HOW TRANSFORMERS
CAN EXPLODE? ALL IT TAKES IS A TRIGGER, A CORRODED OR FAULTY WIRE OR AN OLDER
TRANSFORMER. 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.
On February 12, an underground electrical transformer
exploded in front of a Radio Shack on 6th Avenue, in New York City, emitting a
fireball seven stories high and damaging nearby buildings. Recently, a number of underground explosions have been reported in Co Edison's underground vaults. Here's how this
could have happened.
With a surge of power and corroded wiring, transformers can explode, causing extensive damage.
A
transformer from Consolidated Edison (Con Ed), New York City'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?
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.
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'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.
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.
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'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'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.