What is a sag of transmission line?

The sag of a transmission line refers to the vertical displacement or dip of the line between two support structures, such as towers or poles, due to the weight of the conductor and the tension applied to it. Sag is a crucial factor in transmission line design, as it ensures adequate clearance from the ground and surrounding structures, while also allowing for thermal expansion and contraction of the conductors. Proper sag calculations help prevent mechanical stress and potential failure of the line under various environmental conditions.