How Transformers Can Explode - Popular Mechanics

View full post on X

A transformer from Consolidated Edison (Con Ed), New York City's sole electricity supplier, exploded at a substation in Astoria, Queens, on Thursday, creating a blue glow that could be seen across the city and as far as New Jersey. No injuries have been reported, and investigators are beginning to try and answer the question: Just what lead this transformer to explode?

View full post on X

Electrical transformers transfer energy between circuits, switching energy from one voltage to another. But when flooded with too much electricity, the sudden surge can cause a transformer explosion. As transformers detect an energy spike, they're programmed to turn off, but it can take up to 60 milliseconds for the shutdown. However fast those milliseconds may seem, they still may be too slow to stop the electrical overload.

A chamber full of several gallons of mineral oil keeps the circuits cool, but given too much electricity, the circuits fry and melt, failing in a shower of sparks and setting the mineral oil aflame. Mineral oil, in turn, combusts explosively and rockets transformer scything into the air.

Manhattan houses 35,000 underground and 47,000 overhead transformers for its 10 million residents, and of those 82,000, about 35 fail every year, McGee says. A failure doesn't always equate to a fire or explosion either; in fact, in the steadily decreasing number of failures per year, such an explosion is rare.

It will take time to analyze just what went wrong. Older transformers can explode when their insulating materials begin to fail. This happens as cellulose and oil absorb water over time and degrade cellulose's ability to insulate, triggering an explosion.

The U.S. expanded its electrical structure in the 1950s and '60s, and now, most older transformers have met or are nearing the end of their operational lives of between thirty to forty years.

This story was originally published on February 11th, 2010 and has been updated.