Optimal Coordination of Directional Overcurrent Relays Using BBO when Electromechanical, Static, Digital, and Numerical Relays All Exist

Nowadays, the literature is very rich with many techniques proposed especially for optimal relay coordination (ORC) problems of directional overcurrent relays (DOCRs). Many approaches have been applied to solve this stiff problem by considering different scenarios on protective relays and their network. However, the literature lacks a realistic model to deal with the inevitable fact that modern electric power networks have different relay technologies. Protection engineers could face electromechanical, static, digital “hardware-based”, and numerical “software-based” relays all together in the same network. Thus, existing ORC solvers are inapplicable to optimally coordinate such realistic networks. This paper presents a corrected model to deal with different relay technologies where the original problem dimension increases by 1.5× to indicate the relay types. To validate its correctness, the biogeography-based optimization (BBO) algorithm is used with the IEEE 6-bus, 15-bus, and 42-bus test systems. The results show that this realistic ORC problem can be solved, which means that it is possible to coordinate DOCRs that come with different speeds, coordination time intervals (CTI), and resolutions of time multiplier settings (TMS) and pickup settings (PS).