A Novel Quadratically Constrained Quadratic Programming Method for Optimal Coordination of Directional Overcurrent Relays

The coordination of directional overcurrent relays (DOCRs) in meshed power grids with multiple sources is a constrained optimization problem, which has been stated in recent literature as linear (LP), nonlinear (NLP), and mixed-integer nonlinear programming (MINLP) problem. In this paper, the DOCR coordination NLP problem is reformulated as an equivalent quadratically constrained quadratic programming (QCQP) model, leading to significant reduction of problem complexity. Another contribution of this work is the systematic problem statement using graph theory concepts. The proposed method is applied to three different meshed power systems, employing state-of-the-art optimization software. Simulation results demonstrate the efficacy and superiority of the proposed QCQP model over the prevailing NLP approach.