What is Sag.?
In electrical power transmission and mechanical design of overhead transmission line.
SAG.
A perfectly flexible wire of uniform cross-section, when string between the two supports at the same level, will form a catenary. However, if the sag is very small compared to the span, its shape approximation a parabola.
The difference in level between the point of support and the lowest point on the conductor is known as sag
The factors affecting the sag in an overhead line are given below.
1. Weight of the Conductor,
This affect the sag directly. Heavier the conductor, greater will be the sag. In locations where ice formation takes place on the conductor, this will also cause increase in the sag.
2. Length Of the Span.
This also affect the sag. Sag is directly proportional to the square of the span length Hence other conditions, such as type of conductor, working tension, temperature etc. remaining the same a section with longer span will have much greater sag.
3. Working Tensile Strength.
The sag is inversely proportional to the working tensile strength of conductor if other conditions such as temperature, length of span remain the same. Working tensile strength of the conductor is determined by multiplying the ultimate stress and area of cross section and dividing by a factor of safety.
4. Temperature.
All metallic bodies expand with the rise in temperature and, therefore. The length of the conductor increases with the rise in temperature, and so does the sag.
Reference from .
Transmission and distribution of electrical power by-J.B.Gupta.
