If you suddenly lose power at home, what’s the first thing you do? Most of us keep a torch where we can find it quickly in a blackout (or candles and matches, if we are old school). Once you have light, you can check what is happening and start getting organised. But what happens when the whole power system is blacked out?

It doesn’t happen often – just three times ever in eastern and south-eastern Australia (South Australia in 2016, northern Queensland in 2009, and New South Wales in 1964). But in electricity supply terms, the worst case scenario is when a major disturbance cascades to a point of no return, where the frequency and voltage on the grid can’t be maintained and supply to a big area is completely lost.

A black system means a major part of the system, even a whole state, blacks out and is isolated from everywhere else. (A “brownout” is a major reduction in available power supply to an area, often in an effort to reduce a complete blackout.)

By definition, in a black system, nothing is up and running, so we have to use power from somewhere else to jump start the system in the blacked-out region.

Most generators can’t start themselves – they need power from an energised network. So, to prepare for a rare but potentially catastrophic black system, AEMO has agreements with some generators for system restart services. These agreements are with power station units that are able to start themselves up using a power source outside the network, and then ‘energise’ a section of the blacked out area. Energising the network means getting voltage on the system, so it can start getting ready to transfer power again. Another way of energising the blacked out area might be to reconnect the lines from a neighbouring network area that is still live.

The first section to be energised is then used to start up more generators and build up the network, allowing power to be restored to more and more consumers. Eventually – and as quickly as safely possible – the whole blacked out part of the system can get back to normal operation.

So AEMO prepares for black system events by planning:

  • Which system restart services we will contract for in case they are needed. AEMO aims to contract enough generators to meet the restart standard set for us by an external body called the Reliability Panel, at the lowest available cost. We sign contracts in advance for these generators to be available if they are needed. At the moment, only synchronous generators can provide this service.
  • How we will use the available system restart services and any “live” parts of the system, and build from there to get consumers’ power supply safely flowing again. Together with the network operators, we plan for a few different energisation options, because some parts of the power system may have been damaged in whatever events led up to the black system. From there, the restoration sequence also needs to be carefully coordinated to keep supply and demand in balance to manage frequency across the power system, and regulate voltage to reduce the risk of equipment damage.

System restart services and plans are a key technical requirement for a secure and reliable power system. We hope we never need them but, given the business and community impact of a black system if it happens, we always need to be prepared for the worst.

If you want to know more, AEMO has technical detail about how system restart services operate on our website.