Issues in the West Murray zone - FAQs
Q: What are the issues impacting the electricity network and generators in West Murray?
The scale and pace of new inverter-based generation connected in electrically remote and weak areas of the National Electricity Market is presenting unprecedented technical issues affecting power system security and stability in those areas.
This is the case in the West Murray zone with significant investment in new generation into a low system strength network that is a long distance from major energy usage areas and ‘synchronous’ machines that provide critical system strength services. A minimum level of system strength is required for the power system to remain stable under normal conditions and to return to a steady state condition following a system disturbance.
Further, the transmission infrastructure in this part of the network is subject to thermal and voltage stability constraints, restricting the generation output that can be transferred across this part of the network.
Both the system strength and constraint issues are exacerbated as the number of inverter-based generation connections increase along these lines.
In September 2019, AEMO identified that five solar farms in the West Murray zone produced voltage ‘oscillations’ following a transmission line fault, which exceeded the regulated limits for power system security.
Q: When did AEMO become aware of these issues?
The challenges associated with the West Murray zone being a remote and electrically weak part of the NEM has been publicised over the last few years, including AEMO’s 2016 Victorian Annual Planning Report and the 2018 Integrated System Plan (ISP). Generation maps are also publicly available to facilitate informed investment decisions.
AEMO first published information for Victorian transmission network connection applicants about the impact of thermal limits in the area in late 2015, with multiple updates over time as conditions have changed.
The full extent and causes of the interactions between inverter-based generation as they respond to system disturbances are still emerging. These phenomena have become apparent as the capability has become available for AEMO to develop detailed PSCAD® models extending over a wide area of the network. This phenomenon would not have been uncovered by conventional power system simulation tools used worldwide. It is now possible for detailed analysis of actual system events to be performed and for connection studies to capture potential interactions that may occur with network and inverter-connected plant. Tests performed in late 2019 have confirmed these interactions are occurring in the West Murray zone. They are at the heart of the network constraints that AEMO introduced in September 2019 restricting the output of five constrained solar farms to maintain post-fault stability within regulated power system security limits.
AEMO has not only been working with the impacted solar farms, network service providers and the equipment manufacturer to identify and implement acceptable solutions, but also communicating and engaging with committed and prospective generators in the area directly via email and calls, along with reports, a technical forum and through our AEMO Communications eNewsletter.
Q: Why did AEMO constrain the five solar farms?
As the market and system operator of the NEM, AEMO needed to constrain the output of these solar farms to a level at which it could be satisfied that the integrity of the electricity system would be protected. AEMO’s responsibility for power system security means it must take all available steps to keep the power system within operating limits, both in normal operation and immediately after a credible fault or event that could occur on the power system at any time.
Q: How are current and prospective generators in West Murray impacted?
AEMO has been working closely with the solar generators, their equipment suppliers and network service providers (Powercor and TransGrid), to help develop a solution that would restore operational compliance.
The generators and network service providers now need to complete a regulated process to agree and verify the necessary changes, with AEMO’s approval. However, in these network conditions every adjustment has consequences for generator and system performance, some unforeseen. As a result, regrettably this assessment has been a slow process.
Once tested and implemented, the solution will enable NSPs and AEMO to resume assessments of commissioning and committed generation projects in the West Murray zone. These will need to be conducted sequentially to meet power system security needs.
Q: Do these issues risk the delayed registration/constraints for neighbouring projects around the WMZ?
AEMO and the NSPs will continue with the connection and registration process for projects that are not considered to be within the West Murray Zone. Normal operational constraints will still apply to all regions.
Q: Will AEMO share the contingency events and network conditions for the assessment of each project with all participants?
No, AEMO intends to discuss the contingency events and network conditions with each proponent for its own project.
Q: Are these issues unique to West Murray or do they relate to the rest of the National Electricity Market?
The issue observed in West Murray are unique to the particular electrical topology of the zone. However, there are emerging challenges across the NEM in areas of low system strength and high concentration of inverter-based generation.
Q: If we are in the zone, how does that impact our project?
Projects within the WMZ will require an additional integration assessment. The integration assessment is the final phase in the overall assessment process under clauses 5.3.4A and 5.3.4B. Each project will be allocated a position in the sequence schedule for the integration assessment.
Q: Why has the WMZ changed? What triggered the boundary expansion?
The “Defining System Strength Zone methodology” has been applied to the WMZ to assess the potential for a new generator connection to adversely interact with others due to low system strength. This has facilitated better definition of the WMZ boundary.
Q: How can the limitations be identified early so developers can understand the costs before committing significant financial costs to their projects?
Proponents needs to carry out due diligence and understand the market limits in the regions where investments are being planned and then have early engagement with the respective NSP and AEMO.
Q: Is AEMO planning to restrict connection of smaller (say <5MW ones) inverter-based generation until baseline is established?
The National Electricity Market is an open access market and AMEO does not restrict connections providing they meet the requirements of the National Electricity Rules. Standing exemptions are available to persons who own, operate or control a generating system with a nameplate rating of less than 5MW when fully connected to a transmission or distribution system. – A copy of the Guide to Generator Exemptions and Classification of Generating Units can be found here. This standing exemption is across the entire NEM inclusive of the West Murray Zone.