Possible negative interactions between fast frequency response from utility-scale battery storage and interconnector protection schemes

Grid integration of renewables and replacement of conventional synchronous power plants may significantly decrease system inertia, which can potentially lead to frequency stability issues. Among alternative solutions to support system frequency in low-inertia conditions, and thanks to their unique technology features and highly controllable power electronic converters, utility-scale battery energy storage system (BESS) can be deployed to provide fast frequency response (FFR). However, possible undesired knock-on effects from such FFR operation, e.g., its negative interaction with equipment protection relays, and particularly for interconnectors, have not been adequately investigated. In this context, this paper first demonstrates with an illustrative analytical example how BESS FFR could potentially induce undesired trip in out-of-step interconnector protection schemes. Then, a case study example based on an Australian test system is presented to discuss how FFR from the 100 MW Hornsdale BESS located in South Australia might have contributed to the trip of the Heywood interconnector with Victoria during the August 2018 separation event. Finally, it is shown how FFR from BESS in Victoria could have enhanced frequency control and even prevent system separation, hence highlighting the importance of FFR location.