On the Choice of System Strength Metrics for the Allocation and Sizing of Synchronous Condensers in Power Grids

The integration of high levels of inverter-based generation (IBG) into power grids requires meticulous planning, especially as IBGs lack the inherent short-circuit capacity of conventional generators, potentially weakening system strength. To mitigate this, synchronous condensers (SCs) are deployed in weak areas to enhance fault current and voltage support. Traditional SC allocation methods use the short-circuit ratio (SCR) as a key metric, but this may not account for control interactions in grids with significant IBG penetration. This study compares two approaches for optimizing SC placement and sizing: SCR-based and network-response short-circuit ratio (NRSCR)-based, a metric that captures dynamic IBG interactions. Applying a genetic algorithm (GA) to the Nigerian power grid as a case study, the SCR-based approach identified two critical points of interconnection (PoIs) requiring 68 MVA of SC capacity, while the NRSCR-based method identified four PoIs, requiring a total of 674 MVA. Although the NRSCR-based method significantly improved system performance during faults—offering faster voltage recovery post-fault and higher fault current contributions—it resulted in a cost increase of approximately 7 times. This highlights the trade-off between cost and performance, underscoring the need for utilities to balance economic and technical considerations when deploying SCs in IBG-dominated grids.