<p>With the accelerating transition to low-carbon energy, understanding how topological redundancy and renewable energy source (RES) penetration impact the robustness of decentralized power grids is critical for building resilient infrastructure. This study introduces a reduced, structure-preserving dynamic model that captures the core dynamics of energy resources, including both the conventional synchronous generator and inverter-based RES. The model describes power angle and voltage dynamics in large power grids, enabling a detailed understanding of how key topological parameters–such as decentralized level, RES penetration rate, and network redundancy–affect cascading failures caused by transient power flow overloading. Cascading failures are simulated by randomly removing a transmission line to initiate the first outage, with subsequent failures triggered by line overloads. System robustness is quantified by the average failure ratio and failure propagation time. Simulation results of synthetic power grids and the UK’s high-voltage transmission grid reveal that higher decentralized levels, increased RES penetration rates, and greater global network redundancy lead to smaller average failure ratio and shorter failure propagation time. Additionally, transmission line loading is reduced and failed line clusters become more spatially localized. These findings suggest that future power grids characterized by increased interconnectivity and decentralized RES integration will likely experience smaller-scale cascading failures that propagate more quickly.</p>