Optimal Overcurrent Relay Coordination in Distribution Networks

Over-current relay coordination plays a critical role for effective protection of networks since primary protection is based on over-current detection in distribution systems. Thus, optimal relay coordination must be ensured between relays in faulted condition, providing selectivity and fast operation. Therefore, relay coordination can be designed as an optimization problem with highly constrained equations in such networks.Linear programming, which is simple to be implemented and requires less computation time when compared other optimisation techniques, is widely employed for solving relay coordination problems. To achieve faster and selective protection a number of optimisation algorithms have, also, been customised for the purpose. Water Cycle Algorithm (WCA) is among them and has promising results, already, depicted in the literature.However, capacitive currents may jeopardize traditional optimisation process for earth faults. Thus, in this paper, performance analysis is carried out for earth faults in sample distribution networks constructed with overhead lines and underground cables, separately. The results show that in cabled networks, additional constraints are needed for the optimisation process to provide selectivity. Consequently, optimal relay settings and selective protection are ensured by adding proper constraints into optimisation problem in this paper.