Why Transformers Explode During Storms

Scott Detrow

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Scott Detrow is a congressional correspondent for NPR. He also co-hosts the NPR Politics Podcast.

Detrow joined NPR in 2015 to cover the presidential election. He focused on the Republican side of the 2016 race, spending time on the campaign trail with Donald Trump, and also reported on the election's technology and data angles.

Detrow worked as a statehouse reporter for member stations WITF in Harrisburg, Pennsylvania, and KQED in San Francisco, California. He has also covered energy policy for NPR's StateImpact project, where his reports on Pennsylvania's hydraulic fracturing boom won a DuPont-Columbia and national Edward R. Murrow Award in 2013.

October 30, 2012 | 3:11 PM

The number of Pennsylvanians without power due to Superstorm Sandy has decreased slightly, to 1.23 million, but more than 7 million people remain powerless along the east coast.
Many of these outages were caused by exploding transformers. Why does that happen during storms? The folks at Slate’s Explainer division have an answer:

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.