A survey of sag monitoring methods for power grid transmission lines

The transmission line is a fundamental asset in the power grid. The sag condition of the transmission line between two support towers requires accurate real-time monitoring in order to avoid any health and safety hazards or power failure. In this paper, state-of-the-art methods on transmission line sag monitoring are thoroughly reviewed and compared. Both the direct methods that use the direct video or image of the transmission line and the indirect methods that use the relationships between sag and line parameters are investigated. Sag prediction methods and relevant industry standards are also examined. Based on these investigation and examination, future research challenges are outlined and useful recommendations on the choices of sag monitoring methods in different applications are made.