From the Telegraph:
The North Hyde substation in Hayes is one of several so-called “grid supply
points” serving Heathrow and its immediate surroundings.
It takes electricity from the National Grid at 275,000 volts and transforms
it to a lower voltage of 110kV for distribution around the local area.
North Hyde feeds the north-eastern quadrant of Heathrow airport, The
Telegraph understands.
The fire destroyed a vital transformer at the substation and also a backup
transformer, rendering the substation inoperable.
The airport is also served by two other substations. However, in order for
Heathrow’s other two substations to run the airport, the power supply to
all the terminals needs to be re-engineered.
While this is happening, Heathrow relies on its backup supply, which is not
sufficient to run the entire airport.
Speaking to reporters on Friday night, Thomas Woldbye, Heathrow’s chief
executive explained: “We have three of these substations, each of them has
a backup transformer.
“The backup transformer in this case also went and then we had to
restructure the supply. So we’re not out of power but we have to
restructure our power supply.
“To do that we have to close down systems – that is safety procedure, we
will not go around that.”
He added: “Two substations can run the airport but we need to re-engineer
the structure of the power supply for all the terminals and that’s what we
were doing during the day, and then we have to restart all the systems and
that’s what we’ve done, and we now see operation coming back.”
He described the decision to close the airport as a “very difficult one”
that they took “quite early” when it became clear Heathrow could not be
safely operated.
National Grid did not respond to a request for comment about the
substation.
What is Heathrow’s back-up supply?
Heathrow said in a statement the airport’s back-up energy systems worked
“as expected” when the substation fire started.
This supply consists of diesel generators, which provide emergency power to
areas such as the air traffic control tower to ensure any planes coming
into land at the moment of a power outage can do so safely, and a biomass
generator. However, this only provides light and heating to the terminals
and cannot operate without an external source of power.
Heathrow said: “We have multiple sources of energy into Heathrow. But when
a source is interrupted, we have backup diesel generators and
uninterruptible power supplies in place, and they all operated as expected.
“Our backup systems are safety systems which allow us to land aircraft and
evacuate passengers safely, but they are not designed to allow us to run a
full operation.”
When asked on Friday afternoon if there was a weak point in Heathrow’s
power system, Mr Woldbye said: “You can say that but of course
contingencies of certain sizes we cannot guard ourselves against 100 per
cent and this is one of them.
“This has been a major incident. I mean, short of anybody getting hurt,
this is as big as it gets for our airport and we are actually coming back
quite fast I would say, when you consider the amount of systems that we
have to shut down, then bring back up and make sure that they’re safe.”
A 2023 US government report which called for “electrical resilience” to be
stepped up at major American hubs following a series of power outages,
lists some of the systems “critically affected” by power loss.
A survey found computers and networks controlling baggage handling,
boarding gates, check-in systems, ticket scanners, departure and arrival
screens, escalators, lifts and parking machines and their entrance and exit
barriers had all been shut down by power cuts.
And, once the power is restored, tests to make sure those systems – many of
which are interconnected – are working properly can prove time-consuming.
Warnings were raised in 2022 about demand outstripping supply at the
electrical substations supplying Heathrow.
A London Assembly briefing paper, prepared by SSE Networks (SSEN) and seen
by The Telegraph, detailed how heavily the North Hyde substation was being
used.
Although the substation’s rated power delivery capacity was 76 MVA
(megavolt-amperes, a measure of power capacity), a figure that included a
safety buffer, SSEN said that the maximum recorded usage at the time of
writing was 80.7 MVA.
An upgrade project was planned to add another 22 MVA of capacity to the
substation although no date was given.
What may have caused the fire?
The arrival of counter-terrorism police at the scene increased speculation
that malign forces could have been responsible. Some pondered whether
Russia may have wanted to send a message to the UK after the Government
held meetings with European military leaders over a peacekeeping force in
Ukraine on Thursday.
By lunchtime, the Met had confirmed those officers were leading the
investigation.
However, energy experts believed the real threat may have been far simpler.
Professor Manu Haddad, director at the Advanced High Voltage Engineering
Research Centre at Cardiff University, said: “From the videos I saw, it may
be a fire at the transformer.”
He added: “Transformers are devices that handle the power coming in and
going out of the substation. Usually, the supply power arrives at very high
voltage and is reduced to lower voltages for distribution to customers.”
Dr Robin Preece, reader in future power systems at the University of
Manchester, said: “This is done using transformers which are filled with
oil. The oil is a very good electrical insulator and is needed to stop the
electricity sparking to places it’s not meant to go inside the transformer.
“If there is a catastrophic failure of a component, this can cause a big
electrical spark or flashover which is extremely hot and which can cause
nearby things to catch fire. Unfortunately for a transformer, this can lead
to the oil catching fire – which is why the fire can be so large and
difficult to control.”
Another theory police will be trying to rule out the possibility that scrap
metal thieves could have triggered the fire. Theft of copper cabling and
other metals from the energy networks, including substations, has resulted
in numerous deaths and power cuts.
In July 2011, a 16-year-old boy was killed and three other youths arrested
after they had tried to steal copper from an electrical substation in
Leeds. There were no casualties at the Hayes fire, according to the London
Fire Brigade. However, such thefts have culminated in fires and entire
regions being without power.
Commander Simon Messinger, who has led the Met Police response to the
incident, later said: “After initial assessment, we are not treating this
incident as suspicious, although inquiries do remain ongoing.”
Why are substations so vulnerable to fire?
High voltage electrical transformers such as the ones at North Hyde
substation take electricity from the National Grid and reduce its voltage
to levels that are safe enough for onward transmission around local areas.
All such transformers generate a large amount of heat, requiring a
dedicated cooling system. Thus North Hyde’s transformers were fitted with
systems carrying 25,000 litres of cooling oil. This ignited when the fire
started late on Thursday night.
At a press conference near the scene, Jonathan Smith, London Fire Brigade’s
deputy commissioner, illustrated the size of that very flammable problem.
“The fire involved a transformer comprising 25,000 litres of cooling oil
fully alight,” he said. “This created a major hazard due to the still live
high-voltage equipment and the nature of the oil-fuelled fire.”
Because North Hyde was fully outdoors, fitting fire suppression systems was
likely to be difficult, sources familiar with high-voltage electrical
systems said.
Thanks to the very high voltages in grid transformer stations, they are
typically unmanned – meaning there is no human presence on site unless
maintenance is required. However, there are remote monitoring systems
capable of detecting faults and fires, The Telegraph understands.
Are there security protections?
Exact details of security systems protecting grid substations, which are
classified as critical national infrastructure, are closely guarded.
However, the National Grid’s control centre near Warwick is almost
instantly able to detect faults such as loss of power to a particular
sub-station or row of pylons – known as a transmission circuit – caused by
incidents such as a fire or a cable break.
It is understood that both overt and covert CCTV cameras are installed at
key locations to ensure constant security coverage.