105°C Medium Voltage Polypropylene Insulated Cable Development

Time: 2025-04-14 12:36:34 Source: Henan Province Jianyun Cable Co., Ltd.

1. Introduction
2. Cable Structure and Insulation Design
3. Key Parameters: Thickness, Utilization, and Safety
4. Current-Carrying Capacity Analysis
5. Performance Testing
6. Field Application
7. Conclusion

1. Introduction

Cross-linked polyethylene (XLPE) is widely used in power cables but has limitations including non-recyclability, high energy consumption, and harmful byproducts. In contrast, polypropylene (PP) is a thermoplastic, recyclable material with excellent thermal and mechanical properties. This study presents the design and performance of PP-insulated power cables for 8.7/15 kV and 26/35 kV systems, with enhanced long-term operating temperature of 105°C.

2. Cable Structure and Insulation Design

The cable uses a tri-layer co-extrusion process with PP-based shielding and insulation. Key structural features include PP conductor shielding, insulation layer, insulation shielding, copper tape, fillers, armor, and outer sheath. Temperature control during extrusion ensures low internal stress and improved dielectric performance.

2.1 Insulation Material Composition

Modified PP resin blended with POE elastomer and stabilizers. Dielectric strength: >35 kV/mm; actual: 39–41 kV/mm.

2.2 Nominal Insulation Thickness Calculation

For 26/35 kV systems: theoretical value = 1.38 mm, corrected with temperature, aging, and safety factors = 4.79 mm. For 8.7/15 kV systems: nominal insulation thickness = 3.7 mm. For impulse voltage, final nominal thickness = 7.6 mm.

3. Key Parameters: Thickness, Utilization, and Safety

3.1 Insulation Utilization Factor (η)

Example calculation for 3×300 mm² cable at 26/35 kV yields η = 0.76, confirming efficient electric field distribution.

3.2 Insulation Safety Margin (m)

For 26/35 kV cables, m = 1.39. Range of 1.2–1.6 ensures sufficient overvoltage protection.

4. Current-Carrying Capacity Analysis

Ampacity (carrying current) of PP-insulated cable is calculated using standard formulas, considering 105°C operation.

4.1 Calculated Ampacity

For 3×300 mm² cables:

Voltage Level (kV)	Installation	PP Cable (A)	XLPE Cable (A)	Improvement (%)
26/35	Buried	545	500	9.00
26/35	In Air	591	521	13.44
8.7/15	Buried	545	500	9.00
8.7/15	In Air	582	512	13.67

5. Performance Testing

5.1 Mechanical Tests

Tests include aging, shrinkage, water absorption, thermal shock, and low-temperature tensile. Results meet GB/T 12706.3—2020 standards.

Test Item	Requirement	Group 1	Group 2	Group 3
Tensile Strength (Before Aging)	≥12.5	33	34	31
Elongation at Break (%)	≥450	540	510	530
Shrinkage (%)	≤4	1	1	1
Water Absorption (mg/cm²)	≤1	0.08	0.08	0.09

5.2 Electrical Tests

Test	Condition	Result
tanδ Measurement	110–115°C, 2 kV	2.9×10⁻⁴ (≤1.0×10⁻³)
Impulse Voltage	200 kV, ±10 times	No breakdown
AC Withstand	65 kV, 15 min	No breakdown
Power Frequency Withstand	4U₀, 4 h	No breakdown

5.3 Flame Retardant & Halogen-Free Tests

Item	Standard	Result
Acid Gas Content (%)	≤0.5	<0.5
pH	≥4.3	5.4
Conductivity (μS/mm)	≤10	0.26
Smoke Density (% light transmittance)	≥60	78
Vertical Flame Propagation	≤2.5 m	0.25 m

6. Field Application

A 3×400 mm² PP cable has been in service in Qingdao Industrial Zone since 2023, with no operational issues. Routine inspections and testing confirm compliance with GB 50150-2016 standards.

7. Conclusion

The development of 105°C medium voltage PP-insulated cables offers an eco-friendly, recyclable alternative to XLPE, with improved current-carrying capacity and thermal performance. The cables perform reliably in both laboratory and field environments, with significant benefits in electrical safety margin and environmental impact. Future work will focus on long-term reliability under multiple stress conditions.