What are the effect of temperature on Sag in an overhead line?
What are the effect of temperature on Sag in an overhead line?
Sag is the vertical difference in level between points of support and the lowest point of the conductor. Sag is important to consider because it affects the clearance, tension, and length of the overhead line.
Temperature has a significant impact on sag because it causes the conductor to expand or contract due to thermal expansion and elastic elongation.
When the temperature increases, the conductor expands and becomes longer, which increases the sag and decreases the tension. When the temperature decreases, the conductor contracts and becomes shorter, which decreases the sag and increases the tension.
The formula for calculating sag depends on whether the supports are at equal or unequal levels. For equal level supports, sag can be calculated by using this formula¹:$$S = \\frac{wL^2}{8T}$$where S is sag, w is weight per unit length of the conductor, L is length of the span, and T is tension in the conductor.
For unequal level supports, sag can be calculated by using this formula¹:$$S = \\frac{wL^2}{8T} + \\frac{h^2}{2L}$$where h is the difference in height between the supports.
