Recently, microgrid operation increased significantly with increasing distributed renewable energy resources in the power system. Microgrids can operate with and without utility. Fault currents are significantly different in island and utility connected operation modes. Therefore, microgrid protection is one of the important subjects in microgrid operation. In this paper, a hybrid particle swarm optimization (HPSO) approach has been developed for coordination of directional overcurrent relays (DOCRs) in a microgrid system. The coordination constraints include the utility connected and an autonomous condition of the microgrid operation. In the optimization procedure, the current setting (I set ) of relays is considered as discrete parameters and time multiplier settings (TMS) is assumed as continues parameter. The proposed algorithm has two parts, in the first part, PSO is used to calculate the I set and in the second part, linear programming is applied to calculate the TMS of each relay. In the case study, loads connected to the network are divided into critical and noncritical ones. In normal operation of the system, distributed generators (DGs) operate in parallel with the utility. When a fault occurs on the utility side, noncritical loads are disconnected from the network and DGs are operated in microgrid as islanded mode. Regarding to simulation results, DOCRs have a suitable and reliable operation in both conditions of microgrid operations. In addition, overall operating time of the primary relays is properly minimized.
Conventional power distribution system is radial in nature, characterized by a single source feeding a network of downstream feeders. Protection scheme for distribution system, primarily consisting of fuses and reclosures and, in some cases, relays, has traditionally been designed assuming the system to be radial. In last year extra attention applied in use of distributed generator units in distribution networks. The integration of distributed sources into existing networks brings up several technical, economical and regulatory questions. The connection of distributed generators (DG) to distribution networks also influences the performance of the networks and the impact depends on the number, location and size of injected DG. The presence of distributed generators in the distribution network can cause the mis-coordination of the protection system. In order to overcome this problem, one can change the relay setting based on the number and location of DGs in the network. In this paper, another approach is selected in which, the capacity of DG at each node is determined in such a way, that the mis-coordination does not happen. The proposed method is explained in two cases. In the first case, just one DG at each node is considered, but in the second case existence of two or more DGs in separate nodes is taken into account. The simulation result are presented and discussed in a typical distribution network.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.