The sudden loss of nearly 2GW of generation triggered a stress event and power cuts up and down the UK on the evening of 9 August 2019. The incident was triggered by failures at two large generators, specifically Ørsted’s 1.2GW Hornsea offshore wind farm, and the 727MW Little Barford gas-fired power station operated by RWE . These failures triggered a stress event which saw the transmission grid frequency drop to 48.91Hz, below the 49.5Hz threshold, causing power cuts.
National Grid described the simultaneous loss of two large generators as: “Rare and unusual”, and said that it was working with the parties involved to understand its causes.
Other generators responded to the event by increasing their own output, but the scale of lost generation, nearly 2GW, meant that the response was not sufficient to cover it and, as a result, selected demand across the country was disconnected to protect the system itself.
The incident lasted for approximately 15 minutes, before Distribution Network Operators were given the all-clear.
Experts from the power sector have said that the incident was evidence that there was a need for more flexible generation. Mark Simon, Chief Executive for the battery storage firm Eelpower, said: “These risks will only be balanced by the introduction of high-speed, grid-connected electricity storage distributed across the country, and delivered at scale. It’s vital that the National Grid, local grid companies, and battery storage operators work together to ensure that events like this do not become commonplace. This incident demonstrates with great clarity the need for electricity storage at scale on the UK grid.”