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A special protection scheme (SPS) based on model predictive control (MPC) is proposed to mitigate thermal overloads in advance, and so avoid cascade line tripping. The controller aims to keep the temperatures of conductors below their admissible limits before local relays intervene and trip out the lines. This objective is carried out by properly coordinating different control actions available in power systems, while minimizing a suitable cost function subject to explicit constraints on the conductor temperatures. The temperatures of transmission lines are predicted using a thermal model of bare overhead conductors. The electrical currents are obtained from the dc power-flow approximation of electric networks, whereas dynamic stochastic autoregressive integrated moving average models are used to describe the weather variables. Simulation results reveal that the proposed scheme might increase significantly the reliability of thermal control SPSs and reduce the overall efforts required to fulfill the control objectives.
Date of Publication: Nov. 2010