An examination of pre-connection sub-synchronous oscillation study requirements in GB in an international framework

The rapid growth of inverter-based resources (IBRs) in modern power systems has increased the occurrence of sub-synchronous oscillations (SSOs), particularly in weak-grid conditions. In 2024, the National Energy System Operator (NESO) in Great Britain (GB) introduced new pre-connection SSO study requirements for IBRs. Unlike publications from ERCOT and CIGRÉ, the NESO framework omits preliminary screening stages and mandates a wide range of detailed studies over extensive operating points and frequency ranges, potentially exceeding 22,000 simulation scenarios. This paper benchmarks NESO’s approach against international practice, identifying significant differences in methodology, scope, and efficiency. Key challenges include the lack of targeted frequency screening, the adoption of excessively broad frequency ranges and the dependence on developer-led studies of inconsistent quality. Recommendations are proposed to improve the GB process, including adoption of staged screening to detailed study workflows, optimisation of study ranges, increased use of in-house modelling, and clearer criteria for study scope reduction. These changes aim to streamline connection assessments, reduce cost and complexity, and maintain robust technical evaluation of SSO risks in grids with high IBR penetration.