Method for repairing fault point of magnesium oxide insulation copper sheath cable

Abstract

The invention discloses a magnesium oxide insulation copper sheath cable fault point repairing method comprising the following steps: fault point positioning and pretreatment: positioning a fault point by using a cable fault tester, cleaning the cable surface around the fault point, and drying the cable surface; stripping the copper sheath: stripping the copper sheath at the fault point by using a special tool to prevent the conductor from being damaged; clearing a fault point: clearing magnesium oxide powder and impurities at the fault point, and preliminarily detecting insulation resistance; preparing magnesium oxide mud: mixing magnesium oxide powder and absolute ethyl alcohol into mud; insulating backfilling: extruding and filling the cleaned cavity with magnesium oxide mud, and performing layered compaction; drying and curing; finishing a filling surface: grinding a redundant magnesium oxide layer; groove machining is conducted; pre-welding is conducted; sealing welding and moisture prevention; weld joint finishing and corrosion prevention; and performance detection. According to the method, in-situ accurate repair of the fault point can be realized, the core quality such as insulation performance and sealing performance of the repaired cable is consistent with that of the original cable, and the method has the advantages of low repair cost, high operability, short repair period and the like.

Description

Technical Field

[0001] This invention relates to the field of cable repair technology, specifically to an in-situ repair method for fault points in magnesium oxide insulated copper sheathed cables (BTTZ cables). Background Technology

[0002] Magnesium oxide insulated copper-sheathed cables, also known as mineral-insulated cables, are widely used in key fields such as high-rise buildings, chemical industries, and metallurgy due to their excellent fire resistance, high-temperature resistance, and corrosion resistance. However, their core insulation material, magnesium oxide powder, is highly susceptible to moisture absorption in the air. Moisture absorption significantly reduces insulation resistance, potentially leading to cable insulation failure. Furthermore, during the copper sheath welding, insulation filling, and pre-shipment withstand voltage tests, localized sheath damage and insulation defects are prone to occur. Since rigid cables like BTTZ are produced to a fixed length, traditional cutting and scrapping methods are ineffective in preventing the remaining length from meeting user requirements. Completely scrapping the entire cable also results in significant raw material waste and substantial capital tied up. Additionally, remanufacturing requires a lengthy process, potentially delaying project schedules.

[0003] Chinese patent CN112820479A discloses a method for repairing damaged insulation layers of power cables, which uses hot melt adhesive injection to repair the damaged areas of the power cable insulation layer. This method is only suitable for repairing ordinary cable insulation layers and cannot solve the moisture absorption problem of magnesium oxide insulation layers, resulting in extremely low reliability after repair. Chinese patent CN107275991A discloses a cable repair device and cable repair method, which adopts a mating repair shell injection process. The structure is complex and the sealing performance is poor, making it difficult to meet the high sealing requirements of magnesium oxide insulated cables. In addition, because it is difficult to fill and compact magnesium oxide powder during the repair process of BTTZ cables, the filling degree and moisture resistance of the magnesium oxide insulation layer are difficult to meet the design requirements, and the repaired cable is prone to secondary faults. Summary of the Invention

[0004] The technical problem to be solved by the invention is to provide a method for repairing fault points in magnesium oxide insulated copper sheathed cables. This method can achieve precise in-situ repair of fault points, and the core quality of the repaired cable, such as insulation performance and sealing performance, is consistent with the original cable. It has the advantages of low repair cost, strong operability, and short repair period.

[0005] The technical solution adopted to solve the technical problem: A method for repairing fault points in magnesium oxide insulated copper sheathed cables, characterized by the following steps: S1. Fault location and pretreatment: Use a cable fault tester to locate the fault point, clean and dry the cable surface around the fault point. S2. Copper sheath stripping: Use a special tool to strip the copper sheath at the fault point to avoid damaging the conductor; S3. Fault point cleaning: Remove magnesium oxide powder and impurities from the fault point and perform preliminary insulation resistance testing; S4. Preparation of magnesium oxide mud: Mix magnesium oxide powder and anhydrous ethanol at a mass ratio of 3-3.5:1 to form mud; S5. Insulation backfilling: Extrude and fill the cleaned cavity with magnesium oxide mud and compact it in layers; S6. Drying and curing: Heat with a blowtorch to remove ethanol, then allow to cool naturally; S7. Trim the filling surface: Grind off excess magnesium oxide layer; S8. Beveling: Grinding the original copper sheath and repairing the edges of the copper sheet to form a 45° bevel; S9. Pre-welding: Position welding repairs to copper sheets; S10. Sealing and moisture protection: When welding in sections to the remaining 1 / 4 of the weld, bake the copper sheaths at both ends of the fault point for 1m each and then weld them tightly. S11. Weld repair and corrosion protection: Grind the weld and apply an antioxidant; S12. Performance testing: Conduct withstand voltage and insulation resistance tests according to standards. After repair, the cable quality and overall length integrity meet the usage requirements.

[0006] As a further improvement of the present invention: in step S1, the fault point positioning accuracy is ≤ ±5cm, the working environment humidity is ≤70%, the temperature is 5-35℃, and anhydrous ethanol is used to clean the surface of the copper sheath.

[0007] As a further improvement of the present invention: in step S4, the purity of magnesium oxide powder is ≥99.5%, and magnesium oxide mud is prepared by using a vacuum stirring device, with a material density ≥90%.

[0008] As a further improvement of the present invention: in step S6, the torch baking temperature is 300-400℃, the baking distance is 10-15cm, and the baking continues for 10-15min after the ethanol has completely evaporated.

[0009] As a further improvement of the present invention: in step S10, phosphor bronze welding rods are used for welding, the welding temperature is 1100℃, the baking temperature is 200-250℃, and the baking time is 5-8min.

[0010] As a further improvement of the present invention: In step S12, the withstand voltage test is performed according to the GB / T13033-2007 standard. A 2000V AC voltage is applied to light cables and a 2500V AC voltage is applied to heavy cables, with a holding time of 1 minute. For the insulation resistance measurement, a DC voltage of not less than 80V and not exceeding the peak value of the test voltage is applied. After energizing for 1 minute, the product of the insulation resistance (MΩ) and the cable length (km) is not less than 1000MΩ·km. When the cable length is less than 100m, the measured value is not less than 10000MΩ, which is considered qualified.

[0011] As a further improvement of the present invention: in step S3, a high-pressure airflow of 0.3-0.5MPa is used to clean the fault point, and after cleaning, the insulation resistance is measured with a 500V megohmmeter and is ≥10MΩ.

[0012] As a further improvement of the present invention: in step S8, the bevel depth is 1 / 2 to 2 / 3 of the thickness of the copper sheath, and the material and thickness of the repaired copper sheet are consistent with the original copper sheath.

[0013] Beneficial effects: This invention solves the problem of poor compaction of dry powder filling by using a paste-like mixture of magnesium oxide powder and anhydrous ethanol. Combined with layered compaction and ethanol baking processes, it ensures a dry and dense insulation layer, effectively preventing insulation failure caused by moisture absorption of magnesium oxide. The repaired insulation performance is consistent with the original cable. The "welding interruption - baking at both ends to remove moisture - re-welding and sealing" process precisely avoids the risk of moisture absorption of the magnesium oxide insulation layer due to temperature changes during welding. The sealing reliability far exceeds existing copper tube repair technologies, and testing shows that the repaired cable protection level can reach IP66. This invention enables in-situ repair of fault points without the need for complete cable replacement or cutting. It is particularly suitable for repairing faulty cables during production or withstand voltage testing, strictly ensuring the integrity of the overall cable length and fully meeting user length requirements. Compared to traditional cutting and scrapping methods, it not only avoids the waste of scrapping the entire cable but also reduces the capital investment required for raw material procurement and remanufacturing, lowering the risk of capital tied up by over 90%. Repair time is shortened to 1-2 hours per location, while traditional remanufacturing requires 3-7 days, significantly reducing product backlog and project delays. The method of this invention features a scientifically designed and highly operable process, is applicable to magnesium oxide insulated copper sheathed cables of different specifications, and facilitates large-scale application. Detailed Implementation

[0014] The present invention will now be described in further detail: A method for repairing fault points in magnesium oxide insulated copper sheathed cables includes the following steps: S1. Fault location and pretreatment: Use a cable fault tester to locate the fault point. A pulse reflection tester can be selected for the cable fault tester, and the positioning accuracy is controlled within ±5cm. Clean the dust, oil and corrosion layer on the surface of the cable around the fault point. Wipe the surface of the copper sheath with anhydrous ethanol and let it air dry naturally to ensure that the work area is dry and clean. The humidity of the work environment is ≤70% and the temperature is 5-35℃.

[0015] S2. Copper sheath stripping: Use a special copper sheath stripper or small milling cutter to strip the copper sheath circumferentially and axially along the fault point. The stripping range should be based on fully exposing the fault area, and the stripping length should extend 2-3cm beyond both ends of the fault area. Control the depth of the cutter during the stripping process to avoid damaging the internal conductor of the cable. After stripping, use fine sandpaper to polish the edge of the copper sheath until there are no burrs.

[0016] S3. Fault point cleaning: Use a high-pressure airflow of 0.3-0.5Mpa in conjunction with a cleaning brush to thoroughly remove the damp magnesium oxide powder, impurities and residual conductor debris at the fault point; after cleaning, use a 500V range megohmmeter to initially measure the insulation resistance between the conductor and the copper sheath to ensure that the insulation resistance after cleaning is ≥10MΩ. If it does not meet the standard, expand the cleaning area.

[0017] S4. Preparation of insulation filling material: Select magnesium oxide powder with a purity of ≥99.5% that matches the original cable and mix it with anhydrous ethanol at a mass ratio of 3:1. Stir until it becomes a uniform mud. Avoid mixing in air during the mixing process. A vacuum stirring device can be used to remove air bubbles and ensure that the material density is ≥90%.

[0018] S5. Insulation layer backfilling: Load the prepared magnesium oxide mud into the extrusion caulking gun, aim at the cavity after cleaning the fault point and slowly squeeze to fill, or use a small shovel to press the magnesium oxide mud into the cavity of the fault point; during the filling process, compact in layers along the axial direction, compact once every 2mm of filling thickness, until the filling surface is flush with the original insulation layer to avoid gaps.

[0019] S6. Drying and curing of the insulation layer: Use a blowtorch to evenly bake the filled insulation layer, controlling the baking temperature at 300-400℃ and maintaining a baking distance of 10-15cm to avoid local overheating; observe the surface of the magnesium oxide mud during baking, and when no more ethanol bubbles emerge, continue baking for 10-15 minutes to ensure complete ethanol evaporation; after baking, allow it to cool naturally to room temperature.

[0020] S7. Filling Surface Trimming: After the magnesium oxide insulation layer has completely dried and cured, use fine sandpaper with a mesh size of ≥200 to smooth out the excess magnesium oxide layer on the surface, so that the surface of the insulation layer is smoothly connected to the original cable insulation layer, ensuring the fit of subsequent copper sheath repair.

[0021] S8. Beveling: Grind the edges of the stripped copper sheath into a 45° bevel, with a bevel depth of 1 / 2 to 2 / 3 of the copper sheath thickness; Select a repair copper sheet with the same material and thickness as the original copper sheath, cut the copper sheet according to the size of the stripped area at the fault point, and grind the edges of the copper sheet into a matching 45° bevel as well.

[0022] S9. Pre-welding of copper sheath: Align the repair copper sheet with the stripped area of ​​the copper sheath, and adjust the position to ensure that the copper sheet is aligned with the edge of the original copper sheath; use argon arc welding for positioning welding, with a welding current of 18-20A, and evenly set 4-6 positioning welding points around the copper sheet, with a welding point spacing of 2-3cm, to ensure that the copper sheet is firmly fixed and does not shift.

[0023] S10. Sealing Welding and Moisture-proofing: Weld in sections starting from the positioning weld points, using phosphor bronze welding rods with specifications of 1.3mm×3.2mm×410mm, and controlling the welding temperature at 1100℃; when welding reaches the remaining 1 / 4 weld, temporarily interrupt welding and use a blowtorch to evenly bake the copper sheath within a 1m radius on both sides of the fault point, at a baking temperature of 200-250℃ for 5-8 minutes, to thoroughly remove moisture from inside and around the cable; after baking, immediately continue welding to weld the remaining 1 / 4 weld tightly, ensuring that the weld is full, free of porosity and slag inclusions during the welding process.

[0024] S11. Weld repair and anti-corrosion treatment: After the copper sheath and weld have cooled to room temperature, use fine sandpaper to grind the weld until it is flush with the original copper sheath surface; wipe the welding and baking areas with a neutral cleaner to remove the surface oxide scale, and after drying, apply a copper antioxidant to form an anti-corrosion layer with a thickness of ≤10μm to prevent the copper sheath from oxidizing and rusting.

[0025] S12. Performance Testing: Conduct withstand voltage tests according to GB / T13033-2007 "Mineral Insulated Cables and Terminals with Rated Voltage of 750V and Below". For 500V light cables, apply an AC test voltage of 2000V, and for 750V heavy cables, apply an AC test voltage of 2500V. The minimum voltage increase rate is 150V / s, and the holding time is 1 minute. No breakdown or flashover is acceptable. At the same time, measure the insulation resistance according to the standard requirements. Apply a DC voltage of not less than 80V and not exceeding the peak value of the test voltage. After energizing for 1 minute, measure the insulation resistance (MΩ) and the cable length (km). The product of the insulation resistance (MΩ) and the cable length (km) should not be less than 1000MΩ·km. If the cable length is less than 100m, the measured value should not be less than 10000MΩ to be considered as qualified for repair. Example

[0026] Repair of sheath damage in BTTZ-1×25mm² rigid magnesium oxide insulated copper sheathed cable.

[0027] 1. The HR-6000 cable fault tester was used to locate the fault point, which was a 3cm long tear in the copper sheath. After locating the fault, the copper sheath surface within a 10cm radius of the damaged area was wiped with anhydrous ethanol. After drying, the ambient humidity was confirmed to be 55% and the temperature to be 25℃.

[0028] 2. Use a special copper sheath peeling knife to peel off the copper sheath 2cm from each end of the damaged area, with a peeling length of 7cm. After peeling, grind the edges to remove any burrs.

[0029] 3. Use a 0.4MPa high-pressure airflow and a brush to clean the damp magnesium oxide powder from the damaged area. After cleaning, use a 500V megohmmeter to measure the insulation resistance, which is 15MΩ, meeting the requirements.

[0030] 4. Select magnesium oxide powder with a purity of 99.6% and mix it with anhydrous ethanol at a mass ratio of 3:1. Stir with a small vacuum stirrer for 2 minutes to make a paste.

[0031] 5. Fill the Φ10mm extrusion caulking gun with magnesium oxide mortar, fill and compact it in layers into the cavity until it is flush with the original insulation layer.

[0032] 6. Use a blowtorch 12cm away from the filling surface to bake evenly at a temperature of 350℃. After no more bubbles appear, continue baking for 12 minutes, then let it cool naturally to room temperature.

[0033] 7. Use 200-grit sandpaper to smooth the filling surface to ensure a smooth transition with the original insulation layer.

[0034] 8. Grind the edges of the original copper sheath and the cut 0.8mm thick copper repair piece into a 45° bevel.

[0035] 9. Align the repaired copper sheet and perform locating welding. The welding current is 19A, and 6 locating welding points are set. Use phosphor bronze welding rods to weld in sections. When the remaining 1 / 4 of the weld is welded, use a blowtorch to heat the copper sheath at both ends of the fault point for 1m at a temperature of 220℃ for 6 minutes. Then weld the remaining weld tightly.

[0036] 10. After the weld has cooled to 50°C, grind it smooth with 200-grit sandpaper, wipe it with a neutral cleaner, and then apply copper antioxidant.

[0037] 11. Perform withstand voltage test according to GB / T13033-2007 standard. BTTZ-1×25mm² is a heavy-duty cable. Apply AC test voltage of 2500V and hold for 1 minute without breakdown. Measure insulation resistance according to standard. Apply a DC voltage that meets the requirements. The measured value should meet the requirement that the product of insulation resistance and cable length is not less than 1000MΩ·km. The repair is qualified.

Claims

1. A method of repairing a fault point of a magnesium oxide insulated copper sheathed cable, characterized by Includes the following steps: S1. Fault location and pretreatment: Use a cable fault tester to locate the fault point, clean and dry the cable surface around the fault point. S2. Copper sheath stripping: Use a special tool to strip the copper sheath at the fault point to avoid damaging the conductor; S3. Fault point cleaning: Remove magnesium oxide powder and impurities from the fault point and perform preliminary insulation resistance testing; S4. Preparation of magnesium oxide mud: Mix magnesium oxide powder and anhydrous ethanol at a mass ratio of 3-3.5:1 to form mud; S5. Insulation backfilling: Extrude and fill the cleaned cavity with magnesium oxide mud and compact it in layers; S6. Drying and curing: Heat with a blowtorch to remove ethanol, then allow to cool naturally; S7. Trim the filling surface: Grind off excess magnesium oxide layer; S8. Beveling: Grinding the original copper sheath and repairing the edges of the copper sheet to form a 45° bevel; S9. Pre-welding: Position welding repairs to copper sheets; S10. Sealing and moisture protection: When welding in sections to the remaining 1 / 4 of the weld, bake the copper sheaths at both ends of the fault point for 1m each and then weld them tightly. S11. Weld repair and corrosion protection: Grind the weld and apply an antioxidant; S12. Performance testing: Conduct withstand voltage and insulation resistance tests according to standards. After repair, the cable quality and overall length integrity meet the usage requirements.

2. The magnesium oxide insulated copper sheath cable fault point repair method according to claim 1, characterized by: In step S1, the fault location accuracy is ≤ ±5cm, the ambient humidity is ≤ 70%, the temperature is 5-35℃, and anhydrous ethanol is used to clean the surface of the copper sheath.

3. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to claim 1, characterized in that: In step S4, the purity of magnesium oxide powder is ≥99.5%, and magnesium oxide mud is prepared using a vacuum stirring device with a material density ≥90%.

4. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to claim 3, characterized in that: In step S6, the torch baking temperature is 300-400℃, the baking distance is 10-15cm, and baking continues for 10-15min after the ethanol has completely evaporated.

5. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to claim 4, characterized in that: In step S10, phosphorus copper welding rods are used for welding, and the welding temperature is 1100℃; the baking temperature is 200-250℃, and the baking time is 5-8 minutes.

6. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to any one of claims 1 to 5, characterized in that: In step S12, the withstand voltage test is performed according to GB / T13033-2007 standard. A 2000V AC voltage is applied to light cables and a 2500V AC voltage is applied to heavy cables, with a holding time of 1 minute. For the insulation resistance measurement, a DC voltage of not less than 80V and not exceeding the peak value of the test voltage is applied. After energizing for 1 minute, the insulation resistance (MΩ) is measured. The product of the insulation resistance (MΩ) and the cable length (km) is not less than 1000MΩ·km. When the cable length is less than 100m, the measured value is not less than 10000MΩ, which is considered qualified.

7. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to claim 1, characterized in that: In step S3, a high-pressure airflow of 0.3-0.5MPa is used to clean the fault point. After cleaning, the insulation resistance is measured with a 500V megohmmeter and is ≥10MΩ.

8. The method for repairing fault points in magnesium oxide insulated copper sheathed cables according to claim 1, characterized in that: In step S8, the beveling depth is 1 / 2 to 2 / 3 of the copper sheath thickness, and the material and thickness of the repaired copper sheet are consistent with the original copper sheath.