System Strength Assessment for Inverter-Based Resource Points of Connection

System strength reflects the extent to which the grid behaves as a voltage source at a particular Point of Connection (POC). Traditionally, system strength has been assessed through Short-Circuit Ratio (SCR)-based metrics to estimate the power system stability margin. With the increasing share of inverter-based resources (IBRs), fault levels in the grid tend to decrease, primarily because IBRs have limited short-circuit current contribution compared to synchronous machines. Furthermore, as IBRs become dominant in modern power systems, the limitations of SCR-based indices to characterize system strength become evident. Recognizing these challenges, this paper evaluates the suitability of SCR-based indices for screening candidate POCs through a case study. This is illustrated by evaluating the impact of connecting a new IBR at the weakest and strongest POCs, selected based on SCR-based indices. The impact of each connection is quantified through a contingency severity index, by assessing the dynamic system performance under disturbances using the maximum oscillation amplitude and settling time of voltage at each POC. The performance comparison reveals that the SCR-based indices fail to accurately differentiate between the weakest and strongest POCs and are primarily limited to assessing steady state stability limits. This paper highlights the limitations of current indices, failing as system-wide indicators and emphasizes the need for metrics that clearly align the system strength with the expected system performance.