Real-Time Sag Estimation of Overhead Power Lines Based on Approximate Magnetic Field Model

In contemporary electrical power systems real-time power line monitoring and supervision are commonly performed using simple non-invasive devices with contactless magnetic field measurement. Measured magnetic fields are commonly employed for fault detection in fault passage indicators, but they can also be used to determine electrical and non-electrical power line variables. In this paper a novel adaptive method for conductor sag estimation is proposed, using magnetic field measurement. The method is based on the properly calibrated approximate power line magnetic field model, in which catenary-shaped conductors are modeled by tilted straight-line conductors of infinite length. By this approximation, the overhead power line model can be used in simple devices for power line monitoring in real-time. Applicability and accuracy of the proposed method for power line conductor sag estimation is verified by computer simulations and measurements on a three-phase overhead line model, scaled to laboratory conditions.