A PROJECT REPORT ON PLANNING THE COORDINATION OF DIRECTIONAL OVER-CURRENT RELAYS FOR DISTRIBUTION SYSTEMS CONSIDERING DG

The existing power system was not designed with distribution generation (DG) in mind. As DG penetration is being considered by many distribution utilities, there is a rising need to address many incompatibility issues which put a big emphasis on the need to review and implement suitable protection scheme. The usual practice for existing distribution feeders is the Overcurrent scheme which includes coordination between relays. But when DG is added to the distribution feeder, the configuration is no more radial as there is a contribution of fault currents from the DG’s and if the existing protection scheme is applied then this could lead to various issues like fuse misoperation or nuisance tripping considering temporary and permanent fault conditions. 

Introduction of distributed generation (DG) to the power system may lead to non-selective protection actions. For every future DG installation, the relay settings need to be modified to guarantee protection coordination that can lead to numerous changes in relay settings. Since DG is an intermittent source of power generation, for different power supply different relay coordination is required. 

Protection coordination is the process of determining the primary protective device that is responsible for clearing the fault as quickly as possible. For each fault location, taking into account in the event that any of these devices fail, each should be backup by another protective device. The coordination of these overcurrent relays is a very tedious process, thus, automating the relay settings with the desired coordination time interval is necessary. 

However, in this study, coordination of directional overcurrent relays solved using a genetic algorithm, the test system is IEEE 14-bus bar and a meshed system with DGs. Three case studies have been considered, case 1 with no DG, case 2 with two DGs of fixed size and last case is considering all case scenario. The results of this study are vital to the determination of the best coordination settings of overcurrent relays by minimizing the operation time by optimizing the objective function satisfying all constraints using a simplex method of optimization.

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