Medium-high pressure polypropylene power cable and preparation method thereof

Abstract

The invention relates to the technical field of power cables, and provides a middle-high pressure polypropylene power cable and a preparation method thereof. The cross-linked polyethylene inner protection layer is extruded on the outer wall of the cable core; the outer wall of the crosslinked polyethylene inner protection layer is coated with the armor layer; and the outer protection layer is extruded on the outer wall of the armor layer. Compared with a traditional middle-high voltage cross-linked polyethylene insulated cable, the power cable provided by the invention uses the environment-friendly polypropylene insulated cable core, and combines the inner insulating layer and the cross-linked polyethylene inner sheath of the inner layer, so that the cable keeps excellent mechanical properties and electrical insulating properties while being environment-friendly and recyclable. Meanwhile, by introducing the cross-linked polyethylene inner protection layer, on one hand, mechanical protection is provided between the armor layer and the insulating cable cores to buffer armor pressure and resist internal stress of the cable, and on the other hand, the insulation grade and the voltage-withstanding grade of the cable cores are increased, the voltage-withstanding strength between the shielding layer and the armor layer is improved, and the overall electrical safety of the cable is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of power cables, in particular to medium and high voltage power cables, and in particular to a medium and high voltage polypropylene power cable with improved electrical insulation and cable mechanical properties and a preparation method thereof. Background Art

[0002] Medium and high voltage cross-linked polyethylene insulated (XLPE) power cables, due to their excellent electrical and mechanical properties, have the characteristics of high breakdown strength, low dielectric loss, high temperature operation resistance, low heat generation, high wear resistance and strength. They are an important choice for underground transmission trunk lines and distribution networks, especially medium and high voltage insulated power cables above 110kV, which are the first choice for transmission and transformation lines.

[0003] Currently, cross-linked polyethylene cables form a three-dimensional network structure due to cross-linking. The cross-linking structure is irreversible, which makes it impossible to thermoplastically recycle the cables after they are retired. The cost of environmental protection treatment is high, and they can only be disposed of by landfill or incineration, causing landfill pollution or incineration releasing toxic gases such as dioxins.

[0004] As environmental protection policies become stricter, the industry is exploring alternatives to cross-linked polyethylene (XLPE) for main insulation of power cables, and exploring and trying to replace XLPE with recyclable polypropylene (PP). However, the low-temperature brittleness of polypropylene insulated cables leads to poor performance in low-temperature areas. In addition, the bending fatigue resistance of polypropylene cables is poor, which shortens their service life. This makes it difficult for current polyethylene insulated cables to strike a balance between environmental protection and reliability. Summary of the Invention

[0005] In response to the technical problems of power cables in the existing technology that cannot be balanced between environmental protection, performance, and reliability, the present invention aims to propose a medium- and high-voltage polypropylene power cable, compared to traditional medium- and high-voltage cross-linked polyethylene insulated power cables. The cable uses an environmentally friendly polypropylene insulated cable core, combined with an inner insulation layer and a cross-linked polyethylene inner sheath. While taking environmental protection and recyclability into account, the cable maintains excellent mechanical properties and electrical insulation. At the same time, by introducing a cross-linked polyethylene inner sheath, mechanical protection is provided between the armor layer and the insulated cable core to buffer armor pressure and resist internal cable stress. At the same time, the insulation grade and withstand voltage grade of the cable core are increased, the withstand voltage strength between the shielding layer and the armor layer is improved, and the overall electrical safety of the cable is enhanced.

[0006] According to a first aspect of the present invention, a medium- and high-voltage polypropylene power cable is provided, comprising:

[0007] A cable core with a circular cross-section formed by wrapping multiple tangential wire cores and filling structures;

[0008] A cross-linked polyethylene inner sheath, extruded on the outer wall of the cable core;

[0009] A steel armor layer is wrapped outside the outer wall of the crosslinked polyethylene inner protective layer;

[0010] An outer protective layer is wrapped outside the outer wall of the steel armor layer;

[0011] The wire core comprises:

[0012] The stranded conductor is arranged in a steel-cored aluminum strand structure, the stranded conductor comprises a steel core structure and an aluminum strand structure, the steel core structure is a 1+6 stranded structure, the aluminum strand structure is a 12+18 double-layer stranded structure, and the aluminum alloy wires in the aluminum strand structure are in line contact;

[0013] An inner shielding layer comprises a semi-conductive tape wrapped outside the stranded conductor;

[0014] An inner insulation layer comprises an elastic heat insulation tape wrapped outside the inner shielding layer, and the elastic heat insulation tape is wrapped in a linking manner;

[0015] An insulation layer comprises a polypropylene layer wrapped on the surface of the heat insulation tape;

[0016] The wire core armor layer comprises a hot melt adhesive layer and an aluminum tape cladding layer, and the aluminum tape cladding layer is adhered to the outer surface of the insulation layer through the hot melt adhesive layer.

[0017] Preferably, the steel core structure comprises one first steel wire and six second steel wires, the diameter of the first steel wire is 1.1 times that of the second steel wire, the aluminum strand structure comprises a first layer of aluminum alloy wires and a second layer of aluminum alloy wires, the second steel wires, the first layer of aluminum alloy wires and the second layer of aluminum alloy wires have the same stranded pitch and are all left-handed stranded.

[0018] Preferably, a water-blocking rope is arranged in the outer layer gap of the second layer of aluminum alloy wires, the semi-conductive tape is wrapped outside the second layer of aluminum alloy wires and the water-blocking rope, and the wrapping coverage rate of the semi-conductive tape is 40-50%.

[0019] Preferably, the elastic heat insulation tape comprises a silicone rubber tape or an ethylene-propylene rubber tape, the inner insulation layer comprises a first elastic heat insulation tape wrapping layer and a second elastic heat insulation tape wrapping layer, the thickness of the first elastic heat insulation tape wrapping layer is smaller than that of the second elastic heat insulation tape wrapping layer, the second elastic heat insulation tape wrapping layer covers the joint of the first elastic heat insulation tape wrapping layer and causes the first elastic heat insulation tape wrapping layer to be pre-pressed and deformed.

[0020] Preferably, the hot melt adhesive layer is formed by spraying hot melt adhesive with a thickness of 0.2-0.3 mm, and the aluminum tape cladding layer is formed by longitudinally wrapping an aluminum foil with a thickness of 0.5 mm.

[0021] Preferably, the filling structure comprises a filling strip arranged to have a prefabricated shape section, the filling strip comprises a foamed filling strip, a surface of the foamed filling strip is provided with a semi-conductive layer, the wrapping tape comprises a polyester wrapping tape, and the polyester wrapping tape is wrapped around the surface of the filling strip and the core wire at a lap rate of 60-70%.

[0022] Preferably, the cross-linked polyethylene inner sheath comprises a cross-linked polyethylene insulation structure layer, the armor layer comprises an aluminum alloy wire armor layer, and the outer sheath comprises a PVC sheath.

[0023] Preferably, the aluminum alloy wire armor layer comprises a bundle of aluminum alloy wires wrapped around the surface of the cross-linked polyethylene inner sheath, and the bundle of aluminum alloy wires comprises 1-3 aluminum alloy monofilaments arranged in a linear pattern, the diameter of the aluminum alloy monofilament is 3-4 mm, and the wrapping pitch ratio of the aluminum alloy wire is less than 1.

[0024] The second aspect of the present application provides a technical solution, a preparation method of the above-mentioned medium-voltage polypropylene power cable, comprising the following steps:

[0025] Preparation of the core wire:

[0026] Step 1, twist the steel core structure and the first layer of aluminum alloy wires and the second layer of aluminum alloy wires at the same pitch, control the pitch ratio of the outermost aluminum alloy wire to be 10-12 times, and twist the water-blocking rope in the gap of the second layer of aluminum alloy wires, the pitch ratio of the water-blocking rope being the same as that of the second layer of aluminum alloy wires;

[0027] Step 2, wrap the semi-conductive tape around the surface of the second layer of aluminum alloy wires and the water-blocking rope, and control the wrapping lap rate to be 40-50%, and wrap to form an inner shielding layer;

[0028] Step 3, wrap the first layer of elastic heat insulation tape around the outer layer of the semi-conductive tape in the same direction, wrap the second layer of elastic heat insulation tape around the surface of the first layer of elastic heat insulation tape in the same direction, and form an inner insulation layer;

[0029] Step 4, extrude a polypropylene layer on the surface of the second layer of elastic heat insulation tape to form an insulation layer;

[0030] Step 5, hot spray a hot melt adhesive on the surface of the cooled polypropylene layer, and longitudinally wrap an aluminum tape on the surface of the hot melt adhesive layer to form a core wire armor layer;

[0031] Cabling method:

[0032] Step 6, wrap a plurality of core wires together with the filling structure by the wrapping tape to form a cable core with a circular cross section;

[0033] Step 7, extrude a polyethylene on the surface of the cable core to form an inner sheath after radiation cross-linking;

[0034] Step 8, winding the aluminum alloy wire on the surface of the crosslinked polyethylene inner sheath layer, and controlling the winding pitch ratio of the aluminum alloy wire to be less than 1, and forming an armored layer after winding;

[0035] Step 9, extruding an outer sheath layer on the surface of the armored layer.

[0036] Preferably, in step 3, the pre-tightening force during winding is greater than the pre-tightening force of the first layer of elastic heat insulation tape, and the first layer of elastic heat insulation tape and the second layer of elastic heat insulation tape are wound in a linking manner.

[0037] In step 4, the spraying temperature of the hot melt adhesive is controlled at 90-120 DEG C.

[0038] Compared with the prior art, the significant advantages of the medium and high voltage polypropylene power cable are that:

[0039] Compared with the traditional medium and high voltage crosslinked polyethylene insulated cable, the cable has good mechanical properties and weather resistance by the synergistic innovation of the conductor, the inner insulation layer, the insulation layer, the armored layer and the inner sheath layer, and has good electrical properties.

[0040] In the design of the medium and high voltage polypropylene power cable, the conductors are twisted with the same pitch, the contact between the conductors is changed from point contact to line contact, the deformation space between the single wires of the conductors is large when the cable is bent or the temperature changes, and the outer contour deformation is uniform, so that the extrusion stress to the insulation layer is reduced.

[0041] In addition, by arranging the heat-insulating elastic layer in the inner layer of the insulation, on the one hand, the contact temperature on the conductor side of the polypropylene layer can be reduced, and on the other hand, the deformation stress on the conductor side of the polypropylene layer can be reduced through the deformation of the heat-insulating elastic layer, so that the fatigue aging of the polypropylene layer is prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0042] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures can be represented by a like numeral. For purposes of clarity, not every component is called out in every drawing. Embodiments of various aspects of the present application will now be described, by way of example only, with reference to the drawings.

[0043] Figure 1 is a structural schematic diagram of a medium-high voltage polypropylene power cable according to an embodiment of the present application.

[0044] Figure 2 is a cross-sectional structural schematic diagram of a medium-high voltage polypropylene power cable according to an embodiment of the present application.

[0045] Figure 3 is a structural schematic diagram of a core according to an embodiment of the present application.

[0046] Figure 4 is a cross-sectional structural schematic diagram of a core according to an embodiment of the present application. DETAILED DESCRIPTION

[0047] In order to better understand the technical content of the present application, specific embodiments are described below with reference to the accompanying drawings.

[0048]

Medium-high voltage polypropylene power cable

[0049] According to Figure 1 and Figure 2 , a first aspect of the present application proposes a medium-high voltage polypropylene power cable, comprising a cable core, a crosslinked polyethylene inner sheath 8, an armor layer 9, and an outer sheath 10, the cable core being formed into a circular cross-sectional structure by a plurality of line cores and a filling structure 6 being wrapped by a wrapping tape 7, the crosslinked polyethylene inner sheath 8 being extruded on the outer wall of the cable core, the armor layer 9 being wrapped on the outer wall of the crosslinked polyethylene inner sheath 8, and the outer sheath 10 being extruded on the outer wall of the armor layer 9.

[0050] According to Figure 3 and Figure 4 , each line core comprises a stranded conductor 1, an inner shielding layer 2, an inner insulation layer 3, an insulation layer 4, and a line core armor layer 5.

[0051] The stranded conductor 1 is provided in a steel core aluminum strand structure, and optionally, the stranded conductor 1 comprises a steel core structure 11 and an aluminum strand structure 12, the steel core structure 11 is a 1+6 stranded structure, and the aluminum strand structure 12 is a 12+18 double-layer stranded structure, and the aluminum alloy wires in the aluminum strand structure are in line contact.

[0052] Thus, the stranded conductor 1 has good load capacity, especially when the cable is laid by dragging, the steel core structure 11 bears the tensile stress, and the inner insulation layer 3 is prevented from being deformed by tension. At the same time, the double-layer stranded structure of the aluminum alloy structure is line contact, so that when the cable is bent and expands and shrinks due to temperature changes, the deformation space between each metal wire is large, the stress is small, and local high stress on the inner insulation layer 3 can be avoided.

[0053] In an optional embodiment, the steel core structure 11 includes one first steel wire and six second steel wires, the diameter of the first steel wire is 1.1 times that of the second steel wire, so that the gap between the second steel wires is slightly larger, the aluminum stranded structure 12 includes a first layer of aluminum alloy wires and a second layer of aluminum alloy wires, the stranded pitch of the second steel wires, the first layer of aluminum alloy wires and the second layer of aluminum alloy wires is the same, and they are all left-handed stranded, the second steel wires, the first layer of aluminum alloy wires and the second layer of aluminum alloy wires can be pressed against each other according to the state of the cable and be in different positions, and the stress generated by deformation is reduced by the displacement between the conductor wires.

[0054] In the embodiment, the pitch ratio of the outermost aluminum alloy wire is controlled to be 10-12 times, so that by setting the same pitch for the inner and outer stranded structures of the conductor, the conductor wires are in line contact, and when the cable is bent and expands and shrinks due to temperature changes, the deformation stress of the stranded conductor 1 as a whole can be reduced by mutual extrusion between the conductor wires.

[0055] Further, the outer gap of the second layer of aluminum alloy wires is provided with a water-blocking rope 13, and a semi-conductive tape is wrapped outside the second layer of aluminum alloy wires and the water-blocking rope 13, and the wrapping coverage rate of the semi-conductive tape is 40-50%.

[0056] Thus, the water-blocking rope 13 is arranged outside the conductor and can play a role in radial water blocking, the wrapping of the semi-conductive tape makes the surface of the stranded conductor 1 smooth and compact, and the outer wall has a uniform electric field.

[0057] Further, the inner shielding layer 2 includes a semi-conductive tape wrapped outside the stranded conductor 1, the inner insulation layer 3 includes an elastic heat-insulating tape wrapped outside the inner shielding layer 2, the elastic heat-insulating tape is wrapped in a linking manner, the insulation layer 4 includes a polypropylene layer wrapped on the surface of the heat-insulating tape, the core armor layer 5 includes a hot melt adhesive layer 51 and an aluminum tape coating layer 52, and the aluminum tape coating layer 52 is adhered to the outer surface of the insulation layer 4 through the hot melt adhesive layer 51.

[0058] Thus, the inner layer and the outer layer of the insulation layer 4 are respectively subjected to anti-aging treatment, especially from the radial extrusion stress and the axial tensile stress direction, the high-temperature aging of the inner layer and the oxidation aging of the outer layer, by arranging the elastic thermal insulation tape on the inner layer of the insulation layer 4, the contact temperature of the conductor side of the insulation layer 4 can be reduced, and by the elasticity of the elastic thermal insulation tape, when the conductor is deformed, the stress on the insulation layer 4 can be reduced by the deformation of the elastic thermal insulation tape, the anti-fatigue aging effect is improved, in addition, the aluminum tape coating layer 52 and the hot melt adhesive layer 51 arranged on the outer layer of the insulation layer can make the outer layer of the insulation layer 4 and the aluminum tape coating layer 52 closely adhere to each other, and the oxidation resistance and the tensile resistance of the insulation layer 4 can be improved.

[0059] In optional embodiments, the elastic thermal insulation tape includes a silicone rubber tape or an ethylene-propylene rubber tape, which has better heat resistance and anti-aging performance than polypropylene materials, and has better elasticity, which can play a role in isolation and protection on the inner side of the insulation layer.

[0060] In other embodiments, the elastic thermal insulation tape is a shape memory polymer structure layer, and low-melting-point alloy microcapsules are embedded in the shape memory polymer structure layer, and the melting point of the low-melting-point alloy microcapsules is 60-80°C.

[0061] Thus, when the ambient temperature of the cable is greater than 60°C, the microcapsules melt, the elastic thermal insulation tape softens to absorb the thermal expansion stress of the conductor, and when the ambient temperature of the cable is less than 60°C, the microcapsules solidify, the rigidity of the elastic thermal insulation tape increases, and the cable deformation can be resisted.

[0062] In optional embodiments, the shape memory polymer structure layer uses polycaprolactone polyurethane as a resin matrix, and the glass transition temperature can be adjusted as needed, and the thermal conductivity and the rigidity at low temperature are improved by filling nano boron nitride.

[0063] Further, the low-melting-point alloy microcapsules include a capsule core, a capsule wall, and an interface layer, the capsule core uses a low-melting-point (60°C) alloy such as a bismuth-tin alloy, the capsule wall uses a nano-porous silica shell layer, which can improve the thermal conductivity and the compression resistance, and the interface layer is located on the outer layer of the capsule wall, which can increase the interfacial bonding force with the shape memory polymer structure layer.

[0064] Thus, when the cable is in a low-temperature environment, the hardening of the elastic thermal insulation tape can resist the shrinkage stress of the polypropylene, and the insulation layer is prevented from delaminating, and when the conductor is in an overload state, the microcapsules can melt and absorb heat to delay the temperature rise rate, the shape memory polymer structure can soften to wrap the conductor, increase the thermal contact area, accelerate heat dissipation, and prevent the polypropylene insulation from melting.

[0065] Further, the inner insulation layer 3 comprises a first elastic heat insulation tape wrapping layer and a second elastic heat insulation tape wrapping layer, the thickness of the first elastic heat insulation tape wrapping layer is less than the thickness of the second elastic heat insulation tape wrapping layer, the second elastic heat insulation tape wrapping layer covers the joint of the first elastic heat insulation tape wrapping layer and causes the first elastic heat insulation tape wrapping layer to be pre-pressed and deformed.

[0066] In this way, by wrapping the two layers of elastic heat insulation tapes, the radial propagation of water vapor and oxygen can be prevented, and a smooth surface can be formed on the outer layer of the inner shielding layer 2. After the insulation layer 4 is extruded and wrapped outside the inner insulation layer 3, a regular annular cross-section sleeve is formed, so that the insulation is not prone to local aging.

[0067] In the optional embodiment, the hot melt adhesive layer 51 is formed by spraying hot melt adhesive with a thickness of 0.2-0.3 mm, and the aluminum tape wrapping layer 52 is formed by longitudinally wrapping an aluminum foil with a thickness of 0.5 mm. In this way, the aluminum tape is wrapped around the outer layer of the insulation layer 4 by adhering the aluminum tape to the insulation layer 4 with hot melt adhesive, which can ensure that the aluminum tape and the insulation layer are tightly connected, and the hot melt adhesive and the aluminum tape can greatly improve the oxidation resistance and tensile strength of the insulation layer, so that the surface of the insulation layer is not prone to aging and cracking. This can prolong the service life of the insulation and ensure its electrical insulation performance.

[0068] Further, the filling structure 6 comprises a filling strip arranged to have a pre-shaped cross-section, and the filling strip comprises a foamed filling strip. Optionally, the foamed filling strip is a PP foamed strip or a PVC foamed strip. The surface of the foamed filling strip is provided with a semi-conductive layer 61, which is optionally a semi-conductive adhesive coated on the surface of the foamed strip.

[0069] Further, the wrapping tape 7 comprises a polyester wrapping tape, which is wrapped around the surface of the filling strip and the core at a lap rate of 60-70%.

[0070] Optionally, the cross-linked polyethylene inner protective layer 8 comprises an inner protective layer that can be selected from PVC, PP, XLPE, etc. The inner protective layer can buffer the pressure, so that when the cable is bent, pressed or subjected to external impact, the inner protective layer acts as a buffer pad to isolate the armor layer and the insulation core, preventing the armor from directly rubbing or embedding into the core (especially the insulation layer), thereby protecting the integrity of the insulation. At the same time, the inner protective layer can resist internal stress, so that when the cable is bent or subjected to tension, the inner protective layer can absorb stress and reduce the mechanical force transmitted to the insulation layer, thereby improving the mechanical properties and insulation safety.

[0071] In the embodiment of the present application, in combination with the characteristics of the cable core polypropylene insulation layer (environmentally friendly but low mechanical strength, low temperature brittleness), the inner sheath preferably adopts a cross-linked polyethylene insulation structure layer to form a stable and reliable isolation and buffer between the armor layer and the cable core, and to provide high mechanical wear resistance and pressure resistance, to improve the cable pressure resistance and insulation level through the cooperation of the XLPE structure, to improve the pressure resistance strength between the shielding layer and the armor layer, and to enhance the overall electrical safety of the cable, especially in response to the impact of short-circuit current.

[0072] Optionally, the armor layer 9 includes an aluminum alloy wire armor layer, and the outer sheath 10 includes a PVC sheath. The aluminum alloy wire armor layer includes a bundle of aluminum alloy wires wound around the surface of the cross-linked polyethylene inner sheath 8, and the bundle of aluminum alloy wires includes 1-3 aluminum alloy monofilaments arranged in a linear type, the diameter of the aluminum alloy monofilament is 3-4 mm, and the wrapping pitch ratio of the aluminum alloy wire is less than 1. In this way, due to the high rigidity and light weight of the aluminum alloy, in combination with the filling layer of foaming material, the cable is lightweight while having a heat preservation effect on the core, so that the cable has good low temperature resistance and radial compression resistance.

[0073] In combination with the above, by increasing the tensile, tensile and oxidation aging resistance of the cable, especially for long-distance power cables, mechanical damage of the cable at low temperature can be prevented to ensure normal operation of the cable at low temperature.

[0074] In combination with the power cable structure of the above embodiment, the steel-cored aluminum stranded wire conductor has good tensile properties and lightweight advantages, in addition, the filling layer adopts foaming material, in combination with the wound aluminum alloy wire armor layer, the cable is lightweight while having a heat preservation effect on the core, so that the cable has good radial compression resistance, and the polypropylene insulation is prevented from breaking at low temperature, and the overall cable has the advantages of lightweight, good low temperature resistance, good bending property, fatigue resistance and radial pressure resistance.

[0075]

Method for preparing medium and high voltage polypropylene power cable

[0076] As shown in Figures 1 to 4 , the second aspect of the present application proposes a technical solution, the above-mentioned method for preparing a medium and high voltage polypropylene power cable, including cable core preparation, cabling and outer layer preparation.

[0077] (1) Prepare the cable core:

[0078] Step 1, the same pitch is twisted to form a 1+6 double-layer steel core structure and a 12+18 double-layer aluminum alloy wire, the twisting pitch ratio of the four-layer conductor is the same, and is controlled to be 10-12 times, and 18 water-blocking ropes 13 are synchronously twisted in the gaps of the 18 outermost aluminum alloy wires, and the pitch ratio of the water-blocking ropes is kept the same as that of the second layer of aluminum alloy wires, so that the wire contact between the conductors can be realized through the twisting with the same pitch ratio, a larger deformation space is formed, and local stress is reduced;

[0079] Step 2, the surface of the second layer of aluminum alloy wires and the water-blocking ropes 13 is wrapped with a semi-conductive nylon belt, the wrapping angle is 45 degrees, and the wrapping coverage is controlled to be 40-50%, and the inner shielding layer 2 is formed by wrapping;

[0080] Step 3, a layer of silicon rubber belt with a thickness of 0.3 mm is wrapped on the outer layer of the semi-conductive belt in the same direction, and an ethylene-propylene rubber belt with a thickness of 0.5 mm is wrapped on the surface of the silicon rubber belt in the same direction to form an inner insulation layer 3, wherein the pre-tightening force of the silicon rubber belt is 8N, the pre-tightening force of the ethylene-propylene rubber belt is 15N, and the joint of the first layer is covered, the ethylene-propylene rubber belt can pre-tighten the silicon rubber belt, so that the two layers of elastic heat insulation belts are connected tightly, especially preventing the radial transmission of water vapor, which is beneficial to the anti-aging of the insulation layer 4;

[0081] Step 4, the surface of the ethylene-propylene rubber belt is extruded with high crystallinity PP to form an insulation layer 4, and the extrusion temperature of the head is not more than 180℃;

[0082] Step 5, a hot melt adhesive with a thickness of 0.2-0.3 mm and a temperature of 90-120℃ is sprayed on the surface of the cooled polypropylene layer, and an aluminum belt with a thickness of 0.5 mm is longitudinally wrapped on the surface of the hot melt adhesive layer to form a wire core armor layer 5.

[0083] (2) Cabling method:

[0084] Step 1, a plurality of wire cores and PP foaming strips are wrapped together by polyester non-woven fabric to form a cable core with a circular cross section;

[0085] Step 2, the surface of the cable core is extruded with polyethylene to form a crosslinked polyethylene inner protective layer 8 after irradiation crosslinking, and the inner protective layer is used as a buffer pad to isolate the armor layer and the insulated cable core, prevent the armor from directly rubbing or embedding into the cable core (especially the insulation layer thereof), and protect the integrity of the insulation;

[0086] Step 3, an aluminum alloy wire is wound on the surface of the crosslinked polyethylene inner protective layer 8, and the winding pitch ratio of the aluminum alloy wire is controlled to be less than 1, and the armor layer 9 is formed after winding, since the aluminum alloy has large rigidity and light weight, and is matched with a foaming material filling layer, the light weight of the cable is ensured while the wire core is kept warm, so that the cable has good low-temperature resistance and radial compression resistance;

[0087] Step 4, extruding PVC on the surface of the aluminum alloy wire sparse winding layer to form an outer protective layer 10.

[0088] In step 3, the pre-tightening force of the second layer of elastic insulation band during wrapping is greater than that of the first layer of elastic insulation band, and the first and second layers of elastic insulation band are wrapped in a linking manner; in this way, the second layer of elastic insulation band can pre-tighten the first layer of elastic insulation band, so that the two layers of elastic insulation band are connected tightly, and radial water vapor propagation is particularly prevented, which is beneficial to the anti-aging of the insulation layer 4.

[0089] Further, the metal shielding layer is usually longitudinally wrapped in the form of an aluminum-plastic composite tape outside the insulation layer, which requires thermal compounding at a temperature of more than 200 degrees Celsius. This process is prone to soften the polypropylene insulation, and therefore, in step 4, the spraying temperature of the hot melt adhesive is controlled at 90-120 degrees Celsius. At this temperature, the polypropylene layer will not soften, and therefore, deformation of the polypropylene layer under high temperature can be avoided, and good sealing and tensile resistance effects can be achieved.

[0090] In combination with the above embodiments, the conductor in the present application adopts the same pitch twisting method, and the conductors are in line contact. When the cable is bent or the temperature changes, the deformation space between the single wires of each conductor is large, and the outer peripheral contour deformation is uniform, so as to reduce the extrusion stress to the insulation layer. In addition, by arranging the thermal insulation elastic layer in the inner layer of the insulation, the first aspect can reduce the contact temperature on the conductor side of the polypropylene layer, and the second aspect can reduce the deformation stress on the conductor side of the polypropylene layer through the deformation of the thermal insulation elastic layer, so as to prolong the fatigue aging of the polypropylene layer.

[0091] The present application arranges a hot melt adhesive layer and an aluminum tape cladding layer on the outer layer of the polypropylene layer, and the aluminum tape is bonded by the hot melt adhesive layer. Compared with the traditional extrusion of the semi-conductive layer, the tensile resistance effect and the electric field uniformity of the core can be improved. Compared with the copper / aluminum plastic composite tape, the high-temperature compounding process is not required, the deformation of the polypropylene layer under high temperature is avoided, the hot melt adhesive and the aluminum tape are cladded on the outer surface of the insulation layer, the oxidation resistance and tensile resistance of the polypropylene layer can be improved, and fatigue cracks can be avoided.

[0092] The present application adopts the steel core aluminum stranded conductor, which has good tensile property and light weight advantage. In addition, the filling layer adopts foaming material, and cooperates with the wound aluminum alloy wire armor layer. While ensuring the light weight of the cable, the thermal insulation effect is achieved on the core, so that the cable has good radial compression resistance, the polypropylene insulation is prevented from being broken at low temperature, and the cable as a whole has the advantages of light weight, good low temperature resistance, good bending property, fatigue resistance and radial pressure resistance.

[0093] While the application has been described by way of example with reference to preferred embodiments, it is to be understood that this application is not limited to the embodiments disclosed, but is intended to cover various arrangements or modifications thereof. Therefore, other modifications and embodiments of the application will occur to those skilled in the art upon reading the above description and which are intended to be within the scope of the application. It is intended that the scope of the application be defined by the following claims.

Claims

1. A medium and high voltage polypropylene power cable, characterized in that: include: A cable core having a circular cross-section is formed by wrapping a plurality of tangential wire cores and a filling structure (6) with a tape (7); A cross-linked polyethylene inner sheath (8) is extruded onto the outer wall of the cable core; An armor layer (9) is coated on the outer wall of the cross-linked polyethylene inner protective layer (8); An outer protective layer (10) is extruded onto the outer wall of the armor layer (9); Wherein, the wire core comprises: A stranded conductor (1) is provided with a steel core aluminum stranded wire structure, the stranded conductor (1) comprising a steel core structure (11) and an aluminum stranded wire structure (12), the steel core structure (11) being a 1+6 stranded structure, the aluminum stranded wire structure (12) being a 12+18 double-layer stranded structure, and the aluminum alloy wires in the aluminum stranded wire structure being in line contact; An inner shielding layer (2), the inner shielding layer (2) comprising a semi-conductive tape wrapped around the twisted conductor (1); An inner insulating layer (3), the inner insulating layer (3) comprising an elastic insulating tape wrapped around the outer surface of the inner shielding layer (2), the elastic insulating tape being wrapped in a jointed manner; An insulating layer (4), the insulating layer (4) comprising a recyclable polypropylene layer extruded around the surface of the insulating belt; The wire core armor layer (5) comprises a hot melt adhesive layer (51) and an aluminum tape coating layer (52), and the aluminum tape coating layer (52) is adhered to the outer surface of the insulating layer (4) through the hot melt adhesive layer (51).

2. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: The steel core structure (11) comprises a first steel wire and six second steel wires, the diameter of the first steel wire is 1.1 times that of the second steel wire, the aluminum stranded wire structure (12) comprises a first layer of aluminum alloy wire and a second layer of aluminum alloy wire, the second steel wire, the first layer of aluminum alloy wire and the second layer of aluminum alloy wire have the same twisting pitch and are all left-hand twisted.

3. The medium and high voltage polypropylene power cable according to claim 2, characterized in that: A water-blocking rope (13) is provided in the outer gap of the second layer of aluminum alloy wires, and the semi-conductive tape is wrapped around the outer sides of the second layer of aluminum alloy wires and the water-blocking rope (13), with the wrapping overlap rate of the semi-conductive tape being 40-50%.

4. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: The elastic insulation belt comprises a silicone rubber belt or an EPDM rubber belt or a shape memory polymer structure layer, the inner insulation layer (3) comprises a first elastic insulation belt wrapping layer and a second elastic insulation belt wrapping layer, the thickness of the first elastic insulation belt wrapping layer is less than the thickness of the second elastic insulation belt wrapping layer, the second elastic insulation belt wrapping covers the joint of the first elastic insulation belt wrapping layer, and causes the first elastic insulation belt wrapping layer to undergo pre-compression deformation.

5. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: The hot melt adhesive layer (51) is formed by spraying hot melt adhesive with a thickness of 0.2 to 0.3 mm, and the aluminum strip coating layer (52) is formed by longitudinally wrapping aluminum foil with a thickness of 0.5 mm.

6. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: The filling structure (6) comprises a filling strip configured to have a prefabricated cross-section, the filling strip comprising a foamed filling strip, the surface of the foamed filling strip being provided with a semi-conductive layer (61), and the wrapping tape (7) comprising a polyester wrapping tape, the polyester wrapping tape being wrapped around the surface of the filling strip and the core at an overlap rate of 60-70%.

7. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: The cross-linked polyethylene inner protective layer (8) includes a cross-linked polyethylene insulation structure layer, the armor layer (9) includes an aluminum alloy wire armor layer, and the outer protective layer (10) includes a PVC sheath.

8. The medium- and high-voltage polypropylene power cable according to claim 7, characterized in that: The aluminum alloy wire armor layer comprises a bundle of aluminum alloy wires wound on the surface of the cross-linked polyethylene inner protective layer (8), wherein the bundle of aluminum alloy wires comprises 1 to 3 aluminum alloy single wires arranged in a straight line, the diameter of the aluminum alloy single wire is 3 to 4 mm, and the winding pitch ratio of the aluminum alloy wire is less than 1.

9. The method for preparing a medium- and high-voltage polypropylene power cable according to claim 1, wherein: The following steps are involved: Prepare the wire core: Step 1: twisting a steel core structure and a first layer of aluminum alloy wire and a second layer of aluminum alloy wire at the same pitch, wherein the pitch ratio of the outermost layer of aluminum alloy wire is controlled to be 10 to 12 times, and simultaneously twisting a water-blocking rope (13) in the gap of the second layer of aluminum alloy wire, wherein the pitch ratio of the water-blocking rope is the same as the pitch ratio of the second layer of aluminum alloy wire; Step 2: Wrapping a semi-conductive tape around the surface of the second layer of aluminum alloy wire and the water-blocking rope (13), and controlling the wrapping overlap rate to be 40-50%, to form an inner shielding layer (2); Step 3: Wrapping a first layer of elastic insulation tape in the same direction on the outer layer of the semi-conductive tape, and wrapping a second layer of elastic insulation tape in the same direction on the surface of the first layer of elastic insulation tape to form an inner insulation layer (3); Step 4: Extruding a polypropylene layer on the surface of the second elastic insulating belt to form an insulating layer (4); Step 5: hot-spraying hot-melt adhesive on the surface of the cooled polypropylene layer, and longitudinally wrapping aluminum tape on the surface of the hot-melt adhesive layer to form a wire core armor layer (5); Cabling method: Step 6: Wrapping the plurality of wire cores and the filling structure (6) together with a wrapping tape (7) to form a cable core having a circular cross-section; Step 7: Extruding polyethylene on the surface of the cable core and subjecting it to radiation cross-linking to form a cross-linked polyethylene inner sheath (8); Step 8: Winding aluminum alloy wire on the surface of the cross-linked polyethylene inner sheath (8), and controlling the winding pitch ratio of the aluminum alloy wire to be less than 1, to form an armor layer (9) after winding; Step 9: Extruding an outer protective layer (10) on the surface of the armor layer (9).

10. The medium and high voltage polypropylene power cable according to claim 1, characterized in that: In step 3, the pre-tightening force during wrapping is greater than the pre-tightening force of the first elastic insulation tape layer, and the first elastic insulation tape layer and the second elastic insulation tape layer are wrapped in a jointed manner; In step 4, the spraying temperature of the hot melt adhesive is controlled at 90 to 120 degrees Celsius.

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