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Lightning strike blamed for UK power cut

By JONATHAN POWELL | China Daily Global | Updated: 2019-08-21 14:38

[Photo/Agencies]

An interim report from Britain's energy systems operator National Grid has blamed a lightning strike for a major power outage that affected more than one million homes and businesses across the nation on Aug 9.

Britain's energy regulator, Ofgem, is to investigate whether the electricity network operators breached license conditions in a probe into power cuts that caused the nation's most severe blackout in more than a decade.

The Friday evening outage caused rush hour travel disruption across the United Kingdom's biggest train stations, railways, roads and airports, and left some "critical facilities," such as hospitals, in the dark.

The energy watchdog asked National Grid to give an initial report into what went wrong, while the government announced a separate inquiry. The regulator has the power to fine companies up to 10 percent of their UK turnover.

National Grid initially blamed the "rare and unusual event" on a severe drop in the grid's frequency-a measure of energy intensity flowing around the network-following a pair of major generator outages.

The operator said in its interim report that a lightning strike on a transmission circuit, followed by "two almost simultaneous unexpected power losses" at two power plants, caused the disruption.

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

The two near-simultaneous power plant outages-at the Little Barford gas-fired power plant and the Hornsea off shore wind farm-caused the frequency to drop below the grid's safety limits.

National Grid called on backup electricity providers to ramp up their output within seconds of the unplanned outages. Usually these backup contracts can stabilize the frequency before it drops too far, but in this case the safety net was not enough to stop parts of the grid from automatically shutting down.

The report said this scale of power generation loss meant that the level of backup power required under the regulatory standards was insufficient to cover the loss.

As a result, the system automatically disconnected customers on the distribution network-causing about 5 percent of electricity demand to be turned off to protect the other 95 percent.

Jonathan Brearley, a senior executive at Ofgem, said the regulator had received the report and believed there were still areas that needed to be investigated.

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

"The power cuts of Friday Aug 9 caused interruptions to consumers' energy and significant disruption to commuters. It's important that the industry takes all possible steps to prevent this happening again."

The regulator Ofgem said its investigation into the power cuts would examine the grid's requirements to hold sufficient back-up power to manage loss of generation supplies, how generators met their obligations with respect to the transmission fault and whether distribution network operators complied with their obligations.

National Grid must submit its final detailed technical report to Ofgem by Sept 6.

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