By David Middleton, Head of Commercial Delivery, Origami-Energy
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. While some new power stations are being constructed, progress is slow and it will take time (partly due to the changing investment landscape). 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 also 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.”
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 ~670MW and two minutes later Hornsea (offshore wind farm) tripped, exporting ~650MW.
- Combined loss ~1,320MW which dropped frequency to 48.914Hz.
- Information suggests these were 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.
- The system was operating normally at a grid level within ~15 minutes.
Was this 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. See https://www.theguardian.com/business/2008/may/28/power. There were a number of distributed generators that tripped in the Liverpool / Manchester area which caused local issues due to their protection relays operating (see below).
- And these problems will almost certainly happen again and may happen perhaps more often as distributed generation increases and proliferates
Why were there widespread issues?
- There were customers off supply around England and Wales.
- 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 have standby generation and some companies that do may have had failures to respond.
For more information about Origami visit: www.origamienergy.com