Automatic over-frequency control scheme implementation

The EU Network Code on Requirements for Grid Connection of Generators (2016/631) mandates that generators be equipped with limited frequency sensitive mode — over-frequency (LFSM-O) controllers to decrease active power production when frequency exceeds a designated level and according to the predicted droop. In cases where LFSM-O controllers are insufficient, the EU Network Code on Emergency and Restoration (2017/2196) permits the establishment of an automatic over-frequency control scheme, which involves a step-wise linear disconnection of generation within a load frequency control (LFC) area. During the signing of the Synchronous Area Framework Agreement (SAFA) for Continental Europe in 2019, TSOs from South-East Europe (non-EU countries) required derogations from LFSM-O requirements. Subsequently, the Serbian TSO initiated development activities through EU Horizon 2020 research and innovation projects, Crossbow and R2D2, to devise technical solutions for an automatic over-frequency control scheme at both national and regional levels. This initiative aims to replicate the response of a system with fully equipped LFSM-O controllers, additionally ensuring that, during significant frequency increases, power flows between LFC areas remain stable to prevent transmission lines tripping and system collapse. The recognized basic technical solutions include remote assignment of the set point to the generator, remote individual shutdown of generators in series or groups, and remote setting of local over-frequency protection. Furthermore, these studies explored transitional solutions leveraging existing local over-frequency protections with static (annual) settings to enhance system responsiveness. The researchers' ambitions also went the other way, so a proposal was made to amend the SAFA Policy on Emergency and Restoration in the part related to the automatic over-frequency control scheme. This paper details the conceptual solutions arising from these projects and the forthcoming implementation in the Serbian transmission system.