A low-insulation, compact, medium-voltage power cable and a method for producing the same

Abstract

The present application relates to the technical field of cable, in particular to a low insulation shrinkage compact medium voltage power cable and a preparation method thereof, which comprises a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer and a metal shielding layer arranged from inside to outside, the conductor is tightly compressed and formed by twisting a plurality of trapezoidal monofilaments, the conductor is divided into end sections and middle sections along the length direction, the outer surface of the end sections at both ends is sandblasted to have a roughened layer, the conductor shielding layer, the insulation layer and the insulation shielding layer are integrally extruded on the outer side of the conductor by using a three-layer co-extrusion process; the present application can improve the interfacial adhesion and friction between the trapezoidal conductor and the interface of the conductor shielding layer and the insulation layer, release and eliminate the internal thermal stress generated in the cable processing and crosslinking process, effectively inhibit the axial shrinkage problem of the insulation layer, and reduce the insulation thermal shrinkage rate of the medium voltage conductor cable.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a low-insulation shrinkage compact medium-voltage power cable and its manufacturing method. Background Technology

[0002] Medium-voltage cross-linked polyethylene insulated power cables with rated voltages of 3.6 / 6kV to 26 / 35kV are commonly used key supporting equipment in urban power grid construction and industrial power distribution systems. With technological advancements, to further reduce cable outer diameter, lower raw material consumption, and control production costs, the industry is gradually replacing traditional round single-wire stranded conductors with trapezoidal monofilament stranded conductors. This type of conductor has a compaction coefficient of over 97%, offering significant advantages such as smaller outer diameter, smoother surface, and higher material utilization, and is now widely used in the medium-voltage cable field.

[0003] However, the application of shaped conductors brings a new problem: the thermal shrinkage rate of the cable insulation layer is about 1% higher than that of traditional round conductor cables. The fundamental reason is that the surface of the conductor, formed by the stranding of trapezoidal monofilaments, is extremely smooth, and the monofilaments are tightly joined. This results in insufficient friction and interfacial adhesion between the insulation layer, conductor shielding layer, and conductor matrix after the subsequent three-layer co-extrusion process. During cable processing and cross-linking, internal thermal stress is generated. As this thermal stress is gradually released, the smooth conductor surface cannot provide sufficient constraint to limit the axial shrinkage of the insulation layer, ultimately causing significant insulation shrinkage at the cable ends.

[0004] Therefore, there is an urgent need for a preparation method that can improve the interfacial adhesion and friction between the trapezoidal conductor and the conductor shielding layer and insulation layer, release and eliminate the internal thermal stress generated during cable processing and cross-linking, effectively suppress the axial shrinkage problem of the insulation layer, reduce the insulation thermal shrinkage rate of medium-voltage conductor cables, and improve the production quality and operational stability of medium-voltage cables while retaining the core advantages of small outer diameter of the trapezoidal conductor, high material utilization rate and low production cost, so as to meet the safe service requirements of urban power grids and industrial power distribution systems. Summary of the Invention

[0005] This invention aims to provide a compact medium-voltage power cable with low insulation shrinkage and its manufacturing method. This method can improve the interfacial adhesion and friction between the trapezoidal conductor and the conductor shield and insulation layer, release and eliminate the internal thermal stress generated during cable processing and cross-linking, effectively suppress the axial shrinkage problem of the insulation layer, and reduce the insulation thermal shrinkage rate of the medium-voltage conductor cable. While retaining the core advantages of small outer diameter of the trapezoidal conductor, high material utilization rate, and low production cost, this invention improves the production quality and operational stability of the medium-voltage cable, and meets the safe service requirements of urban power grids and industrial power distribution systems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a low-insulation shrinkage compact medium-voltage power cable, comprising a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer and a metal shielding layer arranged sequentially from the inside to the outside. The conductor is formed by twisting and pressing multiple trapezoidal monofilaments together. The conductor is divided into end sections and middle sections along its length. The outer surface of the end sections at both ends is sandblasted to form a roughening layer. The conductor shielding layer, the insulation layer and the insulation shielding layer are integrally extruded onto the outside of the conductor using a three-layer co-extrusion process.

[0007] Furthermore, the outer surface of the end section of each end of the conductor is sandblasted to form uniform micro-pits, with a surface roughness Ra of 1.6μm to 3.2μm.

[0008] Furthermore, the conductor is formed by concentrically stranding and compacting trapezoidal copper or aluminum monofilaments, with a conductor compaction coefficient of not less than 97%.

[0009] Furthermore, the conductor shielding layer thickness is 0.8±0.1mm, the insulation layer thickness is set according to the national standard for medium voltage cables, the insulation shielding layer thickness is 0.8±0.1mm, the insulation eccentricity of the three-layer co-extruded structure is ≤5%, and the cross-linking degree of the insulation layer is ≥75%.

[0010] Furthermore, the metal shielding layer is a copper strip wrapping structure with a thickness of 0.10 mm, a width of 30 mm, and a wrapping overlap rate of ≥15%.

[0011] The present invention also discloses a preparation method, characterized by comprising the following steps: S1. Stranding of shaped conductors: Trapezoidal monofilaments are concentrically stranded through a frame stranding machine and then compacted into a circular conductor by a compression mold. The conductor length is monitored in real time by a meter measuring device. S2. Selective online sandblasting: The stranded conductor is transported to the sandblasting station by the traction wheel. The end sections of each preset length at both ends of the conductor are sandblasted. After sandblasting, the residual sand particles on the surface of the conductor are removed by air knife. S3. Three-layer co-extrusion processing: The processed conductor is fed into the three-layer co-extrusion production line, and the conductor shielding layer, insulation layer and insulation shielding layer are extruded in sequence using an extrusion die. After cross-linking and cooling, the insulated wire core is obtained. S4. Subsequent forming and processing: The metal shielding wrapping, cabling, inner sheath extrusion, steel tape armoring, and outer sheath extrusion processes are completed on the outside of the insulated core in sequence to obtain the finished cable.

[0012] Furthermore, in S2, the sandblasting medium is selected as 800-mesh quartz fine sand particles, the sandblasting pressure is controlled at 0.3MPa~0.4MPa, and the distance between the sandblasting nozzle and the conductor surface is 15cm~20cm.

[0013] Furthermore, in S3, the extrusion speed of the three-layer co-extrusion production line is controlled at 6.0m / min to 6.5m / min.

[0014] Furthermore, in S4, both the inner and outer sheaths are made of polyvinyl chloride and are formed by extrusion molding using extrusion molds.

[0015] The beneficial effects of this solution are as follows: by adopting segmented differentiated sandblasting treatment, only the end sections at both ends of the cable are roughened, which precisely targets the areas with high insulation shrinkage to strengthen the interface bonding force, while the middle section retains the smooth surface of the conductor, fully preserving its advantages of small outer diameter, high compression coefficient and material saving, while avoiding the increase in process cost caused by full-line sandblasting. Sandblasting the conductor ends creates a rough surface and micro-pit structure, which mechanically interlocks the conductor and the conductor shielding layer, significantly increasing the interface friction. This effectively counteracts the internal thermal stress of the insulation layer, stabilizes and reduces the insulation thermal shrinkage rate, and solves problems such as air gaps, partial discharges, and cable breakdowns caused by insulation shrinkage, thereby improving the safety of cable operation. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view of the present invention; Figure 2 This is a side view of the conductor in this invention.

[0017] The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: Conductor 1, End section 11, Middle section 12, Roughening layer 13, Conductor shielding layer 2, Insulation layer 3, Insulation shielding layer 4, Metal shielding layer 5, Inner sheath 6, Steel tape armor layer 7, Outer sheath 8. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] Example 1 This embodiment describes the preparation of a steel-tape armored cross-linked polyethylene insulated medium-voltage power cable with model number YJV22-8.7 / 15kV 3×300mm² and a single length of 260m, manufactured in accordance with GB / T12706-2020 standard.

[0021] As attached Figure 1 As shown, trapezoidal monofilament stranded and compacted circular conductor 1 is first prepared. Φ8.0mm oxygen-free copper rod is used as raw material, and cold-drawn using a high-speed copper drawing machine combined with continuous annealing to process it into trapezoidal copper monofilaments conforming to a 300mm² specification. The resistivity of the monofilament at 20℃ is controlled to be ≤0.01707Ωmm² / m, the elongation ≥33%, and the surface free of oxidation and scratches. A high-speed frame stranding machine is used to strand the conductor according to a 1+6+11+16 concentric stranding structure, and a special compaction die is used to complete the compaction forming. The compaction coefficient of conductor 1 reaches over 97%. After stranding, the outer diameter of conductor 1 is 19.7mm, and the surface splicing is neat without protrusions or gaps. This cable has a three-core structure with a total conductor length of 780m. The stranded wire production line is equipped with a laser marking machine and a high-precision electronic meter counter with a meter counting accuracy of ±0.1%. It is also linked with the PLC control system to achieve precise length control. This structural design relies on the characteristics of the shaped conductor to reduce the overall cable outer diameter, reduce the amount of copper used, and lower production costs.

[0022] The stranded conductor 1 is fed uniformly into the online sandblasting chamber by a traction wheel. Six sets of high-pressure nozzles are arranged circumferentially within the sandblasting chamber. The distance between the nozzles and the surface of conductor 1 is adjusted to 15cm–20cm. In a preferred embodiment, 800-mesh quartz sand is used as the sandblasting medium, and the sandblasting pressure is set to 0.3MPa–0.4MPa. The PLC system automatically controls the start and stop of the sandblasting device based on the length signal fed back by the meter counter. Sandblasting is performed only on a 20m area at each end of each conductor 1. (See attached diagram.) Figure 2 As shown, for the four end sections 11 of the 780m conductor 1 (0-20m, 240-280m, 500-540m, and 760-780m), after sandblasting, uniform micro-pits are formed on the surface of conductor 1, with the surface roughness Ra controlled between 1.6μm and 3.2μm. The remaining intermediate sections 12 of conductor 1 retain their original smooth state. After sandblasting, residual sand particles are cleaned from the surface using a high-pressure air knife to ensure the cleanliness of conductor 1. Targeted sandblasting forms a roughening layer 13, which only strengthens the surface roughness of the cable end sections 11, improving the bonding force between conductor 1 and the subsequent shielding layer. The intermediate sections 12 are not treated, which avoids the increased process cost of sandblasting the entire line, while retaining the advantages of a smooth surface on the shaped conductor 1 and the difficulty in embedding the shielding material. At the same time, the sandblasting process parameters are optimized to avoid damaging the internal structure, electrical performance, and mechanical strength of conductor 1.

[0023] The processed conductor 1 is fed into a three-layer co-extrusion cross-linked polyethylene production line. The extrusion speed is controlled at 6.0–6.5 m / min. The conductor shielding layer 2, insulation layer 3, and insulation shielding layer 4 are continuously extruded in one go using an extrusion die. The thickness of conductor shielding layer 2 is controlled at 0.8±0.1 mm, the thickness of insulation layer 3 (8.7 / 15kV specification) is 4.5±0.1 mm, and the thickness of insulation shielding layer 4 is 0.8±0.1 mm. The overall insulation eccentricity is ≤5%. After cross-linking treatment in the cross-linking tube, the cross-linking degree of insulation layer 3 is ≥75%, and then it is cooled and shaped through a cooling pipe. In the sandblasting and roughening section of conductor 1, the conductor shielding material of semi-conductive cross-linked polyethylene is embedded in the roughening layer 13 of the end section 11 of conductor 1, forming a mechanical interlocking structure, which improves the interfacial friction and bonding strength, effectively binds the insulation layer 3, and resists the axial shrinkage caused by thermal stress. In the middle section 12 of conductor 1, the shielding layer is tightly attached to conductor 1, ensuring the overall continuity and density of the insulation system.

[0024] Copper tape shielding is wrapped around the outside of the insulated cores. A 0.10mm thick, 30mm wide copper tape is used, with an overlap rate ≥15%. The wrapping tension is maintained uniformly at 15N–20N, and the copper tape shielding layer covers 100% of the surface, achieving good electric field shielding and preventing localized electric field concentration. The three insulated cores are then cabled on a disc-type cabling machine. The cabling pitch ratio is controlled at 38–40 times. Polypropylene tear-film rope is used to fill the gaps between the cores to ensure roundness. The outer layer consists of two layers of 0.1mm thick non-woven fabric wrapped together with an overlap rate ≥10%, providing tight insulation.

[0025] The existing 200mm extruder, paired with a tube-type die, is used to extrude a PVC inner sheath 6. The 200mm refers to the screw diameter on the extruder, with an extrusion thickness of 2.0±0.2mm and an extrusion temperature of 160℃~180℃. After cooling, the inner sheath 6 has a smooth surface free of pores and cracks. A double-strip gap armor is applied to the outside of the inner sheath 6, using 0.8mm thick, 60mm wide hot-dip galvanized steel strips. The strip gap is controlled between 26mm and 29mm, ensuring the armor layer fits tightly against the inner sheath 6, providing mechanical protection for the cable against external pressure and scratches. Finally, the 200mm extruder is used again to extrude a black PVC outer sheath 8, with a thickness of 3.7±0.2mm, at an extrusion temperature of 165℃~185℃. After cooling, the outer sheath 8 has a good appearance and a tight fit, and the finished cable has a nominal outer diameter of 84.9mm.

[0026] After the finished product is manufactured, it is tested according to national standards. The cable ends with sandblasted sections have an insulation heat shrinkage rate of ≤2%, which is lower than the national standard limit of 4%. The cable withstand voltage is 30.5kV / 5min without breakdown or flashover. The partial discharge quantity under 1.73U0 conditions is ≤10pC. The DC resistance of conductor 1 is ≤0.0601Ω / km. All appearance, size and electrical indicators are guaranteed to meet the standards. The low insulation shrinkage compact medium voltage power cable of this application adopts the sandblasting treatment method, which solves the problem of excessive insulation shrinkage of conductor 1 cable. The long-term operation stability of the cable is greatly improved, and it is suitable for urban power grids and industrial medium voltage power distribution scenarios.

[0027] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A low-insulation, shrinkage-compressive medium-voltage power cable, characterized in that: It includes a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, and a metal shielding layer arranged sequentially from the inside out. The conductor is formed by twisting and pressing multiple trapezoidal monofilaments together. The conductor is divided into end sections and middle sections along its length. The outer surface of the end sections at both ends is sandblasted to form a roughening layer. The conductor shielding layer, insulation layer, and insulation shielding layer are integrally extruded onto the outside of the conductor using a three-layer co-extrusion process.

2. The low-insulation shrinkage compact medium-voltage power cable according to claim 1, characterized in that: The outer surface of the end section of each conductor is sandblasted to form uniform micro-pits, with a surface roughness Ra of 1.6μm to 3.2μm.

3. A low-insulation shrinkage compact medium-voltage power cable according to claim 2, characterized in that: The conductor is formed by concentrically stranding and compacting trapezoidal copper or aluminum monofilaments, with a compaction coefficient of not less than 97%.

4. A low-insulation shrinkage compact medium-voltage power cable according to claim 3, characterized in that: The conductor shielding layer thickness is 0.8±0.1mm, the insulation layer thickness is set according to the national standard for medium voltage cables, the insulation shielding layer thickness is 0.8±0.1mm, the insulation eccentricity of the three-layer co-extruded structure is ≤5%, and the cross-linking degree of the insulation layer is ≥75%.

5. A low-insulation shrinkage compact medium-voltage power cable according to claim 4, characterized in that: The metal shielding layer is a copper strip wrapped structure with a thickness of 0.10 mm and a width of 30 mm, and the wrapping overlap rate is ≥15%.

6. A method for manufacturing a low-insulation shrinkage compact medium-voltage power cable, characterized in that, Includes the following steps: S1. Stranding of shaped conductors: Trapezoidal monofilaments are concentrically stranded through a frame stranding machine and then compacted into a circular conductor by a compression mold. The conductor length is monitored in real time by a meter measuring device. S2. Selective online sandblasting: The stranded conductor is transported to the sandblasting station by the traction wheel. The end sections of each preset length at both ends of the conductor are sandblasted. After sandblasting, the residual sand particles on the surface of the conductor are removed by air knife. S3. Three-layer co-extrusion processing: The processed conductor is fed into the three-layer co-extrusion production line, and the conductor shielding layer, insulation layer and insulation shielding layer are extruded in sequence using an extrusion die. After cross-linking and cooling, the insulated wire core is obtained. S4. Subsequent forming and processing: The metal shielding wrapping, cabling, inner sheath extrusion, steel tape armoring, and outer sheath extrusion processes are completed on the outside of the insulated core in sequence to obtain the finished cable.

7. The preparation method according to claim 6, characterized in that: In S2, the sandblasting medium is 800-mesh quartz fine sand particles, the sandblasting pressure is controlled at 0.3MPa~0.4MPa, and the distance between the sandblasting nozzle and the conductor surface is 15cm~20cm.

8. The preparation method according to claim 6, characterized in that: In S3, the extrusion speed of the three-layer co-extrusion production line is controlled at 6.0m / min to 6.5m / min.

9. The preparation method according to claim 6, characterized in that: In S4, both the inner and outer sheaths are made of polyvinyl chloride and are formed by extrusion molding using a tube extrusion die.

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