Calculation and Analysis of Transmission Line Sag Based on Theoretical Mechanics

Sag, as one of the critical parameters relating to the operation and maintenance of overhead transmission lines, directly impacts their safe and stable operation. Various factors, such as line operating load, conductor temperature, stress, overlying ice thickness on the conductor, and surrounding wind speed, can cause fluctuations in the line sag. This paper addresses the issue of overhead transmission line sag by conducting a stress analysis of conductors, proposing a sag calculation method, verifying its accuracy through conductor sag tests, and analyzing the impact of span and conductor temperature on sag. The results revealed that four parameters are required for sag calculation, namely the lowest point stress of the conductor, the unit linear load of the conductor, the angle of elevation between suspension points, and the span. The lowest point stress of the conductor requires solving the equation of state for the conductor, whereas other parameters can be directly acquired from the specific conditions of the transmission line project. As the span increases, the conductor sag increases continuously, and the same holds true for the increase in the conductor sag with temperature.