Applying Multi-Objective Optimization for Enhancing Directional Overcurrent Relays Coordination

Abstract

One of the most important requirements of protection system is to isolate and disconnect faulted parts of the system selectively and quickly. Overcurrent relays are used as primary protection for distribution systems or combined with distance relays for protecting subtransmission systems. Coordination of directional overcurrent relays (DOCRs) is a main challenge in power system protection. This thesis studies DOCRs coordination by achieving two main goals. The first goal is introducing a DOCRs coordination comparative study using single-objective and multi-objective optimization approaches. Different fault locations are considered for each method then the results are compared based on the mean fault clearing time of the system, maximum primary and backup relays operating time and maximum coordination time interval. The second goal is introducing an enhanced two-fault point coordination scheme. The scheme employs severity weighting factors for each relay with respect to fault location. The proposed severity weights are calculated based on the ratio of fault currents that pass through the relay so relays with higher and more severe fault current should operate faster than relays with less severe faults. The study is performed on the meshed power distribution network of the IEEE 14 bus system. Achieved results have shown that applying multi-objective optimization approach using severity weighting factors has reduced the operating time of relays with high fault current which guarantees more reliable and fast protection system as well as less damage to the equipment that experiences fault current.