Around midnight Thursday evening, Mar. 20, a transformer at the North Hyde substation in west London caught fire and failed, interrupting power to some 67,000 customers. Power outages are not that unusual, and this one would not have made the news except for the fact that one of those customers was Heathrow Airport. Although airport authorities claim that the backup emergency-power systems worked as expected, they decided to close the airport, which is the fifth busiest in the world.
It took seven hours for firefighters to quench the blaze, and another twelve or so before power could be fully restored. Consequently, all flights into and out of Heathrow were diverted or canceled until around 6 PM Friday. The knock-on effects from this major disruption will be felt for several more days as stranded travelers find alternate routes and the transportation system strives to return to normal.
One engineering expert interviewed about the incident expressed surprise that there were not alternative supply paths for such an important load as the airport. Apparently one terminal did not lose power, but the expert said that the grid in that area of London is "highly constrained" and has recently been stressed by increased development in the region.
Admittedly, the failure of a substation transformer is an unusual event. Such transformers can be the size of a small bus and cost on the order of a million dollars. Utility companies normally monitor their condition remotely and perform routine maintenance on them such as cleaning or replacing the cooling oil that bathes the tons of steel and copper inside the sealed container that is visible to the eye. Dropping the ball on any of these precautions can lead to a dangerous situation. Impurities such as water can get into the oil, weakening insulation and leading to a sudden arcover and failure.
We will have to wait for investigation results to discover exactly why the transformer caught fire. But another question is: why did Heathrow not have sufficient backup power to continue normal operations?
The best guess is simple economics. A modern airport uses a great amount of power for moving sidewalks, elevators, security equipment, and lighting. Maintaining enough backup generators to provide the entire normal load would be expensive, probably complex because of the load's distributed nature, and would show up as a dead loss on the books of the private company, Heathrow Airport Holdings, which runs the airport. So the bottom line is probably that the firm decided the temporary fallout from a short-term shutdown would be less expensive than paying for a large number of emergency generators that might be used only once every few decades.
No one died or was even injured in the Heathrow shutdown, and in retrospect the decision to limit emergency backup resources was probably a wise one. Nevertheless, this incident brings up an interesting issue with regard to how seriously we should take preparing for unlikely infrastructure failures.
In cases where a power failure could be deadly or extremely costly, institutions and organizations usually buy enough backup power to keep things running almost without interruption. For example, most hospitals have enough backup power to keep operating rooms running normally, although the lights may go out in hallways and patient rooms if the main power fails. You don't want a power failure in the middle of your brain surgery, and so most responsible hospitals make sure this can't happen.
Huge semiconductor plants also typically have enough backup power to keep their essential processes running without a hitch, although the emergency power system forms a costly and seldom-used aspect of the installation. A former student of mine is heading the electrical installations at a major semiconductor plant, and showed me a photo of the ranks of large backup generators that are being installed. If power were to go out in an operating semiconductor fab facility, the entire inventory all along the process lines would have to be scrapped, and this multimillion-dollar potential loss justifies spending extraordinary amounts to ensure that the machines keep running.
On the other hand, while Heathrow is a vital part of Europe's transportation infrastructure, closing it for less than a day has not had many permanent ill effects. The systems that communicate with airliners were unaffected and flights were successfully diverted, so other than a lot of travelers whose plans were disrupted and deliveries delayed, the incident will have few lasting consequences.
Once the cause of the fire has been determined, we may learn something about ways of preventing such fires in the future. If the oil was dirty and led to deterioration in insulation, better maintenance is called for. If the substation was overloaded due to new construction, maybe another substation is needed, or the North Hyde facility needs to be expanded with a second transformer. And if there was some sort of transient or network disturbance that led to a stress failure, new smart-grid technologies can be brought into the picture to alleviate such incidents in the future.
A transformer fire is one of the worst things that can happen to a power grid, but it does seem like some fairly minor changes in the distribution infrastructure could keep this from happening again. A friend of mine who used to work in an aerospace job uses a phrase that would apply to this situation: "single-point failure." If a system has one component whose failure brings down the whole system, that single point is a vulnerability that should be addressed. And maybe last week's shutdown of Heathrow will motivate changes that will keep it from happening again.
Sources: I referred to an Associated Press article on the incident at https://apnews.com/article/britain-london-fire-heathrow-airport-6d63b2f6615e8ff39f2647641bfbc160, a website called Open Conversation at https://theconversation.com/heathrow-closure-what-caused-the-fire-and-why-did-it-bring-down-the-whole-airport-expert-panel-252834, and the Wikipedia article "Heathrow Airport Holdings."
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