UK power cut: how can we avoid future blackouts?
On Friday 9th August at approximately 4.54pm, there was a power cut in the UK that affected many across the country. This resulted in speculation and confusion as to what happened. In this post our Head of Commercial Delivery, David Middleton, lays out the facts of what caused it and how we can prevent it from happening again.
What caused the issue?
The issue was the amount of generation that tripped, not the technologies involved. Just before teatime peak last Friday, Little Barford (gas station) tripped whilst exporting ~660MW and two minutes later Hornsea (offshore wind farm) tripped, exporting ~800MW. The combined loss was ~1,440MW which dropped frequency to 48.8Hz, as measured by one of our Energy Routers stationed at a customer site. This level of frequency is well below the statutory limits imposed on National Grid.
The loss of generation was above the level that National Grid plans for in a largest single loss (currently 1200MW from Sizewell B). Early information suggests these may have been coincidental and unrelated issues. At very low frequency levels, there is automatic load disconnection to protect the system and help to restore frequency to normal levels. If the frequency drop had been allowed to continue, past 47.7Hz for a sustained period, we may have seen more widespread and impactful blackouts.
The system was operating normally at a grid level within ~15 minutes.
Ian Welch of Ian Welch Power added “Two trips are rare, and it would be prohibitively expensive to defend against all eventualities, given the cost versus probability. That said our grid should be stable for a single generation loss of up to 1200MW (rising as new Hinckley nuclear power comes on line) it is difficult to see why an event of this magnitude should have had such a large impact on frequency, though perhaps lighter summer demand means that a large trip has a proportionally greater impact than a mid-winter event.”
Was this unique?
This wasn't unique. A similar problem occurred on 27 May 2008 when 0.5M people were off supply when Sizewell B (nuclear, Suffolk) tripped 2 minutes after a Longannet (coal, Fife) tripped and the system lost 1510 MW of generation. There were several distributed generators that tripped in the Liverpool / Manchester area which caused local issues due to their protection relays operating. It is likely that blackouts of this nature will happen again.
Why were there widespread issues?
Nearly one million people were affected by the outage around England and Wales; predominantly in London, the South East, the Midlands and North West. In some areas the power took an hour to come back on, it was rush hour on a Friday and hospitals and airports were among the affected.
This is likely to have happened as a result of the following;
- automatic load disconnection due to very low frequency levels to protect the system and help to restore frequency to normal levels;
- tripping of distributed generation that can export to the network. This is protected with relays which will self-disconnect generation to protect the generation if either the absolute frequency drops below a threshold level or the rate of change of frequency is greater than a (different) threshold level.
- The reliability of the network means that many organisations don't have standby generation and some companies that do may have had failures to respond.
How can we avoid future blackouts?
As we continue to close large coal, gas, and nuclear power stations, the amount of inertia on the grid is reducing. Inertia is the ability of large synchronous generators, which have rotating shafts, to overcome the immediate imbalance between power supply and demand.
We need to replace the inertia on the grid that is being lost through the closure or mothballing of large generating units. Whilst some new power stations are being constructed, progress is slow, and it will take time (partly due to the changing investment landscape). In addition, using inverters on non-synchronous generation to provide synthetic inertia is feasible. In the meantime, National Grid Electricity System Operator (ESO) should consider purchasing more frequency response to enable the system to recover from major frequency deviations quickly and reliably.
Frequency response is a demand response mechanism that enables demand to be rapidly adjusted on the grid in response to changes in grid frequency. The ESO purchases frequency response through tender and the level varies by time of day and day of week. Increasing frequency response capacity can be achieved quickly.
We need more energy assets that can provide fast response from storage (batteries and hydro) and quickly turning demand (large plant) on or off to balance frequency supported by real-time visibility and control.
Another option is to increase the threshold before distributed generation protection operates. This has been discussed for some years and is in progress, but due to its cost the implementation will not be quick.