nouvelles de l'entreprise How to Protect ACSR and ACCC Conductors from Mechanical Damage During Tension Stringing

ACSR and ACCC fail differently, and treating them the same is how projects lose conductor. ACSR tolerates moderate bending and local pressure but work-hardens and loses strength once strands are nicked or flattened. ACCC, with its composite carbon or glass core, carries tension well but is far less forgiving of sharp bending, localised clamping pressure and any bend beyond its core's elastic limit. The same crew needs two sets of habits, and the difference is measurable in sheave diameter, groove condition and clamp torque.

The construction problem: invisible damage

ACSR damage is usually visible: flattened strands, a polished stripe, broken outer wires. ACCC damage frequently is not. A composite core bent past its limit loses strength permanently without any external sign, and the conductor passes inspection, passes the sag check, and fails later in service. That asymmetry is the reason ACCC work must be controlled by method rather than by inspection.

Technical cause: bending, contact and clamping

Three mechanisms dominate. Bending at sheaves and bull-wheels imposes strain proportional to wire diameter over wheel diameter. Contact pressure at groove and clamp surfaces follows p = 2T/(D·b), so tension and contact width together decide local stress. And clamping introduces a third stress concentration at the jaws, where a radius smaller than the conductor flattens strands and can crush a composite core.

The usual rule for ACSR is a sheave or bull-wheel diameter of at least 40 times conductor diameter with a groove radius within about 5 percent of conductor radius. For ACCC, good practice pushes the ratio to 45 or 50 times diameter, because the core does not yield gracefully. Reverse bending between adjacent blocks is the most damaging configuration of all: it fatigues the aluminium layers on ACSR and is the most common route to core damage on ACCC.

Parameter examples: block and machine ratings

The point of listing ratings is that conductor protection fails most often at the small hardware, not the big machine. A 10 kN block in a 30 kN run, or a seized sheave in a 40 kN run, produces more damage than a slightly undersized bull-wheel ever will.

ACCC also responds differently to clamping. The aluminium layers expand more than the composite core as temperature rises, so an over-torqued clamp concentrates stress at the transition between layers. Jaw radius and clamp length matter as much as clamp tonnage, and if a clamp has to be repositioned mid-section, stop the pull rather than working quickly under load.

Field handling: method control for both conductor types

• Select sheave and bull-wheel diameters against the 40D rule for ACSR and 45 to 50D for ACCC, and record the calculation in the method statement.
• Use conductor-matched pulling grips and come-along clamps, torqued to the manufacturer's figure; over-torque creates ovalisation that later becomes a hot spot.
• Run in a consistent bending direction and design out reverse bends between adjacent blocks.
• Build tension progressively at the start of the pull; a step load is a shock load, and shock is what nicks strands.
• Inspect the first 50 m of conductor immediately after the pull, before accepting the run, and photograph the result.
• Keep tension inside the machine's published continuous range, which is a conductor-protection limit as much as a machine limit.

Matched hardware: the 77 kW GL2×70 twin-bundle tensioner, the aluminium nylon wheel conductor stringing blocks, the GXSH terminal tackle blocks and the seven-sheave running-out block.

FAQ

Can the same sheaves be used for ACSR and ACCC?

Physically yes, but the ACCC run should use the largest sheaves in your inventory and the best-condition grooves. The margin is smaller and damage is not visible.

What does ACCC core damage look like?

Usually nothing externally. Detection depends on bend radius control during installation plus tension and elongation records, not on visual inspection.

Is birdcaging a conductor defect?

Almost never. Birdcaging is an installation event caused by sudden tension release or reverse bending, not a manufacturing fault.