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PlanetChristmas
Pulls A Plug
This is a 1.6 MB movie showing what happens
when someone at TVA pulled the plug on PlanetChristmas.
Click
here to see the movie!
Real Story: The video clip shows a three phase air disconnect
switch attempting to open the high voltage supply to a large three phase 33
Million Volt Ampere Reactive (MVAR) shunt line reactor. The reactor is the huge
transformer-like object behind the truck at the far right at the end of the
clip. The clip was believed to be part of the 500 kV Lugo substation near Los
Angeles, California. Line reactors are large inductors which are used to
compensate for the effects of line capacitance on long extra high voltage (EHV)
transmission lines. The utility was having difficulty cleanly disconnecting the
line reactors and had set up a special test to videotape, and hopefully isolate,
the problem. If you look carefully, you can see evidence of previous arcing -
notice the blackened horizontal bushing (insulator) just behind the bushing that
arcs at the beginning of the MPEG.
Normally, pressurized sulfur hexafluoride (SF6) gas "puffer" interrupters, just
to the right of the air break switches, will first de-energize the circuit so
that the air break switches can the open with no current flowing. The actual
switching elements for the interrupters are hidden inside the horizontal
bushings. However, as the interrupters open, a high voltage switching surge
causes one of the interrupter bushings to flash over. Since this phase remains
energized, the air break switch for this phase opens "hot", and it continues
arcing as the switch swings to the fully "open" position. The arc continues to
grow upward, driven by rising hot gases and writhing from small air currents,
until it easily exceeds 50 feet. Long arcs usually terminate before by
connecting to an adjacent phase or to ground, causing a detectable fault which
then trips out the circuit. This particular arc could have persisted for quite
some time, but the utility manually commanded an upstream Oil Circuit Breaker
(OCB) to open, abruptly extinguishing it.
PlanetChristmas
Shameless Commerce
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As impressive as this may be, the air switch was NOT disconnecting a real load.
The arc is "only" carrying the relatively low (perhaps ~20 amp) magnetizing
current associated with the line reactor. The 94 mile transmission line
associated with the above circuit normally carries over 1,000 megawatts (MW) of
power between Nevada and California. An actual break under normal loading
conditions would have been MUCH hotter and extremely destructive. Imagine a
fatter, blindingly blue-white, 100 foot long welding arc that would vaporize the
contacts on the air break switch and then work its way back to the feeders.
But, you have to admit that this "little" 10 million Volt Ampere reactive arc is
still pretty awe inspiring!
Find more details and some pretty amazing videos by
clicking
here.
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