الفهرس 
ContentsOnly 14 pages are availabe for public view
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Abstract
Protection coordination for the microgrid system in both islanded and grid connected modes is considered a challenge for microgrid operation. The variation in short circuit currents in each mode of operation, limitation of protection curves in the relays, and the need for fast and reliable communication are the main challenges tackled in research. Direction overcurrent relays are considered the main protection instrument for the microgrid. However, one protection setting for both (main and backup) operation does not provide a fast-operating time. On the contrary, the dependence on communication to maintain the proper backup protection operation is not a reliable solution for protection system. Therefore, this thesis introduces a fast, reliable, and simple protection scheme for secure microgrid operation in both islanded and grid connected modes. In this context, one set of protection settings is optimized and used in both modes of operation. A protection setting consists of two time-dial settings and one pickup current setting for each relay. The proposed design technique minimizes the total operating time for both main and backup relays. As all protection functions are executed in the forward direction, no communication is needed among relays. The proposed scheme is tested and verified on a modified portion of IEEE 30 bus test system equipped with distributed generation units. A comparative analysis is carried out and the results demonstrate superior performance by the proposed scheme in comparison with the dual setting scheme with communication. For integration the inrush restraint function into the old version digital Over Current relays, the thesis provides a solution for this issue based on separate inrush detection circuit that can be integrated with this kind of relays as an economic solution. The inrush restraint circuit based on second harmonic detection is designed by using MATLAB Simulink, and verified with the old version Over Current relays. The proposed inrush restraint circuit is successfully tested with the Over Current relays in case of real radial test system, radial test system connected to distributed generation, and microgrid test system. In all cases, the proposed inrush restraint circuit success to restrain the protection relays operation during normal inrush condition, while it does not conflict the relays proper operation to clear faults that occur during energization.