Glue impregnated paper solid stress cone for repairing oil paper submarine cable and control method

Abstract

The invention discloses an impregnated paper solid stress cone for repairing an oil-paper submarine cable and a control method, and relates to the technical field of ultrahigh-voltage alternating-current submarine cable maintenance. The core comprises a composite glue impregnated paper cone, a microporous buffer interface layer and a pre-embedded monitoring optical fiber, the composite glue impregnated paper cone is prepared by dipping crepe paper in an epoxy / zirconia glue solution through gradient curing, and an axial dielectric constant gradient is formed; the microporous buffer interface layer is a conical through hole in the cone surface and is filled with silicone oil; the pre-embedded FBG optical fiber is used for monitoring strain and temperature. The invention further comprises a stress cone manufacturing method, a field installation method and a repair joint structure. According to the scheme, the problems of interface dielectric mismatch, space charge accumulation and structural integrity under deep sea pressure are solved, the oil-solid interface field intensity distortion rate is smaller than or equal to 5%, partial discharge is smaller than 0.5 pC, and the method is suitable for 500kV alternating current system deep sea repair.

Description

Technical Field

[0001] This invention relates to the field of submarine cable repair technology, specifically to a solid stress cone made of resin-impregnated paper for repairing oil-paper submarine cables and a method for controlling it. Background Technology

[0002] 500kV oil-paper submarine cables are core carriers for inter-regional power grids, coastal wind power grid connection, and island power supply. Often laid in deep sea, they face complex operating conditions such as alternating seawater pressure, cyclical temperature fluctuations, and mechanical impacts, making repair urgently needed. Existing technologies have significant drawbacks: traditional rubber stress cones experience severe space charge accumulation under DC fields, with measured charge densities exceeding 5C / m³ as reported in literature, easily leading to insulation breakdown; the dielectric constant at the interface between the impregnated paper and insulating oil changes abruptly (Δε≥1.5), resulting in field strength distortion >35%, becoming a weak point in the insulation; during on-site installation of factory-prefabricated components, temperature differences of -30℃ to 40℃ cause gap changes of up to 0.5mm, affecting sealing and insulation; epoxy resin is prone to cracking under deep-sea pressure, with related patents recording a failure rate of 17%. These problems severely restrict the reliability and safety of ultra-high voltage oil-paper submarine cables after repair, necessitating the development of new repair technologies. Summary of the Invention

[0003] To address the technical problems of existing repair technologies, which suffer from insufficient interfacial performance of stress cone materials, poor environmental adaptability, and lack of effective monitoring methods, leading to severe electric field distortion, unreliable interfacial sealing, and mechanical performance degradation in oil-paper submarine cable repair joints under high-voltage DC fields, thus failing to guarantee long-term safe operation after repair, this invention provides a resin-impregnated paper solid stress cone for oil-paper submarine cable repair and a control method thereon.

[0004] This invention provides a solid stress cone made of impregnated paper for repairing oil-paper submarine cables, comprising a composite impregnated paper cone, a microporous buffer interface layer, and pre-embedded monitoring optical fibers. The composite impregnated paper cone is made of crepe paper impregnated with epoxy / zirconia resin and cured by gradient to form an axial dielectric constant gradient. The microporous buffer interface layer consists of conical through holes distributed on the surface of the cone and filled with silicone oil buffer. Multiple pre-embedded monitoring optical fibers are embedded along the axial direction of the cone for real-time monitoring of strain and temperature.

[0005] Furthermore, the crepe paper in the composite impregnated paper cone is a crepe paper of a specific material, the epoxy / zirconia adhesive contains a specific proportion of zirconia, and the gradient curing process achieves a gradient change in the axial dielectric constant through multi-stage temperature and pressure control.

[0006] Furthermore, the tapered through-holes of the microporous buffer interface layer have a specific pore structure, and the silicone oil buffer filled in the pores is a silicone oil of a specific viscosity type. The interface layer achieves dielectric transition with the insulating oil through the cooperation of the through-holes and the silicone oil.

[0007] Furthermore, the pre-embedded monitoring optical fiber is an FBG optical fiber, with multiple FBG optical fibers distributed at specific intervals along the axial direction of the cone, and both ends of the optical fiber extending to the outside of the cone to facilitate connection with external monitoring equipment.

[0008] Furthermore, the gradient curing process includes three consecutive stages: the first stage maintains a set time at a set temperature and pressure to ensure that the adhesive fully penetrates the crepe paper; the second stage increases the temperature and pressure and maintains the set time to improve the degree of curing; and the third stage further increases the temperature and pressure and extends the holding time to achieve a high degree of curing.

[0009] Secondly, the present invention also provides a method for preparing an adhesive solution for preparing the impregnated paper solid stress cone, comprising ball milling and mixing a specific type of epoxy resin with nano-zirconia, adding a specific type of silane coupling agent during the mixing process, and controlling the mixing process to make the adhesive solution reach the state required for subsequent impregnation.

[0010] Furthermore, this includes placing the crepe paper roll in an environment with a specific vacuum level for impregnation, maintaining the impregnation process for a set time, and controlling the viscosity of the adhesive within a specific range during the impregnation period to ensure that the adhesive fully wets the crepe paper.

[0011] Furthermore, a specific wavelength of ultraviolet laser is used to process conical through holes on the surface of the composite impregnated paper cone after gradient curing. The depth and pore density of the through holes are controlled during the processing to form the microporous buffer interface layer.

[0012] Furthermore, this includes placing the stress cone in a liquid nitrogen chamber for pre-cooling treatment to shrink its inner diameter, completing the alignment and assembly of the stress cone and the submarine cable core within a set low-temperature environmental window, and allowing the stress cone to naturally reheat after assembly to generate radial clamping force.

[0013] Furthermore, it also includes injecting insulating oil into the interface through the through-holes of the microporous buffer interface layer after the stress cone is reheated, and controlling the injection pressure during the oil injection process to ensure that the insulating oil fully fills the through-holes and interface gaps.

[0014] Thirdly, the present invention also provides an oil-paper submarine cable repair joint structure, including the aforementioned impregnated paper solid stress cone and a dual-channel sealing system. The dual-channel sealing system includes an inner channel and an outer channel. The inner channel is composed of an impregnated paper solid stress cone and a silicone oil buffer in a microporous buffer interface layer. The outer channel is a pressure shell made of a specific material and is filled with compressed gas.

[0015] Furthermore, it also includes an intelligent monitoring unit, which is composed of the pre-embedded monitoring optical fiber connected to the demodulator. The demodulator provides real-time feedback on the pressure changes at the connector interface through the signal transmitted via the optical fiber.

[0016] Furthermore, the pressure shell of the outer channel is made of titanium alloy, and the compressed gas inside is nitrogen. The pressure of the nitrogen is set in a specific ratio to the pressure at the working water depth of the submarine cable to balance the deep-sea pressure.

[0017] Furthermore, the demodulator of the intelligent monitoring unit has specific monitoring accuracy and can collect and feedback interface pressure changes in real time, so as to promptly grasp the working status of the joint interface.

[0018] Beneficial effects Compared with the prior art, this invention has several significant advantages: In terms of insulation performance, through the design of nano-modified impregnated paper and microporous buffer interface, zirconia nanoparticles increase the volume resistivity of impregnated paper to 10¹. 6 Ω・m, suppressing space charge, reducing charge accumulation under DC field by 82%, the silicone oil in the micropores forms a dielectric constant transition band, reducing the maximum interfacial field strength from 12.4kV / mm to 6.8kV / mm, with a field strength distortion rate ≤5% and partial discharge <0.5pC, significantly improving insulation reliability; In terms of structural stability, the gradient curing process ensures stress cone curing degree ≥99%, and the low-temperature shrinkage installation process uses liquid nitrogen to form installation gaps, generating an 8MPa radial clamping force after rewarming, avoiding interface separation caused by deep-sea pressure. After 50 thermal cycles, the clamping force decays by only 2%, and no cracking or leakage was observed after 1000 hours of testing at a water depth of 1800m; In terms of maintenance convenience, pre-embedded FBG optical fibers enable real-time monitoring of strain and temperature with accuracy of ±1με and ±0.1℃, respectively. The dual-channel sealing system combined with the intelligent monitoring unit can remotely monitor pressure changes, provide timely early warning of faults, reduce maintenance costs, and ensure the long-term safe operation of 500kV AC submarine cables in deep sea. It can also be extended to other voltage level submarine cable repair scenarios. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the stress cone structure of the resin-impregnated paper provided in an embodiment of the present invention; Figure 2 An enlarged view of the microporous buffer interface provided in an embodiment of the present invention; Figure 3 The gradient curing process flow diagram provided for an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0023] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0024] 500kV AC oil-paper submarine cables, as the core transmission carrier for inter-regional power grids, coastal wind power grid connection, and island power supply, are often laid in deep-sea environments, facing complex operating conditions such as alternating seawater pressure, cyclical temperature fluctuations (-40℃~70℃), marine organism attachment, and mechanical collisions. When submarine cables need repair due to insulation aging, external force damage, or joint failure, traditional repair techniques have three major problems: First, the rubber stress cone is prone to accumulating space charge under a DC field, leading to increased local field strength distortion, which can easily cause insulation breakdown over long-term operation; second, due to the abrupt change in dielectric constant at the interface between the rubber-impregnated paper and the insulating oil, the field strength distortion rate often exceeds 35%, becoming a weak link in the insulation; third, during on-site installation of factory-prefabricated components, the thermal expansion difference caused by temperature differences can easily create installation gaps, which further expand under deep-sea pressure, leading to interface discharge or oil immersion failure.

[0025] refer to Figures 1-3This embodiment provides a solid stress cone for repairing oil-paper submarine cables, including a composite impregnated paper cone 101, a microporous buffer interface layer 102, and a pre-embedded monitoring optical fiber 103. The composite impregnated paper cone is made of crepe paper of a specific thickness impregnated with epoxy / zirconia resin and is subjected to gradient curing to form an axial dielectric constant gradient. The microporous buffer interface layer consists of conical through holes distributed on the surface of the cone and filled with silicone oil buffer. Multiple pre-embedded monitoring optical fibers are embedded along the axial direction of the cone for real-time monitoring of strain and temperature.

[0026] It should be noted that the crepe paper in the composite impregnated paper cone is a crepe paper of a specific material, the epoxy / zirconia adhesive contains a specific proportion of zirconia, and the gradient curing process achieves a gradient change in the axial dielectric constant through multi-stage temperature and pressure control.

[0027] The tapered through-holes of the microporous buffer interface layer have a specific pore structure, and the silicone oil buffer filled in the pores is a silicone oil of a specific viscosity type. The interface layer achieves dielectric transition with the insulating oil through the cooperation of the through-holes and the silicone oil.

[0028] The pre-embedded monitoring optical fiber is FBG optical fiber, with multiple FBG optical fibers distributed at specific intervals along the axial direction of the cone. Both ends of the optical fiber extend to the outside of the cone for easy connection with external monitoring equipment. The gradient curing process includes three consecutive stages. In the first stage, the temperature and pressure are maintained at a set time to ensure that the adhesive fully penetrates the crepe paper. In the second stage, the temperature and pressure are increased and maintained at a set time to improve the degree of curing. In the third stage, the temperature and pressure are further increased and the holding time is extended to achieve a high degree of curing.

[0029] The present invention also provides a method for preparing the adhesive solution for preparing the impregnated paper solid stress cone, comprising ball milling and mixing a specific type of epoxy resin with nano-zirconia, adding a specific type of silane coupling agent during the mixing process, and controlling the mixing process to make the adhesive solution reach the state required for subsequent impregnation.

[0030] Furthermore, this includes placing the crepe paper roll in an environment with a specific vacuum level for impregnation, maintaining the impregnation process for a set time, and controlling the viscosity of the adhesive within a specific range during the impregnation period to ensure that the adhesive fully wets the crepe paper.

[0031] Furthermore, a specific wavelength of ultraviolet laser is used to process conical through holes on the surface of the composite impregnated paper cone after gradient curing. The depth and pore density of the through holes are controlled during the processing to form the microporous buffer interface layer.

[0032] Furthermore, this includes placing the stress cone in a liquid nitrogen chamber for pre-cooling treatment to shrink its inner diameter, completing the alignment and assembly of the stress cone and the submarine cable core within a set low-temperature environmental window, and allowing the stress cone to naturally reheat after assembly to generate radial clamping force.

[0033] Furthermore, it also includes injecting insulating oil into the interface through the through-holes of the microporous buffer interface layer after the stress cone is reheated, and controlling the injection pressure during the oil injection process to ensure that the insulating oil fully fills the through-holes and interface gaps.

[0034] The composite impregnated paper cone is the core insulating component of the stress cone, responsible for uniform electric field distribution, blocking leakage current, and withstanding ultra-high voltage. Its preparation requires strict control over material selection, adhesive formulation, and gradient curing process to ensure synergistic optimization of the axial dielectric constant gradient and mechanical properties. The matrix material of the composite impregnated paper cone is 0.08mm thick Swedish kraft crepe paper. This type of crepe paper features high fiber density (≥80g / m²), high tensile strength (longitudinal ≥2.5kN / m), good oil absorption, and uniform fiber distribution, providing a stable channel for adhesive penetration and preventing uneven insulation caused by fiber agglomeration. During the pretreatment stage, the crepe paper roll is placed in a vacuum drying oven at 60℃ for 4 hours, maintaining a vacuum of 0.05Pa, to remove residual moisture (controlling the moisture content ≤0.5%), preventing moisture from forming bubbles during subsequent curing and affecting insulation performance. After drying, the crepe paper roll is cooled to room temperature and placed in a sealed bag for later use to prevent secondary moisture absorption. The adhesive system consists of epoxy resin, nano-zirconia particles, and a silane coupling agent. The epoxy resin used is E-51 type bisphenol A epoxy resin with an epoxy value of 0.48-0.54 eq / 100g and a viscosity (25℃) of 1100-1400 mPa·s, exhibiting good resistance to damp heat and dielectric properties. The nano-zirconia particles are monoclinic zirconium oxide with a particle size of 50 nm, and its dielectric constant is approximately 25, much higher than that of epoxy resin. By adding these particles, the dielectric constant of the impregnated paper can be adjusted, while simultaneously improving the volume resistivity of the material. The silane coupling agent used is KH-550 type (γ-aminopropyltriethoxysilane), which contains amino and ethoxy groups at both ends of its molecule. The amino group can react with the epoxy group of the epoxy resin, and the ethoxy group can bind with the hydroxyl groups on the surface of zirconium oxide, thereby improving the interfacial bonding between zirconium oxide and epoxy resin and preventing the agglomeration of nanoparticles.

[0035] The preparation of the adhesive solution is divided into three stages: mixing, dispersion, and stabilization. The entire process is carried out in a Class 1000 cleanroom to avoid the introduction of impurities that could affect the insulation performance. First, E-51 epoxy resin and nano-zirconia are weighed according to the formula ratio (10 wt% nano-zirconia and 0.5 wt% silane coupling agent), with the E-51 epoxy resin accounting for 100% - 10% - 0.5% = 89.5 wt%, and the silane coupling agent accounting for 0.5 wt% of the total adhesive solution mass. The epoxy resin is poured into the grinding jar of a planetary ball mill, and zirconia grinding balls (ball-to-material ratio 5:1, grinding ball diameter 5 mm) are added. The speed is set to 300 r / min, and pre-stirring is performed for 10 min to ensure that the epoxy resin is evenly spread on the surface of the grinding balls.

[0036] Subsequently, nano-zirconia particles were added. While the ball mill was running at low speed or paused, the nano-powder was added slowly and in small batches through the feed port of the ball mill jar. After each addition, the ball mill was allowed to run for a period of time to allow the powder to be initially impregnated and dispersed by the resin before adding the next batch and continuing ball milling for 2 hours. In this embodiment, 200 grams of nano-zirconia particles were added. During ball milling, the grinding jar was cooled with circulating water to control the temperature inside the jar to ≤30℃, preventing premature cross-linking of the epoxy resin due to temperature rise. After ball milling, samples were taken and the dispersibility of the zirconia particles was tested using a laser particle size analyzer. The particle size distribution was required to be within the range of 50±5nm, and the proportion of agglomerated particles was required to be ≤5%. If agglomeration was severe, 0.1wt% of dispersant (such as BYK-163) was added, and the ball milling was extended by 30 minutes.

[0037] Finally, add the silane coupling agent KH-550, transfer the grinding jar to a high-speed stirrer, set the speed to 500 r / min, and stir for 30 min to allow the coupling agent to fully react with the epoxy resin and zirconium oxide. After stirring, transfer the adhesive to a vacuum degassing tank, evacuate to 0.01 Pa, and maintain for 15 min to remove air bubbles introduced by stirring. The viscosity of the adhesive after degassing (at 25℃) needs to be controlled within the range of 300-500 cPs. If the viscosity is too high, it can be appropriately heated to 30℃ for adjustment; if the viscosity is too low, it can be allowed to cool to 20℃ to ensure the feasibility of subsequent impregnation processes.

[0038] The pre-treated crepe paper roll is fixed onto a special support inside the impregnation tank. The support is made of polytetrafluoroethylene (PTFE) to prevent chemical reaction with the adhesive and to ensure the crepe paper roll is vertical so that the adhesive can penetrate evenly. After closing the tank door, the vacuum system is activated and the vacuum is evacuated to 0.01 Pa, maintained for 10 minutes to completely remove air from the gaps between the crepe paper fibers and inside the tank. If the vacuum level cannot be achieved, the tank door seal must be checked for integrity, any leaks must be eliminated, and the vacuum should be re-evacuated.

[0039] After vacuum maintenance, the adhesive is slowly injected through the inlet at the bottom of the tank using a hydraulic system, with the injection rate controlled at 5L / min to avoid impacting the crepe paper roll and causing deformation. The amount of adhesive injected should be enough to completely submerge the crepe paper roll, with the liquid level 100mm above the top of the roll. After injection, maintain a vacuum of 0.01Pa and sustain the immersion time for 30 minutes. During this time, the adhesive temperature is stabilized at 25℃ using a constant temperature control system to ensure constant viscosity. The adhesive viscosity is sampled and tested every 10 minutes during immersion. If the viscosity change exceeds ±50cPs, the temperature needs to be adjusted or fresh adhesive needs to be added.

[0040] After impregnation, the vacuum system is shut off, and nitrogen gas is slowly introduced to atmospheric pressure (pressure increase rate 0.02 MPa / min) to prevent the adhesive from generating bubbles due to sudden pressure changes. Then, the impregnated crepe paper roll is removed from the container and hung on a rack to drain excess adhesive for 10 minutes. During draining, the paper roll should be protected from collisions to prevent the adhesive layer from peeling off. After draining, samples are taken to test the adhesive penetration depth. A 10mm thick sample is cut from the paper roll using a slicer and observed under an optical microscope. The adhesive penetration depth should be ≥95%, meaning the unimpregnated area should account for ≤5% of the total area. If the penetration depth is insufficient, vacuum impregnation must be repeated, extending the impregnation time to 40 minutes.

[0041] Gradient curing is a key process for achieving the axial dielectric constant gradient (ε=4.5 at the high-pressure end → ε=3.8 at the low-pressure end) of composite impregnated paper cones. By controlling the temperature and pressure in stages, different cross-linking densities are formed in different regions of the adhesive, thereby achieving a gradual change in dielectric constant. This implementation uses a horizontal constant temperature and pressure curing oven with effective internal dimensions of 1200mm × 500mm × 500mm, equipped with a programmable temperature control system (temperature control accuracy ±1℃) and a hydraulic pressurization system (pressure range 0-10MPa, pressure control accuracy ±0.05MPa).

[0042] Place the drained crepe paper roll into a stainless steel mold. The inner wall of the mold should be pre-coated with PTFE release agent (5-10μm thick) to facilitate demolding of the cone after curing and prevent surface damage. After closing the mold, tighten it with bolts to ensure the mold gap is ≤0.1mm to prevent adhesive leakage. Place the mold into the curing oven, activate the temperature and pressure control system, and execute the curing process in three stages: Phase 1 (Penetration and Strengthening Stage): Set the temperature to 40℃ and the heating rate to 2℃ / min. After the oven temperature stabilizes, activate the hydraulic system to apply a pressure of 0.5MPa at a rate of 0.1MPa / min to prevent sudden pressure increases that could deform the paper roll. Maintain this condition for 2 hours. The purpose of this stage is to allow the adhesive to further penetrate the fiber gaps under low pressure and low temperature conditions, while simultaneously initiating initial cross-linking, laying the foundation for subsequent curing. Record the temperature and pressure every 30 minutes during this period to ensure the parameters remain stable within the set range.

[0043] The second stage (crosslinking acceleration stage): After the first stage, the temperature is raised to 80℃ at a rate of 2℃ / min, and the pressure is increased to 2.0MPa at a rate of 0.2MPa / min, maintained for 4 hours. This increase in temperature and pressure accelerates the crosslinking reaction between the epoxy resin and the curing agent, achieving a curing degree of over 85% and forming a preliminary mechanical structure. To prevent internal stress within the mold, the mold surface temperature must be monitored in real time during the heating process to ensure that the temperature difference at each point is ≤2℃.

[0044] The third stage (complete curing stage): After the second stage, the temperature is raised to 120℃ at a rate of 1℃ / min, and the pressure is increased to 5.0MPa at a rate of 0.3MPa / min, maintained for 6 hours. This stage is crucial for the complete cross-linking of the adhesive. Through a high-temperature and high-pressure environment, the epoxy resin achieves a curing degree of over 99%, forming a dense insulating structure. Simultaneously, a gradient distribution of the axial dielectric constant is achieved—the high-pressure end (closer to the mold) has a higher cross-linking density and a larger dielectric constant (ε=4.5) due to the longer curing temperature and pressure duration; the low-pressure end (farthest from the mold) has a relatively lower cross-linking density and a smaller dielectric constant (ε=3.8). During the curing process, a differential scanning calorimeter (DSC) is used to monitor the curing exothermic peak of the adhesive in real time. When the exothermic peak completely disappears, it indicates that the curing reaction is basically complete, and the third stage can be ended 1 hour earlier.

[0045] After the third stage, shut down the heating system and allow the curing oven to cool down naturally at a rate of 1℃ / min to prevent cracks caused by thermal expansion and contraction due to a sudden temperature drop. When the oven temperature drops to room temperature (20℃), shut down the hydraulic system, remove the mold, loosen the bolts, and detach the composite impregnated paper cone from the mold. The demolded cone must undergo a visual inspection, ensuring the surface is free of cracks, bubbles, and missing corners, with a diameter deviation ≤ ±0.1mm and a length deviation ≤ ±0.5mm. If surface defects are present, gently sand with fine sandpaper (800 grit) to remove the defects and then re-inspect.

[0046] Micro-hole processing equipment and parameter settings: Micro-hole processing is performed using an ultraviolet laser processing machine, model LP-355-10, with a laser wavelength of 355nm (ultraviolet band). This machine features high processing precision and a small heat-affected zone, avoiding damage to the insulation properties of the cone surface during processing. Before processing, the composite adhesive-impregnated paper cone must be fixed on the precision worktable of the processing machine. The worktable is made of marble, with a positioning accuracy of ±0.01mm, and is equipped with a CCD vision positioning system (12 million pixels resolution) to capture the cone surface position in real time, ensuring accurate micro-hole processing.

[0047] First, the processing path for the micro-hole array is drawn using CAD software. The micro-holes are uniformly distributed in a hexagonal pattern, with a hole density set to 200-300 holes / cm² (250 holes / cm² in this embodiment). The holes are conical, with an opening diameter (on the surface of the cone) of 30±5μm, a bottom diameter (near the interior of the cone) of 15±3μm, and a depth of 0.5mm. The processing path is then imported into the control system of the laser processing machine. The CCD vision system is activated, and the laser is aligned with the reference marks (pre-etched crosshairs) on the surface of the cone. After positioning, the laser focus is adjusted to the surface of the cone, with a focus deviation ≤0.005mm.

[0048] The laser processing parameters were set as follows: laser power 5W, pulse frequency 50kHz, scanning speed 100mm / s, single-pass processing depth 0.01mm, and a hole depth of 0.5mm achieved through multiple scans. During processing, nitrogen protection (nitrogen flow rate 5L / min) was used. Nitrogen was ejected from the side hole of the processing head, covering the processing area. This served two purposes: firstly, it cooled the cone surface, preventing the heat generated by the laser from carbonizing the impregnated paper; secondly, it removed processing debris, preventing it from clogging the micropores. After processing 100cm² of area, a 5-minute pause was required to inspect the pore diameter, depth, and wall roughness using a microscope. The required pore diameter deviation was ≤±2μm, depth deviation ≤±0.02mm, and wall roughness Ra≤1μm. If the parameters exceeded the limits, the laser power or scanning speed needed to be adjusted, and the sample reprocessed until the requirements were met.

[0049] After micropore fabrication, the surface of the cone and the interior of the micropores need to be cleaned to remove residual debris and oil, ensuring that the silicone oil can fully fill the cavity. The cleaning process consists of three steps: First, compressed air is used to blow along the cone's axial direction to remove surface dust. Second, the cone is placed in an ultrasonic cleaning tank with anhydrous ethanol as the cleaning solution, an ultrasonic power of 300W, and a cleaning time of 15 minutes to remove fine debris from the micropores using ultrasonic vibration. Third, the cone is removed and placed in a vacuum drying oven at 60℃ for 30 minutes with a vacuum degree of 0.01Pa to remove residual ethanol from the micropores and prevent ethanol from mixing with the silicone oil and affecting the dielectric properties.

[0050] The silicone oil filling process employs vacuum infusion. The silicone oil used is methylphenyl silicone oil with a dielectric constant of 3.2 and a breakdown field strength ≥25kV / mm, exhibiting excellent resistance to high and low temperatures and chemical stability. The infusion equipment is a small vacuum infusion tank with a volume of 500mL, equipped with a vacuum system (ultimate vacuum degree 0.001Pa) and a precision injection pump (flow rate range 0.1-10mL / min).

[0051] Place the cleaned and dried cone into the filling tank with the cone surface facing upwards, exposing the micropore array in the filling space. Close the tank door, start the vacuum system, and evacuate to 0.01 Pa, maintaining this state for 20 minutes to completely remove air from the micropores. If the vacuum level cannot be stabilized, check the cone surface for cracks that could cause air leakage. After troubleshooting, re-evacuate the tank.

[0052] After vacuum maintenance, silicone oil is slowly injected into the filling tank using a syringe pump at a rate of 0.5 mL / min. The injection volume should be sufficient to completely cover the surface of the cone, with the liquid level 5 mm above the cone surface. After injection, maintain a vacuum of 0.01 Pa for 30 minutes, gently shaking the filling tank every 5 minutes to promote silicone oil penetration into the micropores. During the filling process, the dielectric loss of the silicone oil is monitored in real time using a dielectric loss meter (25℃, 50Hz). The dielectric loss should be ≤0.001; if the dielectric loss is too high, the silicone oil must be replaced.

[0053] After infusion is complete, shut off the vacuum system and slowly introduce nitrogen gas to atmospheric pressure to prevent the silicone oil from generating bubbles due to sudden pressure changes. Remove the cone from the infusion tank and gently wipe off any excess silicone oil with a lint-free cloth, avoiding excessive force that could cause silicone oil to overflow from the micropores. After wiping, place the cone in a 25°C constant temperature chamber and let it stand for 24 hours to allow the silicone oil to fully stabilize within the micropores. After standing, use an X-ray fluorescence spectrometer to check the silicone oil filling rate. The filling rate should be ≥99%, meaning the percentage of unfilled micropores should be ≤1%. If the filling rate is insufficient, vacuum infusion must be repeated, extending the infusion time to 40 minutes.

[0054] The pre-embedded monitoring optical fiber is used to monitor the strain and temperature changes during the operation of the stress cone in real time, providing data support for the safe operation and maintenance of the joint structure. Its layout must ensure that the optical fiber is tightly bonded to the paper-impregnated cone, while avoiding damage to the optical fiber that may affect the monitoring accuracy.

[0055] The overall manufacturing process of the resin-impregnated paper solid stress cone requires the organic integration of three stages: composite resin-impregnated paper cone preparation, microporous buffer interface layer preparation, and pre-embedded monitoring fiber deployment. This forms a standardized production process, ensuring the performance consistency of each product. The specific process is as follows: Before production, material inspection, equipment calibration, and environmental control must be completed: Regarding materials, incoming inspections are conducted on crepe paper, epoxy resin, nano-zirconia, silane coupling agents, silicone oil, and FBG optical fibers. Inspection items include appearance, performance parameters, and purity; unqualified materials are prohibited from use. Regarding equipment, the planetary ball mill, vacuum impregnation tank, constant temperature and pressure curing oven, UV laser processing machine, and fiber optic demodulator are calibrated to ensure that equipment parameters meet the required accuracy. For example, the ball mill's rotational speed error should be ≤±5r / min, the curing oven's temperature control accuracy ≤±1℃, and the laser processing machine's positioning accuracy ≤±0.01mm. Regarding the environment, the cleanliness of the cleanroom must be maintained at Class 1000, with a temperature of 25±2℃ and humidity ≤50%, to avoid environmental factors affecting product quality.

[0056] The adhesive solution was prepared in batches according to the formula ratio (E-51 epoxy resin + 10wt% nano-zirconia + 0.5wt% KH-550 silane coupling agent). A 20L planetary ball mill was used for batch mixing at 300 rpm for 2.5 hours, with 10L of adhesive solution prepared per batch. After preparation, samples were taken to test the viscosity (25℃, 300-500 cPs) and zirconia dispersibility (particle size 50±5nm). If qualified, the samples were transferred to a vacuum degassing tank and degassed to 0.01 Pa for 15 minutes. Ten rolls of pre-treated crepe paper (2m each) were fixed in a vacuum impregnation tank, evacuated to 0.01 Pa for 10 minutes, and the batch-prepared adhesive solution was injected. The paper was impregnated for 30 minutes, with the viscosity checked every 10 minutes. If qualified, the paper was drained, and samples were taken to test the penetration depth (≥95%). If qualified, the paper was transferred to the curing process.

[0057] Gradient curing and fiber pre-embedding: The impregnated crepe paper rolls are placed one by one into the mold with fiber positioning grooves, FBG optical fibers are laid, the mold is closed, and the mold is sent into a constant temperature and pressure curing oven for batch curing according to the three-stage curing process. Each oven can cure 5 cones. The fiber performance is monitored in real time during the curing process. After curing, the mold is removed, and the appearance and fiber performance are tested. After passing the test, the process is transferred to the micro-hole processing step.

[0058] The cured cones are fixed on the worktable of the UV laser processing machine. They are then batch-positioned using a CCD vision system and processed into micropores according to the set parameters (power 5W, scanning speed 100mm / s, hole density 250 holes / cm²). Each machine can process 2 cones per hour. After processing, the micropores are cleaned and the micropore parameters (hole diameter 30±5μm, depth 0.5mm) are checked. Once qualified, they are transferred to the silicone oil filling process.

[0059] Place the cone with the micropores into a vacuum filling tank and fill it with silicone oil in batches. Filling parameters are: vacuum degree 0.01Pa×20min, liquid injection rate 0.5mL / min, filling time 30min. After filling, let it stand for 24h and test the silicone oil filling rate (≥99%). If it passes the test, it will be transferred to the finished product inspection process.

[0060] The on-site installation of the stress cone needs to be carried out on the submarine cable repair vessel. In view of the low temperature and high pressure characteristics of the deep sea environment, a low temperature shrinkage installation process is adopted to ensure the tight bond between the stress cone and the submarine cable core, while avoiding damage to the stress cone and the pre-embedded optical fiber during the installation process.

[0061] On-site installation must be carried out in a closed operating chamber with adjustable temperature (-50℃~20℃) and humidity ≤60%. The chamber is equipped with windproof and dustproof facilities to prevent external environmental factors from affecting installation accuracy. Main equipment includes: a liquid nitrogen storage tank (500L capacity, 0.8MPa pressure), a cryogenic operating chamber (1000mm inner diameter, 2000mm length, temperature control range -60℃~20℃, temperature control accuracy ±2℃), a hydraulic lifting platform (500kg load capacity, lifting accuracy ±0.1mm), special positioning clamps (PTFE material, used to fix stress cones and cable cores), a pressure sensor (range 0-20MPa, accuracy ±0.01MPa), an infrared thermometer (range -50℃~100℃, accuracy ±0.5℃), and an FBG fiber optic demodulator.

[0062] Before installation, the equipment needs to be debugged. The pressure of the liquid nitrogen storage tank must be stabilized at 0.6-0.8MPa, and the liquid level must be ≥80%. The temperature of the cryogenic operation chamber should be lowered to -50℃ and maintained for 1 hour. The temperature uniformity should be checked, and the temperature difference at each point in the chamber should be ≤3℃. The lifting rate of the hydraulic lifting platform should be set to 5mm / min to ensure stable operation. The pressure sensor and infrared thermometer must be calibrated and their accuracy must meet the requirements. The demodulator should be connected to the pre-embedded optical fiber of the stress cone, and the optical fiber signal should be checked to ensure that the monitoring function is intact.

[0063] Before repairing a submarine cable, the faulty section must be cut, and the outer armor layer, sheath layer, and outer semi-conductive layer stripped to expose the inner oil-paper insulated cable core. The stripped length of the cable core must be 100mm longer than the stress cone length to facilitate stress cone installation. Cable core pretreatment consists of three steps: First, clean the surface of the cable core. Wipe the surface of the cable core with anhydrous ethanol to remove oil and semi-conductive layer residue. Use a lint-free cloth during the wiping process to avoid fiber residue. If there is an oxide layer on the surface, it needs to be gently sanded with fine sandpaper (1000 grit). Clean it again after sanding to ensure that the surface roughness Ra of the cable core is ≤0.8μm.

[0064] Then, the cable core size is inspected: the outer diameter of the cable core is measured using an outside micrometer (accuracy ±0.001mm). Four measuring points are evenly distributed along the circumference of the cable core, and five points are distributed along the length. The outer diameter deviation is required to be ≤±0.05mm, and the roundness is required to be ≤0.03mm, so as to avoid uneven gaps after the stress cone is installed due to cable core eccentricity.

[0065] Secondly, cable core preheating: The pretreated cable core is placed in the preheating zone of the low-temperature operation chamber, and the temperature is set to -10℃ for 30 minutes to make the cable core temperature close to the subsequent installation environment temperature, so as to avoid condensation due to excessive temperature difference when the stress cone is installed.

[0066] Remove the finished stress cone from the sealed bag and perform pre-installation inspection: First, visually inspect the surface of the stress cone for damage, blockage of micropores, and integrity of the fiber optic lead-out end; second, use an infrared thermometer to check the initial temperature of the stress cone, ensuring it matches the ambient temperature (around 20℃); finally, use a demodulator to check the signal of the pre-embedded fiber optic cable, ensuring normal wavelength and reflectivity, and no signal interruption. After passing the inspection, fix the stress cone onto a special positioning clamp, ensuring the inner wall of the clamp fits tightly against the outer surface of the stress cone to prevent deformation. Apply a small amount of insulating oil (the same type as the insulating oil used inside the submarine cable, alkylbenzene insulating oil) with a thickness of 5-10μm to the inner surface of the stress cone (the surface in contact with the cable core), providing lubrication, facilitating assembly, and enhancing interface sealing.

[0067] The purpose of pre-cooling is to cause the stress cone to shrink at low temperatures, creating an installation gap for easier assembly with the cable core. The clamp holding the stress cone is placed in the cryogenic operating chamber, and the temperature control program is adjusted to set a cooling rate of 5℃ / min and a target temperature of -50±2℃. During cooling, the temperature at different locations on the stress cone is monitored in real time using an infrared thermometer, recorded every 5 minutes to ensure uniform temperature across the entire stress cone, with a temperature difference ≤2℃. If the temperature in a localized area is too low, the air ducts in the operating chamber need to be adjusted to prevent localized overcooling that could cause the stress cone to crack.

[0068] When the stress cone temperature reaches -50±2℃, maintain the temperature for 30 minutes to ensure that the inner diameter of the stress cone fully shrinks. After the temperature maintenance, use an inside micrometer (accuracy ±0.001mm) to measure the inner diameter of the stress cone. The measurement points should be evenly distributed at 4 points along the circumference. The inner diameter shrinkage should be 0.25-0.35mm (in this embodiment, the initial inner diameter of the stress cone is 140.20mm, and the inner diameter after shrinkage is 139.85mm), and the roundness of the inner diameter should be ≤0.02mm. If the shrinkage is insufficient, the temperature maintenance time should be extended to 40 minutes. If the shrinkage is too large, the temperature should be appropriately increased (-48℃), and the temperature maintenance time should be repeated for 20 minutes.

[0069] During the pre-cooling process, the strain change of the stress cone needs to be monitored in real time using an FBG demodulator. The strain value at low temperature should be ≤500με to avoid excessive internal stress caused by low-temperature contraction of the stress cone, which could lead to cracks. If the strain value exceeds 500με, the cooling rate should be reduced to 3℃ / min and the pre-cooling process should be repeated.

[0070] Cryogenic assembly must be completed within an environmental window of -45℃ to ensure that the stress cone remains in a contracted state during assembly, preventing the inner diameter from expanding due to temperature rise and affecting the installation clearance. First, the preheated submarine cable core is sent into the cryogenic operation chamber via a hydraulic lifting platform. The position of the cable core is adjusted so that the axis of the cable core is aligned with the axis of the stress cone, with a coaxiality deviation ≤0.05mm. A laser alignment instrument can be used to assist in positioning to ensure alignment accuracy.

[0071] Subsequently, the hydraulic lifting platform is activated to slowly push the cable core into the inner hole of the stress cone. The pushing speed is controlled at 10mm / min to avoid excessive speed, which could cause friction damage to the surface insulation between the cable core and the inner hole of the stress cone. During the pushing process, a designated person must observe the fit between the stress cone and the cable core. If jamming occurs, pushing must be stopped immediately, and the alignment accuracy or whether there are any protrusions on the surface of the cable core must be checked. Pushing can only continue after troubleshooting. Forced pushing is strictly prohibited to prevent cracking of the stress cone or damage to the cable core.

[0072] When the cable core is advanced to the specified position (the center of the stress cone is aligned with the center of the repair joint of the cable core), stop advancing and use a dial indicator to check the coaxiality of the stress cone and the cable core. The coaxiality should be ≤0.1mm. At the same time, use a feeler gauge to check the gap between the stress cone and the cable core. The gap should be uniform, with a maximum gap ≤0.05mm and a minimum gap ≥0.02mm, to ensure that a uniform radial clamping force can be formed after reheating.

[0073] The environmental window for low-temperature assembly is 15 minutes (from the end of pre-cooling to the completion of assembly). If the window is exceeded, the temperature of the stress cone will rise to above -40°C, the inner diameter will expand, the installation gap will decrease, and pre-cooling treatment will need to be carried out again. Therefore, before assembly, it is necessary to make clear the division of labor among personnel and clarify the operating procedures to ensure that the assembly is completed efficiently within the window period.

[0074] The rewarming locking process utilizes the thermal expansion effect of the stress cone after rewarming to generate radial clamping force, ensuring a tight bond between the stress cone and the cable core, forming a reliable insulation interface. After assembly, the refrigeration system of the cryogenic operating chamber is shut off, allowing the stress cone and cable core to rewarm naturally within the chamber. The rewarming ambient temperature is 20°C, and the rewarming rate is controlled at 2°C / min to prevent relative displacement between the stress cone and the cable core due to excessively rapid rewarming. During the rewarming process, changes in the radial clamping force are monitored in real time using a pressure sensor mounted on the outer surface of the stress cone, in contact with a dedicated clamp, to indirectly measure the radial clamping force (measurement accuracy ±0.05MPa). The clamping force data is recorded every 15 minutes, and the temperature of the stress cone is simultaneously recorded using an infrared thermometer to plot the clamping force-temperature curve. When the stress cone temperature rises to 20°C, the radial clamping force must reach 8±0.5MPa (8.2MPa in this embodiment) and remain stable. A change in clamping force of ≤±0.1MPa within 1 hour indicates that the rewarming locking is complete. If the clamping force is insufficient (<7.5MPa) after rewarming, check if the assembly gap is too large or if the stress cone shrinkage is insufficient. If necessary, re-pre-cool the assembly. If the clamping force is too large (>8.5MPa), appropriately heat the stress cone (raise the temperature to 25℃) to further expand the stress cone and release some pressure until the clamping force drops to within the range of 8±0.5MPa. During the rewarming process, continuously monitor the strain and temperature of the stress cone using an FBG demodulator to ensure that the strain value is within the normal range (≤1000με) and the temperature distribution is uniform (temperature difference ≤3℃). If abnormal strain or uneven temperature occurs, stop the rewarming process, check for assembly deviations or stress cone damage, and troubleshoot before continuing the rewarming process.

[0075] The purpose of interface oil injection is to inject insulating oil into the interface between the resin-impregnated paper and the cable core insulating oil through the micropores on the surface of the stress cone, filling the tiny gaps, further reducing the interface field strength distortion, and enhancing the interface's sealing and aging resistance. Interface oil injection must be performed immediately after the reheating and tightening process to prevent moisture from the air from entering the interface.

[0076] First, prepare the oil filling equipment and materials: the oil filling equipment is a miniature high-pressure oil filling pump (range 0-1MPa, accuracy ±0.01MPa), the oil filling pipe is made of polytetrafluoroethylene (inner diameter 2mm, outer diameter 4mm), and the insulating oil is alkylbenzene insulating oil (dielectric constant 2.2, breakdown field strength ≥30kV / mm, moisture content ≤10ppm). Before oil filling, the insulating oil needs to be dried in a vacuum drying oven for 2 hours (vacuum degree 0.01Pa, temperature 60℃) to remove moisture and impurities.

[0077] Select four evenly distributed oil injection points (connected to the micropore array) on the outer surface of the stress cone. Drill 2mm diameter oil injection holes at each injection point using a special drill bit, with the hole depth reaching the micropore layer (approximately 0.5mm), avoiding drilling through the stress cone. Insert one end of the oil injection pipe into the oil injection hole and connect the other end to the oil injection pump. Seal the oil injection pipe and the oil injection hole with epoxy resin, with a sealing length of 5mm. The curing conditions are room temperature × 30 minutes to ensure no leakage during oil injection.

[0078] Start the oil injection pump and set the injection pressure to 0.1-0.3 MPa (0.2 MPa is used in this embodiment). The injection rate is 1 mL / min. The injection volume is calculated based on the micropore volume of the stress cone (approximately 0.01 mL per cm², 250 pores / cm² × 0.5 mm depth × π × (15 μm)² ≈ 0.01 mL). In this embodiment, the surface area of ​​the stress cone is 0.5 m², and the injection volume is approximately 50 mL. During the injection process, the injection pressure is monitored by a pressure sensor to maintain a stable pressure. If the pressure suddenly drops, it indicates a leak, and the injection must be stopped, the seal checked, and the seal resealed before continuing injection.

[0079] After oil injection is complete, turn off the oil injection pump, maintain the oil injection pressure at 0.2 MPa, and hold the pressure for 10 minutes to ensure that the insulating oil fully fills the micropores and interface gaps. After the pressure holding period, close the oil injection valve, remove the oil injection pipe, and seal the oil injection hole with epoxy resin. The curing conditions are room temperature × 2 hours. After sealing, check whether there is any oil leakage at the sealing point. If there is any oil leakage, it is necessary to re-seal.

[0080] After the interface is filled with oil, the dielectric loss value of the interface (25℃, 50Hz) is tested using a dielectric loss tester. The dielectric loss value is required to be ≤0.0015, which is lower than the dielectric loss value before filling with oil, indicating that the filling effect is good. At the same time, the partial discharge quantity is tested using a partial discharge detector. The partial discharge is required to be <0.3pC, which further verifies the improvement of the interface insulation performance.

[0081] The 500kV oil-paper submarine cable repair joint structure uses a resin-impregnated paper solid stress cone as its core, combined with a dual-channel sealing system and an intelligent monitoring unit, to form a complete repair system, ensuring the long-term safe operation of the submarine cable in the deep-sea environment. Assembly of the joint structure must be completed on the work vessel, and comprehensive performance testing is required after assembly to verify its reliability.

[0082] The dual-channel sealing system includes an inner channel (impregnated paper stress cone + silicone oil buffer layer) and an outer channel (titanium alloy pressure shell + compressed nitrogen). The inner channel is initially formed during the stress cone installation process, while the outer channel needs to be assembled separately. The two work together to achieve sealing protection under deep-sea high pressure.

[0083] The sealing performance of the inner channel depends on the radial clamping force of the stress cone and the effectiveness of the interface oil injection. The sealing performance of the inner channel must be verified before assembling the outer channel. Using an airtightness tester (model HL-2000), the cable cores at both ends of the stress cone are sealed, and compressed air at 0.5 MPa is applied to the inner channel and maintained for 30 minutes. The pressure drop is then measured. A pressure drop ≤ 0.001 MPa indicates a good seal in the inner channel. If the pressure drop exceeds this limit, the interface oil injection must be checked for sufficiency or cracks in the stress cone. If necessary, re-oiling or replacement of the stress cone is required.

[0084] To further enhance the sealing of the inner channel, a semi-conductive tape (0.2 mm thick, 50 mm wide) is wrapped around the joints between the stress cone and the cable core, with a wrapping length of 100 mm. The resistivity of the semi-conductive tape is 10³-10⁻¹⁰. 5 Ω・m can eliminate electric field concentration at the interface. During the winding process, the tension of the semiconducting tape must be kept uniform (50N) and the overlap rate must be 50% to avoid the formation of bubbles or wrinkles. After winding, an insulating coating (consistent with the stress cone adhesive formula) is applied to the surface of the semiconducting tape with a coating thickness of 0.1mm and cured at 80℃ for 1h to enhance sealing performance and aging resistance.

[0085] The titanium alloy pressure shell is used to withstand deep-sea pressure and protect the internal stress cone and cable core. Its selection needs to be calculated based on the working water depth of the submarine cable: the design pressure of the pressure shell is 1.1 times the working water depth pressure (in this example, the working water depth is 1800m, the working pressure is 180bar, and the design pressure is 198bar). The material of the pressure shell is TC4 titanium alloy (tensile strength ≥895MPa, yield strength ≥825MPa, elongation ≥10%), which has high strength, low density and good seawater corrosion resistance.

[0086] The pressure shell has a cylindrical structure with an inner diameter 10mm larger than the outer diameter of the stress cone (for ease of installation) and a length 200mm longer than the stress cone (for sealing at both ends). The wall thickness is calculated based on the design pressure using the thin-walled cylinder formula δ=P×D / (2×[σ]×φ), where P is the design pressure (198bar=19.8MPa), D is the inner diameter of the pressure shell (in this embodiment, the outer diameter of the stress cone is 200mm and the inner diameter of the pressure shell is 210mm), [σ] is the allowable stress of TC4 titanium alloy (taken as 1 / 3 of the tensile strength, approximately 298MPa), and φ is the weld coefficient (0.85). The calculated wall thickness is δ≈(19.8×210) / (2×298×0.85)≈8.2mm. In this embodiment, a wall thickness of 10mm is selected to ensure a safety factor ≥1.2.

[0087] The pressure shell has flanges at both ends, with the flange material matching the pressure shell. The flange sealing surface has a raised face structure and is equipped with high-pressure and oil-resistant fluororubber sealing rings (hardness 70 Shore A, compression ratio 20%). Before assembly, the pressure shell must undergo non-destructive testing: an ultrasonic flaw detector (model USM35) is used to inspect the internal defects of the shell and flanges, requiring no cracks or pores; a hydrostatic test is performed on the pressure shell using a hydrostatic test bench, applying twice the design pressure (396 bar) and maintaining it for 1 hour, requiring no leakage and no permanent deformation.

[0088] The pressure shell assembly steps are as follows: First, place the pressure shell horizontally on the hydraulic lifting platform, open one end flange, and slowly send the submarine cable core with the stress cone installed into the pressure shell. Adjust the position of the cable core so that the stress cone is located in the center of the pressure shell, with the cable cores at both ends extending 500mm from both ends of the pressure shell. Second, place fluororubber sealing rings on the flange sealing surfaces at both ends of the pressure shell and apply a small amount of silicone-based grease to enhance the sealing performance. Finally, close the flange and tighten it with bolts (bolt material is TC4 titanium alloy, specification M20×80mm). The tightening torque of the bolts is set according to the torque wrench (200N・m). Tighten the bolts diagonally and evenly to ensure that the flange sealing surface is subjected to uniform force and there is no leakage.

[0089] The pressure vessel is filled with compressed nitrogen to balance the deep-sea pressure and prevent deformation due to excessive pressure difference between the inside and outside. Nitrogen's inertness also prevents oxidation inside the pressure vessel. The filling equipment includes a nitrogen cylinder (99.999% purity), a pressure reducing valve (range 0-30 MPa, accuracy ±0.1 MPa), a pressure sensor (range 0-30 MPa, accuracy ±0.01 MPa), and a vacuum pump (ultimate vacuum 0.001 Pa).

[0090] Before filling, the inside of the pressure shell needs to be evacuated: connect the vacuum pump to the air extraction port of the pressure shell, evacuate to 0.001Pa, maintain for 30 minutes, and completely remove the air and moisture inside; if the vacuum degree cannot be stabilized, check whether the flange seal is intact, eliminate the leak, and then evacuate again.

[0091] After vacuuming is complete, close the suction valve, connect the nitrogen cylinder to the inlet of the pressure vessel, open the pressure reducing valve, and slowly fill with nitrogen at a rate of 0.5 MPa / min to avoid excessively rapid filling and subsequent temperature rise inside the pressure vessel. When the pressure reaches the design pressure (198 bar), close the pressure reducing valve and maintain pressure stability. Monitor pressure changes using a pressure sensor. A pressure drop of ≤0.005 MPa within 1 hour indicates a good seal on the pressure vessel. If the pressure drop exceeds this limit, check the tightening torque of the flange bolts or the condition of the sealing ring. If necessary, retighten or replace the sealing ring.

[0092] To achieve real-time pressure monitoring and compensation, a pressure transmitter (model PT200, range 0-30MPa, output signal 4-20mA) is installed on the pressure vessel. The transmitter is connected to the shore-based monitoring center via cable to transmit pressure data in real time. When the nitrogen pressure inside the pressure vessel is detected to be lower than 95% of the design pressure (188.1 bar), the shore-based monitoring center issues an alarm signal. Maintenance personnel can then replenish nitrogen into the pressure vessel via a remotely controlled gas replenishment valve until the pressure returns to the design pressure, ensuring that the pressure vessel remains in a state of pressure balance for an extended period.

[0093] The intelligent monitoring unit consists of pre-embedded FBG optical fibers, an optical fiber demodulator, a data acquisition module, and a shore-based monitoring system, enabling real-time monitoring of the joint structure's strain, temperature, and pressure, and providing data support for operation and maintenance.

[0094] First, the FBG fiber from the stress cone is fused to the signal transmission fiber (model G.652D, single-mode fiber, 250μm outer diameter) using a fiber optic fusion splicer (model FSM-60S). The splicing parameters are: discharge current 15mA, discharge time 100ms. After splicing, a heat-shrink tubing (600μm inner diameter, 60mm length) is used to protect the splice. The heat-shrink temperature is 120℃, and the heat-shrink time is 30s, ensuring the tensile strength of the splice is ≥8N and the insertion loss is ≤0.1dB. After splicing, an optical time domain reflectometer (OTDR, model AQ7275) is used to test the splice loss and fiber continuity. The splice loss must be ≤0.1dB, and there must be no fiber breakage. If the loss exceeds the standard, the splice must be re-fused. The fiber optic cable for signal transmission must be laid in a way that avoids the armor and sheath layers of the submarine cable. It is fixed with a special fiber optic slot made of polytetrafluoroethylene and fixed every 500mm to prevent the fiber optic cable from being stretched during the laying of the submarine cable.

[0095] Fiber optic junction boxes are installed at both ends of the signal transmission fiber optic cable (onboard and onshore). These junction boxes are waterproof and moisture-proof (IP68 protection rating) and equipped with internal fiber optic adapters (SC / PC type) for easy connection between the fiber optic cable and the demodulator. The junction boxes are filled with inert gas (nitrogen, 99.99% purity) to prevent internal moisture absorption, and the sealing surfaces use O-rings to ensure long-term resistance to seawater immersion.

[0096] The fiber optic demodulator (model SM130) is installed in the control room of the submarine cable working vessel. The input port of the demodulator is connected to the junction box at the upper end of the signal transmission fiber optic cable on the ship via a fiber optic patch cord (SC / PC-SC / PC type, 5m in length). The output port is connected to the data acquisition module (model DAQ-9178) via an RS485 communication line. The sampling frequency of the data acquisition module is set to 1Hz, and it can simultaneously acquire strain and temperature data of 4 FBG optical fibers.

[0097] The data acquisition module is connected to the ship's industrial computer via Ethernet. The computer has dedicated monitoring software (developed based on LabVIEW) installed. The software can display the center wavelength, strain value, temperature value, and nitrogen pressure value inside the pressure vessel (transmitted via a pressure transmitter) of each optical fiber in real time, and plot the real-time change curves. The software sets alarm thresholds: when the strain value is >1500με, the temperature value is >80℃ or <-50℃, and the nitrogen pressure is <188.1 bar or >207.9 bar, an audible and visual alarm signal is issued, and the alarm information is simultaneously transmitted to the shore-based monitoring center via satellite communication.

[0098] After connection, system debugging is required: First, calibrate the demodulator using a standard FBG fiber (center wavelength 1550nm) as input, and adjust the demodulator's gain and threshold to ensure wavelength measurement accuracy ≤ ±0.1nm; Second, simulate strain and temperature changes: apply a strain of 500με to the fiber, and the strain value displayed by the software should be consistent with the actual value (error ≤ ±1με); place the fiber in a high and low temperature chamber, raising the temperature from -50℃ to 70℃, and the error between the temperature value displayed by the software and the actual temperature should be ≤ ±0.1℃; Finally, simulate nitrogen pressure changes: input pressure signals of 180bar, 198bar, and 210bar to the pressure transmitter through a pressure simulator, and the error between the pressure value displayed by the software and the input signal should be ≤ ±0.1MPa to ensure the accuracy of the monitoring system.

[0099] The shore-based monitoring system is located in the land-based operations and maintenance center and consists of servers, monitors, printers, and communication equipment. The servers are industrial-grade servers (CPU Intel Xeon E5-2690, memory 32GB, hard disk 1TB SSD) and are equipped with the same monitoring software as those on board. They can receive monitoring data transmitted from the ship in real time and store historical data (storage period ≥ 10 years).

[0100] The communication equipment uses a satellite communication terminal (2Mbps bandwidth) to achieve data transmission between the ship and shore, with a transmission latency of ≤1s. Data transmission uses an encryption protocol (AES-256) to prevent data leakage or tampering. The monitoring system's display uses a large 4K resolution screen, which can simultaneously display a 3D model of the joint structure, real-time monitoring data, and alarm information. Maintenance personnel can use a mouse and keyboard to operate the software to view historical data curves, export reports, or set alarm thresholds.

[0101] The shore-based monitoring system also features remote control capabilities: when nitrogen pressure is detected to be below the set value, maintenance personnel can remotely control the onboard replenishment valve via software to add nitrogen to the pressure vessel; when abnormal strain or temperature is detected, the system can remotely activate the onboard backup monitoring equipment to further troubleshoot the fault. The system is also equipped with an automatic reporting function, generating daily, weekly, and monthly monitoring reports. These reports include statistical data, abnormal event records, and maintenance recommendations, facilitating regular maintenance by maintenance personnel.

[0102] After the repaired joint structure is assembled, land-based simulation tests and offshore field tests are required to comprehensively verify its dielectric properties, mechanical properties, and long-term reliability, ensuring that it meets the operational requirements of the 500kV AC submarine cable. The land-based simulation tests are conducted in an ultra-high voltage laboratory and mainly include dielectric property testing, mechanical property testing, and environmental adaptability testing: Dielectric property testing: DC withstand voltage test: According to IEC62895 standard, a DC high voltage generator (model ZGF-2000kV / 5mA) is used to apply a DC voltage of ±1120kV to the joint structure and maintain it for 15 minutes. During this period, the partial discharge quantity is monitored using a partial discharge detector, requiring no breakdown, no flashover, and partial discharge <0.5pC; After the test, the insulation resistance of the joint is measured (using a megohmmeter, range 10¹). 6 Ω), requiring insulation resistance ≥10¹ 5 Ω・m. Power frequency withstand voltage test: Using a power frequency high voltage test transformer (model YD-500kV / 100kVA), apply 1.3 times the rated voltage (650kV) and maintain for 1 minute, requiring no breakdown and no flashover; apply the rated voltage (500kV) and maintain for 24 hours, measure the dielectric loss value (25℃, 50Hz), requiring the dielectric loss value ≤0.002, and the change in dielectric loss value within 24 hours ≤0.0005.

[0103] The electric field distribution test was conducted by establishing an electric field model of the joint structure using finite element simulation software (ANSYS Maxwell) to simulate the electric field distribution under a rated voltage of 500kV. At the same time, the electric field strength at the oil-solid interface was measured using a fiber optic grating electric field sensor (model FBG-EF). The requirements were that the interface electric field distortion rate be ≤5%, the maximum electric field strength be ≤8kV / mm, and the deviation from the simulation results be ≤10%.

[0104] In some embodiments, a response mechanism and processing procedure are also included, typically for fault response: Response Timeframe: Maintenance personnel shall complete preliminary analysis within 30 minutes of receiving the alarm and formulate a verification plan within 24 hours. Handling Steps: First, retrieve historical data from the shore-based monitoring system and compare it with environmental parameters (such as seawater temperature and ocean current speed) from the same time period to determine if the fault is caused by external environmental interference. If it is signal interference, restart the monitoring system and calibrate the demodulator. After eliminating the interference, observe continuously for 2 hours to confirm that the parameters have returned to normal. If it is a slight parameter drift (such as slightly low nitrogen pressure), remotely activate the pressure transmitter's self-calibration function. After eliminating equipment errors, if the pressure still does not recover, arrange for on-site nitrogen replenishment during the next quarterly maintenance.

[0105] Verification criteria: After processing, the parameters return to the normal range and there are no recurrences within 72 hours, and the monitoring system does not trigger secondary alarms. Response time limit: A dedicated processing team shall be established within 1 hour.

[0106] The first step is to cross-verify the fault point through multi-dimensional monitoring data. For example, combining the strain distribution of the FBG optical fiber to determine whether the joint displacement is caused by the stress on the submarine cable, and confirming whether the insulating oil is aging by detecting the dielectric loss value of the oil sample. The second step is to use an ROV equipped with an underwater ultrasonic leak detector to check key parts such as the pressure shell flange sealing surface and the gas replenishment valve. After determining the leak point, stop the submarine cable from overload operation (reduce to 80% of the rated load). When the sea conditions permit (wave height ≤ 1.5m), the work vessel will go to the site to replace the sealing ring or valve at the leak point. If the interface insulation performance is degraded, fresh insulating oil is added through the micro-hole oil injection channel (oil injection pressure 0.25MPa). After oil injection, let it stand for 24 hours and re-measure the dielectric loss value and partial discharge.

[0107] Verification criteria: Within 24 hours after treatment, dielectric loss value ≤ 0.002, strain value ≤ 1500 με, nitrogen pressure stable at 198 bar ± 5 bar, partial discharge < 0.5 pC, and no abnormalities observed during continuous monitoring for 7 days.

[0108] Emergency Fault Response: Response Time Limit: Immediately activate the emergency plan, notify the submarine cable operation and maintenance dispatch center to cut off the power supply to the faulty submarine cable within 5 minutes, dispatch an emergency operation vessel (equipped with a helicopter transfer channel) to the site within 30 minutes, and complete on-site operation preparations within 2 hours. The first step is to confirm the submarine cable is de-energized using a high-voltage detector after a power outage. The ROV then descends to the joint location and takes detailed photographs of external defects (such as pressure shell cracks and oil leaks). Simultaneously, the internal strain of the stress cone is monitored using pre-embedded optical fibers to determine if there is a risk of structural collapse. The second step, if a severe pressure shell leak is found, the emergency work vessel lowers salvage equipment to lift the joint structure to the deck (lifting rate ≤ 0.5 m / min to avoid secondary damage). The damaged pressure shell is removed, replaced with a spare, and refilled with nitrogen (set at 1.1 times the working water depth pressure). The stress cone is then inspected for integrity. If cracks are found, a spare stress cone is replaced, and the cryogenic installation and interface oiling process is repeated. If insulation breakdown is the cause, the faulty section of the submarine cable must be cut, reconnected, and a new repair joint installed. The entire process involves strict control of the construction environment (temperature and humidity) to ensure installation accuracy.

[0109] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A solid stress cone made of resin-impregnated paper for repairing oil-paper submarine cables, characterized in that, This includes a composite paper-impregnated cone, a microporous buffer interface layer, and a pre-embedded monitoring optical fiber; The composite impregnated paper cone is made by impregnating crepe paper with epoxy / zirconia resin and undergoing gradient curing treatment to form an axial dielectric constant gradient distribution. The microporous buffer interface layer is disposed on the surface of the cone and includes a plurality of conical through holes filled with silicone oil buffer. Several pre-embedded monitoring optical fibers are embedded along the axial direction of the cone for real-time monitoring of strain and temperature.

2. The impregnated paper solid stress cone according to claim 1, characterized in that... The zirconium oxide in the epoxy / zirconia adhesive is proportioned, and the gradient curing is achieved by controlling the temperature and pressure in multiple stages, resulting in a gradient change in the axial dielectric constant.

3. The impregnated paper solid stress cone according to claim 1, characterized in that, The tapered through-hole has a specific hole structure, and the silicone oil buffer is a silicone oil of a selected viscosity. The dielectric transition between the through-hole and the silicone oil is achieved through the cooperation between the through-hole and the insulating oil.

4. The resin-impregnated paper solid stress cone according to claim 1, characterized in that, The pre-embedded monitoring optical fiber is FBG optical fiber, and several FBG optical fibers are arranged at a specific interval along the axial direction of the cone, with their two ends leading out of the cone and connected to external monitoring equipment.

5. The resin-impregnated paper solid stress cone according to claim 1, characterized in that, The gradient curing process includes three stages: the first stage involves maintaining a set temperature and pressure for a certain period of time to allow the adhesive to fully penetrate; the second stage involves increasing the temperature and pressure and maintaining the set time to improve the degree of curing; and the third stage involves further increasing the temperature and pressure and extending the duration to achieve an even higher degree of curing.

6. A method for preparing an adhesive solution for preparing the impregnated paper solid stress cone of claim 1, characterized in that, include: Epoxy resin and nano-zirconia are mixed by ball milling, and a silane coupling agent is added during the mixing process. The mixing process is controlled to make the adhesive solution reach a state suitable for impregnation.

7. The method according to claim 6, characterized in that, The impregnation process is carried out under a specific vacuum, in which the crepe paper roll is impregnated with glue. The impregnation time is controlled, and the viscosity of the glue is maintained within a specific range during this period to ensure sufficient wetting.

8. The method according to claim 6, characterized in that, A tapered through-hole is fabricated on the surface of a gradient-cured cone using a specific wavelength of ultraviolet laser. The depth and density of the through-hole are controlled to form the microporous buffer interface layer.

9. The method according to claim 6, characterized in that, include: The stress cone is pre-cooled in a liquid nitrogen chamber to shrink its inner diameter. Within a set low-temperature time window, it is aligned and assembled with the submarine cable core. After assembly, the stress cone naturally warms up to generate radial clamping force.

10. The method according to claim 9, characterized in that, Further, it includes injecting insulating oil into the interface through micropores after the stress cone has been reheated, controlling the injection pressure during the injection process, and filling the through-holes and interface gaps with insulating oil.

11. A repair joint structure for oil-paper submarine cables, characterized in that, The invention includes the impregnated paper solid stress cone as described in claim 1, and a dual-channel sealing system, wherein the inner channel is composed of the stress cone and the silicone oil buffer in the microporous buffer interface layer, and the outer channel includes a pressure shell of a specific material and compressed gas filled therein.

12. The oil-paper submarine cable repair joint structure according to claim 11, characterized in that, It also includes an intelligent monitoring unit, which consists of the pre-embedded monitoring optical fiber connected to the demodulator. The demodulator monitors and provides feedback on the pressure changes at the connector interface in real time through the optical fiber signal.

13. The oil-paper submarine cable repair joint structure according to claim 11, characterized in that, The pressure shell is made of titanium alloy and filled with nitrogen. Its pressure is kept in a specific ratio with the working water pressure of the submarine cable to balance the external deep-sea pressure.

14. The oil-paper submarine cable repair joint structure according to claim 12, characterized in that, The demodulator is used to collect and feedback interface pressure changes in real time and monitor the working status of the connector.

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