Low Road Clearance on a Leaning 11 kV PCC Pole
An 11 kV overhead line crosses a village road on a 65 m span between two 9 m PCC poles. The conductor is ACSR Rabbit and the line was erected three years ago. After a monsoon storm, the road-side pole leans about 4 degrees toward the road, and the conductor sag has increased. At the road centre, the measured clearance is 5.2 m. The required clearance for an 11 kV line across a road is 5.5 m. The pole foundation is in black cotton soil, and the stay wire on the road side is missing. The conductor shows no broken strands, but one insulator has a chipped shed. The road is a bus route and cannot be closed for more than two hours at a time. The lineman has a hydraulic conductor tensioner, a sag template, stay wire and an earth auger, but no new pole of the same length.
1. Assess the immediate risk and decide whether to re-tension, replace the pole, or install a temporary measure. Justify your choice.
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The immediate risk is a bus touching an 11 kV conductor with only 5.2 m clearance, below the required 5.5 m. The leaning pole and missing stay mean the line is moving in the wrong direction. Re-tensioning alone would increase the pull on an already unstable pole and could make it lean further. There is no replacement pole of the same length, so a same-day pole replacement is not realistic. The correct immediate action is to treat the line as unsafe: inform the control room, isolate and earth the section, barricade the road, and arrange a short shutdown. Install a temporary road-side stay or guy to hold the pole, and support the conductor if needed. Plan the permanent repair for a low-traffic window, with a crane or a new pole if the foundation cannot be stabilised.
2. Explain how you would restore clearance using the available resources, including sag and tension considerations.
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First stabilise the pole: excavate around the base, check for rot or cracking, and re-compact or concrete the foundation. Install a proper stay anchor in undisturbed soil on the side opposite the road, with a stay wire and insulator. Then re-string the conductor with the hydraulic tensioner. Use the sag template at the measured conductor temperature and aim for a sag that gives more than 5.5 m clearance at the highest expected temperature, not just at the current morning temperature. Do not over-tension to gain clearance; that increases pole load and reduces safety factor. Replace the chipped insulator. If the stay and re-tensioning cannot achieve the clearance, the span must be shortened with an intermediate pole or the line rerouted; a temporary height barrier is not a substitute for electrical clearance.
3. What safety and road-management measures are required during the work?
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Obtain a permit and a short planned shutdown. Prove dead, apply earths on both sides of the span, and use fall arrest. Set out traffic signs, cones and barricades well before the work area, use trained flagmen, and keep the road open to one lane if possible. Do not work during school opening or bus peak times. Keep the public away from the stay anchor and winch. Use insulated tools and a tested voltage detector. After re-stringing, measure clearance at the road centre and at the edges, record the temperature, remove earths, cancel the permit, and inspect the stay and foundation after the first rain.