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What is restoration?
At the ESO, we operate one of the most reliable and secure electricity systems in the world. But we still prepare for power cuts, even though they are extremely rare.

Restoration refers to the process of restarting the grid following a power cut and it is a requirement for us, as the system operator, to have a process in place in the event of a partial or total shut down.  

How do we restart the system?

In the event of a total shutdown of the system, we need access to providers who can generate electricity without reliance on external supplies. We therefore rely on “self-starting” generators, who are able to start up their generation outside of the grid.

These self-starting generators then act as “power islands” and can gradually support sufficient electricity demand in the area. Once they have started up and are producing electricity, this electricity can be used to start up other power generators close by. In turn, these generators can then power more generators, creating a chain. Gradually we can then restart the grid by connecting these generators to the power islands, which can then power our homes and businesses. As the system starts to progressively restore, we join together multiple power islands to restart the whole system.

If only part of the system has gone down, for example there has been a regional power cut, we can connect that region to generators that are still up and running elsewhere in the country, and gradually restart the region’s power.

How quickly are we able to restart the grid?

We have to restart the grid gradually, ensuring that as we reconnect generators, frequency and voltage remain within our operating limits. To do this requires a coordinated effort right across the system, with the support of the entire network to make sure that we can keep the electricity supply stable as we gradually bring generators back onto the network.

BEIS recently introduced a new standard which requires us to restore 60% of power within 24 hours, and all power within 5 days.

Fortunately, Great Britain has never seen a national power cut. In August 2019, a lightning strike resulted in a power cut in regions of England and Wales, but the system was restored in just 45 minutes.

Who are self-starting generators?

Self-starting generators are able to start up their generation independent of the grid. We procure contracts with these generators, just in case there is a power cut. We have to ensure that we have self-starters in every region across the UK so that we can connect local generators to them quickly and efficiently if needed. Not all power stations have, or are required to have, the capability to provide restoration services.

Self-starting generators are required to fulfil a range of criteria to make sure that they will be up to the task of restoring the grid if needed. This includes their ability to start up without power from the grid, but they also need to be able to supply a large amount of power to start up other generators in the region. As well as this, there are a range of technical requirements that generators providing restoration services need to comply with in order to achieve a safe and reliable return of the electricity system.

How will restoration change with zero carbon electricity?

As we use fewer carbon energy sources, the way that we power the system is changing. Many of the traditional self-starting generators we use today rely on fuels that are not zero carbon, for example coal and gas. However, our Distributed Restart program is looking into how we can get restoration services from zero carbon sources instead. The world-first initiative is exploring how distributed energy resources (DER) such as wind, battery energy storage and hydro, can be used to restore power to the transmission network in the unlikely event of a blackout.

Find out more about Distributed Restart