Overhead Transmission Line Sag Monitoring Using a Chirped-Pulse Phase-Sensitive OTDR

The capacity of overhead transmission lines is fixed and determined by the physical properties of the line, which are estimated based on worst-case weather scenarios. Exceeding the capacity limit can cause the conductor to increase the sag excessively, bringing it too close to the ground and creating a safety risk. Real-time monitoring of the sag value enables dynamic capacity configuration, thereby reducing safety risks and improving the efficiency of the transmission line. Distributed acoustic sensing based on chirped-pulse phase-sensitive optical time-domain reflectometry (CP-
$\Phi $
OTDR) can be used to measure the vibration induced by wind on the cable line taking advantage of the optical fiber already deployed in the power line. An analysis of the recovered strain in the frequency domain reveals multiple frequency components related to the cable’s current mechanical state. By identifying the fundamental frequency, it becomes possible to quantitatively calculate the sag. Tracking the central frequency of each span allows for the monitoring of the sag for each span of the line using just one single-end interrogator.