On August 17th 1993, the Ives Dairy Substation in Miami, Florida experienced
a total system failure. It started with the simple failure of a capacitor
bank (a piece of equipment used to regulate power spikes and momentary drops
coming off the main power grid in to one smooth consistent electrical
current before being distributed to customers).

Unlike a Transformer (which will increase or decrease the amount of voltage
put in to it by a percentage) a Capacitor is like a bucket with a faucet.
The bucket part of the capacitor can hold a certain amount of incoming power
like a buffer, while the faucet part of the capacitor will only let a
precise amount of power through. This way, as other cities pull more power
from the grid and then drop their usage over and over, all this constant
fluctuation of the grid is smoothed out by the capacitor banks before the
electricity gets sent out to customers. Without it, peoples home electronics
would be turning off or dimming one second, and the next second a bunch of
people in another city would turn off their air conditioners (or what have
you) and that sudden surplus of power on the grid would then fry your
computer or TV or burn out your light bulbs, etc. By running the power
through those capacitors, there's a place for excess power to go and a place
to draw power from (the bucket), while the output (faucet) only lets the
correct amount of power through.

So anyway, a huge power surge on the Miami grid fried one of the capacitor
banks, and caused a breaker to trip open when that rush of unregulated power
went through the breaker. Unfortunately, the breaker malfunctioned and
created an arc fault (a continuous lightning bolt that acted like an
uncontrollable welding torch from hell) between the hot side of the breaker
and wherever it could find a ground to complete the circuit, thus pulling
far more current then the facility was designed for.

Unknown to FPL operators at the time, the emergency response system that
would have notified the grid dispatcher of a serious problem (who would have
then cut the power to the substation and neighborhood to kill the arc fault)
was faulty, and no message was ever sent. Since the dispatcher had no way of
knowing about the arc fault, the substation continued to self-destruct.

The uncontrolled arc fault caused the coolant (mineral oil) inside the
primary transformer to overheat to critical levels until it was boiling in a
highly flammable state. This boiling caused pressure to rise inside the
transformer (like a pressure cooker) until the seals finally blew. Mineral
oil vapor proceeded to pour out at that point (the plume of white fog at the
end) which ignited on the arc fault. The flames caused by this immediately
ignited back to the source, (the boiling transformer tank), which ignited
the mother load of oil inside causing the substation to explode in a giant
ball of fire.

The sudden loss of all transformer coolant resulted in a simultaneous
flash-meltdown of the transformers innards, which immediately caused the
main high voltage fuse to overload and blow (the loud explosion at the end),
finally killing the arc.

As a side note, even though it sounds like a million things went wrong,
there were really only two main things that went wrong. Arcing is actually
very common when a breaker opens since the breaker has hundreds of thousands
of volts running through it. And capacitor bank failures are also extremely
common when they can fry in the event of an extreme power surge.

The UNCOMMON event that caused this was the fact that the arc-fault
suppression system (the system that extinguishes the arc), and the Emergency
Response System (that would have told the grid dispatcher that something was
STILL wrong) were both placed on the same circuit breaker, and that breaker
was faulty. Those two backup systems are really the only final thing a
substation has in order to prevent this from happening in your neighborhood,
and both of them were inoperative in this instance because of that bad
circuit breaker, (and the fact that someone put both the backup system and
the auxiliary backup system on the same circuit to begin with - a big no
no).

You can view an aerial photo of the substation location here:
http://maps.google.com/maps?f=q&h... (Note: this is a current map photo of
the newly rebuilt, slimmed down substation that sits where the old
substation used to be.)