Multi-Stage Protection Coordination Optimization for Distribution Systems with Topology Changes

Numerous methods have been proposed to solve the directional overcurrent relays (DOCR) coordination problem in distribution systems with distributed generation (DG); however, transient changes in distribution network topology during fault isolation poses a major challenge. Using transient analysis, this paper demonstrates various coordination violations that may occur due to the faster operation of the primary DOCR on one end of the faulted line with respect to the one on the other end. To address this shortcoming, a modification to existing protection coordination formulation is proposed, which involves (i) addition of new constraints on primary DOCRs, and (ii) identifying and changing the tripping characteristics of some DOCRs to the extremely inverse time characteristic. The performance of the proposed method is evaluated on the CIGRE 14-bus benchmark distribution system.