الفهرس 
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Abstract
Increasing the Distributed Generation (DG) into the power system causes technical problems and bad effects on the safety of the system due to increasing the short circuit levels in transmission and distribution networks. So, there will be miscoordination problems of Directional Over Current Relays (DOCR) when DGs are integrated with looped power delivery systems. One of the traditional methods used for restoring the coordination between protective relays during the fault occurrence is connecting the Fault Current Limiter (FCL) impedance in series with DG. This thesis presents two approaches to overcome the miscoordination problem between directional overcurrent relays connected to Microgrids (MGs) integrated to looped distribution networks. The first approach is implementing a resistive Superconducting Fault Current Limiters (SFCL) with DG units to obtain the optimal setting of protection systems. The protection coordination setting is optimized using Particle Swarm Optimization technique. The approach is tested on a nine-bus looped power Distribution Network (DN) and the effects of SFCL on the protection system of DG-grid connected are analyzed. Three cases are studied: no DG, grid-connected DGs without SFCL and grid-connected DGs with SFCL. The results showed that, using the SFCL with the grid connected to DG can reduce the total operating time of primary relays to 6.14015 sec which is less than the total operating time of primary relays in case of no DG. The second approach implies the use of FCL with an impedance lower than its critical value in series with DG by selecting a definite number of relays to be adaptive to overcome the miscoordination problem at a lower cost. This approach is also tested on the nine-bus looped power DN with connected DGs at different buses. The effect of choosing the number of adaptive relays on the impedance of FCL is analyzed. Six cases are studied: no DG, grid-connected DGs with and without FCL, grid-connected DGs with FCL and one adaptive relay, grid-connected DGs with FCL and two adaptive relays and grid-connected DGs with FCL and three adaptive relays. The cost required to restore coordination between the protective devices in each case is computed and analyzed and a comparison is done to detect the appropriate protection at the minimum cost. The results prove that, the availability of using FCL with impedance value less than critical one to restore relay coordination settings with lower cost than using its critical by making two relays are adaptive. In case of selecting two adaptive relays with the FCL, the total cost required for the protection system is decreased by 65.9 % compared with using FCL only.