Standards: GB/T 7971-2007 'Semiconductive Cable Paper' and IEC 60554. This is a specialised integrated cushioning and shielding material for high-voltage oil-immersed cables, cable accessories, and special-purpose cables for wind power and locomotives. It is a black strip with regular corrugations, combining the dual functions of semiconductive potential-equalising shielding and elastic cushioning.

Production Process

Carbon black is incorporated into the pulp during the papermaking process to form an integrated product (volumetric conductivity, mainstream process), ensuring uniform electrical resistance and preventing the shedding of carbon black particles.

1. Raw Material Preparation
Base pulp: 100% high-purity sulphate softwood insulation pulp, α-cellulose ≥92%, low ash content and low metal ion content, serving as the base insulation substrate;
Conductive filler: nano-conductive carbon black (particle size 25–200 nm), added at 5%–8%, combined with a dispersant to prevent agglomeration;
Water quality: deionised water used throughout the process, free from calcium and magnesium impurities, to prevent partial discharge under high voltage.
2. Production of semi-conductive base paper on a special fourdrinier paper machine
Pulp concentration at the wire: 0.3%–0.5%, evenly distributed via a double-layer flow headbox;
Low-temperature gradient drying (80–110 °C), with finished moisture content controlled at 5%–7%;
Light calendering to ensure a smooth paper surface, in preparation for subsequent creasing.

3. Mechanical longitudinal crimping
The semi-conductive base paper is fed into a specialised crimping machine, where toothed rollers compress it to form regular longitudinal corrugations;
Control of crimp height and elongation rate: elongation at break ≥20%, with recovery after stretching;
4. Post-processing and finished product testing
Slitting: cut into strips according to cable wrapping width (20/25/30/40 mm, etc.);
Comprehensive testing: volume resistivity, elongation, tensile strength, oil absorption, thermal ageing and partial discharge.

Product Characteristics

(I) Semiconductive Electrical Properties:

1. Controllable volume resistivity: 10³–10⁹ Ω·cm, falling between that of conductors and insulators; this enables the stable dissipation of surface charge and the smoothing of electric field gradients;

2. Voltage equalisation to suppress partial discharge: by enveloping the uneven surfaces of stranded conductors, it eliminates electric field concentration at the tips, resulting in a partial discharge level of ≤5 pC;

3. Oil-immersion compatibility: Compatible with transformer oil and cable impregnation oil; electrical conductivity remains stable after oil immersion;

4. Integrated conductivity advantage: Carbon black is distributed within the fibres; no black powder is shed during stretching or bending, thus preventing contamination of the main insulation.

(II) Mechanical cushioning properties of the crinkled structure (unique advantage)

1. Highly elastic expansion: Longitudinal elongation ≥ 20%; adapts to deformation caused by thermal expansion and cable bending;

2. Exceptional conformability: Perfectly envelops multi-strand twisted wires and irregular conductors, filling gaps between conductors without leaving voids;

3. Tear resistance and winding durability: Longitudinal tensile strength ≥ 4.2 kN/m; does not rupture or fray during high-speed winding;

4. Shock Absorption and Vibration Damping: Absorbs thermal expansion and contraction stresses caused by electrical heating, preventing cracking of the insulation layer.

5. Standard Specifications

• Thickness: 0.05 mm, 0.08 mm, 0.13 mm;

• Weight: 112 ± 5 g/m²;

• Colour: Pure black, facilitating identification of the shielding layer during production;

• Elongation: ≥20%;

• Surface resistance: 6 kΩ–20 kΩ (customisable resistance values).

Application Scenarios in the Cable Industry

01/

High-voltage oil-immersed power cables (110 kV–500 kV phase-separated oil-filled cables) Application: Conductor internal shielding buffer layer Process flow: Copper stranded conductor → Multi-layer wrapping with semi-conductive crimped paper → High-voltage cable insulation paper (main insulation) Function: The surface of the stranded conductor is uneven, preventing plain semi-conductive paper from adhering tightly; the crimped paper utilises its elasticity to fill gaps, uniformising the electric field across the conductor surface and eliminating partial discharge; it also cushions thermal expansion stresses on the conductor.

02/

Specialised wind power cables (high-voltage cables for wind turbine towers and nacelles) Wind turbine cables are subject to prolonged torsion, bending and significant temperature fluctuations: semi-conductive crimped paper is used for the inner conductor shielding; Advantages: no decarburisation even after repeated bending; elasticity offsets torsional stress; replaces semi-conductive rubber tape, reducing cable outer diameter and weight.

03/

Rail transport / locomotive traction high-voltage cables

04/

Current transformers, dry-type special-purpose cable leads

05/

High-voltage cable terminations and jointing accessories (core material for stress cones): These cable accessories experience the most severe electric field distortion and are high-risk areas for breakdown:
• Semiconductive crimped paper fills the stress cone, smoothing out the abrupt changes in the electric field at the insulation discontinuity;
• Soft and malleable, it conforms to the complex curved surfaces of the accessories, significantly reducing partial discharge faults at terminations.

06/

Submarine oil-filled cables and long-distance underground power transmission cables, which experience significant thermal expansion and contraction over long distances:
• Combines the dual functions of shielding and oil-storage buffering; stores impregnated oil to compensate for changes in oil volume, preventing air and water ingress into the sheath due to negative pressure.

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