The West Murray Zone 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 the past three years. The scale and rapid pace of inverter-based renewable generator connections has resulted in new technical challenges, impacting grid performance and operational stability.
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 committed to working collaboratively and transparently to find solutions to the challenges presented in the West Murray Zone. This includes working closely with developers, generators, network service providers, equipment manufacturers and industry groups.
These 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)
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
Current and prospective connection applicants
Developers interested in connecting generation in the West Murray Zone 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 developers and current 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 will 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.
Intermittent Power System Oscillations
AEMO has observed intermittent power system oscillations in the West Murray area (VIC/NSW) under a variety of conditions.
On 25 August 2021, AEMO held an industry briefing where we presented information regarding a number of instances of these oscillations.
It was requested at this briefing that AEMO publish some data for stakeholders to analyse. Data for eight events are available. These eight events provide diversity in terms of operating condition, magnitude, time and duration in the occurrence of this oscillation. A User-Guide which has some information on how to interpret this data is also available.
On 16th November 2021, oscillations with large magnitudes reaching 4 % peak-to-peak at Wemen terminal station were observed while a transformer was out of service. The measurements recorded by the CT-Labs1 monitoring equipment installed at Wemen terminal station is shown below. AEMO has initiated a review of this incident under the clause of 4.8.15 of the National Electricity Rules.
As of 30 November 2021, the oscillations remain largely the same size in magnitude and duration with the root-cause remaining largely unknown.
AEMO is working closely with AusNet, Powercor and relevant participants to resolve the issue. AusNet have installed additional CT-Labs1 monitoring equipment around Wemen area which is helping the investigation. AusNet and Powercor are working together to increase high resolution monitoring in the area.
Sub-Synchronous Oscillations in the West Murray area1.08 MB
Final sequencing paper for uncommitted projects198.71 KB
System strength methodology861.79 KB
Proposed sequencing approach for uncommitted projects279.26 KB
ASIG Lessons learned session slide pack2.53 MB
West Murray Zone Sequencing Paper71.99 KB
West Murray Update Webinar Slide Pack965.56 KB
West Murray Technical Forum - 10 February 20201.47 MB
Infographic: Transforming Australia's energy system West Murray344.04 KB
Notice of Victorian Fault Level Shortfall at Red Cliffs375.2 KB
Power system Limitations December 2019421.25 KB
2019 Victorian Annual Planning Report1.75 MB