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"  With a surge of power and corroded wiring, transformers can explode, causing extensive damage. (Photo from Iceman9294/Flicker)  A transformer from Consolidated Edison (Con Ed), New York City&amp;#039;s sole electricity supplier, exploded from beneath the sidewalk in an underground vault yesterday, creating a fiery blast that shattered windows multiple stories high. Though no injuries were reported, offices and stores at the corner of 20th Street were left smoldering.  Investigators are still trying to answer the question: Just what lead this transformer to explode? \u00C2 \u00C2  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&amp;#039;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.  All it takes is a trigger, a corroded or faulty wire, and the circuits surge will get ahead of the breaker--and in New York City, the previous day&amp;#039;s snowstorm could have done the trick. Underground electric systems often suffer problems after heavy snowfall, says Bob McGee, a spokesperson for Con Ed. While salting streets may make vehicles and pedestrians safer, the salt can create hazardous conditions for underground electrical systems--salt that slips through manholes can corrode wires. \u00C2  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&amp;#039;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. \u00C2 \u00C2 \u00C2  Though the snowstorm may have had something to do with the incident, it will take time to analyze just what went wrong. If it turns out the salt from the snowstorm wasn&amp;#039;t to blame, it may have been an older transformer. These can explode when their insulating materials begin to fail. This happens as cellulose and oil absorb water over time and degrade cellulose&amp;#039;s ability to insulate, triggering an explosion. The U.S. expanded its electrical structure in the 1950s and &amp;#039;60s, and now, most older transformers have met or are nearing the end of their operational lives of between thirty to forty years. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/science/energy/a5337/4345791/>