Special deep geocable and its cable manufacturing method

Abstract

The application provides a special deep cable and a cable preparation method thereof, and relates to the technical field of cable preparation.The special deep cable comprises a buried cable and a special protective layer.The pre-stressed reinforcing bar and the double-layer embeddable steel belt armor are matched with each other, the cable can be freely bent in the relaxed state of the pre-stressed reinforcing bar, and the laying is facilitated;after the pre-stressed reinforcing bar is tensioned by the reinforcing bar tensioning device, the double-layer steel belt armor is extruded, and the double-layer steel belt armor is embedded into one whole body with high rigidity, the interlocking structure significantly improves the compression strength of the armor layer, effectively resists the extrusion of underground rocks, the lateral pressure of soil and the shear stress generated by geological movement, and prevents the deformation of the cable or the damage of the internal structure.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, and in particular to a special deep-earth cable and its preparation method. Background Technology

[0002] With the growth of global energy demand and the deepening of underground space development, deep-earth cables are increasingly widely used in geological exploration, oil and gas extraction, deep mineral development, and underground power grid construction. The deep-earth environment is characterized by high pressure, high humidity, strong corrosion, and frequent geological movements, which places stringent requirements on the mechanical strength, weather resistance, deformation resistance, and long-term reliability of cables.

[0003] Traditional cables face numerous challenges in deep underground environments. Traditional deep underground cables often employ single-layer steel tape armor or metal sheaths, which have limited compressive strength and deformation resistance. External forces such as underground rock compression and soil subsidence can easily cause the armor layer to break or deform, thereby damaging the internal insulation structure and leading to short circuits or signal interruptions. Furthermore, the strength of a single-layer armor is predetermined during manufacturing. High strength and rigidity make the cable difficult to lay, while high flexibility facilitates laying but results in low strength and rigidity, making it difficult to achieve both simultaneously. Summary of the Invention

[0004] The purpose of this invention is to provide a special deep-earth cable and its manufacturing method, so as to solve the problem mentioned in the background that traditional cables cannot achieve both flexibility and strength.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a special deep-earth cable, including a buried cable and a special protective layer. The special protective layer is wrapped around the outside of the buried cable, and a foam buffer layer is filled between the special protective layer and the buried cable.

[0006] The special protective layer includes an outer steel strip armor layer and an inner steel strip armor layer. The outer steel strip armor layer wraps around the inner steel strip armor layer. The outer steel strip armor layer includes a first steel strip, which is wound around the first steel strip. A first step is rolled on the first steel strip. The inner steel strip armor layer includes a second steel strip, which is wound around the first steel strip. A second step is rolled on the second steel strip.

[0007] The outer steel strip armor layer is wrapped with a first woven protective layer, and the inner steel strip armor layer is provided with a second woven protective layer and a third woven protective layer in sequence. Six sets of first and second seams are sewn on the second and third woven protective layers by a CNC sewing machine to form evenly distributed limiting grooves. Prestressed tendons pass through the limiting grooves.

[0008] Furthermore, the outermost layer of the buried cable is a composite sheath, the inner side of which is wrapped with an insulating liner, the inner side of which is wrapped with a conductor core, the outer side of which is wrapped with a conductor insulating sleeve, and a filler layer is provided between the conductor insulating sleeve and the insulating liner.

[0009] Furthermore, the tensioning of the prestressed tendon is achieved by a tendon tensioning device, which includes a first ring sleeved on the outside of the buried cable. Six threaded rods are rotatably connected to the first ring in a circumferentially distributed manner. The six threaded rods are fixedly connected to a second ring by threads. The second ring is sleeved on the outside of the buried cable. A tension sensor is installed between the second ring and the prestressed tendon, and the tension sensor is fixedly connected to the prestressed tendon.

[0010] A method for preparing a special deep-earth cable, comprising the following steps:

[0011] S1. Preparation of conductor core and conductor insulation sleeve: A high-conductivity copper alloy is used as the conductor core, which is drawn to the required diameter by a wire drawing machine. Then, a conductor insulation sleeve is wrapped around the conductor core. The insulation material is cross-linked polyethylene, which is uniformly coated by an extruder to form an insulation layer of uniform thickness.

[0012] S2. Processing of insulating liner and filling layer: The insulating liner is made of low-density polyethylene and is covered on the outside of the conductor insulation sleeve by extrusion process. The space between the insulating liner and the conductor insulation sleeve is filled with polymer foam material to form a filling layer.

[0013] S3. Molding of composite sheath: The composite sheath adopts multi-layer co-extrusion technology, with polyvinyl chloride as the inner layer and neoprene as the outer layer, ensuring that the materials of each layer are tightly bonded to form a uniform, bubble-free sheath structure;

[0014] S4. Processing of the third braided protective layer and the second braided protective layer: The third braided protective layer and the second braided protective layer are sequentially applied to the outside of the composite sheath, and a foam buffer layer is filled between the third braided protective layer and the composite sheath. Then, six sets of evenly distributed first and second seams are sewn by machine to form a limiting groove.

[0015] S5. Installation of prestressed tie rods: The prestressed tie rods are inserted into the limiting grooves. The two ends of the prestressed tie rods protrude from the special protective layer and are fixed by the tie rod tensioning device, leaving an interface for subsequent tensioning operations.

[0016] S6. Preparation of inner and outer steel strip armor layers:

[0017] Inner steel strip armor layer: A second step is rolled on the surface of the second steel strip using a high-precision rolling mill, and then wrapped around the outside of the insulating liner in a spiral winding manner. Adjacent second steel strips overlap through the second step to form an interlocking structure.

[0018] Outer steel strip armor layer: After the first step is rolled out, the first steel strip is wrapped around the outside of the inner steel strip armor layer in a spiral winding manner, and the adjacent layers are overlapped by the second step and the first step.

[0019] S7. Processing of the first braided protective layer: The first braided protective layer is made of glass fiber and is tightly wrapped around the outside of the outer steel strip armor layer by braiding.

[0020] Furthermore, both the first steel strip of the outer steel strip armor layer and the second steel strip of the inner steel strip armor layer are made of high-strength low-carbon steel strips, with the steel strip thickness controlled between 1.5mm and 2mm.

[0021] Furthermore, the depth of the second step is the same as the thickness of the second steel strip, and the width of the second step is one-fifth of the width of the second steel strip.

[0022] Furthermore, the depth of the first step is the same as the thickness of the first steel strip, and the width of the first step is one-fifth of the width of the first steel strip.

[0023] Furthermore, the second steel strip and the first steel strip are wound in opposite spiral directions.

[0024] Furthermore, the winding pitch of the first steel strip is 1.5-2 times the width of the first steel strip, and the winding pitch of the second steel strip is 1.5-2 times the width of the second steel strip.

[0025] Furthermore, the first and second steel strips are pre-galvanized, and after winding, epoxy resin or polyurethane coatings are sprayed onto the surfaces of the inner and outer steel strip armor layers.

[0026] Compared with the prior art, the beneficial effects of the present invention include: the special deep-earth cable and its cable preparation method proposed in the present invention, through the cooperation of prestressed tendons and double-layer interlocking steel strip armor, allows the cable to bend freely when the prestressed tendons are relaxed, facilitating laying. After the prestressed tendons are tensioned using a tendon tensioning device, the double-layer steel strip armor is compressed, causing them to interlock into a highly rigid whole. This interlocking structure significantly improves the compressive strength of the armor layer, effectively resisting underground rock compression, soil lateral pressure, and shear stress generated by geological movement, preventing cable deformation or damage to the internal structure. Attached Figure Description

[0027] Figure 1The schematic diagram shows a cross-sectional structure of a special deep-earth cable according to an embodiment of the present invention;

[0028] Figure 2 The illustration schematically shows a special deep-earth cable according to one embodiment of the present invention. Figure 1 Enlarged structural diagram at point A in the middle;

[0029] Figure 3 The schematic diagram illustrates a layered cable structure of a special deep-earth cable according to an embodiment of the present invention.

[0030] Figure 4 The schematic diagram shows a structural diagram of the outer steel strip armor layer of a special deep-earth cable according to an embodiment of the present invention;

[0031] Figure 5 The schematic diagram shows a structural diagram of the inner steel strip armor layer of a special deep-earth cable according to an embodiment of the present invention.

[0032] Figure 6 The schematic diagram shows a cross-sectional structure of the outer steel strip armor layer of a special deep-earth cable according to an embodiment of the present invention;

[0033] Figure 7 The illustration schematically shows a special deep-earth cable according to one embodiment of the present invention. Figure 6 Enlarged structural diagram at point B;

[0034] Figure 8 The schematic diagram shows a cross-sectional structure of the inner steel strip armor layer of a special deep-earth cable according to an embodiment of the present invention.

[0035] Figure 9 The illustration schematically shows a special deep-earth cable according to one embodiment of the present invention. Figure 8 Enlarged structural diagram at point C;

[0036] Figure 10 The diagram illustrates the structure of a tensioning device for a special deep-earth cable according to an embodiment of the present invention.

[0037] The diagram labels are as follows: 1. Buried cable; 101. Composite sheath; 102. Insulating liner; 103. Conductor core; 104. Conductor insulation sleeve; 105. Filler layer; 2. Special protective layer; 3. Outer steel strip armor layer; 301. First steel strip; 302. First step; 4. Inner steel strip armor layer; 401. Second steel strip; 402. Second step; 5. First braided protective layer; 6. Second braided protective layer; 7. Third braided protective layer; 8. First seam; 9. Second seam; 10. Limiting groove; 11. Prestressed tie bar; 12. Foam buffer layer; 13. Tie bar tensioning device; 1301. First collar; 1302. Threaded rod; 1303. Second collar; 1304. Tension sensor. Detailed Implementation

[0038] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0039] According to one embodiment of the present invention, Figure 1-10 As shown. A special deep-earth cable mainly consists of two parts: a buried cable 1 and a special protective layer 2. The two are designed together to achieve high efficiency and reliable performance.

[0040] like Figure 1 As shown, the underground cable 1, as the core of power transmission, adopts a layered composite structure. The outermost layer is a composite sheath 101, the inner layer of which is made of chlorinated polyethylene or chlorosulfonated polyethylene. This material has excellent chemical corrosion resistance and can effectively resist the erosion of underground saline and acidic / alkaline soils. The middle layer is embedded with a glass fiber braided layer, which significantly enhances the tensile strength and puncture resistance of the sheath, with a breaking strength of over 500 MPa. The outer layer is covered with low-density polyethylene with added carbon black, which improves the wear resistance of the outer layer. This multi-layered composite design allows the composite sheath 101 to protect the internal structure while extending the overall service life of the cable.

[0041] The composite sheath 101 is wrapped with an insulating liner 102, which is molded from epoxy resin or polyimide. Epoxy resin has good insulation properties and mechanical strength, while polyimide is resistant to high temperatures and chemical corrosion; both provide stable support for the internal structure. The surface of the insulating liner 102 is provided with annular grooves, which not only enhance the mechanical engagement with the composite sheath 101 but also accommodate filler material during manufacturing, improving the overall structural stability.

[0042] The insulating liner 102 contains a conductor core 103, which is composed of multiple strands of twisted wire. By optimizing the cross-sectional shape of the single filaments, such as fan-shaped or tile-shaped, and the twisting direction, the fill factor can be increased to over 0.92, significantly reducing the outer diameter of the conductor core and lowering material loss. The conductor surface is drawn using precision molds, with a roughness controlled below 0.1 μm. This treatment effectively avoids partial discharge phenomena under high-voltage electric fields and improves the electrical performance of the cable.

[0043] The conductor core 103 is wrapped with a conductor insulation sleeve 104, made of high-insulation materials such as cross-linked polyethylene or ethylene propylene rubber (EPR). These materials have excellent insulation properties and temperature resistance, and can withstand temperatures above 120°C. Furthermore, by adding fillers such as nano-silica and silicon nitride, the insulation layer's resistance to electrical treeing aging is significantly enhanced, ensuring a breakdown strength ≥30kV / mm, thereby extending the service life of the insulation layer.

[0044] Between the conductor insulation sleeve 104 and the insulation liner 102, the filler layer 105 is made of low-density polyurethane foam or nitrile rubber. This closed-cell filler material can effectively absorb external impact forces, protecting the internal conductor and insulation layer from mechanical damage; at the same time, the closed-cell structure can also block the water penetration path, preventing groundwater from corroding the inside of the cable. The Shore hardness of the filler layer 105 is controlled between 40 and 50A, balancing buffering performance and structural support, ensuring that the cable can maintain a stable shape when subjected to external pressure.

[0045] like Figure 2 and Figure 3 As shown, the special protective layer 2 serves as the core of the cable's mechanical protection and consists of a double-layer steel tape armor layer, a three-layer braided protective layer, and a bracing system.

[0046] like Figure 2 - Figure 9 As shown, the outer steel strip armor layer 3 is formed by winding the first steel strip 301, with a thickness of 1.5-2.0 mm. The first step 302 formed during rolling tightly overlaps adjacent steel strips, creating a "dog-tooth" mechanical interlocking effect. This design significantly improves the compressive strength of the armor layer, increasing the overall compressive strength by more than 40%. The inner steel strip armor layer 4 is formed by winding the second steel strip 401, and similarly, the second step 402 overlaps to form an interlocking structure, further enhancing the mechanical strength of the armor layer. The winding direction of the outer steel strip armor layer 3 is opposite to that of the inner steel strip armor layer 4. This reverse winding design effectively counteracts the torque stress generated when the cable bends, enhancing the cable's bending resistance. Both steel strip armor layers are coated with epoxy resin powder to form a 50-80 μm thick anti-corrosion coating, which can withstand the corrosion of chloride ions and sulfides in underground environments and has a salt spray corrosion resistance time of over 1000 hours, ensuring the long-term stability of the armor layer.

[0047] like Figure 2 As shown, the outer steel strip armor layer 3 is wrapped with a first braided protective layer 5, made of anti-corrosion and rust-proof material. Its function is to protect the steel strip armor layer from direct corrosion by the external environment, further extending the service life of the armor layer. The inner steel strip armor layer 4 has a second braided protective layer 6 and a third braided protective layer 7 arranged sequentially on its inner side, both woven from high-strength aramid fibers. Aramid fibers have high tensile strength, high modulus, excellent chemical resistance and flame retardancy, providing additional mechanical protection for the internal structure. Six sets of first seams 8 and second seams 9 are sewn onto the surface of the braided layer using a CNC sewing machine, forming evenly distributed limiting grooves 10. These limiting grooves 10 precisely fix the position of the prestressing tendons 11, ensuring that the tendons are evenly distributed inside the cable, thereby generating uniform stress during tensioning.

[0048] like Figure 1 , Figure 3 and Figure 10 As shown, six prestressed tie rods 11, made of carbon fiber reinforced composite material, run through the limiting groove 10, with a tensile strength ≥2000MPa. The specific strength of carbon fiber composite material is more than 5 times that of traditional steel, and its coefficient of linear expansion is only 1 / 4 that of steel. This allows the prestressed tie rods 11 to effectively reduce stress fluctuations caused by temperature changes while withstanding high tension. The two ends of the prestressed tie rods 11 protrude from the special protective layer 2 and are used in conjunction with the tie rod tensioning device 13. By applying prestress, the steel strip armor layer is transformed from a loose state to a tight whole, significantly improving the cable's resistance to compression and tension.

[0049] like Figure 10 As shown, the tensioning of the prestressed tendon 11 is achieved through the tendon tensioning device 13. The tendon tensioning device 13 includes a first collar 1301 sleeved on the outside of the buried cable 1. This collar is made of high-strength aluminum alloy, and its inner diameter is precisely matched with the outer diameter of the cable to avoid local damage to the cable during tensioning. Six threaded rods 1302 are rotatably connected to the first collar 1301 in a circumferentially distributed manner. The threaded rods 1302 convert rotational motion into axial displacement through a precision thread pair. The second collar 1303 is threadedly engaged with the threaded rods 1302 and can move along the axial direction of the cable. A tension sensor 1304 is installed between the second collar 1303 and the prestressed tendon 11. It is a high-precision strain gauge sensor with a range of 0-500kN and an accuracy of ±0.5%, which can monitor the tendon tension in real time and feed it back to the control system.

[0050] During the cable laying stage, the prestressed tendons 11 are in a relaxed state, and the steel tape armor layers are not fully engaged. At this time, the cable can be bent freely, facilitating laying in complex underground paths. After a section of cable is laid and connected, a special tool is used to rotate the threaded rod 1302, driving the second collar 1303 to move away from the first collar 1301. Tension is applied to the prestressed tendons 11 through the tension sensor 1304. Simultaneously, the first collar 1301 applies axial pressure to the special protective layer 2, causing the first steel strips 301 of the outer steel tape armor layer 3 to interlock through the first step 302, and the second steel strips 401 of the inner steel tape armor layer 4 to interlock through the second step 402. The originally loose steel tape armor layers thus form a rigid whole, significantly improving the mechanical strength of the cable and making it more difficult to bend, thereby enhancing the protection of the buried cable 1. The tension sensor 1304 monitors the tension of the six prestressed tendons 11 in real time, ensuring that its uniformity is controlled within ±5%. When the buried cable 1 is disturbed by external factors in the later stage, the tension of the six prestressed tie rods 11 will change differently. The tension sensor 1304 can capture these changes in time and give early warning, providing real-time monitoring for the safe operation of the cable.

[0051] A method for manufacturing a special deep-earth cable includes the following steps:

[0052] 1. Preparation of conductor core 103 and conductor insulation sleeve 104: High conductivity copper alloy or aluminum alloy is used as conductor core 103. It is drawn to the required diameter by a wire drawing machine to ensure that the surface is smooth and free of defects. Then, conductor insulation sleeve 104 is wrapped around conductor core 103. The insulation material is cross-linked polyethylene or polytetrafluoroethylene. It is uniformly coated by an extruder to form an insulation layer of uniform thickness, which improves voltage resistance and corrosion resistance.

[0053] 2. Processing of the insulating liner 102 and the filling layer 105: The insulating liner 102 is made of low-density polyethylene or ethylene propylene rubber and is covered on the outside of the conductor insulation sleeve 104 by extrusion process to form a buffer structure. The space between the insulating liner 102 and the conductor insulation sleeve 104 is filled with polymer foam material or asbestos fiber to form the filling layer 105, which is used to absorb external impact energy and enhance the cable's vibration resistance and bending resistance.

[0054] 3. Molding of composite sheath 101: Composite sheath 101 adopts multi-layer co-extrusion technology. The inner layer is polyvinyl chloride or thermoplastic polyurethane, which provides basic mechanical protection. The outer layer is neoprene rubber or silicone rubber, which enhances weather resistance and chemical corrosion resistance, ensuring that the materials of each layer are tightly bonded to form a uniform, bubble-free sheath structure.

[0055] 4. Processing of the third braided protective layer 7 and the second braided protective layer 6: The third braided protective layer 7 and the second braided protective layer 6 are sequentially fitted onto the outside of the composite sheath 101, and a foam buffer layer 12 is filled between the third braided protective layer 7 and the composite sheath 101. The third braided protective layer 7 and the second braided protective layer 6 are made of high-strength polyester fiber or nylon fiber, and six sets of evenly distributed first seams 8 and second seams 9 are sewn by machine to form a limiting groove 10. This braided structure not only provides positioning for the subsequent prestressed reinforcing bars 11, but also enhances the cable's internal friction and impact resistance.

[0056] 5. Installation of prestressed tie rod 11: The prestressed tie rod 11 is inserted into the limiting groove 10. The tie rod material is selected from high-strength carbon fiber composite material or titanium alloy, with a diameter of 3-5mm, ensuring its tensile strength exceeds 1.5 times the cable's design tension. Both ends of the prestressed tie rod 11 protrude beyond the special protective layer 2 and are fixed by the tie rod tensioning device 13, reserving interfaces for subsequent tensioning operations. The uniform distribution design of the tie rods ensures balanced stress on the cable after tensioning, improving the overall structural stability.

[0057] 6. Preparation of the inner steel strip armor layer 4 and the outer steel strip armor layer 3: The inner steel strip armor layer 4 is made of high-strength, low-carbon steel strip with a thickness of 1.5mm-2mm. A second step 402 with a depth consistent with the steel strip thickness and a width of one-fifth of the steel strip width is rolled on the surface of the second steel strip 401 using a high-precision rolling mill. It is then wrapped around the outside of the insulating liner 102 in a left-hand spiral winding manner, with adjacent steel strips overlapping through the second step 402 to form an interlocking structure. The outer steel strip armor layer 3 also uses high-strength, low-carbon steel strip. After rolling out the first step 302, it is wrapped around the outside of the inner steel strip armor layer 4 in a right-hand spiral winding manner, with a winding pitch of 1.5-2 times the width of the steel strip. Adjacent steel strips overlap through the first step 302. The reverse winding design of the two steel strips utilizes the torque cancellation effect to significantly enhance the overall rigidity of the armor layer. The steel strip surface is pre-galvanized or aluminized, and after winding, an epoxy resin or polyurethane coating is sprayed onto the armor layer surface to improve chemical corrosion resistance and oxidation resistance.

[0058] 7. Processing of the first braided protective layer 5: The first braided protective layer 5 is made of glass fiber or aramid fiber and is tightly wrapped around the outside of the outer steel tape armor layer 3. This braided layer not only protects the steel tape armor layer from external puncture damage, but also further enhances the cable's tensile and shear resistance, adapting to the complex stresses in deep underground environments.

[0059] Working principle: After the cable is laid and connected, the threaded rod 1302 of the tensioning device 13 is rotated using a special tool. The threaded rod 1302 is rotatably connected to the first collar 1301, and its rotational motion converts the torque into the axial displacement of the second collar 1303 through the threaded pair. When the second collar 1303 moves axially along the buried cable 1, tension is applied to the prestressed tendons 11 through the tension sensor 1304. The tension sensor 1304 monitors the tension value in real time to ensure that the uniformity of the force on the six prestressed tendons 11 is controlled within ±5%. As the tension increases, the prestressed tendons 11 are gradually straightened and produce elastic deformation. At the same time, the first collar 1301 applies axial pressure to the special protective layer 2, causing the steel strip armor layer to mechanically interlock.

[0060] During rolling, the first steel strip 301 of the outer steel strip armor layer 3 and the second steel strip 401 of the inner steel strip armor layer 4 form a first step 302 and a second step 402, respectively. When axial pressure is applied to the special protective layer 2, the first steel strip 301 of the outer steel strip armor layer 3 undergoes slight displacement due to compression, and the first steps 302 of adjacent steel strips interlock, forming a "dog-tooth" interlocking structure; similarly, the second steel strip 401 of the inner steel strip armor layer 4 is interlocked through the second step 402. Since the winding directions of the two steel strips are opposite, this interlocking not only enhances the longitudinal bonding force of the armor layer, but also, through the counteracting torque effect, makes the entire armor layer form a rigid whole in the axial direction. In underground environments, cables often bear external forces such as soil lateral pressure and rock compression. After the steel strip armor layer forms a rigid whole, its compressive strength increases by more than 40%, which can effectively disperse external pressure and prevent the cable from deforming or its internal structure from being damaged due to compression. Deep geological activities may also cause the cable to be subjected to tensile or shear stress. The rigid armor layer, through a mechanical interlocking structure, evenly distributes localized stress throughout the cable, avoiding stress concentration at single points and thus extending the cable's service life. Simultaneously, the rigid overall structure reduces cable creep underground, especially under high-voltage conditions, maintaining the cable's geometric stability and preventing insulation fatigue aging or poor conductor contact caused by long-term deformation.

[0061] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A special deep-earth cable, characterized in that, It includes a buried cable and a special protective layer, wherein the special protective layer is wrapped around the outside of the buried cable, and a foam buffer layer is filled between the special protective layer and the buried cable; The special protective layer includes an outer steel strip armor layer and an inner steel strip armor layer. The outer steel strip armor layer wraps around the inner steel strip armor layer. The outer steel strip armor layer includes a first steel strip, which is wound around the first steel strip. A first step is rolled on the first steel strip. The inner steel strip armor layer includes a second steel strip, which is wound around the first steel strip. A second step is rolled on the second steel strip. The outer steel strip armor layer is wrapped with a first woven protective layer, and the inner steel strip armor layer is sequentially provided with a second woven protective layer and a third woven protective layer. Six sets of first and second seams are sewn on the second and third woven protective layers by a CNC sewing machine to form a uniformly distributed limiting groove. A prestressed tie rod runs through the limiting groove. The tensioning of the prestressed tendon is achieved by a tendon tensioning device, which includes a first ring sleeved on the outside of the buried cable. Six threaded rods are rotatably connected to the first ring in a circumferentially evenly distributed manner. The six threaded rods are fixedly connected to a second ring by threads. The second ring is sleeved on the outside of the buried cable. A tension sensor is installed between the second ring and the prestressed tendon, and the tension sensor is fixedly connected to the prestressed tendon.

2. A special deep-earth cable as described in claim 1, characterized in that, The outermost layer of the buried cable is a composite sheath, the inner side of which is wrapped with an insulating liner, the inner side of which is wrapped with a conductor core, the outer side of which is wrapped with a conductor insulating sleeve, and a filler layer is provided between the conductor insulating sleeve and the insulating liner.

3. A method for preparing a special deep-earth cable, used to prepare the special deep-earth cable as described in claim 2, characterized in that, Includes the following steps: S1. Preparation of conductor core and conductor insulation sleeve: A high-conductivity copper alloy is used as the conductor core, which is drawn to the required diameter by a wire drawing machine. Then, a conductor insulation sleeve is wrapped around the conductor core. The insulation material is cross-linked polyethylene, which is uniformly coated by an extruder to form an insulation layer of uniform thickness. S2. Processing of insulating liner and filling layer: The insulating liner is made of low-density polyethylene and is covered on the outside of the conductor insulation sleeve by extrusion process. The space between the insulating liner and the conductor insulation sleeve is filled with polymer foam material to form a filling layer. S3. Molding of composite sheath: The composite sheath adopts multi-layer co-extrusion technology, with polyvinyl chloride as the inner layer and neoprene as the outer layer, ensuring that the materials of each layer are tightly bonded to form a uniform, bubble-free sheath structure; S4. Processing of the third braided protective layer and the second braided protective layer: The third braided protective layer and the second braided protective layer are sequentially applied to the outside of the composite sheath, and a foam buffer layer is filled between the third braided protective layer and the composite sheath. Then, six sets of evenly distributed first and second seams are sewn by machine to form a limiting groove. S5. Installation of prestressed tie rods: The prestressed tie rods are inserted into the limiting grooves. The two ends of the prestressed tie rods protrude from the special protective layer and are fixed by the tie rod tensioning device, leaving an interface for subsequent tensioning operations. S6. Preparation of inner and outer steel strip armor layers: Inner steel strip armor layer: A second step is rolled on the surface of the second steel strip using a high-precision rolling mill, and then wrapped around the outside of the insulating liner in a spiral winding manner. Adjacent second steel strips overlap through the second step to form an interlocking structure. Outer steel strip armor layer: After the first step is rolled out, the first steel strip is wrapped around the outside of the inner steel strip armor layer in a spiral winding manner, and the adjacent layers are overlapped by the second step and the first step. S7. Processing of the first braided protective layer: The first braided protective layer is made of glass fiber and is tightly wrapped around the outside of the outer steel strip armor layer by braiding.

4. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, Both the first steel strip of the outer steel strip armor layer and the second steel strip of the inner steel strip armor layer are made of high-strength low-carbon steel strips, with the steel strip thickness controlled between 1.5mm and 2mm.

5. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, The depth of the second step is the same as the thickness of the second steel strip, and the width of the second step is one-fifth of the width of the second steel strip.

6. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, The depth of the first step is the same as the thickness of the first steel strip, and the width of the first step is one-fifth of the width of the first steel strip.

7. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, The second steel strip and the first steel strip are wound in opposite spiral directions.

8. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, The winding pitch of the first steel strip is 1.5-2 times the width of the first steel strip, and the winding pitch of the second steel strip is 1.5-2 times the width of the second steel strip.

9. The method for preparing a special deep-earth cable as described in claim 3, characterized in that, The first and second steel strips are pre-galvanized, and after winding, epoxy resin or polyurethane coating is sprayed onto the surfaces of the inner and outer steel strip armor layers.

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