Question

A transmission line has a span of 200 metres between level supports. The conductor has a cross-sectional area of 1.29 cm² , weighs 1,170 kg/km and has a breaking stress of 4,218 kg/cm² . Calculate the sag for a factor of safety of 5 allowing a wind pressure of 122 kg per m² of projected area. What is the vertical sag?

Answer 1

working stress = 4,218/5 = 843.6 kg/cm²

Working tension T = 843.6 × 1.29 = 1,088 kg.wt 

∴ W = 1,170 kg/km = 1.17 kg.wt/metre

Let us now find diameter of the conductor from the equation

πd² /4 = 1.29 or d = 1.28 cm

∴ Projected area of the conductor per metre length is = 1.28 × 10⁻² × 1 = 1.28 × 10⁻² m²