Production technology of 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable

Abstract

The present invention discloses a production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable, comprising the following steps: compacting a circular conductor into an inner conductor core, twisting Z-shaped conductors into an outer conductor core, passing the resulting conductor core wire through a preheater to form an insulated core wire, passing through a post-preheater, performing multi-stage cooling and cross-linking, degassing, forming a tape-wrapped core wire, longitudinally wrapping the wire with aluminum tape to form a smooth aluminum sheath, reducing the diameter of the smooth aluminum sheath, spraying hot melt adhesive, extruding an outer sheath, cooling, and winding. The present invention provides a production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable that ensures the roundness of the conductor core wire, reduces cross-linking thermal stress of the insulation layer, and prevents ablation of the buffer layer.

Description

Technical Field

[0001] The invention relates to the field of cables, in particular to a production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable. Background Art

[0002] With the continued growth of global energy demand and the large-scale development and utilization of renewable energy, the market demand for ultra-high voltage cables, a key technology for long-distance, high-capacity power transmission, is expected to continue to expand. In particular, ultra-high voltage cables play an irreplaceable role in connecting remote renewable energy bases (such as wind and solar power plants) with load centers.

[0003] In the process of manufacturing 750kV power cables, there are currently some technical difficulties, such as the difficulty in controlling the roundness of large-section conductors, the thick insulation layer resulting in large cross-linking thermal stress, the heavy cable weight, and the easy flattening of the sheath during production. At the same time, in recent years, high-voltage cable failures or shutdowns due to the ablation of the cable's semi-conductive buffer layer have occurred frequently at home and abroad. The small contact area between the cable's corrugated aluminum sheath and the semi-conductive buffer layer, and uneven contact are important factors leading to the ablation of the buffer layer. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable that ensures the roundness of the conductor core, reduces the cross-linking thermal stress of the insulation layer, and avoids ablation of the buffer layer.

[0005] The technical solution adopted by the present invention to solve the above problem is a production process of a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable, comprising the following steps:

[0006] S1: Use round conductor to compress and form the conductor core;

[0007] S2: Use Z-shaped wire conductors to twist into a ring-shaped conductor outer core and fit the conductor inner core;

[0008] S3: passing the conductor core wire consisting of the conductor inner core and the conductor outer core through the preheater to perform electromagnetic induction preheating on the conductor core wire;

[0009] S4: Co-extrude the inner shielding layer, the insulating layer and the outer shielding layer on the surface of the conductor core wire to form an insulated core wire;

[0010] S5: Passing through the post-preheater, the conductor core wire inside the insulated core wire is subjected to electromagnetic induction heating to reduce the cross-linking internal stress;

[0011] S6: The insulated core wire passes through the cross-linking tube, which is heated and cross-linked at the inlet end, and then cross-linked by multi-stage cooling;

[0012] S7: The insulated core wire is placed in a convection drying room for degassing;

[0013] S8: Wrap a layer of semi-conductive butyl tape, two layers of semi-conductive water-resistant tape, and a layer of semi-conductive water-resistant copper wire shielding tape around the outer layer of the insulated core wire in sequence to form a tape-wrapped core wire;

[0014] S9: longitudinally wrap aluminum tape on the surface of the tape-wrapped core wire;

[0015] S10: Perform argon arc welding on the longitudinal connection of the aluminum strip to form a smooth aluminum sleeve;

[0016] S11: Perform online eddy current testing on the welds of smooth aluminum sleeves;

[0017] S12: reducing the diameter of the smooth aluminum sheath so that the smooth aluminum sheath and the insulated core wire are pressed together to form an aluminum sheathed core wire;

[0018] S13: spraying hot melt adhesive on the surface of the smooth aluminum sleeve;

[0019] S14: extruded outer sheath;

[0020] S15: cooling;

[0021] S16: Reel in the line.

[0022] Compared with the prior art, the advantages of the present invention are: the conventional conductor core wire is a circular compact structure, which is formed by twisting a number of circular conductor monofilaments of the same diameter. There are gaps between the conductor monofilaments of the outermost layer. During the cross-linking process, the inner shielding layer material is easily randomly embedded under the high pressure of extrusion, resulting in uneven thickness and waste of inner shielding layer material. At the same time, compared with the profile wire, the compaction coefficient is low and the amount of copper used is increased. Through the steps S1 and S2, a hybrid conductor production process is adopted, the center adopts circular compaction to form the conductor inner core, and the outer layer uses Z-shaped profile wires to twist into a ring-shaped conductor outer core, wherein the Z-shaped profile wire twisting does not require mold cold drawing, and the heat generated during twisting is small, which greatly reduces the increase in the resistivity of the conductor due to lattice distortion, thereby meeting the electrical requirements. Under the premise of meeting the resistance requirements, the copper cross-section can be reduced. The copper consumption of the conductor outer core structure can save 1%~2.5% compared with the conventional circular compact structure. At the same time, the outer Z-shaped wires are closely connected, the contact area between each other is large, the contact resistance is reduced, and the gaps between each other are small. In the three-layer co-extrusion process, the extrusion pressure can make the Z-shaped wires more closely connected under pressure like the wedge-shaped wires, and it is not easy to loosen, thereby solving the problem of embedded inner shielding layer material. Compared with the traditional circular compact structure, the inner shielding layer material can be saved by 1%-5%, and the outer diameter of the conductor core wire is stable, the surface is smooth and round, the bending radius is smaller than that of the full-shaped wire conductor, and the structure is stable and reliable. This structure takes into account the advantages of circular monofilament compaction and wire twisting;

[0023] In steps S3-S6, through step S3, the conductor core wire can be heated to increase the temperature of the conductor core wire, which helps to improve the cross-linking efficiency and increase the adhesion between the conductor and the inner shielding layer. At the same time, it can also play a role in drying and removing moisture. Through the design of step S5, the conductor core wire can continue to be heated after the three-layer co-extrusion, and the heat can be transferred from the conductor core wire to the three-layer co-extrusion, reducing the temperature difference between the inner and outer rings of the three-layer co-extrusion, and improving the uniformity and sufficiency of the cross-linking. Then in step S6, the cross-linking heat of the three-layer co-extrusion can be transferred in two directions from the inner layer and the outer layer respectively, thereby improving the cross-linking efficiency. By using software to calculate and set the temperature of the conductor core wire and the cross-linking tube, the absorbed heat is sufficient to fully promote the cross-linking reaction, shortening the cross-linking time. The multi-stage cooling cross-linking design along the cross-linking tube can reduce the surface temperature of the insulation core wire, allowing the insulation core wire to enter the cooling section at a lower temperature, shortening the cooling time. By reducing the surface temperature difference between the conductor core wire and the insulation core wire, it also improves thermal stress and uneven crystallization in the three-layer co-extrusion. During the three-layer co-extrusion cross-linking process, heat is transferred from the outer layer to the inner layer, ensuring that the cross-linking condition of the inner ring of the insulation layer is good and that the outer ring of the insulation layer does not over-cross-link.

[0024] In step S7, according to the XLPE insulation manufacturing principle, after XLPE is chemically cross-linked, small molecular byproducts such as methane, water, cumyl alcohol, and acetophenone will be generated, which will remain in the insulation layer and affect the product performance of the high-voltage cable. In addition, the insulation layer of the 750kV ultra-high voltage cable is thick, so a reasonable degassing method needs to be adopted to eliminate internal gas byproducts, reduce and redistribute solid byproducts, reach a degassing equilibrium point, and thus ensure that the cable performance is not affected; the traditional heat conduction system uses electric heating equipment around the turntable for heat conduction, and the hot air is naturally transmitted from the outside to the inside, which has a low heat transfer efficiency, resulting in the cable in the inner circle of the drying room being difficult to heat and slowly heating up, and the degassing time is too long, affecting production efficiency and product delivery cycle; to address the above problems, on the basis of the traditional degassing equipment, the heat transfer function of heat convection is added, thereby increasing the heat transfer efficiency, reducing the degassing time, and improving production efficiency;

[0025] Through the design of step S8, after the smooth aluminum sleeve is subsequently formed, the smooth aluminum sleeve is fully pressed and compacted with a layer of semi-conductive butyl tape, two layers of semi-conductive water-blocking tape, and a layer of semi-conductive water-blocking copper wire shielding tape to form a negative gap, thereby ensuring good electrical conductivity and reliable electrical connection. This avoids the risk of suspended discharge and ablation caused by poor contact due to the gap between the wrinkled aluminum sleeve and the water-blocking tape.

[0026] The S9-S12 design can form a high-quality smooth aluminum sheath, ensuring the safe use of UHV cables and avoiding the risk of ablation.

[0027] As an improvement of the present invention, in step S3, the preheating temperature of the front preheater is set at 80-100°C; in step S5, the preheating temperature of the rear preheater is set at 140-160°C; in step S6, the multi-stage cooling cross-linking process is seven stages, and the temperatures are 280°C, 270°C, 265°C, 260°C, 255°C, 250°C, and 240°C, respectively. Through the improvement, the front preheater and the rear preheater are used to reduce the temperature difference between the inner and outer rings of the three-layer co-extrusion, improve the uniformity and sufficiency of cross-linking, and through precise calculation by VCV special calculation software TCC, the cross-linked tube adopts seven heating sections, the temperature is reduced section by section, the front preheater and the rear preheater are enabled, and the internal and external heating methods are used to reduce the temperature of the cross-linked tube. Degree, strive to reduce the temperature gradient during the three-layer co-extrusion cross-linking to keep it heated evenly, while maintaining a good degree of cross-linking. During the heating process, the temperature of the outer ring of the insulation layer quickly rises to 230°C, so that the outer ring of the insulation layer is quickly cross-linked, reducing the melting and sagging of the polyethylene melt under gravity. As the insulation layer moves in the cross-linked tube, the middle layer area of ​​the insulation layer slowly rises from 135°C to 195°C, and the temperature of the inner ring of the insulation layer slowly rises to 163°C. At 60 meters, the degree of cross-linking of the insulation layer reaches more than 93%, and at 80 meters, the degree of cross-linking reaches more than 98%. In addition, the temperature is reduced section by section. After the insulation core wire exits the heating section and enters the cooling section at 20 meters, the surface temperature drops to 45°C. The cooling is timely and sufficient, and the generation of cross-linked internal stress is reduced.

[0028] As an improvement of the present invention, after step S6 is completed, the insulating core wires are layered and raised when winding the wires to increase the gap between each layer of insulating core wires. The raising is performed using hollow pads. Through the improvement, the gap between each layer of cables is increased, which is conducive to faster and more uniform transfer of heat to the surface of each layer of cables when hot air convection is formed, thereby accelerating the degassing efficiency.

[0029] As an improvement of the present invention, a heating tube for heating the convection drying room is provided on the inner wall of the convection drying room, a support frame for supporting the insulating core wire is provided on the axis of the convection drying room, the support frame is rotatably connected in the convection drying room, the insulating core wire is spirally stacked on the support frame, the support frame includes an air transmission tube provided on the axis, a supporting square tube is connected to the circumference of the air transmission tube, air outlet holes are evenly arrayed on the supporting square tube, air transmission holes are provided at the connection between the air transmission tube and the supporting square tube, an exhaust fan is provided below the air transmission tube, and an air outlet is provided above the air transmission tube. Valve, through the improvement, in order to form the air convection phenomenon, there are two main ways, one is to use the increased air pressure to send air to achieve convection, the other is to use the reduced air pressure to gather wind to achieve convection, and the convection drying room is large in size. If the convection is formed by increasing the air pressure, the requirements for the booster fan are high. It is necessary to ensure the adaptability between the booster fan and the convection drying room, and to ensure the sufficiency and integrity of the convection, thereby causing a substantial increase in the degassing cost. By reducing the air pressure to gather wind, it is only necessary to ensure the centrality of the gathering position to ensure the uniformity of the convection. , and can ensure the comprehensiveness of convection. The convection drying room has low requirements for its adaptability. Therefore, the method of forming convection by negative pressure wind gathering is more valuable in the convection drying room than the method of forming convection by increasing air supply. The setting of the rotating connection of the support frame can enhance the air flow in the convection drying room, help the transmission of high temperature, and improve the degassing efficiency. The design of the air transfer pipe and the exhaust fan can form an axial air flow area on the axis of the convection drying room. In addition to the air flow moving along the axial direction, a negative pressure area will be formed in the air transfer pipe, and the heating pipe on the inner wall will heat the inner wall area. A high-pressure area is formed, so that heat can be quickly transferred from the inner wall area to the axial area, thereby improving the degassing efficiency. The traditional structural design, in which the heating tube is heated in the inner wall area, has a heat transfer efficiency much lower than the transfer efficiency of the negative pressure area designed on the axis. The design of the air outlet and the air transfer hole is to ensure the high pressure of the inner wall and the low pressure of the axis. The air flow is fluid, and the heat is transferred quickly. The supporting square tube is a hollow pad. As the heat passes through the air outlet, the cable on the supporting square tube is driven to heat up. Compared with the traditional heat transfer method, the temperature rises faster.

[0030] As an improvement of the present invention, an air inlet is provided on the outside of the convection drying chamber, and the direction of the air inlet of the air inlet is arranged along the tangential direction of the convection drying chamber. The heating tube is extended and spirally ascended in the direction of the air inlet, and the rotation direction of the spiral ascending heating tube is the same as the rotation direction of the support frame. The inner side of the top surface of the convection drying chamber is in an inverted cone shape. With this improvement, through the design of the air inlet and the heating tube, a spiral upward airflow can be formed on the inner wall of the convection drying chamber. When the airflow contacts the top surface of the convection drying chamber, it will converge toward the center. Then, because the heat of the spiral upward airflow is higher than that of the air transfer tube, the spiral upward airflow will spiral downward along the air transfer tube to achieve heat transfer on the axis, thereby accelerating the heating rate of the cable in the inner circle of the spiral, thereby accelerating the heating rate of the cable as a whole, and improving the degassing efficiency of the cable. The rotation direction of the spiral ascending heating tube is the same as the rotation direction of the support frame, so that the rotation of the support frame can enhance the spiral upward speed of the airflow on the heating tube.

[0031] As an improvement of the present invention, a ventilation duct is provided between the air outlet valve and the air inlet fan. Through the improvement, the air flow in the convection drying room forms a closed-loop reflux, thereby preventing the air pressure in the convection drying room from rising with the operation of the air inlet fan during the flow of the air. In actual operation, if the air inlet fan always draws external air into the convection drying room, on the one hand, it will bring in colder air into the convection drying room, thereby affecting the heating efficiency of the convection drying room, and on the other hand, it will cause the air pressure in the convection drying room to rise rapidly. In order to ensure the safety of the convection drying room, it is necessary to release the pressure in time, which can easily increase the operating cost of the convection drying room. At the same time, in the process of forming negative pressure wind gathering in the air transfer duct, the air inlet fan can enhance the negative pressure of the air transfer duct, use an exhaust fan at one end to supply air, and use an air inlet fan at the other end to exhaust air, so as to achieve the smooth flow of negative pressure airflow in the air transfer duct.

[0032] As an improvement of the present invention, in step S9, during the longitudinal wrapping process of the aluminum strip, it passes through the forming wheel, four to six horn dies, and the sizing die in sequence and then converges into a circle. The sizing die adopts a nano-diamond coated sizing die. Through the improvement, the diameter reduction of the multi-channel horn die can better achieve the alignment of the two sides of the aluminum strip during the longitudinal wrapping process, reduce the high and low misalignment, and enhance the welding reliability of the weld. The sizing die adopts the design of a nano-diamond coated sizing die, which can reduce traction resistance and ensure that the surface of the formed aluminum sleeve is bright, which helps to improve the quality of the weld.

[0033] As an improvement of the present invention, in step S11, when a leaky weld or a cold weld is detected, a cold welding machine is used for online repair welding. Through the improvement, the cold welding machine adopts the principle of capacitor energy storage to instantly release current between the tungsten electrode and the workpiece in the form of a high-frequency pulse arc. It only takes a dozen milliseconds to complete the welding of a weld point. The heat input is concentrated, and the time for arcing and arcing is fast. There is no continuous heating of the workpiece, thereby achieving a cold welding effect, which can effectively ensure the quality of the repair welding. At the same time, after the repair welding is completed, it is necessary to ensure that the inner surface of the aluminum sleeve is not deformed.

[0034] As an improvement of the present invention, in step S12, multiple groups of rollers are used for rolling to perform gradual diameter reduction. The roller group includes four rollers, and the four rollers are arranged in the center along the circumference to form a diameter reduction hole for diameter reduction. The diameters of the diameter reduction holes of the multiple groups of rollers are reduced in sequence. During the diameter reduction process, the rollers rotate, and a rotating connecting buckle is provided at the connection of the two connected rollers. The rotating connecting buckle includes a parallel groove and a parallel block that fit together. The parallel block is provided on one roller, and the parallel groove is provided on the other roller. The parallel block is provided along the radial direction of one roller, and the parallel groove is provided along the axial direction of the other roller. The rollers are made of MC nylon. The improvements described above, through the design of multiple roller groups, can reduce the cable diameter. This not only allows for a tighter fit between the aluminum tape and the semi-conductive butyl tape, semi-conductive water-resistant tape, and semi-conductive water-resistant copper wire shielding tape, but also reduces the overall cable diameter, thereby reducing the amount of outer sheath used on the aluminum tape, reducing cable weight, and lowering cable production costs. The connection design between the rollers in each roller group ensures rotational stability and prevents disconnection between the rollers. The rollers are made of MC nylon, which has high strength, can withstand long loads, has strong wear resistance and self-lubricating properties, and can absorb noise and shock. Roll-forming eliminates lubricating oil stains, facilitating subsequent hot-melt adhesive processing.

[0035] As an improvement of the present invention, in step S13, before spraying the hot melt adhesive, the smooth aluminum sleeve is preheated, the core wire of the aluminum sleeve is passed through the circumferential heating device, and infrared heating is used to raise the surface temperature of the smooth aluminum sleeve to 60 degrees, and then a plurality of atomizing spray guns evenly distributed along the circumference are used for spraying. Through the improvement, preheating the smooth aluminum sleeve is not only beneficial to the adhesion between the smooth aluminum sleeve and the hot melt adhesive, but also helps to prolong the solidification time of the hot melt adhesive. In S14, the bonding strength between the outer sheath and the hot melt adhesive after extrusion is enhanced, so that the smooth aluminum sleeve, hot melt adhesive and outer sheath are tightly bonded, and the design of multiple atomizing spray guns helps to control the spraying thickness and spraying uniformity of the hot melt adhesive, thereby improving the spraying quality of the spray adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the cross-sectional structure of the cable of the present invention.

[0037] Figure 2 It is a schematic diagram of the structure of the three-layer co-extrusion process of the conductor core wire of the present invention.

[0038] Figure 3 It is a schematic diagram of the cross-linking degree and temperature curve of the three-layer co-extrusion of the insulated core wire of the present invention.

[0039] Figure 4 It is a schematic diagram of the internal structure of the convection drying room of the present invention.

[0040] Figure 5 It is a schematic diagram of the connection structure between the supporting square tube and the air transmission tube of the present invention.

[0041] Figure 6 It is a schematic diagram of the top view of the support frame of the present invention.

[0042] Figure 7 It is a schematic diagram of air flow in the convection drying room of the present invention.

[0043] Figure 8 It is a structural diagram of the smooth aluminum sleeve forming process of the present invention.

[0044] Figure 9 It is a structural schematic diagram of the aluminum strip longitudinal wrapping process of the present invention.

[0045] Figure 10 It is a structural schematic diagram of the roller group of the present invention.

[0046] As shown in the figure: 1. Conductor core wire, 1.1. Conductor inner core, 1.2. Conductor outer core, 2. Preheater, 3. Insulation core wire, 3.1. Inner shielding layer, 3.2. Insulation layer, 3.3. Outer shielding layer, 4. Three-layer co-extrusion extruder, 5. Post-preheater, 6. Cross-linking tube, 6.1. Heating section, 6.2. Cooling section, 7. Convection drying room, 7.1. Heating tube, 7.2. Support frame, 7.2.1. Air transfer tube, 7.2.2. Support square tube, 7.2.3. Air outlet, 7.2.4. Air outlet, 7.2.5. Exhaust fan, 7.2.6. Air outlet valve, 8. Air inlet fan, 8.1. Ventilation duct, 9. Semi-conductive buffer layer, 10. Aluminum strip, 11. Smooth aluminum sheath, 12. Aluminum sheath core wire, 13. Outer sheath, 14. Forming wheel, 15. Horn die, 16. Sizing die, 17. Roller assembly, 17.1. Reduction hole, 17.2. Rotating connecting buckle, 17.2.1. Parallel groove, 17.2.2. Parallel block, 18. Atomizing spray gun, 19. Insulated core wire pay-off stand, 20. Aluminum strip pay-off stand, 21. Argon arc welding gun, 22. Online eddy current flaw detector, 23. Aluminum sheath preheating machine, 24. Outer sheath extruder, 25. Cooling water trough, 26. Cable take-up stand. DETAILED DESCRIPTION

[0047] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0048] like Figure 1 As shown, a production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable comprises the following steps:

[0049] S1: Use round conductor to compress and form the conductor core 1.1;

[0050] S2: Z-shaped wire conductors are twisted into a ring-shaped conductor outer core 1.2 and are tightly wrapped around the conductor inner core 1.1;

[0051] S3: Passing the conductor core wire 1 consisting of the conductor inner core 1.1 and the conductor outer core 1.2 through the preheater 2 to perform electromagnetic induction preheating on the conductor core wire 1;

[0052] S4: Co-extruding the inner shielding layer 3.1, the insulating layer 3.2, and the outer shielding layer 3.3 on the surface of the conductor core wire 1 to form the insulated core wire 3;

[0053] S5: passing through the post-preheater 5, electromagnetic induction heating is performed on the conductor core wire 1 inside the insulated core wire 3 to reduce the cross-linking internal stress;

[0054] S6: The insulated core wire 3 passes through the cross-linking tube 6, which is heated and cross-linked at the inlet end, and then cross-linked by multi-stage cooling;

[0055] S7: The insulated core wire 3 is placed in a convection drying room 7 for degassing;

[0056] S8: Wrap a layer of semi-conductive butyl tape, two layers of semi-conductive water-repellent tape, and a layer of semi-conductive water-repellent copper wire shielding tape around the outer layer of the insulated core wire 3 in sequence to form a tape-wrapped core wire;

[0057] S9: longitudinally wrap an aluminum tape 10 on the surface of the tape-wrapped core wire;

[0058] S10: Argon arc welding is performed on the longitudinal connection of the aluminum strip 10 to form a smooth aluminum sleeve 11;

[0059] S11: Performing online eddy current testing on the weld of the smooth aluminum sleeve 11;

[0060] S12: reducing the diameter of the smooth aluminum sheath 11 so as to press the smooth aluminum sheath 11 and the taped core wire together to form the aluminum sheath core wire 12;

[0061] S13: spraying hot melt adhesive on the surface of the smooth aluminum sleeve 11;

[0062] S14: extruded outer sheath 13;

[0063] S15: cooling;

[0064] S16: Reel in the line.

[0065] like Figure 2 、 Figure 3 As shown, the conductor core wire 1 passes through the preheater 2, the three-layer co-extrusion extruder 4, the post-preheater 5 and the cross-linking tube 6 in sequence to complete the cross-linking. In step S3, the preheating temperature of the preheater 2 is set at 100°C; in step S5, the preheating temperature of the post-preheater 5 is set at 140°C; in step S6, the multi-stage cooling cross-linking process is seven stages, and the temperatures are 280°C, 270°C, 265°C, 260°C, 255°C, 250°C, and 240°C in sequence; the cross-linking tube 6 includes a heating The multi-stage cooling cross-linking process of the heating section 6.1 and the cooling section 6.2 all take place in the heating section 6.1, and the cross-linking tube 6 is a nitrogen-sealed space. Through the VCV dedicated calculation software TCC, the cross-linking tube 6 adopts seven-stage heating, the heating temperature is gradually reduced, the pre-heater 2 and the post-preheater 5 are activated, and the internal and external heating methods are used. As the heating temperature of the heating section 6.1 decreases, the temperature gradient formed in the insulated core wire 3 is strived to be reduced to keep it heated evenly, while maintaining a good degree of cross-linking. Figure 3 In the figure, green (Cure) is the cross-linking curve, blue (Zone Temp) is the multi-segment zone temperature curve, and red (Surface (Pink) is the temperature curve of the outer ring of insulation layer 3.2, and (pink) (Conductor) is the temperature curve of the conductor core. During the heating process, within the first section of heating section 6.1 (280°C), the outer ring temperature of insulation layer 3.2 rapidly rises to 230°C. This rapidly crosslinks the outer ring of insulation layer 3.2, reducing the sag of the polyethylene melt under gravity. As insulation layer 3.2 moves through cross-linked tube 6, the middle layer slowly rises from 135°C to 195°C, while the inner ring temperature of insulation layer 3.2 slowly rises to 163°C. At 60 meters, the degree of cross-linking of insulation layer 3.2 reaches over 93%, and at 80 meters, it reaches over 98%. The temperature then decreases step by step. After insulation core 3 exits heating section 6.1 of cross-linked tube 6 and enters cooling section 6.2 at 20 meters, the surface temperature of insulation core 3 drops to 45°C. This timely and sufficient cooling reduces the generation of cross-linked internal stress.

[0066] like Figure 4-6As shown, after step S6 is completed, the insulating core wires 3 are layered and raised when the wires are wound up to increase the gap between each layer of the insulating core wires 3. The raising is performed by hollow pads. A heating tube 7.1 for heating the convection drying room 7 is provided on the inner wall of the convection drying room 7. A support frame 7.2 for supporting the insulating core wires 3 is provided on the axis of the convection drying room 7. The support frame 7.2 is rotatably connected to the convection drying room 7. The insulating core wires 3 are spirally stacked on the support frame 7.2. The support frame 7.2 includes an air transmission pipe 7.2.1 provided on the axis. A supporting square tube 7.2.2 is connected to the circumference of the air transmission pipe 7.2.1. The supporting square tube 7.2.2 is a hollow pad. The supporting square tube 7.2.2 is evenly arrayed with air outlet holes 7.2.3, and there are air outlet holes on the left and right sides and the upper and lower sides of the supporting square tube 7.2.2. 7.2.3, an air transmission hole 7.2.4 is provided at the connection between the air transmission pipe 7.2.1 and the supporting square pipe 7.2.2, an exhaust fan 7.2.5 is provided below the air transmission pipe 7.2.1, and an air outlet valve 7.2.6 is provided above the air transmission pipe 7.2.1. An air inlet fan 8 is provided on the outside of the convection drying room 7, and the direction of the air inlet of the air inlet fan 8 is arranged along the tangent direction of the convection drying room 7. The heating pipe 7.1 is extended and spirally ascended along the direction of the air inlet. The heating pipe 7.1 is shown as a schematic distribution curve in the figure. In actual production, the heating pipe 7.1 is distributed throughout the inner wall of the convection drying room 7. The spiral ascending direction of the heating pipe 7.1 is the same as the rotation direction of the supporting frame 7.2. The inner side of the top surface of the convection drying room 7 is inverted conical, and a ventilation duct 8.1 is provided between the air outlet valve 7.2.6 and the air inlet fan 8.

[0067] like Figure 7 As shown, four air flows are eventually formed in the convection drying room 7: an air flow spiraling upward along the outer circle, an air flow spiraling downward along the outer wall of the air transfer tube 7.2.1, an air flow vertically upward inside the air transfer tube 7.2.1, and a pressure difference air flow flowing in the opposite radial direction. This allows heat to quickly diffuse in the convection drying room 7, achieving rapid heating and degassing of the insulated core wire 3 as a whole, and improving the degassing efficiency.

[0068] like Figure 8 As shown, after the degassing of the insulating core wire 3 is completed, the insulating core wire 3 needs to start from the insulating core wire pay-off frame 19 and be wrapped with a layer of semi-conductive butyl tape, two layers of semi-conductive water-resistant tape and a layer of semi-conductive water-resistant copper wire shielding tape. The combination of a layer of semi-conductive butyl tape, two layers of semi-conductive water-resistant tape and a layer of semi-conductive water-resistant copper wire shielding tape is called a semi-conductive buffer layer 9. Then, it passes through the aluminum strip pay-off frame 20, the forming wheel 14, the horn mold 15, the sizing mold 16, the argon arc welding gun 21, the online eddy current flaw detector 22, the roller group 17, the aluminum sheath preheating machine 23, the atomizing spray gun 18, the outer sheath extruder 24, and the cooling water tank 25 in sequence, and arrives at the cable take-up frame 26 to complete the storage of the formed cable.

[0069] During the winding process of the semi-conductive buffer layer 9, the semi-conductive water-blocking copper wire shielding tape is 0.5 mm thick and 80 mm wide, with no less than 20 copper wires, each with a diameter of no less than 0.2 mm. The copper wires are tinned and woven longitudinally in a wavy pattern. The volume resistivity is less than 500 Ω·cm, and the surface resistance is less than 100 Ω. The good electrical conductivity enables it to maintain a more reliable electrical connection with the smooth aluminum sleeve 11. Subsequently, the smooth aluminum sleeve 11 will be reduced in diameter by multiple sets of rollers 17, so that a buffer space is reserved for the semi-conductive buffer layer 9. After the smooth aluminum sleeve 11 is reduced in diameter, it will be in close surface contact with the semi-conductive buffer layer 9, maintaining reliable and good electrical performance and avoiding the risk of suspended discharge caused by poor contact due to the gap between the wrinkled aluminum sleeve and the water-blocking tape.

[0070] like Figure 9 As shown, in step S9, when the insulated core wire 3 passes through the aluminum strip pay-off frame 20, it will be placed on the center line of the aluminum strip 10, and then the aluminum strip 10 is longitudinally wrapped to form a smooth aluminum sleeve 11 under the action of the forming wheel 14, the horn mold 15, the sizing mold 16, and the argon arc welding gun 21. During the longitudinal wrapping process of the aluminum strip 10, there are two forming wheels 14. The forming wheel 14 located upstream is used to first lift the two side edges of the aluminum strip 10, and the forming wheel 14 located downstream is used to directionally bend the aluminum strip 10 and form an arc as a whole. When the aluminum strip 10 then enters the horn mold 15, the convergence direction of the aluminum strip 10 can be guaranteed, thereby ensuring the forming quality and uniformity of the aluminum strip 10. Then, the insulated core wire 3 and the semi-circular aluminum strip 10 pass through the six-channel horn mold 15 in turn, so that the arc diameter of the aluminum strip 10 gradually decreases, and finally passes through the sizing mold 16. The aluminum strip 10 converges into a circle to form a smooth aluminum sleeve 11, which wraps the insulated core wire 3. The sizing die 16 will make the aluminum strip 10 in close contact with the semi-conductive buffer layer 9, and accordingly the sizing die 16 will be in close contact with the aluminum strip 10. In order to ensure the quality of the aluminum strip 10, the sizing die 16 adopts a nano-diamond coating sizing die, which can reduce the traction resistance and ensure that the surface of the formed smooth aluminum sleeve 11 is bright, which helps to improve the quality of the weld.

[0071] A brush may be added above the horn mold 15 to filter out debris and impurities generated by friction between the aluminum strip 10 and the various molds after trimming and during the forming process, thereby increasing welding reliability.

[0072] The argon arc welding torch 21 is affected by the operating status of the outer sheath extruder 24 and cannot be shut down for operation. During the production of the smooth aluminum sleeve 11, the tungsten electrode and gas cylinder cannot be replaced during shutdown. Therefore, dual welding torch technology is required in the argon arc welding process to avoid missed welds and repair welds caused by tungsten electrode replacement. The shielding gas cylinders are connected in series to ensure the production of long lengths. During the online eddy current flaw detection process, an automatic weld tracking system is used. Through visual guidance, the weld initial point is automatically identified and the weld is automatically tracked and controlled. Simultaneously, horizontal and vertical tracking information can be obtained. This greatly reduces the requirements for environmental conditions and improves anti-interference performance, sensitivity, and measurement accuracy. This significantly reduces missed welds and cold welds during welding, ensuring the welding quality of the smooth aluminum sleeve 11.

[0073] like Figure 8 As shown, a repair welding space is provided between the online eddy current flaw detector 22 and the roller group 17. In step S11, when a leaking weld or a cold weld is detected, a cold welding machine will be used for online repair welding. The cold welding machine adopts the principle of capacitor energy storage and releases current between the tungsten electrode and the workpiece in the form of a high-frequency pulse arc instantly. It only takes a dozen milliseconds to complete the welding of a weld point. The heat input is concentrated, and the time for arcing and arcing is fast. The workpiece is not continuously heated, thereby achieving a cold welding effect, which can effectively ensure the quality of the repair welding. At the same time, after the repair welding is completed, it is necessary to ensure that the inner surface of the smooth aluminum sleeve 11 is not deformed.

[0074] like Figure 8 、 Figure 10 As shown, after the welding of the smooth aluminum sleeve 11 is completed, in step S12, multiple groups of roller groups 17 are used to roll and perform gradual diameter reduction, so that the smooth aluminum sleeve 11 and the semi-conductive buffer layer 9 are more closely fitted, while improving the tightness of the cable and reducing the cable diameter. The roller group 17 includes four rollers, and the four rollers are arranged in the center along the circumference to form a diameter reduction hole 17.1 for diameter reduction. The diameters of the diameter reduction holes 17.1 of the multiple groups of roller groups 17 are reduced successively. During the diameter reduction process, the rollers rotate, and a rotating connecting buckle 17.2 is provided at the connection of the two connected rollers. The rotating connecting buckle 17.2 includes a matching parallel groove 17.2.1 and a parallel block 17.2.2. The parallel block 17.2.2 is provided on one roller, and the parallel groove 17.2.1 is provided on the other roller. The parallel block 17.2.2 is provided along the radial direction of one roller, and the parallel groove 17.2.1 is provided along the axial direction of the other roller. Each roller assembly 17 controls the reduction ratio to 2-3%, ultimately achieving an outer diameter reduction ratio of 8-17 mm for the smooth aluminum sleeve 11, while maintaining a roundness of ≥99%. The rollers are made of MC nylon, which boasts high strength, long-term load bearing capacity, strong wear resistance, and self-lubricating properties, absorbing noise and shock. Furthermore, the roll-forming process eliminates lubricant contamination, facilitating subsequent hot-melt adhesive processing.

[0075] In step S13, the smooth aluminum sleeve 11 is preheated before the hot melt adhesive is sprayed. Multiple atomizing spray guns 18, evenly distributed along the circumference, are used for spraying. The hot melt adhesive must be non-toxic, odorless, chemically stable, and environmentally friendly. It must not react chemically with aluminum or plastic molecules during repeated heating. Furthermore, its softening point must be above the most demanding operating temperature of the cable to ensure proper operation.

[0076] During the extrusion process of the outer sheath 13 , the outer sheath 13 of different thicknesses has an impact on the bending performance of the cable, as shown in Table 1.

[0077] Table 1 Influence of outer sheath thickness on cable bending performance

[0078]

[0079] Through experiments, it was found that in actual production, the thicker the non-metallic outer sheath 13, the stronger the bending resistance of the smooth aluminum sheathed cable, and the maximum equivalent plastic strain on the bending compressive side continued to decrease. It is recommended that 750kV ultra-high voltage cross-linked polyethylene smooth aluminum cable use an outer sheath 13 of more than 5mm.

[0080] The above description is merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the scope of the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

Claims

1. A production process for a 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable, characterized in that: The following steps are involved: S1: Use round conductor to compress and form the conductor core (1.1); S2: A Z-shaped conductor is twisted into a ring-shaped conductor outer core (1.2) and is fitted around a conductor inner core (1.1); S3: passing the conductor core wire (1) composed of the conductor inner core (1.1) and the conductor outer core (1.2) through the preheater (2) to preheat the conductor core wire (1) by electromagnetic induction; S4: performing co-extrusion of an inner shielding layer (3.1), an insulating layer (3.2), and an outer shielding layer (3.3) on the surface of the conductor core wire (1) to form an insulating core wire (3); S5: passing through the post-preheater (5), performing electromagnetic induction heating on the conductor core wire (1) inside the insulated core wire (3), thereby reducing cross-linking internal stress; S6: the insulated core wire (3) passes through the cross-linking tube (6), and the cross-linking tube (6) starts to be heated and cross-linked at the inlet end, and then adopts multi-stage cooling cross-linking; S7: The insulated core wire (3) is placed in a convection drying room (7) for degassing; S8: wrapping a layer of semi-conductive butyl tape, two layers of semi-conductive water-resistant tape and a layer of semi-conductive water-resistant copper wire shielding tape around the outer layer of the insulated core wire (3) in sequence to form a tape-wrapped core wire; S9: longitudinally wrapping an aluminum tape (10) on the surface of the tape-wrapped core wire; S10: Argon arc welding is performed on the longitudinal connection of the aluminum strip (10) to form a smooth aluminum sleeve (11); S11: Performing online eddy current testing on the weld of the smooth aluminum sleeve (11); S12: reducing the diameter of the smooth aluminum sleeve (11) so as to press the smooth aluminum sleeve (11) and the taped core wire together to form an aluminum sleeve core wire (12); S13: spraying hot melt adhesive on the surface of the smooth aluminum sleeve (11); S14: extruded outer sheath (13); S15: cooling; S16: Reel in the line; After step S6 is completed, the insulating core wires (3) are layered and raised when the wires are taken up, and the gap between each layer of the insulating core wires (3) is increased. The raising is performed by hollow pads. A heating pipe (7.1) for heating the convection drying room (7) is provided on the inner wall of the convection drying room (7). A support frame (7.2) for supporting the insulating core wires (3) is provided on the axis of the convection drying room (7). The support frame (7.2) is rotatably connected in the convection drying room (7). The insulating core wires (3) are spirally stacked on the support frame (7.2). The support frame (7.2) includes an air transmission pipe ( 7.2.1), the air transmission pipe (7.2.1) is connected to a supporting square pipe (7.2.2) in the circumferential direction, the supporting square pipe (7.2.2) is provided with air outlet holes (7.2.3) in a uniform array, the connection between the air transmission pipe (7.2.1) and the supporting square pipe (7.2.2) is provided with air transmission holes (7.2.4), an exhaust fan (7.2.5) is provided below the air transmission pipe (7.2.1), and an air outlet valve (7.2.6) is provided above the air transmission pipe (7.2.1). In step S12, a plurality of roller groups (17) are used for rolling to perform gradual diameter reduction. The roller group (17) includes four rollers, and the four rollers are arranged in the center along the circumferential direction to form a diameter reduction for diameter reduction. The diameters of the shrinking holes (17.1) of the plurality of roller groups (17) are reduced in sequence. During the shrinking process, the rollers rotate, and a rotating connecting buckle (17.2) is provided at the connection of the two connected rollers. The rotating connecting buckle (17.2) includes a parallel groove (17.2.1) and a parallel block (17.2.2) that fit together. The parallel block (17.2.2) is provided on one roller, and the parallel groove (17.2.1) is provided on the other roller. The parallel block (17.2.2) is provided along the radial direction of one roller, and the parallel groove (17.2.1) is provided along the axial direction of the other roller. The rollers are made of MC nylon.

2. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 1, characterized in that: In step S3, the preheating temperature of the preheater (2) is set at 80-100°C; In step S5, the preheating temperature of the post-preheater (5) is set at 140-160°C; In step S6, the multi-stage cooling cross-linking process consists of seven stages, and the temperatures are 280°C, 270°C, 265°C, 260°C, 255°C, 250°C, and 240°C, respectively.

3. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 1, characterized in that: An air inlet fan (8) is provided on the outside of the convection drying room (7), and the direction of the air inlet of the air inlet fan (8) is arranged along the tangential direction of the convection drying room (7). The heating tube (7.1) is extended and spirally ascended along the direction of the air inlet. The rotation direction of the spiral ascending of the heating tube (7.1) is the same as the rotation direction of the support frame (7.2). The inner side of the top surface of the convection drying room (7) is in an inverted cone shape.

4. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 3, characterized in that: A ventilation duct (8.1) is provided between the air outlet valve (7.2.6) and the air inlet fan (8).

5. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 1, characterized in that: In step S9, during the longitudinal wrapping process of the aluminum strip (10), the aluminum strip (10) passes through the forming wheel (14), the four to six horn dies (15), and the sizing die (16) in sequence, and then converges into a circle. The sizing die (16) adopts a nano-diamond coating sizing die.

6. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 1, characterized in that: In step S11, when a leaky weld or a cold weld is detected, a cold welding machine is used to perform online repair welding.

7. The production process of the 750kV ultra-high voltage cross-linked polyethylene smooth aluminum sheathed cable according to claim 1, characterized in that: In step S13, before the hot melt adhesive is sprayed, the smooth aluminum sleeve (11) is preheated, and the aluminum sleeve core wire (12) is passed through the encircling heating device. Infrared heating is used to raise the surface temperature of the smooth aluminum sleeve (11) to 60 degrees, and then a plurality of atomizing spray guns (18) uniformly distributed along the circumference are used for spraying.

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