Causes and Solutions for Conductor Pull-out in High-Voltage Cables

The fundamental causes and systematic solutions for conductor pull-out (commonly called "core slippage") in high-voltage cables are as follows:

Cause Analysis

1. Interface Bonding Failure
Cross-linking process defects: Insufficient steam cross-linking temperature (<200°C) or duration (<4h), preventing effective chemical bonding between XLPE and conductor
Contamination layer: Residual drawing lubricant (oil film thickness >0.5μm) or oxide layer (Cu₂O >100nm) on conductor surface
2. Material Compatibility Issues
Substandard conductor roughness: Ra >1.6μm (GB/T 3953 requires 0.8-1.2μm)
Insulation material defects: Tensile strength <15MPa (IEC 60502 requires ≥17MPa)
3. Mechanical Stress Imbalance
Thermal shrinkage mismatch: XLPE shrinkage rate (1.5%) vs. metal conductor (0.017%)
Insufficient bending radius: Installation bending radius <12D (D=cable OD) causing interfacial shear stress >3N/mm²

Solutions

1. Process Optimization
Conductor treatment:
Plasma cleaning (Ar gas, 300W power, 5m/min speed)
Silane coupling agent coating (KH-550, 0.2-0.5μm thickness)
Cross-linking process:
Temperature gradient: 180℃→220℃→250℃ (≥30min per stage)
Nitrogen dew point: <-60℃
2. Material Upgrades
Conductor with micron-level alumina sandblasting (Ra=1.0±0.1μm)
Modified XLPE (0.5wt% maleic anhydride graft additive)
3. Structural Improvements
Add semi-conductive buffer layer (0.5mm thickness, 10²-10³Ω·cm resistivity)
Stranded conductor compression rate ≥15% (compaction factor 0.90-0.93)

Key Testing Standards

1. Peel Force Test (GB/T 12706.2)
≥50N/cm at 25°C
≥30N/cm at 90°C
2. Thermal Cycling Test (IEC 60840)
Displacement <5mm after 3 cycles (-30℃~+130℃)
3. Cross-section Analysis
SEM observation of interface diffusion layer (>5μm thickness)

Engineering Preventive Measures

1. Installation Specifications:
Minimum bending radius ≥15D (dynamic) or 12D (static)
Maximum pulling tension ≤20N/mm² (copper) or 15N/mm² (aluminum)
2. Online Monitoring:
IR thermography for conductor preheat (80±5℃)
Laser roughness meter for real-time monitoring (Ra alarm threshold >1.5μm)
Case Study: A 110kV cable increased peel force from 28N/cm to 65N/cm by adding semi-conductive water-blocking tape + conductor sandblasting.
Note: High-voltage cables refer to power cables with rated voltage ≥35kV.