On 20 April 2023, the Australian Energy Market Commission (AEMC) published a final rule and determination that revises the minimum access standards that specify the nature of the reactive current response that inverter-connected generators must provide in response to a fault. 

The final rule offers the following key benefits: 

• lower the cost of connecting renewable generators by lowering the amount of reactive current capability they would need to provide
• improve system security outcomes by establishing a better balance between response speed and stability 
• ensure the provision of voltage support equipment at least cost over time by acknowledging the role of NSPs in assessing the costs and benefits of these investments.

The final rule will achieve this by making the following key changes to the rules: 

• It will lower the reactive current capability requirement to a level that is greater than (but not equal to) zero
• It will reformulate existing requirements to incentivise a fast and stable response by requiring that responses commence within 40 milliseconds and lengthen the rise time requirement from 40 ms to 80 milliseconds.
• It will further clarify several other aspects of the rules, on matters such as active power recovery and the voltage at which reactive current responses should commence, to support faster connection negotiations between connecting generators, NSPs and AEMO
• It will address several issues with the definitions for maximum continuous current, continuous uninterrupted operation raised by stakeholders through consultation on the draft rule and determination.

The Commission acknowledges stakeholder feedback that the reactive current capability standard should be set at a level that appropriately incentivises generators to tune inverters to optimally use their latent capability. The Commission has balanced this with feedback from other stakeholders that the minimum access standard does not incentivise investment in reactive current control equipment that is not needed. The Commission also notes that AEMO is currently reviewing the Access Standards framework and is seeking stakeholder feedback on elements of the access standards that are related to this rule change – such as the automatic access standard for reactive current. 

Background

The AEMC initiated consultation on a consolidated rule change request from two proponents, one from a consortium of wind turbine original equipment manufacturers and the other from Renewable Energy Revolution (RER) Pty Ltd on 26 May 2022. 

The Commission consulted on these issues together because they cover similar issues. Both proposed that the standards specifying the reactive current fault-response that should be required of connecting plant be changed and set at a level that better reflects the locationally specific needs of the power system.

Inverter connected resources such as batteries currently have to demonstrate that they comply with the minimum access standards specified in Schedule 5.2.5.5 of the NER. Network service providers are not able to provide connection approval to parties that do not meet this minimum standard. 

RER’s proposal considered that the existing reactive current fault-response requirements are not appropriate for locations in the network with low inductance resistance ratios and recommended a move away from the current static maximum reactive current fault-response requirement of 100% of the unit’s maximum continuous current. Instead, they proposed a maximum reactive current response that is less than 100% and varies based on the impedance at the connection point described by the local reactance to resistance ratio.

The wind turbine OEMs’ proposal noted that the standards are set at an inappropriate level, compliance is not defined in a way that is mutually understood by AEMO, TNSPs and connecting proponents, and inconsistencies exist between these and some related standards that make it difficult to comply with all of them. To address these issues, their proposal recommended that: 

• the minimum level of reactive current capability that generators have to install at the connection point be lowered to zero to resolve the risks to the commercial viability of new generation and investment duplication;
• the point of compliance assessment be shifted from the connection point to the generator unit terminals to resolve the challenges with controlling a generator's reactive current response
• the standards describing the characteristics of a response (i.e. how quickly the response should rise, and stabilise) be made less onerous
• resolve other issues that are creating uncertainties for the grid approvals process by clarifying potential conflicts between obligations to provide a reactive power response that helps maintain stable voltage levels and an active power response that helps maintain stable frequencies.

The Commission initiated its assessment of the rule change requests on 26 May 2022 with the publication of a consultation paper. After this, we held three technical working group meetings and invited all the parties that had made submissions to the consultation paper to provide feedback on the principles that should guide revision of these standards, options for revision, and our preliminary views on the draft rule. 

The Commission extended the timeframe to make a draft determination to 15 December 2022 because there was a material change in circumstances that made this extension necessary. Earlier, the timeline to make a draft determination was extended to 3 November 2022 upon commencement of the rule change process, due to the complexity of the issues raised in the rule change requests.

The Commission received 12 submissions in response to the draft determination, which can be found below. The Commission also extended the timeframe for publishing the final determination by five weeks from 17 March 2023.