Short-Circuit Ratio with Interaction Factors¶

SCRIF. The ratio between short circuit apparent power from a 3LG fault at a given location in the power system to the rating of the location.

Definition by NERC¶

Source: ¹ (p3)

SCR with Interaction Factors (SCRIF) has been proposed to capture the change in bus voltage at one bus corresponding resulting from a change in bus voltage at another bus. Electrically close inverter-based resource buses will have a relatively higher Interaction Factor (IF) than inverter-based resource buses that are electrically separated. When multiple inverter-based resources are located very close to each other, they share the grid strength and short circuit level; hence, the grid strength is actually much lower than the overall short circuit level calculated at that bus or buses. SCRIF captures the voltage sensitivity between inverter-based resources as a screening tool for potential controls issues by using inverter-based resource interaction factors, as follows:

\(SCRIF_{i} = \frac{S_{i}}{P_{i} + \sum_{j} (IF_{ji} \cdot P_{j})}\)

Where \(IF\) is the change in bus voltage at bus \(i\) (\(\Delta V_{i}\)) for a change in bus voltage at bus \(j\) (\(\Delta V_{j}\)), as follows:

\(IF_{ij} = \frac{\Delta V_{i}}{\Delta V_{j}}\)

An advantage of the use of SCRIF is that it can be readily amended to cater for any conceivable configuration for connection of multiple inverter-based resources.

Last modified: 2025-11-29

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NERC (2017). Integrating Inverter-Based Resources into Low Short Circuit Strength Systems. https://www.nerc.com/globalassets/who-we-are/standing-committees/rstc/irpwg/item_4a.integrating-_inverter-based_resources_into_low_short_circuit_strength_systems-_2017-11-08-final.pdf ↩