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Abstract
This thesis introduces three new approaches to enhance the directional overcurrent relays (DOCRs) coordination for electric distribution systems incorporating DG units. Firstly, a proposed scheme including fault current limiter (FCL) has been introduced to achieve DOCRs coordination in case of DGs existing; the obtained value of FCL in such proposed scheme is lower than the critical value that obtained based on conventional techniques. Secondly, a proposed scheme including FCL has been introduced for the same purpose with re-adjusting settings for minimum possible number of relays (only one relay) in case of adding DGs. Besides, the new obtained value of FCL is lower than the critical value that developed based on conventional scheme. The proposed scheme has been extended to include re-adjusting setting for two relays with less value of FCL. These two proposed schemes have succeeded in achieving the economical challenge especially in case of superconducting FCL. Finally, a new third proposed scheme without using FCL has been introduced to achieve DOCRs coordination when adding DGs with minimum possible number of re-adjusted relays settings. The results ensured the effectiveness of the proposed scheme compared with other previously published technique. The three schemes have been implemented and tested on IEEE-39 bus system taking into consideration the active reactance FCLs type in the first two proposed schemes