A 10-35kV cable insulation layer non-cut core in-situ hot melt regeneration repair method and repair structure

Abstract

This invention discloses an in-situ thermal melting regeneration repair method and structure for 10-35kV cable insulation without cutting the conductor core. The method involves removing the damaged insulation layer and machining a pencil-tip conical surface without cutting the conductor core. Then, an inner semi-conductive vulcanized tape and a cross-linked polyethylene insulating vulcanized tape are sequentially wound around it. Using a wrapping method, the cold-shrink tape is stretched 150%-200% and tightly wound, utilizing its self-fusion property to eliminate overlap gaps and form a closed tubular structure. Its self-shrinkage property applies a continuous radial clamping force to the inner insulating vulcanized tape. After wrapping with tin foil, a flexible heating tape is wound and heated to 180℃-190℃ and held for 30-40 minutes, causing the insulating vulcanized tape to melt and fuse with the original insulation layer to form a pore-free, non-embedded integrated structure. After cooling, the cold-shrink tape is removed, and the layers are polished and restored. This invention solves the problems of cutting the conductor core, molten material overflow, residual pores, and tape embedding in existing technologies. It is suitable for on-site emergency repairs and online repairs on production lines of 10-35kV cables.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage power cable manufacturing and repair technology, specifically relating to a repair method and the resulting repair structure for 10kV to 35kV cross-linked polyethylene (XLPE) power cables. This method utilizes a self-fusion and self-shrinking cold-shrink tape as an external constraint mold to achieve in-situ thermal melting regeneration of the insulation layer, without cutting the conductor core. This method is not only suitable for on-site cable repair but can also be applied to repairing insulation layer damage caused by external factors (such as extrusion defects, bubbles, impurities, and mechanical forces) during cable production. Background Technology

[0002] Cross-linked polyethylene (XLPE) power cables are widely used in urban power grids and industrial power distribution. During cable operation, overvoltage, external mechanical shock, water treeing, aging, or manufacturing defects often lead to localized breakdown or damage to the main insulation layer, while the conductor core (copper or aluminum core) remains intact. Regarding this "intact conductor core, insulation breakdown only" fault, existing technologies have the following drawbacks:

[0003] Traditional intermediate joint method: This method requires cutting the cable and remaking a cold-shrink or heat-shrink cable intermediate joint. The wire core is crimped with copper or aluminum connecting tubes. This method has multiple interfaces at the joint, resulting in severe electric field distortion and poor waterproofing and sealing performance, making it a high-risk point for failure.

[0004] Cable fusion splicing: Although it performs better than ordinary splicing, it still requires cutting the cable core and re-welding (such as exothermic welding or argon arc welding), which disrupts the continuity of the conductor, introduces welding resistance, and the high temperature of welding can damage the nearby insulation.

[0005] Existing hot-melt repair methods, such as the one disclosed in Chinese patent CN105845261B, use polytetrafluoroethylene (PTFE) tape as an anti-sticking isolation layer and rely on an outer copper tape to provide clamping force. However, this method has the following inherent drawbacks:

[0006] Polytetrafluoroethylene (PTFE) tape does not have self-fusion properties. When heated, the interlayer overlaps of the tape cannot close, and the molten insulation material easily overflows from the gaps, leading to repair failure.

[0007] Polytetrafluoroethylene (PTFE) tape lacks self-shrinking properties and cannot provide active and uniform radial pressure to the internal molten insulation material. It is prone to developing pores or voids after cooling, which can lead to partial discharge.

[0008] Polytetrafluoroethylene (PTFE) tape has extremely low surface energy, making it prone to sticking or embedding with molten insulating materials. After cooling, it is difficult to peel off completely, which damages its electrical properties.

[0009] Therefore, there is an urgent need for a new in-situ repair method for insulation layers that does not require cutting the wire core and can overcome the above-mentioned defects. Summary of the Invention

[0010] Purpose of the invention: The present invention aims to provide an in-situ thermal fusion regeneration repair method and repair structure for 10-35kV cable insulation without cutting the conductor core, so as to solve the technical problems of cutting the conductor core in the prior art, as well as the overflow of molten material, residual pores and tape embedding in the existing thermal fusion repair method. Technical solution

[0011] A method for in-situ thermal melting regeneration repair of 10-35kV cable insulation without cutting the conductor core, characterized by comprising the following steps:

[0012] Step S1: Removal of outer sheath and metal armor After identifying the fault location, the outer sheath, steel armor, and inner sheath of the cable were removed in sequence to expose the cable's internal filler and damaged core.

[0013] Step S2: Filler stripping and preparation Remove the filler around the damaged core and clean it thoroughly for later use in restoring the inner lining.

[0014] Step S3: Removal of copper shielding layer and semiconductive layer Remove the copper shielding layer from the damaged wire core. Then, remove the outer semiconductive layer from the outer surface of the insulation layer.

[0015] Step S4: Remove damaged insulation (Key point: expose the wire core but do not break the core) Using cable strippers or specialized cutting tools, precisely remove the damaged main insulation layer until the inner conductor core is completely exposed. During the process, it is strictly forbidden to damage the conductor core itself; maintain its integrity and continuity.

[0016] Step S5: Conical shaping of the pencil tip Using a specialized taper tool or rotary cutting tool, cut the original main insulation layer into a pencil-tip shaped bevel or stepped cone at both ends of the cut area, exposing the inner semiconductive layer 2-5mm at the tip of the cone. The ratio of the axial length L of the cone to the insulation thickness T satisfies L≥3T.

[0017] Step S6: Cleaning Use anhydrous alcohol or a special cleaning agent to thoroughly clean the exposed core surface, pencil tip cone, and inner semiconductive layer to remove oil, dust, and moisture.

[0018] Step S7: In-situ restoration of the inner semiconducting layer Take the inner semiconductive vulcanized tape (heat-fusible semiconductive polymer tape), tightly wrap it around the exposed wire core, and overlap its two ends with the original inner semiconductive layers at both ends to form a continuous inner shielding layer.

[0019] Step S8: Main insulation layer wrapping and forming Take cross-linked polyethylene (XLPE) insulating vulcanized tape and wrap it in multiple layers around the restored inner semiconductive layer to fill the entire cut-out gap. The outer diameter of the wrapping should be 3-5 mm higher than the outer diameter of the original cable main insulation layer to compensate for the allowance for subsequent hot-melt pressing and polishing.

[0020] Step S9: Fabrication of the external constraint mold – using a cold shrink tape with self-fusion and self-shrinking properties (core step) On the surface of the wound insulating vulcanized tape, the high-temperature resistant cold shrink tape is stretched by 150%-200% and tightly wound by wrapping, and then wrapped with a layer of tin foil to form an external constraint mold.

[0021] The self-fusion property refers to the self-adhesive nature of the cold-shrink tape, which automatically bonds itself during wrapping and overlapping, eliminating the overlap gaps without additional heating and forming a continuous, sealed tubular structure. This property prevents the molten insulating vulcanized tape inside from leaking out of the overlap gaps during subsequent heating, ensuring a reliable seal during the repair process.

[0022] The self-shrinking property refers to the continuous radial shrinkage force generated by the cold-shrink tape when stretched by 150%-200% (similar to a stretched rubber band). This shrinkage force originates from physical stretching and is unrelated to heating. The cold-shrink tape begins to shrink immediately after wrapping, applying continuous and uniform clamping pressure to the internal insulating vulcanized tape. This shrinkage force is maintained during subsequent heating, but heating does not alter its shrinkage behavior.

[0023] The synergistic effect of self-shrinking and self-fusion: Self-shrinking begins to expel air bubbles between the layers of the insulating vulcanized tape and compress the material immediately after wrapping, while self-fusion seals the overlap seams during wrapping to prevent subsequent molten material from overflowing. Both processes complete sealing and pre-compression before heating, preparing the material for the heating and melting stage.

[0024] The function of the tin foil is to reflect heat, even out the heating temperature, and prevent the heating equipment from directly contacting the cold shrink tape.

[0025] Step S10: External heating and hot melt regeneration Using a heating element connected to a flexible heating tape, the heating tape is tightly wound around the outermost layer of the area containing tin foil, cold shrink tape, and internal insulating vulcanized tape. After the heating element is powered on, the heating tape generates heat, which, through heat conduction, sequentially heats the tin foil and cold shrink tape, ultimately bringing the internal insulating vulcanized tape to its melting temperature. The heating parameters are 180℃-190℃, held for 30-40 minutes, to ensure the XLPE insulating vulcanized tape fully melts and cross-links.

[0026] Heating parameters: Heat to 180℃-190℃ and hold for 30-40 minutes to allow the XLPE insulating vulcanized tape to fully melt and crosslink.

[0027] The purpose of heating is solely to melt the internal insulating vulcanized tape, transforming it from a solid to a molten state. Under the self-shrinking pressure of the cold-shrink tape, it flows, fills, and cross-links, fusing with the original insulation layer. Heating does not alter the shrinkage behavior of the cold-shrink tape; the shrinkage force of the cold-shrink tape is already present after wrapping and continues to act until cooling.

[0028] Hot-melting process: The inner insulating vulcanized tape melts completely after being heated; at the same time, the outer cold-shrink tape continuously applies radial pressure due to its self-shrinkage property (this pressure is independent of heating and exists after wrapping), pressing the molten material tightly; due to its self-fusion property, the overlap seam of the cold-shrink tape always remains closed to prevent the molten material from overflowing.

[0029] Fusion result: The molten insulating vulcanized tape cross-links and fuses with the original cable main insulation layer and inner semiconductive layer to form an integrated regenerated insulation layer without interfaces, pores, or embedded materials.

[0030] Non-adhesive properties: During the heating process, the cold-shrink tape does not chemically adhere to the molten XLPE insulation material. Its self-fusion property occurs only between the tape layers and does not react with the insulation layer being repaired. Therefore, after cooling, the cold-shrink tape can be completely peeled off from the surface of the regenerated insulation layer without embedding or leaving any material, ensuring a smooth and clean repair layer surface.

[0031] Step S11: Cooling and Demolding Stop heating and allow to cool naturally or by air to room temperature (below 40°C). Once the internal material has completely cured and set, remove the outer foil and high-temperature shrink tape. Because the shrink tape does not adhere to the molten insulation layer, it can be completely peeled off, leaving a smooth surface with no embedded or residual tape.

[0032] Step S12: Finishing and Polishing Use a belt sander or fine sandpaper to finely polish the surface of the insulation layer in the repair area, making it smooth and with a radius completely consistent with the original cable insulation layer. Ensure there are no sharp corners, burrs, or air gaps to prevent partial discharge.

[0033] Step S13: Restoration of outer semiconductive layer and shielding layer Outer semiconductive layer: On the smooth surface of the main insulation layer, wrap or coat semiconductive tape / coating to restore the outer semiconductive layer and ensure good overlap with the original outer semiconductive layer.

[0034] Copper shielding layer: Use copper braided mesh or copper strip to wrap and restore the copper shielding layer to ensure good conductivity.

[0035] Step S14: Inner sheath and armor layer restoration Inner sheath: Use the original filler material prepared in step S2 to fill the gaps between the wire cores; then wrap waterproof tape around to restore the inner sheath.

[0036] Steel armor connection: Copper braided straps are used to bridge the steel armor at both ends via constant force springs or welding to ensure electrical continuity of the armor.

[0037] Outer sheath: Wrap waterproof tape and armor tape (high-strength fiberglass tape) in sequence to restore the mechanical protection and waterproof seal of the outer sheath.

[0038] The repair structure formed by the above method is characterized by comprising: A continuous, uncut conductor core; A regenerated inner semiconductive layer located outside the conductor core, formed by the hot melting of a semiconductive vulcanized strip; An integrated regenerated main insulation layer located outside the regenerated inner semiconductive layer, formed by the thermal fusion of the insulating vulcanized tape and the original insulation layer; An outer semiconductive layer, restored by semiconductive tape, located outside the regenerated main insulation layer; The outer surface or inner interlayer of the regenerated main insulation layer has a spiral overlapping texture formed by wrapping with cold shrink tape. This texture is different from the continuous annular texture formed by traditional cold shrink tube molds and can serve as indirect evidence of the implementation of the method of the present invention. Beneficial effects

[0039] Compared with the prior art, the present invention has the following beneficial effects: Maintain conductor integrity: The conductor core is not cut, 100% of the original current carrying capacity and tensile strength of the cable are preserved, and welding resistance and heat-affected zone are avoided.

[0040] Unique "stretch wrapping + self-fusion and self-shrinking" cold shrink tape mold: Stretch self-shrinking: By stretching 150%-200%, the cold shrink tape acquires self-shrinking properties, and radial pressure begins to be applied immediately after wrapping, independent of heating. No external pressurization equipment is required, operation is simple, and pressure is uniform.

[0041] Self-fusion seal: The self-adhesive properties of the strip itself allow the overlap seams to bond and seal instantly without heating, forming a perfectly sealed tubular structure.

[0042] Non-stick properties: It can be completely peeled off after cooling without embedding or leaving any residue.

[0043] The three components work together to complete the sealing and pre-compression before heating. The heating stage is only used for melting the insulating material, achieving a perfect "sealing-pressurization-forming-demolding" of the molten insulating material, which is something that existing materials such as PTFE tape cannot achieve.

[0044] Optimized heating parameters: heating conditions of 180℃-190℃ for 30-40 minutes ensure that XLPE is fully melted and crosslinked without damaging the material.

[0045] Excellent electrical performance: After repair, there are no air gaps, sharp corners, or interface contamination.

[0046] Easy to operate: The cold shrink tape is wrapped around the cable, so it does not need to be slipped onto the cable end, making it perfect for on-site conditions where there are no broken cores or free ends.

[0047] Low cost and high efficiency: No custom metal molds are required, it is suitable for cables of various cross-sections, and the overall repair time is reduced by more than 50% compared with the traditional core breakage method.

[0048] Wide range of applications: It can be used for both on-site cable repair and online insulation repair during cable production. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of a cable fusion splice in the prior art, which requires cutting off the wire core.

[0050] Figure 1A This is a schematic diagram showing the overflow of molten material from the overlap seam when polytetrafluoroethylene tape (such as CN105845261B) is used in the prior art.

[0051] Figure 2 This is an axial sectional view (core illustration) of the cold shrink tape wrapping mold during the repair process of this invention.

[0052] Figure 3 for Figure 2 The enlarged view of region B shows the structure where the overlap disappears after the cold shrink tape self-fused.

[0053] Figure 4 This is a process flow diagram of the repair method of the present invention.

[0054] Figure 5 This is an axial sectional view of the final product of the repair structure of the present invention. Detailed Implementation

[0055] Example 1: Repair of Mechanical Damage to Insulation Layer of 10kV XLPE Power Cable A 10kV YJV22-3×240 cable was scratched by an excavator during installation, resulting in damage to the outer sheath and a 3mm deep damage to the main insulation layer (total thickness 4.5mm). However, the conductor core was found to be intact upon inspection.

[0056] Perform steps S1 to S14.

[0057] in: Cold shrink tape selection: Commercially available high-temperature resistant silicone rubber self-fusion tape, with an elongation of 200%, radial shrinkage rate ≥15%, and temperature resistance of 200℃.

[0058] Cold shrink tape wrapping operation: Stretch the cold shrink tape to 200% and then wrap it tightly. The overlapping parts of the wrapping will immediately self-adhere, forming a closed tubular structure. After wrapping, the cold shrink tape will begin to shrink, applying radial pressure to the internal insulating vulcanized tape.

[0059] Heating parameters: Connect the heating element to the flexible heating tape and tightly wrap the heating tape around the outermost layer of the area containing the aluminum foil, cold shrink tape, and internal insulating vulcanized tape. After the heating element is powered on, the heating tape generates heat, which, through heat conduction, sequentially heats the aluminum foil and cold shrink tape, ultimately bringing the internal insulating vulcanized tape to its melting temperature. The heating parameters are 180℃-190℃, held for 30-40 minutes, to ensure the XLPE insulating vulcanized tape fully melts and cross-links. Heating is only used to melt the insulating vulcanized tape; the shrinkage pressure of the cold shrink tape is present before heating and remains until cooling.

[0060] Repair results: After demolding, the cold shrink tape was completely peeled off without any embedding, and the surface of the regenerated insulation layer was smooth.

[0061] The recycled insulation layer has no pores or overflow marks.

[0062] Tested according to GB / T 12706.4 standard: No breakdown at power frequency withstand voltage of 35kV / 5min.

[0063] Comparative example (refer to CN105845261B): Repair using polytetrafluoroethylene tape Using the same 10kV XLPE cable sample, the method described in Chinese patent CN105845261B was adopted: polytetrafluoroethylene tape was used as an insulating layer, copper tape was wrapped around it, and it was heated in an electric furnace.

[0064] result: When heated, molten XLPE overflows in large quantities from the lap joints of the PTFE tape.

[0065] After cooling, the PTFE tape partially embeds into the recycled insulation layer, making it difficult to peel off and damaging the surface smoothness.

[0066] The partial discharge level is as high as 50pC or more at 15kV, which poses a risk of breakdown.

[0067] Conclusion: Polytetrafluoroethylene tape cannot independently complete high-quality repair due to its lack of self-fusion and self-shrinkage properties; this invention, through the synergistic effect of "stretching and wrapping + self-fusion and self-shrinkage" cold-shrink tape, successfully achieves high-quality insulation regeneration under the condition of no core breakage, which is a significant improvement. Industrial applicability

[0068] The method of this invention is simple and reliable. The cold shrink tape, vulcanizing tape, heating equipment and other materials used are all commercially available or easily customized products, making it suitable for large-scale application in cable field emergency repair and online repair by cable manufacturing enterprises.

Claims

1. A method for in-situ thermal melting regeneration repair of 10-35kV cable insulation without cutting the conductor core, characterized in that, Includes the following steps: a. Remove the outer sheath, steel armor, and inner sheath of the faulty section of the cable to expose the filler and damaged core; this method is also applicable to the repair of insulation damage caused by external factors during cable production. b. Remove the copper shielding layer and outer semiconductive layer from the damaged wire core; c. Remove the damaged main insulation layer until the continuous and complete conductor core is exposed, and process the original main insulation layer into a pencil-tip-shaped conical surface at both ends of the removed area to expose the inner semiconducting layer. d. Restore the inner semiconductive layer by wrapping inner semiconductive vulcanized tape around the core surface; e. Use cross-linked polyethylene insulating vulcanized tape to wrap around the outside of the restored inner semiconductive layer to form a temporary main insulator, and the outer diameter of the wrapping is 3-5 mm higher than the outer diameter of the original main insulation layer; f. Using a wrapping method, the high-temperature resistant cold-shrink tape is stretched by 150%-200% and then tightly wrapped around the outside of the temporary main insulator formed in step e, and then wrapped with tin foil to form an external constraint mold; the cold-shrink tape has self-fusion properties and self-adhedes during the wrapping overlap, making the overlap gap disappear and forming a continuous, closed tubular structure; the cold-shrink tape has self-shrinking properties due to being stretched, and after wrapping, it begins to apply a continuous radial clamping force to the internal insulating vulcanized tape, and this shrinkage force is independent of heating; g. Using a heating host connected to a flexible heating belt, the heating belt is wound around the outermost layer of the assembly in step f, and then heated to 180℃-190℃ for 30-40 minutes. This melts the internal insulating vulcanized tape and, under the radial pressure provided by the self-shrinking property of the cold shrink tape, fuses with the original insulation layer to form a pore-free, non-embedded integrated structure. Heating is only used to melt the insulating vulcanized tape and does not change the shrinkage behavior of the cold shrink tape. At the same time, the cold shrink tape will not stick to the molten insulation layer and can be completely peeled off after cooling. h. After cooling, remove the tin foil and shrink tape, and polish and shape the repaired insulation layer; i. Restore the outer semiconductive layer, copper shielding layer, inner sheath, steel armor connection, and outer sheath in sequence.

2. The method according to claim 1, characterized in that, In step c, the ratio of the axial length L of the pencil-shaped conical surface to the insulation thickness T satisfies L≥3T.

3. The method according to claim 1, characterized in that, The self-fusion property of the cold shrink tape described in step f is that the tape itself has self-adhesive properties, and it will self-adhere when wrapped and overlapped, without the need for additional heating, so that the overlap gaps disappear and a continuous closed tubular structure is formed.

4. The method according to claim 1, characterized in that, The self-shrinking property of the cold shrink tape mentioned in step f comes from the stretching during wrapping: after stretching the cold shrink tape by 150%-200% and then wrapping it, the stretched tape generates a continuous radial shrinkage force after wrapping. This shrinkage force is independent of heating, starts to work after wrapping, and continues to be maintained during subsequent heating.

5. The method according to claim 1, characterized in that, The self-shrinking and self-fusion properties of the cold shrink tape work synergistically: the self-shrinking property begins to expel internal air bubbles and compress the molten material after wrapping, while the self-fusion property seals the overlap seam during wrapping to prevent the molten material from overflowing. Together, they ensure that the repair layer is dense inside, smooth on the surface, and free of tape embedding.

6. The method according to claim 1, characterized in that, The difference between the cold shrink tape and the PTFE tape is that the PTFE tape does not have self-fusion and self-shrinking properties, and is only used as an anti-sticking isolation layer. It cannot independently achieve the sealing and pressurization of molten insulating materials.

7. The method according to claim 1, characterized in that, In step h, a belt sander is used to polish the surface of the repaired area to ensure that the surface roughness Ra is ≤ 0.4μm and there are no sharp corners or burrs.

8. The method according to claim 1, characterized in that, When restoring the copper shielding layer in step i, a copper braided mesh is used to overlap the original copper shielding layer, with an overlap length of not less than 20mm.

9. The method according to claim 1, characterized in that, When restoring the steel armor connection in step i, the electrical bridging of the steel armor at both ends is achieved using copper braided tape via constant force springs or welding.

10. The method according to claim 1, characterized in that, When restoring the outer sheath in step i, waterproof tape and armor tape are wrapped in sequence to form a composite sheath layer with sealing and radial mechanical strength.

11. A repair structure for the insulation layer of a 10-35kV cable obtained by the method described in any one of claims 1 to 10, characterized in that, include: A continuous, uncut conductor core; A regenerated inner semiconductive layer located outside the conductor core, formed by the hot melting of a semiconductive vulcanized strip; An integrated regenerated main insulation layer located outside the regenerated inner semiconductive layer, formed by the thermal fusion of the insulating vulcanized tape and the original insulation layer; An outer semiconductive layer, restored by semiconductive tape, located outside the regenerated main insulation layer; The outer surface or inner interlayer of the regenerated main insulation layer has a spiral overlapping texture formed by wrapping with cold shrink tape.

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