10
LONDON
Power cut
down to a
combination
of factors
A COMBINATION of factors led to the
rush-hour London power cut, says
National Grid Transco.
These were:
q planned normal summer maintenance
work meant that Wimbledon and New
Cross and Hurst and Littlebrook were
connected by only one circuit
q an alarm indicated a fault at Hurst
substation, a transformer was taken out
of service and power rerouted into
London through other circuits
q within seven seconds another fault
occurred, stopping flows on a 275,000volt underground cable between New
Cross and Wimbledon substations. At
this point, electricity supplies to the
affected areas could not be maintained.
The problem — an incorrect
protection relay installed in 2001 when
old equipment was replaced — was
identified, fixed within half an hour and
full power was restored to the
transmission system. Fifteen minutes
later distribution company EDF Energy
re-energised its system.
“Of course, if the two circuits which
were being maintained had been in
service, there would not have been a
power cut,” said Nick Winser, NGT
group director of UK and US
transmission.
“The maintenance, however, was
necessary and the security of the
system had been properly planned for,
including EDF’s pre-planned response
in the event of a transformer failure.”
The incorrect relay — one amp
instead of five — had not been detected
during the 2001 commissioning and
quality control checks.
“We are inspecting all 43,000 similar
types of equipment and also
implementing other actions to make
sure we learn the \