Abstract for: When the Grid loses it's Grip

As renewable generation displaces synchronous machines, power systems lose rotational inertia — the physical buffer that resists frequency change after disturbances. Lower inertia means faster frequency drops, deeper nadirs, and shorter operator response windows. Yet system dynamics models of electricity have largely ignored this short-timescale, feedback-rich phenomenon, leaving a methodological gap. The swing equation, governor droop, secondary control, and demand-side response are translated into a three-stock, three-flow system dynamics model. Five derivation steps map engineering physics onto stocks (frequency, supply, demand) and control-driven bi-flows. Scenarios systematically vary disturbance size, inertia, and droop gain across a 25-second simulation horizon. Lower inertia worsens both RoCoF and nadir nonlinearly and amplifies recovery oscillations. Droop control helps arrest the decline but has negligible effect on the initial frequency drop, which is almost purely inertia-dependent. Causal loop analysis reveals that balancing loops remain structurally present but become functionally weaker as inertial buffering declines. Declining inertia is simultaneously a stability problem and a systems problem — it links physical buffering, control speed, operator decision windows, and economic exposure. The modular stock-and-flow form can embed within broader market or transition models. Reduced-order approaches may support near-real-time resilience tools, as recent events like the 2025 Iberian blackout underscore. Review paper for language and summary, image generation