System strength: From by-product to necessity

Last week, AEMO published a notice of fault level shortfall in North Queensland at the Ross node. This announcement represents the latest case of system strength issues in the National Electricity Market (NEM). It joins a growing list of areas where intervention (through direction or constraints) is required to ensure a minimum level of system strength and remediation is a necessary action. First in South Australia, then Tasmania, then North-West Victoria (Red Cliffs) and now North Queensland (Ross).

There is a common denominator amongst these cases – the transition of the power system to incorporate more asynchronous generation (wind, solar and batteries). Historically, the NEM had more than enough system strength provided simply as a function of large traditional synchronous generation being dispatched in the wholesale market. However, this feature is decreasing as the fuel mix evolves.

* The Ross node replaces the Nebo node to better represent system strength conditions in North Queensland

In comparison to the most recent fault level shortfall notice (Red Cliffs), AEMO’s projection for the Ross node are much less dire with projections of breach 5% of the time over the next five years; and an immediate 90 MVA fault level shortfall. AEMO has asked Powerlink to address this at the earliest opportunity with an agreement that the services should be in place by 31 August 2021 – a 16-month lead time.

There is a long time between now and then – the immediate solution from AEMO is the implementation of dispatch constraints designed to constrain the output of three generators in North Queensland to maintain power system security if minimum generator combinations are not present. The impacted generators are Mt Emerald Wind Farm, Haughton Solar Farm and Sun Metals Solar Farm.
This approach is similar to those used in South Australia in the presence of low demand and high wind conditions.

It is left to be seen if this cascade of events stops at the Ross node. As the NEM transitions to include increased asynchronous generation, new frameworks will need to be established to ensure that the power system is able to operate in a safe and secure state as well as deliver the least-cost solution for consumers over the long term. In addition to this we will also have the compounding issue of large coal synchronous generators leaving the NEM, which will then exacerbate any current issues resulting for higher renewable penetration.

This need to procure at least a minimum level of system strength coincides with the AEMC launching an investigation into developing a new system strength framework that is robust enough to meet current and future requirements of the NEM (EPR0076). The current framework has been designed to ensure that there exists a minimum level of system strength for parts of the network; however there is not a clear mechanism to incentivise participants to provide the service.

This review is a clear message from the AEMC that they envision formal mechanisms to be developed to incentivise participation in the market for system strength. The mechanism / framework that prevails is likely to vary depending on the objective and level of system strength procured.

We cover this investigation and much more as part of our Market Alert Service. We are also holding a webinar next week where we will look at all regulatory issues currently affecting the NEM. Get in contact if you would like to know more: