Analysis and Design of Overload Protections for HV Lines with a Probabilistic Approach

Up to now, to analyze and design the operational limits of transmission lines, many utilities still apply traditional deterministic approaches, which have long been recognized as excessively conservative. In this work, we propose a different overload protection scheme in order to increase the line ampacity. The main idea is to include the thermal model of overhead lines inside the protection and then to compare explicitly the conductor temperature instead of the current. The proposed approach has been investigated for both deterministic and probabilistic thermal ratings. In the latter case, the conductor temperature is estimated using analytical expressions for the evolution of moments (mean value and variance) of a stochastic process using the linearized thermal model. Results show that the ampacity might be increased in cold seasons, whereas in hot seasons the line capacity must be reduced to avoid excessive heating.