National Grid has confirmed a lightning strike on a transmission line contributed to the loss of 1.7GW of generation – including from an offshore wind farm – that led to over 1 million people losing electricity in the UK, according to a final report on the incident.
The report said transmission protection systems worked “in line with design” following a strike on the Eaton Socon-Wymondley circuit between Cambridgeshire and Hertfordshire on 9 August.
However, the incident precipitated the de-loading of 737MW from Orsted’s 1.2GW Hornsea 1 wind farm off Yorkshire and power from RWE’s Little Barford gas-fired plant.
Back-up power was not enough to replace the lost generation, which included 500MW of embedded generation, and resulted in the power outage across large parts of the UK for between 15 and 45 minutes.
“This generation would not be expected to trip off or de-load in response to a lightning strike. This therefore appears to represent an extremely rare and unexpected event,” stated the report.
National Grid has said a wider review of “security standards” following the incident should be undertaken.
This will “determine whether it would be appropriate to provide for higher levels of resilience in the electricity system” and “should be done in a structured way to ensure a proper balancing of risks and costs”.
The company has also identified several areas where lessons can be learned, it said, including in relation to communications on such an event.
The company has recommended that the facilities connected to the Low Frequency Demand Disconnection scheme be reviewed to “ensure no critical infrastructure or services are inadvertently placed at undue risk of disconnection”.
Ofgem said the final report will inform its investigation into the incident.