Why do Transformers Explode in a Storm?

Answers to your questions about the news.
Oct. 30 2012 2:05 PM

Why Do Transformers Explode?

A mini-Explainer on how a little moisture may have blacked out much of Manhattan.

154992815
A transformer explosion knocked out power to parts of Manhattan during Hurricane Sandy.

Photo by Spencer Platt/Getty Images

Read Slate’s complete coverage of Hurricane Sandy.

A transformer explosion knocked out power to a wide swath of Manhattan on Monday night. ConEd says it could take up to a week to restore power to tens of thousands of customers. It’s not yet clear whether the explosion was directly related to the storm. How can a hurricane cause a transformer explosion?

By degrading the insulation. Electrical transformers are composed of a series of coiled electrical wires. The wires are sheathed in paper-based insulation, which prevents electricity from jumping across wires within the coil. Over the course of 20 to 60 years, depending on how hard the apparatus is made to work, the insulation in a well-maintained transformer degrades from 1,200 molecules thick to 200 molecules thick, at which point the coils should be replaced. Water accelerates that degradation process immensely. When the insulation fails, parts of the coil touch, causing a “turn-to-turn fault”—a form of short-circuit that creates a spark inside the transformer. The spark ignites the oil surrounding the coils, and the resulting explosion can be massive, as video from Monday night’s failure demonstrates.

It’s not yet clear whether water penetration caused the explosion in Manhattan, or, if it did, how much water was involved. It doesn’t take much, though. Even small amounts of water can quickly be fatal to an electrical transformer. Transformers are usually protected by air dryers to remove humidity from the air, and engineers regularly replace the insulation surrounding the entire machine. Even water released from inside the transformer—as organic materials in the system heat up and age—can pose a problem. Modern transformers are also equipped with a tank of silica gel that absorbs water from air entering the electrical system.

Got a question about today’s news? Ask the Explainer.

Explainer thanks P.K. Sen of the Colorado School of Mines.

Brian Palmer is Slate's chief explainer. He also writes How and Why and Ecologic for the Washington Post. Email him at explainerbrian@gmail.com. Follow him on Twitter.

TODAY IN SLATE

Foreigners

More Than Scottish Pride

Scotland’s referendum isn’t about nationalism. It’s about a system that failed, and a new generation looking to take a chance on itself. 

What Charles Barkley Gets Wrong About Corporal Punishment and Black Culture

Why Greenland’s “Dark Snow” Should Worry You

Three Talented Actresses in Three Terrible New Shows

Why Do Some People See the Virgin Mary in Grilled Cheese?

The science that explains the human need to find meaning in coincidences.

Jurisprudence

Happy Constitution Day!

Too bad it’s almost certainly unconstitutional.

Is It Worth Paying Full Price for the iPhone 6 to Keep Your Unlimited Data Plan? We Crunch the Numbers.

What to Do if You Literally Get a Bug in Your Ear

  News & Politics
Weigel
Sept. 16 2014 7:03 PM Kansas Secretary of State Loses Battle to Protect Senator From Tough Race
  Business
Moneybox
Sept. 16 2014 4:16 PM The iPhone 6 Marks a Fresh Chance for Wireless Carriers to Kill Your Unlimited Data
  Life
The Eye
Sept. 16 2014 12:20 PM These Outdoor Cat Shelters Have More Style Than the Average Home
  Double X
The XX Factor
Sept. 15 2014 3:31 PM My Year As an Abortion Doula
  Slate Plus
Slate Plus Video
Sept. 16 2014 2:06 PM A Farewell From Emily Bazelon The former senior editor talks about her very first Slate pitch and says goodbye to the magazine.
  Arts
Brow Beat
Sept. 16 2014 8:43 PM This 17-Minute Tribute to David Fincher Is the Perfect Preparation for Gone Girl
  Technology
Future Tense
Sept. 16 2014 6:40 PM This iPhone 6 Feature Will Change Weather Forecasting
  Health & Science
Bad Astronomy
Sept. 17 2014 7:30 AM Ring Around the Rainbow
  Sports
Sports Nut
Sept. 15 2014 9:05 PM Giving Up on Goodell How the NFL lost the trust of its most loyal reporters.