The Australian Energy Market Operator (AEMO) as the network planner for Victoria and Market Operator for the National Electricity Market (NEM), provides a detailed overview of System Strength with an extract from AEMO’s website as follows:
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).