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UK energy regulator asks National Grid for urgent report into country-wide blackout

13 August 2019

Britain’s energy regulator Ofgem has asked National Grid for an urgent report into the power cut which caused chaos across the country on the evening of August 9. National Grid, said the power cuts happened after a rare and unusual issue which had led to the almost simultaneous loss of output from two generators.

Representative image: Shutterstock
Representative image: Shutterstock

Ofgem said National Grid, which operates the electricity transmission system in England and Wales, must report initial findings by August 16, with a final technical report due by September 6.

The hour-long outage left almost 1 million homes without power while two of London’s busiest train stations closed at rush-hour because of overcrowding as services were cancelled or delayed.

National Grid put the blackout down to “incredibly rare” circumstances following the unexpected shutdown of two power generators. The blackout took place after two near-simultaneous power plant outages – at RWE’s Little Barford gas-fired power plant and Orsted’s giant Hornsea offshore wind farm – caused the frequency to drop below the grid’s safety limits.

RWE said its power plant shut down automatically due to a technical issue which is “not uncommon” at power plants. Orsted declined to comment on why its giant windfarm went offline while it investigates the issue alongside the energy regulator.

National Grid gave the all-clear for these networks to begin restarting their system 15 minutes after the outages, but transport disruption, particularly on the rail networks, continued until the next day.

The company said it was working with the regulator, the generators and other stakeholders to “understand the lessons learned” from the blackout.

According to industry sources quoted by the Guardian, near-misses are on the rise and the system operator has been aware of the growing potential for a wide-scale blackout for years.

A key part of the operator’s job is to keep the frequency of the grid steady at around 50Hz; a deviation of more than 1% in either direction is enough to cause parts of the energy system to automatically shutdown as a safety precaution.

In the last 12 weeks the grid’s frequency has fallen dangerously low, below 49.6Hz, on three separate occasions. Prior to these near-misses the grid’s frequency had not fallen to this extent for at least the last four years.

Update: On August 20, UK electricity regulator Ofgem said network operator National Grid had concluded the August 9 outage was caused by a lightning strike.

Ofgem commissioned a report into the causes of the outages from National Grid and said it would open its own investigation to establish whether any of the grid and network operators or generators breached their licence conditions.

National Grid said the power cuts were the result of an unusual issue that led to the almost simultaneous loss of output from two generators - Orsted’s Hornsea off-shore windfarm and RWE’s Little Barford gas-fired plant.

There were many lightning strikes that hit the electricity grid that day, but only one had a significant impact - on a transmission line at 1652 local time, which returned to normal operation after around 20 seconds, the grid’s report said.

Around 500 megawatts of generation capacity was also disconnected - all of which is normal for such events.
However, immediately after the lightning strike and within seconds of each other, Hornsea and Little Barford reduced supply to the grid, disconnecting 1,378 MW of generation.

“As generation would not be expected to trip off or de-load in response to a lightning strike, this appears to represent an extremely rare and unexpected event,” National Grid said.

National Grid said it will deliver its final report to Ofgem by September 6, in which it will examine the exact failure mechanisms at Little Barford and Hornsea, as well as demand side impacts and communication processes.

Separately, an emergency committee will also investigate the incident, the government said last week.


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