An improved pilot protection for distribution network with Inverter-Interfaced Distributed Generations

Inverter-Interfaced Distributed Generation (IIDG) connected to distribution network with a teed line may cause protective relay tripping failure even using conventional current differential protection, which is regarded as one of the most effective protection for distribution network with distributed generations. Therefore, the impacts of IIDGs on traditional current differential pilot protection is analyzed firstly in this paper. Next, the fault characteristics of IIDG are introduced and the fault model of IIDG is established, in which IIDG is viewed as a current source controlled by the positive-sequence voltage at the point of common coupling. Then, based on the three-phase voltage and current on both sides of line, an improved pilot protection is proposed, which consists of a negative-sequence current differential protection as an auxiliary criterion for the conventional pilot protection. Finally, the effectiveness of the improved protection scheme is verified by a 10kV distribution network with multi-IIDGs established in PSCAD/EMPDC. The simulation results indicate that the proposed protection can effectively reduce or eliminate IIDG's impacts on current differential protection, particularly for an asymmetric fault, under various conditions involving different IIDG's output and fault resistance, thereby improve its reliability significantly.