Describe the term "sag" in the context of overhead power lines.

In the context of overhead power lines, "sag" refers specifically to the downward curve of a cable that occurs as a result of the weight of the cable and the tension applied to it. When a power line is installed between two poles, the cable is subject to gravitational forces that cause it to bend or sag in the middle. This sag is essential for a few reasons, including ensuring that the cable maintains the proper tension and avoids excessive strain on the supporting structures. Additionally, sag allows for thermal expansion and contraction of the cable, as well as accommodating wind and environmental factors without compromising the integrity of the installation. Properly managing sag is crucial for maintaining safe clearances above the ground and ensuring reliable operation of the power transmission system.