This paper details the integration of a large-scale Grid-Forming Battery Energy Storage System (GFM-BESS) - the Darwin-Katherine BESS (DKBESS) - into Australia's Northern Territory's Darwin-Katherine Network (DKN). The NT is undergoing a rapid energy transformation with ambitious renewable energy targets, aiming for 50% by 2030 and potentially 100% by 2040. This significant increase in inverter-based resources (IBRs) presents challenges to system strength and frequency/voltage stability, traditionally maintained by synchronous generators. The DKN is a relatively small network with loads typically between 60MW and 300MW, and forecasted minimum demand reducing further, which magnifies the impact of these changes. The DKBESS, located at Channel Island Power Station, is the first grid-forming BESS in the DKN with a 35MVA (45.6 MW overload) capacity, primarily intended to replace a retiring gas-fired generator by providing critical Ancillary Services like reactive power, voltage control, FCAS, inertia, and system strength (fault current). The integration process necessitated the development of aggregated RMS and EMT system models and presented complexities related to grid code compliance, as existing codes didn't fully accommodate modern grid-forming IBRs. This required negotiated positions on testing and performance standards, alongside the development and implementation of innovative control systems and novel approaches such as the Virtual Feeders concept, a novel On-Load Tap Changer (OLTC) control method based on 132 kV voltage feedback, and tuning of Rate-of-Change-of-Frequency (ROCOF) relays.

Modelling studies were essential for assessing the DKBESS's performance and validating these novel approaches. Key results demonstrated the BESS's capability to provide superior Ancillary Services relative to the retiring generator (except peak fault current), its substantial overload capacity, and fault current contribution. The novel control methods, such as the Virtual Feeders and the refined OLTC control, showed effectiveness in simulations for managing power flows and voltage control. Tuning of ROCOF relay settings and logic mitigated the risk of spurious tripping during disturbances. Comparisons of inertial response showed that the DKBESS with Virtual Synchronous Machine (VSM) technology could deliver/absorb the same energy as the gas turbine generator with identical inertia time constants but offered better damping without relying on power system stabilisers. Furthermore, tuning the frequency measurement filtering time in the DKBESS was crucial to prevent unstable frequency oscillations caused by interactions with other generators in the network. The project is undergoing its final commissioning and compliance testing in mid 2025. In conclusion, the DKBESS project is a crucial pilot for grid-forming technologies in the NT, enabling the integration of IBRs and operation under low system loads by providing essential synchronous-like services. The project successfully addressed significant challenges related to modelling and technical compliance through careful consideration, pragmatic reasoning, and close collaboration. The outcomes of this ongoing project are expected to establish a precedent for future grid-forming connections in the NT and provide valuable lessons for larger interconnected grids transitioning to higher levels of renewable generation.