Optimal Coordination of Directional Overcurrent Relays in Interconnected Networks utilizing User- Defined Characteristics and Fault Current Limiter

In this paper, the effect of using user defined characteristics relay on the sizing of fault current limiters (FCLs) are investigated. FCL is implemented in series with utility to tackle protection issues in looped networks due to incorporation of distributed generation (DG) in distribution systems. A protection coordination strategy is applied through employing user-defined characteristics which classifies directional overcurrent’ constants for relay characteristics (A) and for the inverse time type (B) as adjustable setting variables in addition to conventional setting variables; pick-up current (IP) and time multiplier setting (TDS). The four relay settings are picked up optimally along with optimum value of FCL. The problem is formulated as a constrained non-linear programming (NLP) problem with main objective of minimizing overall operating time of relays. The proposed approach is tested on meshed power distribution network of IEEE 30-bus. Results achieved by the proposed strategy show a reduction in overall relay operating time and the minimum value of FCL.