A Modified Scheme for Relays Coordination in Distribution Networks Considering the Transient Stability Criterion

Considering environmental issues and the use of green energy resources has led to the increase of Distributed Generations (DGs) connection to electric power grid. Beside many benefits, these generations impose challenges to the electric system. Two main challenges investigated in this article are related to the impact of DGs on the Protective Devices (PDs) coordination and the transient stability of these resources at the fault time incidence. As for Synchronous-based Distributed Generations (SBDGs), the challenge of protection coordination arises from the injection current rate of these generations under fault circumstances and the transient stability challenge is due to the low inertia constant. In proposed method, by shifting the relay characteristic curve downwards and repositioning the curve below the Critical Clearing Time (CCT), not only the coordination of the PDs will be improved, but also the instability of SBDGs will be eliminated. This paper presents a modified time-current-voltage characteristic curve for the overcurrent relays. The simulation results done by ETAP software confirm the effective performance of the proposed method.