[SMCARA] a 500 kV line being opened under full load

[JD Delancy]

Here's some explanation about the 500KV line being opened while under load.

------ Forwarded Message

From: "Pete Norloff" <pnorloff15@toward.com>
Date: Sat, 7 Feb 2004 13:31:59 -0500
Subject: RE: a 500 kV line being opened under full load

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.

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!

From:
 http://www.planetchristmas.com/PullThePlug.htm

There's also a link to some more incredible video.

73,
Pete