The reduction in the energy supply from the Hornsea One offshore wind farm on 9 August was caused by a lightning strike, an initial report from National Grid Electricity System Operator (NGESO) has revealed.
Following the lighting strike, Hornsea One immediately de-loaded from 799MW to 62MW, the report said.
The wind farm lost modules 2 and 3 following the lightning strike, totalling 737MW. Module 1 continued to operate smoothly at 50MW throughout the event, according to the report.
Hornsea has confirmed that the equipment at the wind farm saw a system voltage fluctuation with unusual characteristics coincident with the lightning. The initial reaction from Hornsea’s systems was as expected in attempting to accommodate and address the system condition, but very shortly afterwards as the reaction expanded throughout the plant, the protective safety systems activated, the report said.
Following an initial review, adjustments to the wind farm configuration, and fine tuning its controls for responding to abnormal events, the wind farm is now operating robustly to such millisecond events.
The lightning strike was also responsible for Little Barford gas power station reducing its energy supply to the grid. The total generation lost from these two transmission connected generators was 1,378MW.
Following the release of the report, Ofgem launched an investigation into the power cuts which saw nearly one million people lose power in England in Wales.
Ofgem’s investigation will seek to establish what lessons can be drawn from the power cut to ensure that steps can be taken to further improve the resilience of Britain’s energy network.
It will also seek to establish whether any of the parties involved, including Ørsted, the owner and developer of the 1,214MW wind farm, breached their licence conditions.