<b>Dynamic stability assessment of Nigerian power grid under high wind and solar PV penetration </b>

The increasing integration of renewable energy is essential for improving energy security, reducing greenhouse gas emissions, and meeting growing electricity demand. However, integrating large-scale variable renewable energy (VRE), particularly wind and solar photovoltaic (PV) systems, into Nigeria's weak and aging transmission network presents significant technical challenges related to voltage stability, frequency regulation, and system strength. This study assesses the impact of large-scale wind and solar PV integration on the stability of the Nigerian 330-kV transmission grid and determines the maximum VRE penetration level that can be accommodated without violating system stability limits. A detailed model of the 52-bus Nigerian transmission network was developed in DigSILENT PowerFactory. Base-case load flow, Short Circuit Ratio (SCR), Site-Dependent Short Circuit Ratio (SDSCR), contingency, and dynamic simulations were performed. DFIG-based wind energy conversion systems and solar PV plants were modelled as PQ buses and integrated into selected weak and strong buses with VRE penetration increased incrementally by 3%. The results identified the weak and strong buses, evaluated the system strength at VRE connection points, and established the corresponding voltage stability margins. The analysis showed that the Nigerian grid can accommodate up to 15-25% VRE penetration while maintaining bus voltages and system frequency within acceptable operating limits. In addition, a seven-point framework is proposed to support the reliable integration and management of VRE in the Nigerian power system. The findings provide practical guidance for renewable energy integration and future grid planning in Nigeria.