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Home Technical Articles Optimization of MPP Power Pipes ——Long-Term Reliability Design for 10kV-35kV Cable Current Carrying Capacity

Technical Articles

Optimization of MPP Power Pipes ——Long-Term Reliability Design for 10kV-35kV Cable Current Carrying Capacity

/ Post by by 孙飞虎

1. Research Background


MPP (Modified Polypropylene) power pipes play a critical role in urban power grid upgrades due to their Vicat Softening Temperature (VST) ≥ 120℃, outperforming ordinary PE pipes. However, State Grid testing reveals:


  • When cable current exceeds 600A, long-term operating temperature reaches 85-95℃
  • Traditional MPP pipes exhibit 3.2% creep strain at 80℃/10MPa after 5000 hours (close to failure threshold 3.5%)

2. Core Issue: Thermo-Mechanical Coupling Failure Mechanism

2.1 Three-Stage Creep Process


Through Dynamic Mechanical Analysis (DMA) and long-term hydrostatic tests (GB/T 6111-2018), MPP pipe creep behavior is divided into: ![Creep Curve Schematic](Figure 1)


  • Instantaneous Elastic Deformation (0-100h): Strain <0.5%
  • Steady-State Creep (100-5000h): Strain rate 0.002%/h
  • Accelerated Failure (>5000h): Plastic deformation from crystalline melting

2.2 Key Influencing Parameters


Parameter GB Requirement Field Measurement Influence
Melt Index (MI, g/10min) ≤0.5 0.6-0.8 ★★★★☆
Crystallinity (%) - 42-45 ★★★☆☆
Thermal Conductivity (W/(m·K)) 0.22-0.24 0.20-0.21 ★★☆☆☆

3. High-Temperature Modification Experiments

3.1 Multi-Scale Composite Reinforcement


Developed "organic-inorganic" hybrid modification with a three-layer structure (Figure 2):


  • Inner Layer: 5% graphene thermal conductive layer (conductivity increased to 0.35W/(m·K))
  • Middle Layer: 20% long glass fiber reinforcement (modulus +120%)
  • Outer Layer: POE toughening layer (elongation at break >300%)

3.2 Thermo-Mechanical Properties


Material Type VST(℃) 80℃/10MPa Creep Strain (5000h) Coefficient of Thermal Expansion (×10⁻⁵/℃)
Traditional MPP 125 3.2% 10.5
Modified MPP 138 1.8% 7.2
CPVC 110 2.5% 7.8

4. Engineering Solutions

4.1 Current-Carrying Capacity-Creep Co-Design


Established cable-pipe heat transfer model (Figure 3):\(T_{pipe} = T_{ambient} + \frac{Q \cdot R_{th}}{2\pi L}\) Where:


  • Q = cable loss (W/m), \(R_{th}\) = thermal resistance (m·K/W)
  • Target: \(T_{pipe} \leq 0.8 \cdot VST\)

4.2 Layered Laying Construction


For ≤110kV cable trenches:


  1. Insulation Layer: 50mm aerogel mat (thermal resistance >1.5m·K/W)
  2. Heat Dissipation Layer: T-shaped fins every 20m (surface area +40%)
  3. Monitoring Layer: Fiber Bragg grating sensors (accuracy ±0.5℃)

5. Field Test Case: Substation Outlet Project


Index Traditional MPP Modified MPP Standard Requirement
Long-term temp (℃) 92 81 ≤90
5-year creep strain (%) 2.7 1.2 ≤3.0
Cable current (A) 650 780 -

6. Future Technologies

6.1 Shape Memory Alloy Composite Pipe


Embedded NiTi alloy wires (Figure 4) trigger self-constrained deformation at >100℃, achieving 75% creep reduction.

6.2 Smart Creep Warning System


Based on LSTM neural network, predicts:


  • Remaining service life (±10% accuracy)
  • Critical current threshold (warning lead time >30 days)


Conclusion This paper solves creep issues under high current through material modification + thermal design + intelligent monitoring. As a professional supplier, we offer: ✅ Customized high-temperature pipes (VST 120℃-150℃) ✅ Cable-pipe thermal matching calculations ✅ Creep failure life assessment reports


Keywords: MPP power pipe, high-temperature creep, current carrying capacity, long-term reliability, power pipeline

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