Erection and Stringing
Domain 7 - Erection and Stringing. Questions focus on the order of operations, sag control, binding, jointing and pre-charging checks.
Method
- Pay out conductor over rollers or running-out blocks; never drag ACSR along the ground or around sharp bends.
- HT work uses tension stringing with a puller and brake; LT work is commonly hand-pulled with a dynamometer and come-along.
- Set sag from the stringing chart for the actual conductor temperature, measured with a sag template or by sighting, and record temperature, tension and sag.
- Bind conductor to pin insulators with the correct binding wire, using armour rods or tape on aluminium to prevent abrasion; dead-end with strain clamps; make jumpers with proper clamps, never twists.
- Fit phase plates and guard wires at crossings, then check clearances, continuity and insulation resistance before charging.
Worked example
For a 60 m span with 0.75 m sag, the conductor is longer than the span by 8S²/(3L) = 8(0.75)²/(3 × 60) = 0.025 m, that is 25 mm per span. Over 100 spans, about 2.5 m of extra conductor must come from the drum; if the store issues exactly the route length, the final spans will come up short and a joint will be forced into a bad location.
Traps
- Setting sag by eye without noting conductor temperature, so a cold-morning sag becomes excessive at noon.
- Over-tensioning to make the line look straight, overloading poles and stays.
- Placing joints in road crossing spans or stayed spans.
- Charging a completed line without verifying phase sequence and insulation resistance.