Method for restoring insulation shield of a submarine cable soft joint

Abstract

The application relates to the field of submarine cable soft joint forming, and discloses a submarine cable soft joint insulation shielding recovery method.The method comprises the following steps: extruding a semi-conductive composite material to obtain a tubular embryo, and then performing pre-crosslinking treatment and cooling and shaping; then performing preheating treatment on the tubular embryo, and then performing secondary expansion and secondary cooling and shaping to obtain a prefabricated sleeve; pre-arranging the prefabricated sleeve and an auxiliary cold shrink tool sleeve on the outside of cables to be connected; connecting the conductors of the two cables to be connected, and polishing the outer surface of the recovered main insulation layer; moving the prefabricated sleeve to the surface of the polished main insulation layer, heating the prefabricated sleeve, moving the auxiliary cold shrink tool sleeve to the outside of the heated prefabricated sleeve, and then performing secondary heating, removing the auxiliary cold shrink tool sleeve after cooling, and polishing the overlapped part.The method improves the longitudinal flatness of the interface between the insulation shielding layer and the insulation layer, has high process digitization degree, and effectively shortens the insulation shielding recovery period.

Description

Technical Field

[0001] This invention relates to the field of submarine cable flexible joint forming, and specifically to a method for restoring the insulation shielding of submarine cable flexible joints. Background Technology

[0002] The demand for long-length, high-capacity submarine cables is increasing daily in key projects such as offshore wind power and island power grid interconnection. Submarine cable expansion joints, as a crucial component connecting two cable sections, are a core part of long-distance transmission lines and a technological bottleneck in the development of long-length, high-capacity submarine cable systems, directly impacting the safety and reliability of the entire submarine cable system.

[0003] The manufacturing process of submarine cable expansion joints mainly includes: conductor welding, conductor shielding layer restoration, insulation layer extrusion and vulcanization, insulation shielding layer restoration, and sheath restoration. Among these, the insulation shielding layer is the core functional layer of high-voltage and ultra-high-voltage submarine cables, serving to homogenize the electric field distribution, provide a path for short-circuit current, and limit electromagnetic interference. It requires the insulation shielding layer to be flat and tightly fitted to the insulation surface to avoid electrical breakdown risks during operation (such as partial discharge in AC submarine cables and space charge accumulation in DC submarine cables).

[0004] Currently, there are two main methods for restoring the insulation shielding layer of submarine cable flexible joints: (1) Coating the surface of the insulation layer with semi-conductive paint, and then wrapping it with semi-conductive self-adhesive tape (such as CN102664380A, CN102593764A, etc.). This method is not suitable for wet submarine cable joints, and the coating thickness and uniformity are difficult to control, resulting in poor process stability. (2) Wrapping a semi-conductive shielding tape made of the same material as the cable body around the surface of the insulation layer and performing vulcanization treatment (such as CN114050518A). In this method, the semi-conductive shielding tape retains tension inside, and there is overlap between the wrapping layers. During the temperature rise and vulcanization process, step-like marks are inevitably formed on the smooth and flat insulation surface, causing the insulation shielding layer to form a wavy deformation along the longitudinal direction on the side close to the insulation layer, which in turn causes obvious electric field distortion. At the same time, in the area of ​​the restored insulation stress cone, due to the change in diameter, the wrapping process is prone to air gaps due to uneven stress. Furthermore, the stepped marks on the outer side of the insulating shielding layer require complex manual repair and polishing, significantly prolonging the recovery cycle. They also rely heavily on human experience in process control, making quantitative control of process parameters difficult. In summary, both existing methods suffer from complex processes, poor process stability, and inconsistent product quality.

[0005] Therefore, there is an urgent need to develop an insulation shielding layer restoration method that ensures tight bonding between the insulation shielding layer and the insulation layer, improves the longitudinal flatness of the interface between the insulation layer and the insulation shielding layer, realizes digital control of process parameters, and shortens the insulation shielding restoration cycle. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor interface flatness, long recovery cycle, and poor process stability in the restoration process of the insulation shielding layer of submarine cable flexible joints in the existing technology. This invention provides a method for restoring the insulation shielding of submarine cable flexible joints. This method significantly improves the longitudinal flatness of the interface between the insulation shielding layer and the insulation layer, has a high degree of process digitization, reduces reliance on manual experience, and effectively shortens the insulation shielding restoration cycle, thereby significantly improving the product qualification rate and process stability of submarine cable flexible joints.

[0007] To achieve the above objectives, the present invention provides a method for restoring the insulation shielding of a submarine cable flexible joint, comprising the following steps: S1. The semi-conductive composite material is extruded to obtain a tubular preform; the tubular preform is pre-crosslinked and then cooled and shaped; wherein the degree of pre-crosslinking of the tubular preform is 20%-80% of that in the fully crosslinked state, and the inner diameter of the tubular preform is 0.65-1.05 times the outer diameter of the insulation shielding layer of the cable body to be connected. S2. The tubular preform obtained in step S1 after cooling and shaping is preheated, and after secondary expansion processing, it is cooled and shaped again to obtain a heat-shrinkable insulating shielding preform. S3. The prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are pre-fitted onto the outside of the insulation shielding layer of the cable body to be connected. S4. Connect the conductors of the two sections of cable to be connected, restore the main insulation layer at the conductor connection point, and grind the outer surface of the restored main insulation layer smooth. S5. Move the prefabricated sleeve described in step S3 to the surface of the main insulation layer after grinding and smoothing, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected; heat the prefabricated sleeve to shrink it and wrap it to fit the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve described in step S3 is moved and wrapped around the outside of the prefabricated sleeve after heating in step S5. It is then heated a second time to make the prefabricated sleeve cross-link and solidify and cross-link and bond with the main insulation layer. After cooling, the auxiliary cold shrink tooling sleeve is removed, and the overlap of the prefabricated sleeve and the insulation shielding layer of the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0008] Preferably, the thickness of the tubular preform is 1-1.6 times the thickness of the insulation shielding layer of the cable body to be connected.

[0009] Preferably, the pre-crosslinking treatment is carried out by thermal crosslinking, and the conditions include: temperature of 140-170℃ and time of 1-30min.

[0010] Preferably, the expansion ratio of the secondary expansion is 1.5-2.2.

[0011] Preferably, the heating conditions in step S6 include: heating at 150-200°C under an inert gas atmosphere, and holding the heating temperature for 0.5-1.5 hours after it stabilizes; the pressure of the inert gas is 0.5-2 MPa.

[0012] Through the above technical solution, the present invention has the following beneficial effects: (1) The method for restoring the insulation shield of submarine cable flexible joints provided by this invention solves the long-standing problem of poor interface flatness during the restoration process by using an integrally extruded pre-molded insulating shielding sleeve that undergoes specific pre-crosslinking treatment and secondary expansion. The integrally molded sleeve avoids the step-like marks caused by overlapping and tension during the wrapping process, ensuring a very high longitudinal flatness between the insulating shielding layer and the insulating layer interface, and significantly reducing the risk of electric field distortion. The use of semi-crosslinking technology effectively improves the ductility of the semi-conductive shielding material, enabling the sleeve to fully expand to ensure reasonable dimensions. The shape memory effect and post-crosslinking process ensure full adhesion between the restoration layer and the body layer, avoiding interface separation. This method has a high degree of digitalization, reduces reliance on manual experience, shortens the insulation shielding restoration cycle, and helps promote the intelligent manufacturing of flexible joints.

[0013] In preferred cases, multi-layer composite prefabricated sleeves are used. By adding a space charge suppression layer and ensuring its uniform coverage, the injection of space charge into the DC cable is effectively suppressed, which is more conducive to promoting the intelligent manufacturing of flexible joints.

[0014] (2) The method for restoring the insulation shield of submarine cable flexible joints provided by the present invention, through the process design of "first fitting and then processing", prefabricated insulation shield sleeves and auxiliary cold shrink tooling sleeves are pre-fitted on the outside of the cable to be connected and temporarily stored. After the main insulation layer at the conductor connection is restored, they are pulled back and installed in sequence, avoiding the complicated multi-layer wrapping and manual trimming and polishing process, which greatly shortens the insulation shield restoration cycle. The whole process is highly digitalized, which significantly reduces the dependence on manual experience and greatly improves the process stability and pass rate of the product. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the heating mold in this invention; Figure 2 This is a schematic diagram of the assembly relationship between the prefabricated sleeve and the auxiliary cold shrink tooling sleeve in this invention; Figure 3 This is a schematic diagram of the complete assembly structure after the heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve in this invention.

[0016] Explanation of reference numerals in the attached figures 1. Mold body; 2. Nitrogen inlet; 3. Pressure gauge; 4. Nitrogen outlet; 5. Heating plug; 6. Thermocouple plug; 7. Bolt; 8. Cooling water interface; 9. Mold cooling zone; 10. Pre-fabricated sleeve after heating; 11. Auxiliary cold shrink tooling sleeve; 12. Cable body. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] This invention provides a method for restoring the insulation shielding of a submarine cable flexible joint, comprising the following steps: S1. The semi-conductive composite material is extruded to obtain a tubular preform; the tubular preform is pre-crosslinked and then cooled and shaped; wherein the degree of pre-crosslinking of the tubular preform is 20%-80% of that in the fully crosslinked state, and the inner diameter of the tubular preform is 0.65-1.05 times the outer diameter of the insulation shielding layer of the cable body to be connected. S2. The tubular preform obtained in step S1 after cooling and shaping is preheated, and after secondary expansion processing, it is cooled and shaped again to obtain a heat-shrinkable insulating shielding preform. S3. The prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are pre-fitted onto the outside of the insulation shielding layer of the cable body to be connected. S4. Connect the conductors of the two sections of cable to be connected, restore the main insulation layer at the conductor connection point, and grind the outer surface of the restored main insulation layer smooth. S5. Move the prefabricated sleeve described in step S3 to the surface of the main insulation layer after grinding and smoothing, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected; heat the prefabricated sleeve to shrink it and wrap it to fit the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve described in step S3 is moved and wrapped around the outside of the prefabricated sleeve after heating in step S5. It is then heated a second time to make the prefabricated sleeve cross-link and solidify and cross-link and bond with the main insulation layer. After cooling, the auxiliary cold shrink tooling sleeve is removed, and the overlap of the prefabricated sleeve and the insulation shielding layer of the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0019] In this invention, the method for restoring the insulation shield of a submarine cable flexible joint solves the long-standing problem of poor interface flatness during the insulation shield restoration process by using an integrated extrusion molding process followed by specific pre-crosslinking treatment and secondary expansion to obtain an insulation shield prefabricated sleeve. The integrated molding sleeve avoids step-like marks caused by overlapping and tension during the wrapping process, maintaining extremely high longitudinal flatness at the interface between the insulation shield and the insulation layer, significantly reducing the risk of electric field distortion. The use of semi-crosslinking technology effectively improves the ductility of the semi-conductive shielding material, allowing for full expansion of the sleeve to ensure dimensional rationality. The shape memory effect and post-crosslinking process ensure full adhesion between the restoration layer and the body layer, preventing interface separation. This invention employs a "pre-installation, post-processing" process design, pre-installing the insulation shield prefabricated sleeve and auxiliary cold-shrink tooling sleeve on the outside of the cable to be connected and temporarily storing them. After the main insulation layer at the conductor connection is restored, they are sequentially pulled back for installation, significantly shortening the insulation shield restoration cycle. The entire process is highly digitized, significantly reducing reliance on manual experience and greatly improving the product's process stability and yield rate.

[0020] According to a preferred embodiment of the present invention, the inner diameter of the tubular preform is 0.65-1.05 times the outer diameter of the insulation shielding layer of the cable body to be connected. For example, it can be 0.65 times, 0.7 times, 0.75 times, 0.8 times, 0.85 times, 0.9 times, 0.95 times, 1 time, 1.05 times, or any value within the range of any two of the above values, preferably 0.8-0.95 times. Using the above embodiment ensures that the prefabricated sleeve can be smoothly fitted into the cable to be connected and provides a suitable interference fit for subsequent heat shrinkage, allowing it to generate uniform radial shrinkage pressure during heating, tightly adhering to the insulation layer, which is beneficial for achieving high interface flatness and no marks. The above preferred range has even better effects.

[0021] According to a preferred embodiment of the present invention, the thickness of the tubular blank is 1-1.6 times the thickness of the insulation shielding layer of the cable body to be connected. For example, it can be 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6 times, or any value within the range of any two of the above values, preferably 1.05-1.25 times. Using the above embodiment is more conducive to maintaining the consistency of the thickness of the restored insulation shielding layer and the main body insulation shielding layer, thus improving the restoration effect.

[0022] According to the present invention, the diameter of the tubular embryo is measured using a vernier caliper, and the thickness is measured using a thickness gauge.

[0023] According to the present invention, the material of the insulation shielding layer of the cable body to be connected has a wide range of selection. Preferably, the semi-conductive composite material is the same as the material of the insulation shielding layer of the cable body to be connected. Using the above embodiment helps to eliminate the risk of electric field distortion at the interface caused by differences in material properties from the root cause.

[0024] According to the present invention, the extrusion method and conditions are not particularly limited, and extrusion methods and conditions conventionally used in the art can be adopted, as long as the tubular preform can be obtained. Preferably, the extrusion temperature is 110-125°C, for example, it can be 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 125°C, or any value within the range of any two of the above values. In the present invention, the extrusion is preferably performed using a single-screw extruder.

[0025] According to a preferred embodiment of the present invention, the pre-crosslinking degree of the tubular preform is 20%-80% of that of the fully crosslinked tubular preform, for example, it can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value within the range of any two of the above values, preferably 40%-60%. Using the above preferred embodiment is more advantageous in allowing the tubular preform to fully expand to the required size after preheating, while retaining the shape memory effect, ensuring that it can completely shrink and adhere to the surface of the insulating layer during secondary heating.

[0026] According to the present invention, the pre-crosslinking degree of the tubular embryo is tested by the gel content test method: xylene is selected as solvent, a certain amount of sample is weighed and placed in a copper mesh bag, and then placed in a three-necked flask and heat-treated at 120°C for 3 hours; after the heat treatment, the solvent is removed, and the sample is vacuum dried in a vacuum oven at 120°C for 6 hours; after the treatment, it is cooled to room temperature and weighed, and the ratio of the residual mass to the initial mass is taken as the degree of crosslinking.

[0027] According to the present invention, the method of pre-crosslinking treatment has a wide range of options and can employ various pre-crosslinking methods conventionally used in the art, with thermal crosslinking being preferred.

[0028] According to a preferred embodiment of the present invention, the conditions for the pre-crosslinking treatment include: a temperature of 140-170°C and a time of 1-30 min. Preferably, the conditions for the pre-crosslinking treatment include: a temperature of 145-155°C and a time of 15-30 min.

[0029] According to the present invention, preferably, the cooling and shaping temperature in step S1 is 10-20°C. Using the above embodiment helps to ensure stable geometric dimensions of the prefabricated sleeve. The cooling and shaping method of the present invention is not particularly limited; for example, a cooling system conventionally used in the art can be employed.

[0030] According to a preferred embodiment of the present invention, the preheating conditions include: a preheating temperature of 60-90°C and a preheating time of 1-30 minutes. Preferably, the preheating conditions include: a preheating temperature of 70-80°C and a preheating time of 10-20 minutes. Using the above-mentioned preferred preheating conditions is more conducive to subsequent secondary expansion.

[0031] According to a preferred embodiment of the present invention, the expansion ratio of the secondary expansion is 1.5-2.2, for example, it can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, or any value within the range of any two of the above values, preferably 1.8-2.1. This embodiment ensures that the prefabricated sleeve can be smoothly fitted into the cable while retaining sufficient shrinkage allowance. This facilitates the shape memory effect, allowing the secondary expanded sleeve to shrink and tightly adhere to the insulation layer during subsequent heating, and also prevents sleeve breakage during the secondary expansion process. The preferred embodiment described above offers superior performance.

[0032] According to the present invention, preferably, the temperature for the secondary cooling and shaping is 10-20°C. Using the above embodiment helps to maintain the stability of the dimensions of the prefabricated sleeve after secondary expansion. The method for secondary cooling and shaping described in this invention is not particularly limited; for example, a cooling system conventionally used in the art can be employed.

[0033] According to a preferred embodiment of the present invention, step S1 includes: melt-blending an insulating material with a space charge inhibitor to obtain a blend; and then extruding the blend with a semi-conductive composite material to obtain a tubular preform comprising a blend layer and a semi-conductive composite material layer.

[0034] According to a preferred embodiment of the present invention, based on the total weight of the insulating material and the space charge inhibitor, the content of the space charge inhibitor is 0.5-8 wt%, for example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, or any value within the range of any two of the above values, preferably 1-5 wt%.

[0035] According to the present invention, the type of insulating material has a wide range of selection. Preferably, the insulating material is the same as the insulating layer material of the cable to be connected.

[0036] According to the present invention, preferably, the space charge suppressor is selected from inorganic nanofillers. Preferably, the inorganic nanofiller is selected from at least one of nano-SiO2, SiC, and MgO. The present invention provides a wide range of choices for the particle size of the inorganic nanofiller; preferably, the average particle size of the inorganic nanofiller is less than 200 nm.

[0037] According to the present invention, the method and conditions for melt blending are not particularly limited, and methods and conditions conventionally used in the art can be adopted, as long as melt blending can be achieved. Preferably, the melt blending is performed using a twin-screw extruder.

[0038] According to the present invention, the method and conditions for extruding the blend and the semi-conductive composite material are not particularly limited, and extrusion methods and conditions conventionally used in the art can be adopted, as long as the tubular preform can be obtained. Preferably, the extrusion temperature is 110-125°C. In the present invention, the extrusion of the blend and the semi-conductive composite material is preferably carried out using a single-screw extruder.

[0039] According to the present invention, the extrusion is preferably multilayer co-extrusion. The present invention does not particularly limit the number of layers in the multilayer co-extrusion; those skilled in the art can choose according to their needs, as long as the outermost layer is a semi-conductive composite material layer. The inner layers may include multiple blended layers or a single blended layer. Preferably, the multilayer co-extrusion is a two-layer co-extrusion, with the inner layer being a blended layer and the outer layer being a semi-conductive composite material layer.

[0040] In this invention, the inner layer comprises multiple blended layers. The content of space charge inhibitor in each blended layer can be the same or can vary in a gradient. Those skilled in the art can choose according to their needs, and this invention does not limit it.

[0041] According to a preferred embodiment of the present invention, the thickness ratio of the blend layer to the semi-conductive composite material layer in the tubular preform is 0.01-0.3, for example, it can be 0.01, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, or any value within the range of any two of the above values, preferably 0.08-0.2. Using the above preferred embodiment, while ensuring electrical performance, it is more conducive to the uniform molding of the blend layer.

[0042] In this invention, a multi-layer composite prefabricated sleeve including a blended material layer and a semi-conductive composite material layer is used. By adding a space charge suppression layer and ensuring its uniform coverage, the injection of space charge in the DC cable is effectively suppressed, which can solve the problem of space charge accumulation in ultra-high voltage DC submarine cables and is more conducive to promoting the intelligent manufacturing of flexible joints.

[0043] According to the present invention, in step S3, the prefabricated sleeve and the auxiliary cold shrink tooling sleeve can be sleeved on the outside of the insulation shielding layer of the same section of cable body to be connected, or they can be sleeved on the outside of the insulation shielding layers of two sections of cable body to be connected respectively. Preferably, the prefabricated sleeve and the auxiliary cold shrink tooling sleeve are sleeved on the outside of the insulation shielding layer of the same section of cable body to be connected.

[0044] According to the present invention, in step S3, the prefabricated sleeve can be first placed on the outside of the insulation shielding layer of the section of cable to be connected, and then the auxiliary cold-shrink tooling sleeve can be inserted; alternatively, the auxiliary cold-shrink tooling sleeve can be first placed on the outside of the insulation shielding layer of the section of cable to be connected, and then the prefabricated sleeve can be inserted. Preferably, the auxiliary cold-shrink tooling sleeve is first placed on the outside of the insulation shielding layer of the section of cable to be connected, and then the prefabricated sleeve is inserted.

[0045] According to the present invention, in step S4, the method for connecting the conductors of the two sections of the cable to be connected has a wide range of options and can be any of the conductor connection methods commonly used in the art, such as conductor welding.

[0046] According to the present invention, in step S4, the method for restoring the main insulation layer at the conductor connection has a wide range of options. It can be a method for restoring the insulation layer of various cables conventionally used in the art. For example, the main insulation layer at the conductor connection can be restored by the "melt extrusion-high temperature vulcanization" method.

[0047] According to the present invention, in step S4, the degree of polishing and smoothing is subject to a wide range of selection, as long as the restored surface of the insulation layer after polishing and smoothing is smooth and free of obvious protrusions and scratches. Preferably, the surface roughness Ra of the restored main insulation layer surface after polishing and smoothing is ≤0.4μm. The present invention does not particularly limit the method of polishing and smoothing; various polishing methods conventionally used in the art are applicable to the present invention, such as manual polishing using sandpaper or sanding belt and mechanically assisted polishing.

[0048] According to the present invention, preferably, the overlap distance in step S5 is 1-6 cm, for example, it can be 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, or any value within the range of any two of the above values. By adopting the above implementation method, it is ensured that the restored main insulation shielding layer and the body insulation shielding layer of the two cable sections form an electrical path, while the step area is controlled within a reasonable range, facilitating subsequent grinding and finishing.

[0049] In this invention, the overlap distance between the prefabricated sleeve and the insulation shielding layer of the two cable sections to be connected can be the same or different, as long as the overlap distance meets the above-mentioned range.

[0050] According to a preferred embodiment of the present invention, the heating conditions in step S5 include: a heating temperature of 100-180°C and a heating time of 0.5-15 min. Preferably, the heating conditions in step S5 include: a heating temperature of 120-150°C and a heating time of 5-10 min. Using the above preferred embodiment is more conducive to triggering the shape memory effect, allowing the prefabricated sleeve to quickly shrink and adhere to the surface of the insulation layer, laying the foundation for tight bonding during subsequent secondary heating.

[0051] According to the present invention, preferably, the heating in step S5 is performed using a hot air gun. More preferably, heating the prefabricated sleeve from the middle to both ends is more conducive to causing the prefabricated sleeve to shrink and adhere to the surface of the insulation layer.

[0052] According to the present invention, in step S6, the auxiliary cold shrink tooling sleeve can press the shielding layer prefabricated sleeve tightly onto the restoring insulation surface, which helps the bonding between the two.

[0053] According to the present invention, in step S6, the degree of polishing and finishing is subject to a wide range of selection, as long as the polished and finished overlapping area is smooth and free of obvious protrusions and scratches. Preferably, the surface roughness Ra of the polished and finished overlapping area is ≤5μm. The present invention does not particularly limit the polishing and finishing method; various polishing methods conventionally used in the art are applicable to the present invention, such as manual polishing using sandpaper or sanding belt and mechanically assisted polishing.

[0054] According to a preferred embodiment of the present invention, the conditions for secondary heating in step S6 include: heating at 150-200°C under an inert gas atmosphere, and maintaining the temperature for 0.5-1.5 hours after stabilization; the pressure of the inert gas is 0.5-2 MPa. Preferably, the conditions for secondary heating in step S6 include: heating at 160-190°C under an inert gas atmosphere, and maintaining the temperature for 0.8-1.2 hours after stabilization; the pressure of the inert gas is 0.8-1 MPa. The inert gas used in the present invention is preferably nitrogen. Using the above preferred embodiments is more conducive to transforming the prefabricated sleeve from physical bonding to chemical bonding, promoting full cross-linking and bonding between the prefabricated sleeve and the insulating layer, and ensuring tight interface adhesion.

[0055] According to the present invention, preferably, the secondary heating in step S6 is performed using a heating mold. More preferably, step S6 includes: shifting the auxiliary cold-shrink tooling sleeve described in step S3 to cover the outside of the prefabricated sleeve after heating in step S5, and installing a heating mold on the outside of the auxiliary cold-shrink tooling sleeve for secondary heating, so that the prefabricated sleeve cross-links and solidifies, and undergoes a cross-linking reaction to bond with the main insulation layer; after cooling, removing the heating mold and the auxiliary cold-shrink tooling sleeve, and grinding and finishing the overlapping area.

[0056] According to a preferred embodiment of the present invention, the structural schematic diagram of the heating mold used in the present invention is as follows: Figure 1 As shown in the figure, the assembly relationship diagram of the prefabricated sleeve and the auxiliary cold shrink tooling sleeve in this invention is as follows. Figure 2 As shown in the figure, the complete assembly structure of the auxiliary cold shrink tooling sleeve after the heating mold is installed on the outside is illustrated in the following diagram. Figure 3 As shown, the heating mold includes a mold body 1, which is provided with a nitrogen inlet 2, a pressure gauge 3, a nitrogen outlet 4, a heating plug 5, a thermocouple plug 6, a bolt 7, and a cooling water interface 8. The mold body 1 is provided with a mold cooling zone 9 inside.

[0057] The heating mold is used according to the following steps: the pre-fabricated sleeve 10 after heating is installed on the outside of the insulation shielding layer of the cable body 12, the auxiliary cold shrink tooling sleeve 11 is installed on the outside of the pre-fabricated sleeve 10 after heating, and then the heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve 11. The mold body 1 is locked and fixed by bolts 7; the power is turned on by heating plug 5 to heat the mold. During the heating process, nitrogen is introduced into the mold through nitrogen inlet 2 and discharged from nitrogen outlet 4 to promote the tight adhesion between the pre-fabricated sleeve 10 after heating and the main insulation layer. The temperature inside the mold is monitored in real time by thermocouple plug 6; after heating and heat preservation, cooling water is introduced into the cooling area 9 of the mold through cooling water interface 8. After cooling, the heating mold and auxiliary cold shrink tooling sleeve 11 are removed. The pre-fabricated sleeve 10 after heating and the overlapping parts of the two sections of the insulation shielding layer to be connected are polished and repaired to complete the restoration of the insulation shielding layer of the cable joint.

[0058] The present invention will be described in detail below through embodiments.

[0059] Example 1 S1. The semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, is melted and plasticized by an extruder and then extruded through an extrusion die to obtain a tubular preform. The obtained tubular preform is subjected to pre-crosslinking treatment, and the degree of pre-crosslinking is controlled to be 50% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.8 times the outer diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.25 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 150℃, and the pre-crosslinking time is 25min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0060] Example 2 S1. The semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, is melted and plasticized by an extruder and then extruded through an extrusion die to obtain a tubular preform. The obtained tubular preform is subjected to pre-crosslinking treatment, and the degree of pre-crosslinking is controlled to be 40% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.9 times the diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.1 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 145℃, and the pre-crosslinking time is 25min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0061] Example 3 S1. The semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, is melted and plasticized by an extruder and then extruded through an extrusion die to obtain a tubular preform. The obtained tubular preform is subjected to pre-crosslinking treatment, and the degree of pre-crosslinking is controlled to be 60% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.95 times the diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.05 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 150℃, and the pre-crosslinking time is 30min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0062] Example 4 The method is the same as in Example 1, except that... In step S1, the pre-crosslinking degree is controlled to be 20% of that in the fully crosslinked state; the pre-crosslinking temperature is 145℃ and the pre-crosslinking time is 12min.

[0063] Example 5 The method is the same as in Example 1, except that... In step S1, the inner diameter of the tubular preform is 1 times the outer diameter of the insulation shielding layer of the cable body to be connected; the thickness of the tubular preform is 1 times the thickness of the insulation shielding layer of the cable body to be connected.

[0064] Example 6 The method is the same as in Example 1, except that... In step S2, the expansion ratio of the secondary expansion is 2.2.

[0065] Example 7 S1. Polyethylene insulation material, identical to the insulation layer material of the cable to be connected, and nano-SiO2 (spherical, average particle size 10nm) are melt-blended using a twin-screw extruder to obtain a blend; wherein, based on the total amount of the polyethylene insulation material and nano-SiO2, the nano-SiO2 content is 5wt%; The obtained blend and the semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, are melt-plasticized in an extruder and then extruded through a double-layer co-extrusion die to obtain a tubular preform (composite sleeve) with an inner layer of blend and an outer layer of semi-conductive composite material, with a thickness ratio of 0.2. The obtained tubular preform is pre-crosslinked, and the degree of pre-crosslinking is controlled to be 50% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.8 times the diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.25 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 150℃, and the pre-crosslinking time is 25min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0066] Example 8 S1. Polyethylene insulation material, identical to the insulation layer material of the cable to be connected, and nano-SiO2 (spherical, average particle size 10nm) are melt-blended using a twin-screw extruder to obtain a blend; wherein, based on the total amount of the polyethylene insulation material and nano-SiO2, the nano-SiO2 content is 3wt%; The obtained blend and the semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, are melt-plasticized in an extruder and then extruded through a double-layer co-extrusion die to obtain a tubular preform (composite sleeve) with an inner layer of blend and an outer layer of semi-conductive composite material, with a thickness ratio of 0.2. The obtained tubular preform is pre-crosslinked, and the degree of pre-crosslinking is controlled to be 50% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.8 times the diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.25 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 150℃, and the pre-crosslinking time is 25min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0067] Example 9 S1. Polyethylene insulation material, identical to the insulation layer material of the cable to be connected, and nano-SiO2 (spherical, average particle size 10nm) are melt-blended using a twin-screw extruder to obtain a blend; wherein, based on the total amount of the polyethylene insulation material and nano-SiO2, the nano-SiO2 content is 1wt%; The obtained blend and the semi-conductive composite material, which is the same as the insulation shielding layer material of the cable body to be connected, are melt-plasticized in an extruder and then extruded through a double-layer co-extrusion die to obtain a tubular preform (composite sleeve) with an inner layer of blend and an outer layer of semi-conductive composite material, with a thickness ratio of 0.2. The obtained tubular preform is pre-crosslinked, and the degree of pre-crosslinking is controlled to be 50% of that in the fully crosslinked state. Then it is cooled and shaped by a cooling system at a temperature of 15°C. The extrusion temperature is 120℃; the inner diameter of the tubular preform is 0.8 times the diameter of the insulation shielding layer of the cable body to be connected, and the thickness of the tubular preform is 1.25 times the thickness of the insulation shielding layer of the cable body to be connected; the pre-crosslinking temperature is 150℃, and the pre-crosslinking time is 25min. S2. The cooled and shaped tubular preform is pulled into the secondary heating chamber, preheated at 80°C, and then expanded twice. The expansion ratio of the secondary expansion is 2. Then it is cooled and shaped twice at a cooling temperature of 15°C to obtain a heat-shrinkable insulating shielding preform. S3. Before making the submarine cable flexible joint, the prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are first put on the outside of the insulation shielding layer of a section of the cable body to be connected. S4. After completing the conductor connection of the two sections of cable to be connected and restoring the main insulation layer at the conductor connection, grind the outer surface of the restored main insulation layer to make it smooth. S5. Move the prefabricated sleeve from step S3 to the outer surface of the main insulation layer after it has been polished and smoothed, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected, with an overlap distance of 2cm; use a hot air gun to heat the prefabricated sleeve from the middle to both ends, with a heating temperature of 150℃ and a heating time of 5min, so that the prefabricated sleeve shrinks and wraps and adheres to the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve from step S3 is moved and wrapped around the outside of the prefabricated sleeve heated in step S5. Then, a heating mold is installed on the outside of the auxiliary cold shrink tooling sleeve for heating at 180°C. The heating temperature is maintained for 1 hour after it stabilizes. During the heating process, nitrogen gas is introduced into the heating mold at a pressure of 1 MPa to crosslink and solidify the prefabricated sleeve and allow it to crosslink and bond with the main insulation layer. After the heating and heat preservation are completed, cooling water is introduced into the cooling area of ​​the heating mold for cooling. After cooling is completed, the heating mold and auxiliary cold shrink tooling sleeve are removed, and the overlap of the insulation shielding layer of the prefabricated sleeve and the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

[0068] Example 10 The method is the same as in Example 7, except that... In step S1, the pre-crosslinking degree is controlled to be 20% of that in the fully crosslinked state; the pre-crosslinking temperature is 145℃ and the pre-crosslinking time is 12min.

[0069] Example 11 The method is the same as in Example 7, except that... In step S1, the inner diameter of the tubular preform is 1 times the outer diameter of the insulation shielding layer of the cable body to be connected; the thickness of the tubular preform is 1 times the thickness of the insulation shielding layer of the cable body to be connected.

[0070] Example 12 The method is the same as in Example 7, except that... In step S2, the expansion ratio of the secondary expansion is 2.2.

[0071] Example 13 The method is the same as in Example 7, except that... In step S1, the amount of SiO2 added is 0.

[0072] Comparative Example 1 The method is the same as in Example 1, except that... In step S1, the pre-crosslinking degree is controlled to be 10% of that in the fully crosslinked state; the pre-crosslinking temperature is 140℃ and the pre-crosslinking time is 15min.

[0073] Comparative Example 2 The method is the same as in Example 1, except that... In step S1, the inner diameter of the tubular preform is 1.1 times the outer diameter of the insulation shielding layer of the cable body to be connected.

[0074] Comparative Example 3 The method is the same as in Example 7, except that... In step S1, the pre-crosslinking degree is controlled to be 10% of that in the fully crosslinked state; the pre-crosslinking temperature is 140℃ and the pre-crosslinking time is 15min.

[0075] Comparative Example 4 S1. The same semi-conductive composite material as the insulation shielding layer material of the cable body to be connected is melted and plasticized in an extruder, then extruded through an extrusion die, and the shielding tape obtained after slitting has a thickness of 100μm; wherein, the extrusion temperature is 120℃. S2. Wrap the obtained shielding tape around the outer surface of the restored insulation layer after fine repair and polishing. The wrapping thickness is the same as the insulation thickness of the cable body to be connected, and the distance between the wrapping tape and the shielding layer of the two sections of the cable body to be connected is 2cm. S3. Install the heating mold and heat it to a temperature of 180℃. After the heating temperature stabilizes, maintain the temperature for 1 hour. During the heating process, introduce nitrogen gas into the heating mold at a pressure of 1MPa to cause the prefabricated sleeve and the insulation layer to undergo a cross-linking reaction and bond. After the heating and heat preservation are completed, cool the heating mold by introducing cooling water into the cooling area. After cooling is completed, polish the insulation shielding layer.

[0076] Table 1. Parameters of each embodiment and comparative example

[0077] Test Example 1 The submarine cables with restored insulation and shielding prepared in Examples 1-6 and Comparative Examples 1, 2 and 4 were tested. The test items included: observing the deformation at the interface between the restored insulation layer and the insulation shielding layer within a 5cm length range using an optical microscope, modeling based on the observation results, and using COMSOL electric field simulation to calculate the maximum rate of change of electric field intensity at the interface between the restored insulation layer and the insulation shielding layer. Electrical routine tests were conducted in accordance with the national standard GB / T 41629.1-2022. Ten parallel samples were prepared for each of the above embodiments and comparative examples for testing. The percentage of samples that passed out of the total number of samples (i.e., the pass rate) was taken as the electrical routine test result of that embodiment / comparative example. The calculation formula is: Pass rate = Number of samples that passed / Total number of samples × 100%; The time required from the completion of the grinding and smoothing process on the outer surface of the main insulation layer to the completion of insulation shielding restoration was recorded for each embodiment and comparative example. This time was recorded as the molding cycle, and the reduction in molding cycle compared to Comparative Example 4 was calculated. The test results are shown in Table 2.

[0078] Table 2 AC Cables

[0079] As can be seen from the AC cable test results in Table 2, the maximum electric field strength change rate of the submarine cable flexible joint insulation shielding restoration method provided by the present invention is no higher than +14%, which improves the interface flatness and significantly reduces electric field distortion. In the embodiment, the pass rate of routine electrical tests is no less than 90%, which significantly improves the performance of products prepared by traditional wrapping technology. At the same time, the molding cycle is short, which improves the insulation shielding restoration efficiency.

[0080] Test Example 2 The submarine cables with restored insulation shielding prepared in Examples 7-13, Comparative Examples 3 and 4 were tested. The test items included: space charge testing using PEA (electroacoustic pulse method), and analysis of the space charge change rate at the restored insulation-insulation shielding layer with the cable body as the reference. Electrical routine tests were conducted in accordance with the national standard GB / T 31489.1-2015. Ten parallel samples were prepared for each of the above embodiments and comparative examples for testing. The percentage of samples that passed out of the total number of samples (i.e., the pass rate) was taken as the electrical routine test result of that embodiment / comparative example. The calculation formula is: Pass rate = Number of samples that passed / Total number of samples × 100%; The time required from the completion of the grinding and smoothing process on the outer surface of the main insulation layer to the completion of insulation shielding restoration was recorded for each embodiment and comparative example. This time was recorded as the molding cycle, and the reduction in molding cycle compared to Comparative Example 4 was calculated. The test results are shown in Table 3.

[0081] Table 3 DC Cables

[0082] As can be seen from the test results of the DC cable in Table 3, the insulation shielding restoration method for submarine cable flexible joints provided by this invention, which uses multi-layer composite prefabricated sleeves and adds a space charge suppression layer, effectively suppresses the injection of space charge in the DC cable; the pass rate of routine electrical tests in the embodiments is not less than 70%, which significantly improves the performance of products prepared by traditional wrapping technology; at the same time, the molding cycle is short, which improves the insulation shielding restoration efficiency.

[0083] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for restoring the insulation shielding of a submarine cable flexible joint, characterized in that, Includes the following steps: S1. The semi-conductive composite material is extruded to obtain a tubular preform; the tubular preform is pre-crosslinked and then cooled and shaped; wherein the degree of pre-crosslinking of the tubular preform is 20%-80% of that in the fully crosslinked state, and the inner diameter of the tubular preform is 0.65-1.05 times the outer diameter of the insulation shielding layer of the cable body to be connected. S2. The tubular preform obtained in step S1 after cooling and shaping is preheated, and after secondary expansion processing, it is cooled and shaped again to obtain a heat-shrinkable insulating shielding preform. S3. The prefabricated sleeve and auxiliary cold shrink tooling sleeve obtained in step S2 are pre-fitted onto the outside of the insulation shielding layer of the cable body to be connected. S4. Connect the conductors of the two sections of cable to be connected, restore the main insulation layer at the conductor connection point, and grind the outer surface of the restored main insulation layer smooth. S5. Move the prefabricated sleeve described in step S3 to the surface of the main insulation layer after grinding and smoothing, so that both ends of the prefabricated sleeve overlap with the insulation shielding layer of the two sections of the cable body to be connected; heat the prefabricated sleeve to shrink it and wrap it to fit the surface of the main insulation layer. S6. The auxiliary cold shrink tooling sleeve described in step S3 is moved and wrapped around the outside of the prefabricated sleeve after heating in step S5. It is then heated a second time to make the prefabricated sleeve cross-link and solidify and cross-link and bond with the main insulation layer. After cooling, the auxiliary cold shrink tooling sleeve is removed, and the overlap of the prefabricated sleeve and the insulation shielding layer of the two sections of the cable body to be connected is polished and repaired to complete the insulation shielding restoration of the cable joint.

2. The method according to claim 1, characterized in that, The inner diameter of the tubular preform is 0.8-0.95 times the outer diameter of the insulation shielding layer of the cable body to be connected; The thickness of the tubular blank is 1-1.6 times the thickness of the insulation shielding layer of the cable body to be connected; The pre-crosslinking degree of the tubular embryo is 40%-60% of that of the fully crosslinked tubular embryo.

3. The method according to claim 2, characterized in that, The thickness of the tubular preform is 1.05-1.25 times the thickness of the insulation shielding layer of the cable body to be connected.

4. The method according to claim 1, characterized in that, The semi-conductive composite material is the same as the insulating shielding layer material of the cable body to be connected. The extrusion temperature in step S1 is 110-125℃.

5. The method according to claim 1, characterized in that, The pre-crosslinking treatment is performed by thermal crosslinking, and the conditions include: temperature of 140-170℃; time of 1-30 min. The cooling and shaping temperature in step S1 is 10-20℃.

6. The method according to claim 1, characterized in that, The preheating conditions include: a preheating temperature of 60-90℃ and a preheating time of 1-30 min; The expansion ratio of the secondary expansion is 1.5-2.2; The temperature for secondary cooling and shaping is 10-20℃.

7. The method according to claim 1, characterized in that, Step S1 includes: melt-blending an insulating material with a space charge inhibitor to obtain a blend; then extruding the blend with a semi-conductive composite material to obtain a tubular preform comprising a blend layer and a semi-conductive composite material layer.

8. The method according to claim 7, characterized in that, Based on the total weight of the insulating material and the space charge inhibitor, the content of the space charge inhibitor is 0.5-8 wt%; The space charge inhibitor is selected from inorganic nanofillers, which are selected from at least one of nano-SiO2, SiC and MgO; In the tubular preform, the thickness ratio of the blended layer to the semi-conductive composite material layer is 0.01-0.

3.

9. The method according to claim 1, characterized in that, The distance between the overlapping covers in step S5 is 1-6cm.

10. The method according to claim 1, characterized in that, The heating conditions described in step S5 include: a heating temperature of 100-180℃ and a heating time of 0.5-15 min.

11. The method according to claim 1, characterized in that, The conditions for the secondary heating in step S6 include: heating at 150-200℃ under inert gas, holding the temperature for 0.5-1.5h after it stabilizes; and the pressure of the inert gas being 0.5-2MPa.

12. The method according to claim 1, characterized in that, The secondary heating described in step S6 is performed using a heated mold; The heating mold includes a mold body, which is provided with a nitrogen inlet, a pressure gauge, a nitrogen outlet, a heating plug, a thermocouple plug, bolts, and a cooling water interface. The mold body is provided with a mold cooling zone inside.

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