الفهرس 
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Abstract
Recently, the penetration of distributed generation (DG) is increased which is connected to the distribution network. DGs have many benefits in many aspects such as reliability and system efficiency. Despite these benefits, this penetration causes challenges for the protection system such as blinding of overcurrent relay, false tripping, and loss of main protection, and these issues varying depending on DG type, allocation and network configuration. Normally, the distribution system is protected by fuse-recloser combination and overcurrent relays, and because of the negative impacts of the DG penetration, the coordination between these devices will be affected. One of the most common solutions for DG’s penetration negative impact in protection system is the use of a fault current limiter (FCL) technique. During fault occurrence in the network, FCL reduces the magnitude of fault current to the level before DGs penetration. In this thesis, the optimal deployment of FCLs in a variable-topology distribution network with distributed generators (DGs) is analyzed. A proposed multi-objective optimization scheme is applied to maximize the mitigation effect of FCLs and minimize the total cost. The scheme determines the optimal locations of the FCLs and the associated optimal impedance values. Meanwhile, a particular focus is kept on preserving the coordinated operation of the protective directional overcurrent relays (DOCRs) of the distribution network under many operating conditions. DOCRs coordination preservation is merged into the FCLs allocation problem by a compulsory set of main-backup DOCRs pairs operation constraint for both near-end and far-end faults for every possible network topology. Furthermore, to lessen the cost of FCLs, a new hybrid approach is developed. Firstly, optimal re-adjustment of a selected small percentage of the DOCRs is accomplished for just one time at nearly zero cost. Then, the FCLs allocation problem is solved. Different engineering strategies for maintaining DOCRs coordination are compared for a 33 kV meshed case study system. Typically, steady-state fault current and static protective device characteristics are used to determine optimal settings of devices such that coordinated operation is verified. Since fault current is not a steady signal and protection devices have dynamic behaviors, the conventionally determined settings of devices can lead to loss of coordination jeopardizing system reliability. In this paper, a two-layer protection scheme is proposed for a distribution network with DGs. The first layer has DOCRs to protect main feeders. The second has auto reclosers and fuses to protect lateral feeders. Optimal settings of devices are determined to achieve both local-layer and inter-layer coordination of devices by constrained nonlinear optimization. Full dynamic models of every component and transient data of fault current are considered. Furthermore, to sustain coordination with DGs utilization, a hybrid superconducting fault current limiter (HSFCL) with high temperature superconducting resistive element is connected in series to each DG. Dynamic modeling based on HSFCL cost minimization is searched by multi-objective optimization. The approach is applied to two distribution networks and simulation results are analyzed.