A non-standard protection scheme for coordinated and stable SDGs operation

The integration of distributed generation, especially synchronous distributed generators, into power distribution networks has introduced new protection and stability challenges. One critical issue is that the coordination of protection devices could be disrupted because of the fault current provided by distributed generations. Another problem is the transient instability of synchronous distributed generators due to their low inertia during fault events. This paper presents a novel protection strategy that simultaneously addresses both problems. A customized non-standard time-current-voltage characteristic is proposed for overcurrent relays where the adaptive coordination is obtained. It also improves stability while satisfying both Coordination Time Interval and Critical Clearing Time constraints. This approach includes an offline phase involving power flow, fault, and protection coordination studies. If transient stability constraints are violated, an online adaptive phase is activated by using local voltage measurements at the synchronous distributed generator buses. The proposed method is implemented and validated on the IEEE 33-bus distribution system by using ETAP software. Simulation results confirm the effectiveness of the method to maintain coordination time intervals and ensuring synchronous distributed generators stability, even under severe fault conditions.