The national grid is under investigation as the lights go out

The UK Electricity System Operator is subject to governmental and regulatory investigations after the largest power outage in more than a decade.

More than one million electricity customers were without power for up to 50 minutes on 9th August this year, with some systems affected for close to 24 hours, after a lightning strike apparently led to a loss of generation from two independent generation sites.

According to the National Grid ESO’s Interim Report, which was demanded by Ofgem within hours of the power being restored, a lightning strike on the Easton Socon-Wymondley Main transmission circuit may have triggered a series of events which led to a drop in frequency below the 49.5Hz threshold.

Although the strike – one of many during in day of heavy rain and storms – was dealt with by the system in under 0.1 seconds and normal operation apparently resumed within some 20 seconds, the two generation plants – Hornsea Offshore windfarm and Little Barford gas power station – unexpectedly went offline immediately after the strike and within seconds of each other. 

While the automatic backup power of 1,000MW was immediately deployed, along with additional battery storage power of around 472MW, it was not enough to make up for the shortfall and frequency dropped to 48.8Hz.

According to the Report, the significant loss in frequency meant: “secondary backup systems were required to disconnect some demand (the Low Frequency Demand Disconnection scheme) and these automatically kicked in to recover the frequency and ensure the safety and integrity of the network.

“This system automatically disconnected customers on the distribution network in a controlled way and in line with parameters pre-set by the Distribution Network Operators. In this instance c. 5% of GB’s electricity demand was turned off (c. 1GW) to protect the other 95%. This has not happened in over a decade and is an extremely rare event. This resulted in approximately 1.1m customers being without power for a period.”

The report reinforced the fact that the Grid’s protection and safety systems worked as expected and the Distribution Network Operators were able to restore power supplies to consumers within 31 minutes of the event. However, amongst the systems affected were a number of South-East Rail trains, whose own systems had to be reset, in some cases by engineers attending trains that were stranded on the tracks. Ipswich Hospital and Newcastle Airport were also affected.

While so far no involvement of infrastructure at the sub-station level of the distribution system has been identified as part of the event, Fundamentals Ltd Business Development Director, Vincent Thornley commented: “Managing frequency through effective voltage control is certainly one area where solutions are available to mitigate these type of events. Electricity North West’s Customer Load Active Systems Services (CLASS) Project, which uses Fundamentals’ voltage control technology, has demonstrated that this type of system management model could be a gamechanger in managing load and generation balance across the entire network. We are convinced that rolling-out a CLASS model nationally could help avoid the effects of this type of event we witnessed last month.”     

In a statement by National Grid CEO, John Pettigrew, on the organisation’s website the day after the blackout, he used honesty, clarity and an element of humour to try and explain the situation as investigations began. He stated: “There is never a good time for a power cut. But ten to five on a Friday afternoon in August, when people are trying to get home to their families and friends after a hard week at work, is one of the worst.”

He continued: “Since that partial power cut, thousands of colleagues across the industry have been working hard to ensure the system is robust and to understand exactly what happened, and what we should do differently in the future.”

As well as a demand from Ofgem for a full report by 6th September (the results of which had not been revealed publicly, at least, by the beginning of the following week) the Government’s Department for Business Energy and Industrial Strategy (BEIS) has asked its Energy Emergencies Executive Committee (E3C) to review the incident, a moved welcomed by the EOS in helping to: “identify lessons and recommendations for the prevention and management of future power disruption events.”