ERCOT subsynchronous resonance topology and frequency scan tool development

This paper presents a comprehensive two-step topology and frequency scan tool (TFST) developed by ERCOT to assess the potential subsynchronous resonance (SSR) vulnerability associated with the series compensations in the meshed transmission networks and various generation resources, including synchronous generators and inverter technology based generators. In the first step, the topology scan applies the max-flow min-cut theorem on the transmission network to identify the critical contingency set (N-x as number of transmission circuits) corresponding to the radial connection between the generation resource and the series compensated transmission circuits. If x is small, the frequency scan will be conducted as the second step to derive the frequency dependent Thevenien impedance as viewed from the generator neutral point. A generic frequency dependent impedance table is designed as a template to cover all types of generator resources whose impedance could be derived by TFST or provided by the manufacturers. ERCOT is currently utilizing TFST as the screening tool to assess the potential SSR vulnerability associated with numerous generation resources in the vicinity of multiple series compensated transmission circuits in ERCOT system.