Pagsasapi ng metal na sheath ng mataas na boltyaheng kable

I. Mga Punsyan ng Metal na Sheath at Necessity ng Repair

Ang metal na sheath ng high-voltage cables ay isang metal shielding structure na nakalagay sa labas ng insulation layer, kabilang dito ang mga lead sheaths, aluminum sheaths, at steel wire armor. Ang mga pangunahing punsyan nito ay kasama ang mechanical protection (resistensya laban sa external impact at compression), electrochemical corrosion protection (paghihiwalay ng moisture at soil pollutants), electromagnetic shielding (reduksyon ng electromagnetic interference sa kapaligiran), at pagbibigay ng grounding path (pag-ensure ng ligtas na discharge ng fault currents). Kapag nasira, maaaring magresulta ito sa pagpasok ng moisture sa insulation layer, local electric field distortion, o kahit na malubhang aksidente tulad ng cable breakdown at short circuits. Kaya't mahalaga ang eksaktong repair na may direksiyon sa iba't ibang uri ng pinsala upang matiyak ang mahabang-termino at ligtas na operasyon ng cable system.

II. Fault Diagnosis at Assessment Bago ang Repair

(A) Pagkakilala ng Uri ng Pinsala

• Mechanical Damage: Nakikilala sa pamamagitan ng mga dents, cracks, o punctures sa sheath, karaniwang dulot ng mechanical rolling o sharp object punctures sa panahon ng installation, o tensile rupture dahil sa matagal na foundation settlement.

• Electrochemical Corrosion: Ang stray currents sa lupa o acidic/alkaline environments ay maaaring magdulot ng electrochemical corrosion sa sheath, inilalarawan ng localized bulging, rust, perforation, at white/green corrosion products (aluminum sheath) o black sulfides (lead sheath).

• Thermal Aging Damage: Ang matagal na overload operation ay nagdudulot ng embrittlement ng sheath material, nagresulta sa cracking at delamination, karaniwang natatagpuan sa joints o areas na may mahinang heat dissipation.

(B) Application ng Detection Technologies

• Visual Inspection: Gamitin ang endoscopes o infrared thermal imagers upang obserbahan ang surface ng sheath, nakatuon sa pag-identify ng obvious damage points at hot spots.

• Sheath Withstand Voltage Test: I-apply ang DC withstand voltage (10 kV para sa 1 minuto) upang suriin ang integrity ng sheath insulation. Ang abnormal increase sa leakage current (>10 μA) ay nagpapahiwatig ng pinsala.

• Partial Discharge Detection: Gamitin ang high-frequency current sensors (HFCT) upang i-capture ang partial discharge signals sa damage points, na may location accuracy na ±0.5 m.

• Soil Corrosivity Assessment: I-collect ang soil samples mula sa cable laying environment upang suriin ang pH, chloride ion concentration, at stray current density, nagbibigay ng basehan para sa pagpili ng repair materials.

III. Pagpili ng Repair Materials at Tools

(A) Core Repair Materials

• Metallic Sheath Replacement Materials:

• Aluminum Alloy Compression Sleeve: Angkop para sa aluminum sheath repair, may mahusay na ductility at corrosion resistance. Dapat tugma sa outer diameter ng cable (tolerance ≤ ±0.5 mm).

• Lead-Tin Alloy Tape: Ginagamit para sa lead sheath repair, mababang melting point (~183°C), madali para sa thermal welding, sumasang-ayon sa GB/T 12706.2 purity requirements (lead content ≥ 99.9%).

• Stainless Steel Corrugated Tube: Para sa steel armor damage, gawa ng 304 stainless steel, wall thickness ≥ 0.8 mm, may resistensya laban sa impact at soil stress.

• Insulation and Sealing Materials:

• Cross-Linked Polyethylene (XLPE) Heat-Shrink Tubing: Nagshrink sa 120–140°C, shrink ratio ≥ 2:1, breakdown strength ≥ 25 kV/mm, nangangailangan ng hot-melt adhesive para sa sealing.

• Silicone Rubber Cold-Shrink Tubing: Umumuwi sa elastic recovery para sa sealing, walang heating required, angkop para sa limited spaces, Shore hardness 60 ± 5 Shore A, tanδ ≤ 0.003 (20°C, 50 Hz).

• Butyl Rubber Sealing Tape: Ginagamit bilang auxiliary sealing layer, tensile strength ≥ 3 MPa, elongation at break ≥ 400%, aging resistance retains ≥ 80% performance after 100°C × 168 h thermal aging.

• Corrosion Protection Materials:

• Zinc-Aluminum Alloy Sacrificial Anode: Para sa high-corrosion soil environments, anode purity ≥ 99.5%, current density ≥ 15 mA/m², design life ≥ 20 years.

• Polyvinyl Chloride (PVC) Corrosion-Resistant Tape: Thickness ≥ 0.4 mm, tensile strength ≥ 18 MPa, environmental stress cracking resistance (ESCR) ≥ 1000 h.

(B) Specialized Tools

• Preparation Tools: Angle grinder (may 80-grit alumina grinding wheel), wire brush, anhydrous ethanol cleaner, stainless steel scraper (para sa pag-alis ng corrosion products).

• Forming Tools: Hydraulic crimping tool (crimping range 60–200 mm²), heat gun (temperature range 50–600°C), lead sealing dedicated torch (flame temperature ≤ 300°C).

• Testing Tools: Megohmmeter (2500 V, range 0–10000 MΩ), double-arm bridge (contact resistance measurement, accuracy ±0.1 μΩ), ultrasonic thickness gauge (resolution 0.01 mm).

IV. Detailed Repair Procedures by Damage Type

(A) Mechanical Damage Repair (Aluminum Sheath Example)

• Damage Area Preparation

• Gamitin ang angle grinder upang buksan ang damaged sheath axially, na may cut length na 5 beses ang damage diameter (minimum ≥ 100 mm), na nagpapakita ng clean insulation shield.

• Alisin ang burrs mula sa edges ng sheath gamit ang stainless steel scraper, sand to metallic luster, linisin ang oil gamit ang ethanol, at dry for ≥ 15 min.

• Metallic Sheath Restoration

• Pumili ng aluminum alloy compression sleeve na may inner diameter na 1 mm mas malaki kaysa sa cable outer diameter, uniformly coat inner wall with conductive grease (nickel-based filler, volume resistivity ≤ 5×10⁻⁴ Ω·cm).

• Ilipat ang sleeve sa damaged area, gamitin ang Staggered Crimping method, crimp from center to ends. After crimping, hexagonal opposite-side deviation ≤ ±0.1 mm, contact resistance ≤ 20 μΩ.

• Sealing and Anti-Corrosion Treatment

• I-wrap ang butyl rubber sealing tape na may 50% overlap, porma ng sealing layer ≥ 3 mm thick, extending ≥ 50 mm beyond undamaged sheath on both ends.

• Install heat-shrink tubing, heat gradually from center to ends (120°C → 140°C) to avoid bubbles. After cooling, check uniform shrinkage (post-shrinkage wall thickness ≥ 2 mm).

• Wrap PVC corrosion-resistant tape externally in a half-overlap spiral, secure ends with stainless steel straps (torque 15–20 N·m).

(B) Electrochemical Corrosion Repair (Steel Armor + Lead Sheath Composite Sheath)

• Corrosion Product Removal

• Gamitin ang sandblasting (quartz sand 80–120 mesh, pressure 0.4–0.6 MPa) upang alisin ang rust mula sa steel armor, nagpapakita ng gray-white metal base, surface roughness Sa2.5 grade.

• Trim lead sheath corrosion area with a lead plane, forming a smooth transition with slope ≥ 1:5 to avoid stress concentration.

• Sacrificial Anode Protection

• Symmetrically install 2 zinc-aluminum alloy anodes (100 mm × 50 mm × 10 mm) on both sides of the repair section, connected to steel armor via copper braid (cross-section ≥ 16 mm²), welded (lap length ≥ 30 mm, welding current 120–150 A).

• Fill gap between anode and cable sheath with petroleum jelly, encapsulate externally with high-density polyethylene (HDPE) housing to ensure full soil contact.

• Dual Sealing Structure

• Inner layer: cold-shrink silicone rubber tubing, inner wall coated with semiconductive water-blocking gel (volume resistivity 10–100 Ω·cm). Maintain at room temperature for 24 h after recovery for curing.

• Outer layer: pour epoxy resin (E-51 type, curing agent T-31, ratio 100:25), mold sealed at 0.2 MPa pressure, cure ≥ 48 h at 25°C. Post-cure Shore hardness ≥ 85 Shore D.

(C) Thermal Aging Cracking Repair (XLPE Insulated Cable)

• Crack Area Reinforcement

• Cut a V-groove along the crack direction (depth 1/3 of sheath thickness, angle 60°), fill with heat-resistant silicone rubber (temperature rating ≥ 180°C, tear strength ≥ 15 kN/m), level with scraper, cure at room temperature for 2 h.

• Wrap glass fiber cloth (0.2 mm thick, 16×16 threads/cm), impregnate with epoxy resin (solid content ≥ 70%) to form a reinforcement layer. Tensile strength ≥ 200 MPa after curing.

• Heat Dissipation Optimization

• Install aluminum heat sinks (1.5 mm thick, fin spacing 5 mm) externally on the repair section, bonded to sheath with thermal grease (thermal conductivity ≥ 1.5 W/(m·K)) to reduce local temperature rise (≤ 5°C).

• Monitor operating temperature with infrared thermal imager, ensuring temperature difference from undamaged section ≤ 2°C.

V. Quality Control and Acceptance Standards

(A) Key Parameter Testing

• Electrical Performance: Sheath insulation resistance ≥ 1000 MΩ (2500 V megohmmeter), partial discharge ≤ 5 pC (at 1.73U₀ voltage).

• Mechanical Performance: Impact resistance of repair section ≥ 10 J (at -30°C), bending radius ≥ 20 times cable outer diameter (no obvious deformation).

• Sealing Performance: After immersion test (room temperature, 24 h), sheath leakage current change rate ≤ 10%, no bubbles or water ingress.

(B) Long-Term Reliability Verification

• Accelerated Aging Test: Place repair sample in thermal aging chamber (135°C × 1000 h), after removal insulation resistance retention ≥ 80%, tensile strength degradation ≤ 20%.

• Soil Burial Test: Simulate actual laying environment, buried depth 1 m, duration 1 year, check for no corrosion perforation or seal failure.

VI. Safety Operation Regulations

• Power-Off Work Requirements: Follow "power-off - voltage test - grounding wire installation" procedure before repair. Hang "Do Not Close" warning signs on cable terminations, set safety barriers (distance ≥ 8 m) within work radius.

• Hot Work Management: When using torches or welding, equip dry powder fire extinguishers (ABC type, capacity ≥ 4 kg), clear flammable materials within 3 m, assign a dedicated supervisor.

• Personal Protective Equipment (PPE): Wear insulated gloves (35 kV rating), goggles, flame-resistant workwear. Use safety harness (static load test force 2205 N, hold 3 min without break) for work at heights (≥ 2 m).