UK regulator Ofgem launches probe into August 9 power cuts

London — Ofgem has launched an investigation into power cuts across England and Wales August 9 to see if network operators or generators were in breach of license conditions, the energyregulator said Tuesday.

Ofgem said an investigation would focus on National Grid's requirement to hold sufficient backup power to manage generation losses.

The parties under investigation include National Grid, the 12 distribution network operators in England and Wales, and generators RWE Generation, which operates the Little Barford power station, and Hornsea offshore wind farm operator Orsted. The two sites experienced large outages within seconds of each other, following a lightning strike to a transmission line, removing a total of 1,378 MW in supply to the grid.

The investigation would seek to learn lessons and take steps "to further improve the resilience of Britain's energy network," Ofgem said.

The investigation could take the form of inertial response (from large rotating turbines) by generators already running and connected, and frequency response from rapid sourcesof additional power such as batteries.

It would look at whether distribution system operators complied with low frequency demand disconnection obligations, and whether the right customers were disconnected.

The regulator was already liaising with rail regulator the Office of Rail and Road to understand why the drop in frequency led to disruption for passengers.

It is also supporting the government's Energy Executive Emergency Committee in its investigation into the power failure.

"Having received National Grid ESO's interim report, we believe there are still areas where we need to use our statutory powers to investigate these outages," Ofgem's ExecutiveDirector Jonathan Brearley said.

"This will ensure the industry learns the relevant lessons and to clearly establish whether any firm breached their obligations to deliver secure power supplies to consumers," he said.

LIGHTNING STRIKE

In its report, National Grid described a chain of events on August 9 that began with a lightning strike on the Eaton Socon-Wymondley transmission line in Hertfordshire at 4:52 pm.

Protection systems operated and cleared the lightning in under 0.1 seconds and the line returned to normal operation after 20 seconds.

There was loss of small embedded generation connected to the distribution system amounting to 500 MW due to the lightning strike.

Immediately following the lightning strike and within seconds of each other both Hornsea offshore windfarm and Little Barford gas power station reduced energy supply to the grid, removing a total 1,378 MW.

"This unexpected loss of generation meant that the frequency fell very quickly and went outside the normal range of 50.5 Hz - 49.5 Hz," National Grid said.

National Grid had 1,000 MW of automatic backup power at that time as required under Security and Quality of Supply Standards, designed to cover the loss of the single biggest generator to the grid.

All this plus other tools the system operator uses to manage frequency were used, including 472 MW of battery storage.

Nevertheless frequency fell to 48.8 Hz, a level where secondary backup systems were required to disconnect some demand.

This automatically disconnected customers on the distribution network in a controlled way and in line with parameters pre-set by distribution network operators.

Around 5% or 1 GW of Great Britain's electricity demand was turned off to protect the other 95%, something that has not happened in over a decade. Some 1.1 million customers were cut off.

Grid actions then returned the system to a normal stable state by 5:06 pm, while DNOs reconnected customers and supply was returned to all customers by 5:37 pm.

A number of a particular class of trains operating in the southeast were unable to stay operational throughout the event and, in a number of cases, required an engineer to be sent out to the individual train.

Other critical facilities were affected including Ipswich hospital and Newcastle airport.

In its own preliminary conclusions, National Grid said the "exceptional generation loss was beyond the levels to which we are required to secure the system."

Voltage performance of the system was within requirements and analysis showed the transmission system "operated in line with the Security Standards and the Grid Code," it said.

-- Henry Edwardes-Evans, henry.edwardes-evans@spglobal.com

-- Edited by James Burgess, james.burgess@spglobal.com