Conductor damage at the bull-wheel rarely announces itself. It appears at the end of a pull as a polished stripe along one side of the conductor, a flattened band of outer strands, or a scatter of broken aluminium wires two spans back from the tower. By the time the crew sees it, the machine has already done the work. Almost every case traces back to three geometric parameters fixed long before the pull started: bull-wheel diameter, groove radius and groove lining.
Field damage on tension-stringed conductor falls into recognisable patterns. Flattening or ovalisation of the outer layer points to excessive radial contact pressure. A bright polished stripe with aluminium smearing points to sliding contact, meaning the conductor was slipping or the groove lining was worn through to steel. Broken outer strands close to a suspension clamp usually mean accumulated bending fatigue, each pass over an undersized sheave taking a small bite out of the strand's fatigue life. Birdcaging is different again and normally comes from a sudden tension release rather than from the wheel itself.
As a conductor wraps a bull-wheel, the outer wires are stretched and the inner wires compressed. The strain in the outermost wire is approximately the wire diameter divided by the wheel diameter, ε ≈ dwire / Dwheel. A 3.2 mm outer aluminium strand on a 1300 mm wheel sees 0.25 percent strain; on a 960 mm wheel, 0.33 percent; on a 660 mm sheave, 0.48 percent. Aluminium begins to yield and work-harden in the region of 0.3 to 0.5 percent, so a small sheave consumes fatigue life on every pass, silently and irreversibly.
Common design guidance is at least 40 times conductor diameter for ACSR and about 25 times for earth wire or OPGW, so a 40 mm conductor wants 1600 mm of wheel diameter to stay inside the safe band.
The conductor must sit on an arc, not on two shoulders. Radial contact pressure per unit length follows p = 2T / (D · b), where b is the effective contact width. At 40 kN on a 1300 mm wheel with 50 mm of contact, that is about 1.2 MPa. At 120 kN on a 960 mm wheel with only 40 mm of effective contact, it rises to roughly 6.3 MPa, five times higher on a machine that is only three times stronger. Reduce the contact width by using a groove worn below its shoulders and the pressure climbs again. On a multi-pass pull the outer layer can be visibly flattened without any single overload event.
Steel-on-aluminium contact both abrades the conductor and provides a low, unstable coefficient of friction. Interchangeable nylon or polymer groove sectors, as used on our hydraulic puller-tensioners, deform locally under load, spread the pressure over a wider arc and raise friction against aluminium. That combination protects the surface and increases holding capacity at the same time, which is why high-resistance interchangeable nylon sectors are specified on machines intended for conductor rather than pilot rope.
| Model | Bull-wheel | Grooves | Max rope | Published rating |
|---|---|---|---|---|
| GX60 / SA-QY60 puller | 1300 / 1500 mm | 7 | 18 mm | 60 kN intermittent, 50 kN continuous |
| SA-QY120 puller | 1300 / 1500 mm | 7 | 18 mm | 120 kN intermittent, 100 kN continuous, 129 kW (173 hp) |
| GS280 quad puller | 960 mm | 11 | 38 mm | 280 kN max, 250 kN sustained at 2.5 km/h |
| GL2×70 tensioner | 1300 / 1500 mm | twin capstan | — | twin bundle 630 mm² in mountains, 720 mm² on flat land |
| GXSHS running-out block | 508 × 75 mm or 660 × 100 mm | 7 sheaves | conductor ≤ 400 mm² | rated load 40 kN |
| GXSH80J terminal block | 180 × 56 mm | single | — | rated load 80 kN |
Read the table as a design pattern: the 960 mm wheel on a 280 kN puller trades diameter for eleven grooves because wrap angle carries the load at 38 mm rope, while 1300 to 1500 mm wheels on 60 to 120 kN machines protect a 40 mm conductor from bending strain. These are published catalogue ratings; the binding numbers for a project are the FAT record and the site tension log.
Representative hardware for this analysis: the GX60 seven-slot 60 kN hydraulic puller, the SA-QY120 120 kN puller, the GS280 quad conductor puller and the seven-sheave running-out block.
For bending strain, yes, until the machine becomes impractical to move. Beyond roughly 1500 mm the gain per extra millimetre is small, and groove condition and lining matter more than another 100 mm.
Only at reduced tension with matched, nylon-lined grooves. Twenty-four times diameter is below the 40D guideline, so expect measurable outer strand strain and inspect the run immediately afterwards.
Before every new site, after every 30 to 50 km of conductor pulled, and after any incident where the rope jumped the groove.
اتصل شخص: Mr. Marble Wu
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