The National Grid Electricity System Operator has welcomed the investigation into Friday's power cut, having already initiated its own internal review.
It has said it will be “collaborating closely with Ofgem, local distribution networks and affected power stations / generators to understand the cause”.
Secretary of State for Business, Energy and Industry Strategy, Andrea Leadsom, ordered an inquiry after one million people were affected by the cut on late Friday afternoon.
A malicious attack and the wind conditions have already been ruled out, with operations director Duncan Burt quick to establish that.
He told how it was a physical event on the network, stating it was an “incredible rare event of two power stations disconnecting near-simultaneously”, in an interview on BBC Radio Four’s Today programme.
It was also revealed that the loss of the two generators – Hornsea One and Little Barford – was larger than back-up could cater for, triggering secondary back up systems. The latter action, automatic in response, saw strategic decisions already in play actioned on which demand would not be met in the UK.
Mr Burt said: “It wasn’t the case that the wind had got too strong. Their automatic protection systems fired to disconnect those two generating units from the grid and that then led to a sequence of events which resulted in the disconnecting of some demand in the country.
“The loss from those two generators is larger than our standards would routinely secure for, so that took the grid to a place which meant we needed secondary back up systems to come in and keep the system safe.”
He told how the two events happened “very, very quickly , in a matter of a few seconds – maybe a couple of minutes maximum,” adding: “The events have nothing to do with changing in wind speed or variability of wind.
“We are already very confident no malicious intent or cyber attack involved. We can see the fault reading, the event reading from our systems that show what was happening electrically on the network and we can see it was a physical event out on the network with the connection of those generators.
“We will provide a detailed technical report and will grow that over the coming days and weeks as we work with generators and the distribution companies as information becomes clear. This will require careful study to make sure we do learn any lessons that come out of it and the next time this happens disruption is minimised and a lot less than this night.”
The last time a similar dual-disconnection came was in 2008.
Little Barford is a 727MW plant owned by RWE. Orsted’s Hornsea One will be a 1.2GW wind farm when complete, but is currently understood to be operating at around 868MW as the final 50 turbines are installed before the year’s out. It brings power onshore at Horseshoe Point on the Lincolnshire coast, skirting Grimsby to an onshore substation at North Killingholme.
A spokesperson for Orsted said: “Hornsea One lost load around the same time as another generation source lost load. We are investigating the cause, working closely with National Grid System Operator, which balances the UK’s electricity system.”
