Connections in Low System Strength Zones

Introduction

Low system strength zones are typically electrically weak and remote parts of the network that have attracted high volumes of renewable resources due to favourable wind and sun conditions. The scale and rapid pace of inverter-based renewable generator connections in these areas and changes in operating patterns for synchronous generators has resulted in new technical challenges, impacting grid performance and operational stability. Further information regarding system strength shortfalls can be found on the System Security Planning webpage.

West Murray Zone

The West Murray Zone (WMZ) is an area of the National Electricity Market (NEM) with low system strength, extending across parts of Victoria and New South Wales. This area has attracted significant investment in grid-scale solar and wind generation in recent years. The WMZ continues to pose operational challenges for AEMO, Network Service Providers (NSP) and generator developers following power system oscillations observed in 2019. The nature, extent and causes of these issues only become apparent with the advanced and detailed modelling capability that is now essential for technical assessments in weak areas of the grid.

AEMO is continuing to work collaboratively and transparently to find solutions to the challenges presented in the West Murray Zone. This includes working closely with developers, generators, NSPs, equipment manufacturers and industry groups.

Historical solutions and milestones include:

• Declared a system strength gap (December 2019)
• Held West Murray Zone technical forum (February 2020)
• Established assessment sequence (March 2020)
• Lifted the generation constraints for five solar farms (April 2020)
• Secured short term system strength solution (August 2020)
• Published methodology to define system strength zones (August 2020)
• Published the proposed sequencing approach for uncommitted projects (October 2020)
• Finalised the sequencing approach for uncommitted projects (February 2021)
• De-establishment of sequencing process (December 2022)

AEMO is also working on long-term solutions:

• Develop novel technical solutions to reduce interactions causing system instability, e.g. via the Advanced System Integration Group
• Ongoing validation of system model against measured event data to enable operation closer to system capability
• Review the regulated connections process to facilitate coordinated assessment of multiple connection projects that may impact each other.
• Support and lead network augmentations via the current Regulated Investment Test for Transmission (RIT-T) processes and the Integrated System Plan
• Resolution of intermittent power system oscillations.

West Murray Zone Sequencing process – December 2022

AEMO has discontinued the need for sequenced generator connections in the West Murray Zone (WMZ).

This process was established in February 2021, in consultation with stakeholders, to manage the complexity and detail of studies required to confirm the impact of a new connections on system security and quality of supply in the WMZ.

From December 2022, AEMO will assess connecting generators in the WMZ, in the same manner as all other connections in the NEM and in collaboration with the local network service provider. Wide area power system modelling and due diligence review will be undertaken by the relevant AEMO Onboarding and Connections regional team and generators connecting in low system strength areas may require detailed review.

For more information about this change to the connection process, reach out to the Onboarding and Connections at contact.connections@aemo.com.au. 

Prospective connection applicants

Developers interested in connecting generation in Low System Strength Zones, including the WMZ and surrounding area, should contact their local network service provider (NSP) before making any financial commitments, to discuss whether, when and how they might be able to progress their project.

Prospective applicants should be aware of the following:

• The capacity of the existing network in the WMZ to host large scale inverter-connected generation has likely been reached, or will be reached by the time already-committed projects are integrated. New and existing generation across large parts of the WMZ will be materially constrained for significant periods of time pending large-scale network investment. This will not only restrict commercial output, but may prevent or delay completion of commissioning for new projects.
• Connections that rely on future regulated upgrades to the network cannot be assessed until those upgrades are substantially complete.
• There may be significant delays in NSP and AEMO project assessments due to the complexity and detail of studies required to confirm the impact of a new connection on system security and quality of supply.
• Very low system strength increases the potential for interaction of inverter-based resources to produce unacceptable voltage oscillations. For system security reasons, any proposed generating plant that is shown to contribute to instability will not be connected.
• AEMO and NSPs will not be able to progress any assessment of proposed performance standards without a complete, site-specific PSCAD model, incorporating all information required by AEMO’s Power System Model Guidelines.
• A full system strength impact assessment will be required for all new and modified connections proposed. System strength connection works or remediation schemes will be needed, which will require additional capital investment – there is no scope to add generation runback or inter-trip schemes.

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