When an eerie blue glow lit up the sky above New York City last December, some were disappointed to learn that aliens weren’t involved. The cause was, in fact, terrestrial: a transformer had exploded at a local power plant.
For the most part, transformers—which help power companies transmit electricity efficiently by altering voltages—are relatively safe. Fewer than one percent explode—but those explosions can be deadly, and result in flying projectiles, toxic fires, or oil spills.
Transformers rupture due to a buildup of excess pressure in the tank in which they are encased, which is usually filled with mineral oil that acts as a coolant. Contaminants within the oil, the degradation of transformer parts, and electrical storms can all cause a fault, called an internal arc, that results in a rapid release of energy.
“When you have an arc inside the transformer, it heats up the oil and the oil burns to create a gas, which causes high pressure,” explains Samuel Brodeur, a senior mechanical engineer at the power and technology firm ABB, who is based in Varennes, Canada. Conventional tank designs are limited in their capacity to withstand such fault energies—which in severe cases, can reach as high as 150 megajoules (MJ), the equivalent of 150 sticks of dynamite—and so Brodeur and his colleagues have spent the past seven years working to devise a stronger, more resilient transformer tank.
Their solution, described in a paper published 12 June in IEEE Transactions on Power Delivery, is called TXpand. The idea is startlingly simple: design a tank that’s flexible enough to deform to absorb all that extra pressure without rupturing.
“It’s a bit like blowing [up] a balloon,” says Jean-Bernard Dastous, a research scientist from Canadian power supplier Hydro-Québec, which collaborated with ABB on the project. “If it’s very rigid, it will be difficult to expand the balloon. But if it’s made of a very flexible material, it’s easier for you to inflate it.”
ABB, which currently supplies roughly 70 percent of Hydro-Québec’s transformers, alters tank flexibility by using different types of steel, varying the thickness of the wall and cover, and reinforcing weak points such as the corners, among other things.
To design what ABB calls an “arc resistant” tank, the team first had to create a mechanical model that could predict the pressure at which a given tank would deform and subsequently rupture, based on its size and material properties. Hydro-Québec, in particular, wanted ABB to build a tank that could withstand 20 MJ of energy without rupturing—a level that would cause a “catastrophic failure” in most transformers and one that Dastous says “would cover 95 percent of faults occurring on the network.”
And so ABB plugged equations into its numerical model and spent months building a full-size tank (roughly 5 meters long, 2.5 meters wide, and 4 meters high). For safety reasons, the tank was filled with water instead of oil, and contained a replica of the active part of a transformer. The first test, carried out on a frigid winter’s day in November 2017 in an open field at Hydro-Québec’s research facilities close to Montreal, was meant to demonstrate the tank could withstand the specified 20 MJ. Until then, the highest energy levels tested were just over half that value.
The team injected pressurized air measuring 200 atmospheres, which is equivalent to the pressure experienced two kilometers below sea level. The tank bulged at its sides, but did not explode.
The second test, they hoped, would demonstrate that at a given pressure, the tank would rupture at a chosen point. “We wanted to make sure that failure happens at the top of the transformer because when it happens there, less oil will spill into the environment,” explains Dastous.
Following an injection of 30 MJ of energy, the test tank did exactly this, proving that “our calculations and numerical test methodologies worked,” he says. The results have enabled Hydro-Québec to come up with “new improved arc-resistant specifications” for its suppliers to follow. The specifications, to be implemented in the coming months, will hopefully lead to fewer transformers exploding. ABB, on the other hand, has since applied its TXpand solution to more than 50 transformer designs.
Brodeur says: “Because we are able to prevent most of the tank rupture cases, it’s safer for the people who work around the transformer and it’s also very good for the environment because we can prevent major oil spills and toxic fires.”
Sandy Ong is an independent science journalist based in Singapore. For IEEE Spectrum, she often writes about the quest for better batteries. Ong also covers stories about health, tech, and the environment in Asia and beyond. Her writing has appeared in The Atlantic, Newsweek, WiredUK, and other publications. You may have even heard her on BBC Radio 5 Live’s “Up All Night” if you were listening at just the right time. Ong holds a bachelor’s degree in life sciences and a master’s degree in forensic science, and is a graduate of New York University’s Science, Health, and Environmental Reporting Program.