This paper presents a protection methodology for distributed generation (DG) with respect to transient instability, using the Enugu distribution network as a case study. A detailed ETAP model of the network was developed, incorporating an integrated microgrid consisting of photovoltaic systems, diesel generation, and battery energy storage. The study investigates the impact of DG on both steady-state and dynamic system performance. Analyses conducted include load flow studies, transient stability simulations under various fault conditions, and protection coordination assessments. Both conventional and adaptive overcurrent protection schemes were evaluated at increasing DG penetration levels. Case studies, including three-phase faults at selected buses, demonstrate that properly coordinated primary relays can effectively isolate faults. For instance, OCR-8 at Bus 602 successfully cleared a fault without unnecessary backup relay operation. Results show that DG integration significantly alters the magnitude and direction of fault currents, making conventional static relay settings inadequate. This necessitates the use of adaptive protection schemes incorporating directional elements and dynamic relay settings to maintain selectivity and prevent mis-operations. This work contributes by developing a reproducible ETAP-based model of a DG-integrated distribution network, quantifying the impacts of DG on protection and transient stability, and demonstrating that optimized relay settings can restore coordination. The study highlights adaptive relaying as an effective solution for enhancing protection performance. It is recommended that utilities conduct detailed ETAP-based protection studies prior to DG integration, deploy adaptive relays on feeders with high DG penetration, and that regulatory standards be updated to ensure proper protection coordination and system stability.
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