LONDON (Reuters)
An undersized fuse that lay undetected for two years caused the blackout
which paralysed rush-hour London last month, the electricity network
operator has revealed.National Grid Transco, under pressure to find fast
answers, was providing an update into the August 28 power cut that trapped
thousands of commuters underground and cut supplies to 400,000 customers
across the south of the capital.
Chief Executive Roger Urwin said the incident was caused by a single item of
the wrong gauge equipment that was only put between Londoners and their
electricity supply by an unlucky "one-off" chain of events. But he was not
complacent.
"This is a serious incident for us," he said. "We will need to examine
rigorously our supply and commissioning procedures."
Four main power lines serve the southern part of the city, including the
input for its Underground railway.
On Thursday, August 28, two of these lines were out of action for routine
maintenance.
Just after 6 p.m., an alarm -- of a type that goes off on average once a
month around the network -- sounded on one of the remaining two lines,
causing engineers to shut it down.
This left all power for a swathe of south London dependent on a single line
as dusk gathered and commuters headed home.
OOPS! ONE AMP FUSE
Two years previously, engineers had installed on that last remaining line a
shoebox-sized item called a protection relay, which is designed to act like
a normal domestic fuse, isolating parts of the network in the event of an
excessive power load.
They had installed by mistake a one ampere version, instead of the five
ampere model for which it was designed. Engineers said the two look very
alike.
The one installed was designed to trigger at a current of just 1,020
amperes, one fifth of the actual danger level.
When power surged to just 1,460 amperes to take the full strain on the last
remaining line in service, the oversensitive fuse was triggered. The lights
went out in parts of the capital, prompting scenes reminiscent of the
blackout that hit eastern North America earlier in August.
National Grid said it was extending its investigation to try to ensure no
similar incident can happen again. Urwin said the probe would not
significantly impact profits for the privatised group. Its shares were
unaffected, rising one percent to 381-1/2 pence in line with other
utilities, but analysts said the new findings pointing at faulty workmanship
were a concern.
"This development means that National Grid is now more likely to have some
financial exposure to the incident," said Fraser McLaren of ING. "There
is... a risk that the authorities will seek to capitalise on this admission
and pin the blame through financial penalty."
The Department of Trade and Industry said it had launched its own
investigation in conjunction with industry regulator Ofgem. This probe will
also look into another outage that struck Britain's second city, Birmingham,
last week.
The oversensitive fuse has since been replaced and 20 percent of 43,000
similar systems on the grid had been surveyed so far, with no like cases
found. National Grid said the remainder would be checked within four weeks.
CEO Urwin dismissed suggestions that he should resign if such an event
occurred again. "The investigation has concluded that there was not a
significant failure of management systems or competence," he said. "That
does not arise."
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