Energy Explained: System Strength

15/07/2020
3 min

As our energy system transforms, you might be hearing the term System Strength a lot more. This explainer will run you through what System Strength is, and why it’s so important.  

What is System Strength?  

System strength is a complex and evolving concept. It is strongly related to the integrity of voltage and the voltage waveform. We’ve explained the key terms below:  

·         Voltage is the pressure that moves power around our energy system. It is made up of waveforms.  

·         Voltage waveforms are the pressure rhythms that pump power from a generation source, down the transmission lines to wherever it needs to be consumed. A strong voltage waveform means that this pressure rhythm cannot be easily disrupted, and all the equipment attached to the power lines can operate securely, and reliably.  

·         System Strength is our power system’s ability to maintain the correct voltage waveforms. High system strength improves our grids resilience to disturbances. If there’s a fault or unexpected change on the grid (like a lightning strike or a transmission line falling down), the voltage waveforms won’t change much and will recover quickly, allowing us to operate our power system safely and stably with minimal impact to the end-consumer.  

Graphs denoting high and low system strength

What provides System Strength?

System Strength is primarily supplied by hydro, coal and gas generators, and synchronous condensers. Collectively these technologies are known as ‘synchronous machines,’ and help keep the voltage waveform strong by being connected to the system and simply spinning in synchronism.

If a fault occurs that disturbs the voltage waveforms, these synchronous machines can provide short bursts of energy far above their normal maximums, which helps restore those voltage waveforms to the right shape and levels.

Generally, system strength is high in areas of the network with these synchronous machines or where the transmission network is strongly interconnected. It is lower in areas far from synchronous machines or where there is a high density of inverter-based generators (like wind and solar).

What happens if we have low system strength?

In circumstances where there is low system strength, which can be caused by an outage of a synchronous machine or major power system element like a transmission line, inverter-based resources (like wind and solar) may be unable to operate in a stable or predictable manner.

Such undesirable performance could mean an ongoing power and voltage ‘tug-of-war’ between nearby generators, or even generator disconnections, which could lead to supply disruptions and cascading failures of the power system. It could also mean that protection systems, designed to keep both people and the power system safe, may not be able to operate correctly.

How is System Strength managed in the NEM?

Maintaining system strength is the responsibility of many different organisations, including Network Service Providers (the organisations managing the poles and wires), AEMO, and some power generators.

Here are some ways the industry manages System Strength:

  • Conducts detailed modelling to understand system strength impacts of new or modified generators in the current power system
  • Determines whether there will be an adverse system strength impact and assess solutions addressing the adverse impact.
  • Conduct detailed modelling to assesses future power system needs including retirement or decommitment of synchronous generators (typically five-years ahead).
  • Identifies any System Strength shortfalls and releases a notice to the market requesting for solution proposals.

To learn more about system strength from a more detailed, technical perspective, click here.

Want to know more about the basics of our energy system? Click here to view AEMO’s Industry Course Calendar and register your interest for a more in-depth dive into Australia’s energy system.

You can also contact media@aemo.com.au to let us know what explainers you would like to see!

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