Skip to content

Inertia

https://australiainstitute.org.au/wp-content/uploads/2021/03/VEPC-system-security-report-FINAL.pdf

Electric system inertia is a measure of energy that is stored in large rotating machines that are synchronized to the grid at 60 Hz.

Inertia refers to the extent to which the power system resists (in micro-second time scales) changes to demand and supply.

System strength refers to the extent to which a stable voltage waveform is maintained after disturbances to the system, such as from a short circuit.

Batteries' inertia is not limited by the kinetic energy of coal generators' storage capacity. Whereas coal generators are only able to provide an inertial response equal to its capacity for around three seconds, batteries can provide this for far longer than the inertial response needed.

While inertia is most often multi-regional, system strength is mostly a local or regional issue, and so supplies of it need to be sourced locally.

The Rate of Change of Frequency (RoCoF) is measured in Hz per second. In the NEM, the automatic access standard is to be able to operate continuously with a RoCoF of 4 Hz/s for 0.25 seconds, and 3 Hz/s for more than one second.

Reliable power system frequency operation requires a combination of:

  • Inertia acting in the first second after a disturbance, used to slow the rate of change of system frequency and allow generation to respond.

  • Fast-acting generation responding in the first thirty seconds after a disturbance (primary frequency control) and used to keep the frequency in a safe operating range.

  • Slower acting generation greater than thirty seconds after a disturbance (secondary frequency control), used to bring the system back to 50Hz

In NEM, most inertia is provided by coal, gas and hydro generators. A substantia amount of inertia is also provided by the inductance in the transmission system and in the rotating on the demand side. Primary frequency control is provided by automatic generation control (AGC), regulation frequency control ancillary services (FCAS) and 6 Second contingency FCAS.