Heathrow shut down after electrical substation fire: the experts explain

More than 1,300 flights around the world have been affected when a fire at an electrical substation caused Heathrow Airport to close late yesterday evening (Thursday 20 March). But why did this happen?

The UK’s busiest airport shut after the blaze at the North Hyde substation in Hayes, west London. With the airport closed until at least midnight tonight, and passengers across the globe wondering what caused the disruption and how long it will persist for, engineering experts from the Institution of Engineering and Technology (IET) help to explain the situation.

What are substations?

Professor John Loughhead CB OBE CEng, Fellow and electrical engineering expert at the Institution of Engineering and Technology (IET), said: “An electrical substation is where high voltage electricity from the National Grid is transformed to lower voltages and distributed to users, and contains various switches and safety devices. It is therefore the supply point for users. It is surprising that, as a part of our national critical infrastructure, Heathrow does not have an alternative supply point in case of accidents like this.”

Mark Coles, Head of Technical Regulations at the IET, added: “Electrical substations are a critical part of the electrical distribution system. Power stations generate electricity which is then distributed across the country at high voltage. Substations connect the power station to the distribution network and then, at the other end, substations connect the distribution network to where power is needed.

“Substations are electro-mechanical installations. Transformers are used in substations to raise the voltage for distribution across long distances and then to lower the voltage to a more usable level for use in electrical installations in, for example, commercial buildings and homes.”

Graham Kenyon, an electrical engineering expert at the IET, commented: “An electrical substation like this takes very high voltage power from the National Grid, and switches it to various transformers, distribution protection equipment, and other substations that eventually supplies end users such as homes, businesses and airports with power.

“This particular substation is a major distribution centre for the National Grid, in a very populated area of the city. In addition to Heathrow Airport and local residences and businesses, there is a significant amount of commercial and industrial power use in that area.”

Why has this fire happened?

“Fires do occasionally, but not frequently, occur at substations and can have various causes – from electrical short circuits to failures in transformers,” explained Prof Loughhead.

“It’s not stated what caused this one and it may take a while for what happened to be determined. A fire within a substation area can damage switchgear, transformers, measurement and control equipment, and cables. Fires are not unprecedented but also not frequent. If they damage equipment any user ‘downstream’ of the substation will lose all power. In this case Heathrow just happens to be the key user, although it seems other users are also affected.”

Mark added: “The law, that is the Electricity at Work Regulations 1989, requires that all electrical installations are maintained in order to be safe for continued use. This applies to electrical substations which should be regularly checked. As part of this, records will have been kept of testing and inspection and, for example, thermal imaging cameras will have been used to make sure connections aren’t overheating. Maintenance work will look to diagnose possible failures of equipment and then any required repair work can be carried out.

“For this situation, the investigation will look at the history of the equipment, such as the manufacturer’s data from when it was manufactured. The investigation will be far reaching, and every aspect will be looked at to ascertain what has happened. It is very unusual for one incident to cause the entire shut down of an entire site like Heathrow airport.”

Graham said: “It’s too early to provide a definite answer on what has happened here. Heathrow airport has multiple supplies from the National Grid, and means of diverting power if it is safe to do so. Power in an airport is required for safety equipment for flight operations and safety and security of the public in and around airport terminals.”

When will the power be back on?

“To restore power, supply companies may be able to route power to Heathrow through an alternative circuit, although it seems this is not easily done or may not be possible, or any damaged equipment will need to be replaced to get the substation back into service,” Prof Loughhead commented.

“To determine the original cause will mean examination of the damaged equipment and operating records to judge the sequence of events leading to the fire which may be obvious or require some time to work out.”

Graham concluded: “The Civil Aviation Authority has rules that govern the impact of power loss on airport operations, which includes consideration as to how long the loss of some, or all, power at an airport is expected to last. Airport operations can also be affected by the consequences of a major incident in the vicinity of the airfield or flight paths, for example smoke affecting flights.”