Re: High voltage switch (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 23 Jan 2004 22:55:58 -0600
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: High voltage switch (fwd)

John,

The story about this is at: http://205.243.100.155/frames/longarc.htm

"The video clip shows a three phase air disconnect switch opening the
high voltage connection to line reactors (the huge object that looks
like a transformer at the far right at the end of the clip) in a 500 kV
substation near Los Angeles, California. Line reactors (or inductors)
are used to offset the effects of line capacitance on long high voltage
transmission lines. The utility was having difficulty cleanly
disconnecting these line reactors and had set up a special test to help
monitor and isolate the problem. A set of SF6 (pressurized sulfur
hexafluoride) gas "puffer" interrupters, to the right of the air break
switch, first try to open the circuit so that the air break switches can
disconnect the reactors with no current flowing. The actual switching
elements for the SF6 interrupters are hidden inside the horizontal
insulators (bushings).

However, as one of the interrupters opens, a high voltage switching
surge is generated, causing the interrupter's bushing to externally
flash over, and it fails to cleanly disconnect the circuit.  This
results in one phase of the air break switch opening "hot", and it
continues to arc as the switch swings over to the "open" position. The
arc continues to grow upward, driven by its own hot gases and writhing
from small currents, until it easily exceeds 50 feet. Under similar
conditions, high voltage transmission lines arcs have exceeded 130 feet.
The arc would  have continued to grow except that the utility commanded
an upstream Oil Circuit Breaker (OCB) to open, de-energizing the circuit
and abruptly extinguishing the arc.

As impressive as this may be, the switch was NOT breaking a real load.
The arc is "only" carrying the relatively low charging current
associated with energizing the line capacitance of a relatively short
section of unloaded transmission line - perhaps ~20 amps. The 94 mile
transmission line associated with the above circuit normally carries
1,000 megawatts (MW) of power. An actual break under normal power
loading conditions would have been MUCH hotter and would also have been
extremely destructive. Imagine a fatter, blindingly blue-white, 100 foot
long welding arc that would melt/vaporize the contacts on the air break
switch.  But, you've gotta' admit that this "little" 10 million Volt
Ampere reactive arc is still pretty awe inspiring!

And who says utility guys don't have any fun - just listen to lineman on
the right whooping it up at the end of the clip!"

-- Bert --
-- 
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High Voltage list wrote:

> Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Fri, 23 Jan 2004 12:51:03 -0800
> From: John Pepper <jspepper@xxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: High voltage switch
>
> Greetings all,
> Someone sent  me an e-mail with a spectacular mpeg video of a BIG hv
> switch.  I have no idea of its origin or location.
>
>  http://www-eng.lbl.gov/~jspepper/
>
> Enjoy,
> John
>
>
>
>
> .
>