMPTMA) 0.8%;

[0173] - Primary antioxidant 4,4'-thiobis(6-tert-butyl-3-methylphenol) 0.1%;

[0174] - Voltage stabilizer 5-oleoyloxy-naphthoquinone 0.3%;

[0175] - Space charge inhibitor hydroxylated molybdenum disulfide 0.4%;

[0176] -Polar compatibilizer MAH-g-PE (maleic anhydride grafted polyethylene) 1.8%;

[0177] - Synergistic charge inhibitor nano-SiO2 (hydroxylated) 0.5%;

[0178] - Lubricant zinc stearate 0.2%;

[0179] -Acid scavenger calcium oxide 0.8%.

[0180] The method for preparing the cross-linked polyethylene insulation material for the medium voltage DC cable comprises the following steps:

[0181] (1) Filler pretreatment: MoS2-OH and nano-hydroxylated SiO2 were pretreated with KH550 silane coupling agent (1-2mas%) in a fluidized bed reactor at a temperature of 65°C to enhance compatibility with the matrix.

[0182] (2) Premixing: KH550-MoS2-OH and KH550-SiO2 were added to the internal mixer with MAH-g-PE respectively, and mixed at 140 °C for 10 minutes to form a pre-dispersed masterbatch.

[0183] (3) Melt blending: The pre-dispersed masterbatch, polyethylene, DCP and other components were melt blended and granulated using a twin-screw extruder at 150°C.

[0184] (4) Drying: Drying the mixture obtained in step (3) at a drying temperature of 80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0185] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0186] Specifically, the conductive core in this embodiment is formed by twisting at least two tinned copper wires.

[0187] Specifically, the conductor shielding in this embodiment is formed by wrapping the conductor with a semi-conductive tape and then extruding a peroxide cross-linked semi-conductive shielding material.

[0188] Specifically, the insulation shield in this embodiment is composed of an extruded peroxide cross-linked semi-conductive shielding material and a semi-conductive tape wrapped around the outer surface.

[0189] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0190] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0191] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0192] Specifically, the metal shielding in this embodiment is a composite shielding of copper wire and copper tape.

[0193] Specifically, the isolation layer in this embodiment is made of extruded polyvinyl chloride or polyethylene material to improve the overall waterproof performance of the cable.

[0194] Specifically, the armor layer in this embodiment is a double-layer wrapped steel tape, which improves the compression and tensile strength of the cable.

[0195] Specifically, the outer sheath in this embodiment is made of extruded polyethylene material.

[0196] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0197] Example 5

[0198] The insulating layer 3 in this embodiment is a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that the raw material formula of the peroxide cross-linked polyethylene insulation material for medium-voltage DC cables includes the following components in percentage by mass:

[0199] - Low-density polyethylene 93.3%;

[0200] - Cross-linking agent dicumyl peroxide (DCP) 1.8%;

[0201] - Cross-linking agent trimethylolpropane trimethacrylate (TMPTMA) 0.8%;

[0202] - Primary antioxidant: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] 0.1%;

[0203] - Voltage stabilizer 5-oleoyloxy-naphthoquinone 0.4%;

[0204] - Space charge inhibitor hydroxylated molybdenum disulfide 0.5%;

[0205] -Polar compatibilizer MAH-g-PE (maleic anhydride grafted polyethylene) 1.6%;

[0206] - Synergistic charge inhibitor nano-SiO2 (hydroxylated) 0.5%;

[0207] - Lubricant zinc stearate 0.2%;

[0208] -Acid scavenger calcium oxide 0.8%.

[0209] The method for preparing the cross-linked polyethylene insulation material for the medium voltage DC cable comprises the following steps:

[0210] (1) Filler pretreatment: MoS2-OH and nano-hydroxylated SiO2 were pretreated with KH550 silane coupling agent (1-2mas%) in a fluidized bed reactor at a temperature of 62°C to enhance compatibility with the matrix.

[0211] (2) Premixing: KH550-MoS2-OH and KH550-SiO2 were added to the internal mixer with MAH-g-PE respectively, and mixed at 125 °C for 10 minutes to form a pre-dispersed masterbatch.

[0212] (3) Melt blending: The pre-dispersed masterbatch, polyethylene, DCP and other components were melt blended and granulated using a twin-screw extruder at 130°C.

[0213] (4) Drying: Drying the mixture obtained in step (3) at a drying temperature of 72° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0214] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0215] Specifically, the conductive core in this embodiment is formed by twisting at least two aluminum wires.

[0216] Specifically, the conductor shielding in this embodiment is formed by wrapping the conductor with a semi-conductive tape and then extruding a peroxide cross-linked semi-conductive shielding material.

[0217] Specifically, the insulation shield in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0218] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0219] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0220] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0221] Specifically, the metal shielding in this embodiment is a copper tape shielding.

[0222] Specifically, the isolation layer in this embodiment is composed of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon to improve the overall waterproof performance of the cable.

[0223] Specifically, the armor layer in this embodiment is composed of sparsely wound steel wires, which improves the compression and tensile strength of the cable.

[0224] Specifically, the outer sheath in this embodiment is made of extruded polyethylene material.

[0225] Test results

[0226] like Figures 2 to 8 As shown, the cross-linked polyethylene insulation material for medium voltage DC cables obtained in Examples 2-5 above was tested at an electric field strength E of 30 kV / mm and 23°C, and the electric field distortion rate was calculated as δ 30 =(Emax-30) / 30. This formula refers to Appendix B of GB / T31489.1-2015. The results show that these materials all have low space charge distortion rates and excellent performance (the space charge inside the insulating material (such as positive and negative ions or electron accumulation) will distort the original electric field distribution, causing the local field strength to increase or decrease abnormally, forming electric field distortion).

[0227]

[0228] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0229] Example 6

[0230] This embodiment provides a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that its raw material formula includes the following components by mass percentage:

[0231] - Low-density polyethylene 93%;

[0232] - Cross-linking agent dicumyl peroxide (DCP) 1.9%;

[0233] - Cross-linking agent pentaerythritol tetraacrylate (PET4A) 0.7%;

[0234] - Primary antioxidant: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] 0.15%;

[0235] - Voltage stabilizer 2,5-di-tert-butyl-p-benzoquinone 0.4%;

[0236] - 0.6% of fluorinated graphene (F / C≈0.3), a space charge inhibitor;

[0237] -Polar compatibilizer GMA-g-PE (glycidyl methacrylate grafted polyethylene) 2.0%;

[0238] - Synergistic charge inhibitor hydroxylated boron nitride nanosheets 0.4%;

[0239] - Lubricant ethylene bisstearamide (EBS) 0.15%;

[0240] -Acid scavenger nano-flaky magnesium hydroxide 0.7%.

[0241] This embodiment provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cables, comprising the following steps:

[0242] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 64°C to enhance compatibility with the matrix;

[0243] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and polar compatibilizer into an internal mixer and mix at 135°C for 8 minutes to form a pre-dispersed masterbatch;

[0244] (3) Melt blending: melt blending and pelletizing the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 140°C;

[0245] (4) Drying: Dry the mixture obtained in step (3) at a drying temperature of 76° C., and then cool it to room temperature to obtain a cross-linked polyethylene insulation material.

[0246] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0247] Specifically, the conductive core in this embodiment is formed by twisting at least two aluminum alloy wires.

[0248] Specifically, the conductor shielding in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0249] Specifically, the insulation shield in this embodiment is composed of an extruded peroxide cross-linked semi-conductive shielding material and a semi-conductive tape wrapped around the outer surface.

[0250] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0251] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0252] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0253] Specifically, the metal shielding in this embodiment is a composite shielding of copper wire and copper tape.

[0254] Specifically, the isolation layer in this embodiment is composed of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon to improve the overall waterproof performance of the cable.

[0255] Specifically, the armor layer in this embodiment is composed of sparsely wound steel wires, which improves the compression and tensile strength of the cable.

[0256] Specifically, the outer sheath in this embodiment is made of extruded polyvinyl chloride material.

[0257] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0258] Example 7

[0259] This embodiment provides a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that its raw material formula includes the following components by mass percentage:

[0260] - Low-density polyethylene 94.5%;

[0261] - Cross-linking agent dicumyl peroxide (DCP) 1.8%;

[0262] - Cross-linking agent pentaerythritol tetraacrylate (PET4A) 0.6%;

[0263] - Primary antioxidant tris[2,4-di-tert-butylphenyl]phosphite 0.1%;

[0264] - Voltage stabilizer 5-oleoyloxy-naphthoquinone 0.2%;

[0265] - Space charge inhibitor hydroxylated molybdenum disulfide 0.4%;

[0266] -Polar compatibilizer MAH-g-PE (maleic anhydride grafted polyethylene) 1.5%;

[0267] - Synergistic charge inhibitor hydroxylated boron nitride nanosheets 0.3%;

[0268] - Lubricant zinc stearate 0.1%;

[0269] -Acid scavenger calcium oxide 0.5%.

[0270] This embodiment provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cables, comprising the following steps:

[0271] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 70°C to enhance compatibility with the matrix;

[0272] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and polar compatibilizer into an internal mixer and mix at 140°C for 6 minutes to form a pre-dispersed masterbatch;

[0273] (3) Melt blending: melt blending and pelletizing the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 155°C;

[0274] (4) Drying: Dry the mixture obtained in step (3) at a drying temperature of 78° C., and then cool it to room temperature to obtain a cross-linked polyethylene insulation material.

[0275] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0276] Specifically, the conductive core in this embodiment is formed by twisting at least two strands of copper wire, tinned copper wire, aluminum wire, or aluminum alloy wire.

[0277] Specifically, the conductor shielding in this embodiment is formed by wrapping the conductor with a semi-conductive tape and then extruding a peroxide cross-linked semi-conductive shielding material.

[0278] Specifically, the insulation shield in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0279] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0280] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0281] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0282] Specifically, the metal shielding in this embodiment is a copper tape shielding.

[0283] Specifically, the isolation layer in this embodiment is made of extruded polyvinyl chloride or polyethylene material to improve the overall waterproof performance of the cable.

[0284] Specifically, the armor layer in this embodiment is a double-layer wrapped steel tape, which improves the compression and tensile strength of the cable.

[0285] Specifically, the outer sheath in this embodiment is made of extruded polyethylene material.

[0286] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0287] Example 8

[0288] This embodiment provides a peroxide cross-linked polyethylene insulation material for medium-voltage DC cables. The difference from Example 2 is that its raw material formula includes the following components by mass percentage:

[0289] - Low-density polyethylene 87%;

[0290] - Cross-linking agent dicumyl peroxide (DCP) 2.2%;

[0291] - Cross-linking agent trimethylolpropane trimethacrylate (TMPTMA) 0.8%;

[0292] - Primary antioxidant 4,4'-thiobis(6-tert-butyl-3-methylphenol) 0.2%;

[0293] - Voltage stabilizer 2,5-di-tert-butyl-p-benzoquinone 0.4%;

[0294] - Space charge inhibitor hydroxylated molybdenum disulfide 0.6%;

[0295] -Polar compatibilizer GMA-g-PE (glycidyl methacrylate grafted polyethylene) 2.0%;

[0296] - Synergistic charge inhibitor nano-SiO2 (hydroxylated) 0.5%;

[0297] - Lubricant zinc stearate 0.2%;

[0298] -Acid scavenger nano-flaky magnesium hydroxide 0.8%.

[0299] This embodiment provides a method for preparing the above-mentioned peroxide cross-linked polyethylene insulation material for medium voltage DC cables, comprising the following steps:

[0300] (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 68°C to enhance compatibility with the matrix;

[0301] (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and polar compatibilizer into an internal mixer and mix at 120°C for 12 minutes to form a pre-dispersed masterbatch;

[0302] (3) Melt blending: melt blending and pelletizing the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 175°C;

[0303] (4) Drying: Drying the mixture obtained in step (3) at a drying temperature of 80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

[0304] This embodiment provides a medium-voltage DC cable, comprising a conductive core, a conductor shield, an insulation layer, an insulation shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, arranged in sequence from the inside out. The insulation layer is made by extruding the peroxide cross-linked polyethylene insulation material used in the medium-voltage DC cable.

[0305] Specifically, the conductive core in this embodiment is formed by twisting at least two strands of copper wire, tinned copper wire, aluminum wire, or aluminum alloy wire.

[0306] Specifically, the conductor shielding in this embodiment is made of extruded peroxide cross-linked semi-conductive shielding material.

[0307] Specifically, the insulation shield in this embodiment is composed of an extruded peroxide cross-linked semi-conductive shielding material and a semi-conductive tape wrapped around the outer surface.

[0308] The conductor shield, insulation layer, insulation shield and conductive core constitute an insulated core.

[0309] Specifically, the semi-conductive tape in this embodiment is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape;

[0310] The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

[0311] Specifically, the metal shielding in this embodiment is a composite shielding of copper wire and copper tape.

[0312] Specifically, the isolation layer in this embodiment is made of extruded polyvinyl chloride or polyethylene material to improve the overall waterproof performance of the cable.

[0313] Specifically, the armor layer in this embodiment is composed of sparsely wound steel wires, which improves the compression and tensile strength of the cable.

[0314] Specifically, the outer sheath in this embodiment is made of extruded polyvinyl chloride material.

[0315] The peroxide cross-linked polyethylene insulation material for medium-voltage DC cables and its preparation method, as well as the medium-voltage DC cables in this embodiment, adopt a unique formula of insulating materials that incorporate a charge suppression system, polar interface regulation, and thermal stability synergy (antioxidant + acid scavenger) to achieve a breakthrough improvement in DC insulation performance. This can significantly enhance the cable's space charge suppression capability and is particularly suitable for medium-voltage DC transmission scenarios.

[0316] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A peroxide cross-linked polyethylene insulation material for medium voltage DC cables, characterized in that: The raw material formula includes the following ingredients by mass percentage: Low-density polyethylene 87% to 94.5%; Cross-linking agent 1.8% to 2.2%; Cross-linking agent 0.6% to 0.8%; Main antioxidant 0.1% to 0.2%; Voltage stabilizer 0.2% to 0.4%; Space charge inhibitor 0.4% to 0.6%; Polar compatibilizer 1.5% to 2.0%; Synergistic charge inhibitor 0.3% to 0.5%; Lubricant 0.1% to 0.2%; Acid scavenger 0.5%-0.8%.

2. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The ash content of the polyethylene is ≤10ppm, the surface residue content is ≤1000ppm, the moisture content is ≤200ppm, and the molecular weight distribution is 4.5-5.

8.

3. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The cross-linking agent is dicumyl peroxide; The auxiliary cross-linking agent is trimethylolpropane trimethacrylate or pentaerythritol tetraacrylate.

4. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The main antioxidant is one of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, tris[2,4-di-tert-butylphenyl] phosphite and 4,4'-thiobis(6-tert-butyl-3-methylphenol).

5. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The voltage stabilizer is 5-oleoyloxy-p-naphthoquinone or 2,5-di-tert-butyl-p-benzoquinone.

6. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The space charge inhibitor is hydroxylated molybdenum disulfide or fluorinated graphene.

7. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The polar compatibilizer is maleic anhydride grafted polyethylene or glycidyl methacrylate grafted polyethylene.

8. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The synergistic charge inhibitor is nano-hydroxylated SiO2 or hydroxylated boron nitride nanosheets.

9. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The lubricant is zinc stearate or ethylene bisstearamide.

10. The peroxide cross-linked polyethylene insulation material for medium voltage DC cable according to claim 1, characterized in that: The acid scavenger is calcium oxide or nano-flaky magnesium hydroxide.

11. A method for preparing a peroxide cross-linked polyethylene insulation material for a medium voltage DC cable according to any one of claims 1 to 10, characterized in that: The following steps are involved: (1) Filler pretreatment: The space charge inhibitor and the synergistic charge inhibitor were pretreated with KH550 silane coupling agent in a fluidized bed reactor at a temperature of 60-70°C; (2) Premixing: Add the pretreated space charge inhibitor and synergistic charge inhibitor and the polar compatibilizer into an internal mixer, mix at 120°C to 140°C for 6 to 12 minutes to form a pre-dispersed masterbatch; (3) Melt blending: melt blending and granulating the pre-dispersed masterbatch, polyethylene, crosslinking agent and other components of the insulation material formula using a twin-screw extruder at 120°C to 175°C; (4) Drying: Drying the mixture obtained in step (3) at a temperature of 70-80° C., and then cooling to room temperature to obtain a cross-linked polyethylene insulation material.

12. A medium voltage DC cable, characterized in that: The cable comprises a conductive core, a conductor shield, an insulating layer, an insulating shield, a metal shield, an isolation layer, an armor layer, and an outer sheath, which are arranged in sequence from the inside to the outside. The insulating layer is made of the peroxide cross-linked polyethylene insulating material for medium-voltage DC cables according to any one of claims 1 to 10.

13. The medium voltage DC cable according to claim 12, characterized in that: The conductive wire core is formed by twisting at least two strands of copper wire, tinned copper wire, aluminum wire, or aluminum alloy wire; The conductor shield is made of extruded peroxide cross-linked semi-conductive shielding material, or wrapped with semi-conductive tape and then extruded with peroxide cross-linked semi-conductive shielding material; The insulating shield is composed of an extruded peroxide cross-linked semi-conductive shielding material or an extruded peroxide cross-linked semi-conductive shielding material plus a semi-conductive wrapping tape wrapped around the material.

14. The medium voltage DC cable according to claim 13, characterized in that: The semi-conductive tape is a semi-conductive nylon tape or a semi-conductive nylon water-blocking tape; The peroxide cross-linked semi-conductive shielding material has a volume resistivity of less than or equal to 100Ω·cm at 23°C and a volume resistivity of less than or equal to 500Ω·cm at 90°C.

15. The medium voltage DC cable according to claim 12, characterized in that: The metal shield is a copper tape shield or a copper wire plus copper tape composite shield; The isolation layer is made of extruded polyvinyl chloride or polyethylene material, or a combination of extruded polyethylene and an aluminum-plastic composite tape longitudinally wrapped thereon; The armor layer is composed of double-layer wrapped steel tape or sparsely wound steel wire; The outer sheath is made of extruded polyvinyl chloride or polyethylene material.

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