As power systems shift toward inverter-based resources (IBRs), maintaining stability depends on both total available inertia and system strength. This paper addresses frequency security by determining the required frequency response reserves (FRR) as an explicit function of the short-circuit capacity (SCC) at the renewable interconnection bus. For a fixed contingency, lower SCC at the connection point increases the required FRR and raises the secure operating level of inertia (SOLI); conversely, higher SCC reduces both for the same event. We show that, for a fixed contingency and nadir standard, lower local SCC at the renewable interconnection bus systematically increases both the required FRR and the SOLI. This SCC–FRR formulation enables system operators to set region-specific FRR targets and to assess the impact of renewable siting in weak versus strong areas without changing the underlying frequency-security standard. We substantiate this with a regional analysis on KEPCO’s system, using data-driven operating snapshots and dynamic frequency simulations for three areas with different SCC and renewable siting patterns. The results reveal local system strength differences across areas and demonstrate that relocating renewable connections alters FRR needs and shifts SOLI in proportion to local SCC. Jeonnam needs approximately 14–23% higher SOLI and 28–45% more FRR than other areas under the same nadir criterion.

This paper proposes an analytic method for estimating frequency nadir in power systems dominated by fast frequency response resources (FFRRs). The proposed method approximates the frequency response of FFRRs, which could be either complex or whose internal logic is not disclosed generally. This is because commercial-level models are typically provided as black box systems in large power system analysis. With the approximated transfer function, the frequency response following a major disturbance is represented by a simple equation that resembles the general solution for a second-order system's impulse response. The proposed method is validated through case studies of Jeju Island's power system in South Korea, employing user-defined models (UDMs) for high-voltage direct current (HVDC) systems. Results demonstrate that the proposed method predicts frequency nadir with high accuracy, which is almost identical with those of PSS/E.

This paper proposes a real-time oscillation monitoring framework based on an enhanced Geometric Feature Extraction (GFE) algorithm. The method utilizes high-resolution synchrophasor measurements from Phasor Measurement Units (PMUs) and employs a sliding window approach to identify oscillatory behavior in power systems. To improve detection robustness, the algorithm integrates signal-to-noise ratio (SNR) filtering and adaptive estimation of the Radius of Trajectory (RoT), which characterizes geometric patterns in reconstructed phase-space trajectories. A real-time alarming index is computed for each sample, and an oscillation alarm is triggered when the proportion of oscillatory samples within a window exceeds a predefined threshold. The proposed method was validated using actual PMU data recorded during a forced oscillation event caused by a Thyristor-Controlled Series Capacitor (TCSC) in the KEPCO power system. Experimental results demonstrate that the algorithm accurately captures the initiation, persistence, and attenuation of oscillatory behavior, offering both high detection sensitivity and low computational overhead suitable for real-time deployment.