Transient Stability Constrained Protection Coordination Scheme in Distributed Generation Based System with User-Defined Relays

In distribution networks, overcurrent relays serve as primary protective devices. However, prolonged relay operating times, especially when coupled with the low inertia time constant of distributed generators (DGs), can lead to instability during fault clearance. This necessitates the use of fast and sensitive relays in DG based networks. In this context, this paper presents a comparative study involving three distinct user-defined relays to tackle the transient stability-constrained protection coordination problem. Transient stability constraints are integrated with essential coordination constraints to determine optimal relay settings for fast fault detection. The study of coordination is performed on an IEEE-15 bus distribution system equipped with synchronous-based DG. Using Dig-SILENT Programming Language (DPL), critical clearing time curves for DG at various fault locations (F.L.) are determined. The optimal solution to the relay coordination problem is determined using genetic algorithm (GA). The results obtained are compared to investigate fastest and most reliable relay characteristics to retain the transient stability.