[sdiy] OT: very BIG capacitor

[Scott E.]

Kind of reminds me of the bug zapper in my folk's back yard. (They don't 
like bugs).

Scott
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J. Larry Hendry wrote:

> Excused the OT, but I think you will all enjoy the link.  A little
> entertainment I'll call "another day at the office" in the utility business.
> Actually, the link below will take you to a truly amazing video (about
> 1.5Mb).  You will be looking at a 1/2 million volt AC arc which I am certain
> exceeds 50 feet in length.
> 
> I have not yet uncovered all the facts about this video that was sent to me
> today.  But, I will fill in the details I know from my observation of the
> event.  The file name Lugo suggests a large California substation that is
> populated with 500KV and 230 KV switching devices.  This one is clearly
> 500KV (I can tell by the size).  The switch being opened is called a
> "circuit switcher."  It consists of 2 series SF6 gas puffer interrupters
> (kind of like a circuit breaker) and an integrated center-break disconnect.
> The way they are supposed to work is the interrupters both trip, grading
> capacitors or resistors cause the open circuit voltage to split evenly
> across the two interrupters, the switch blades open with no current flow,
> and the interrupters close as the switch reaches the full open position.
> 
> I titled this "very BIG capacitor" because that is what unloaded
> transmission line looks like.  The parallel wires have a huge capacitive
> effect between ground and each other.  On a 500KV line like this the current
> (leading the voltage by 90 degrees) required to energize this capacitor is
> approximately 2 amps per mile of line per phase.  That's 2 amps per phase at
> 500KV, or about 1.7 MegaVars (million volt amps reactive).
> 
> The switch operation you see in this video in my opinion is a failed attempt
> to interrupt that charging current.  I am going to take a SWAG guess and say
> we are looking at ~ 25 amps (I've seen a few of these in a smaller scale),
> or about 7 Mega Vars.  Funny that it is only called "apparent" power, heh?
> 
> The failure appears to be that the far right interrupter does not open or
> the grading device has failed.  The voltage across the open interrupter
> exceeds the rating and it flashes over (you can see the first arc develop
> across the interrupter).  Therefore, the switch blades are left to interrupt
> the current (not designed to do that) as they open.  As the interrupter
> closes you can see the arc across it go out.  However, the arc across the
> switch gets as tall as a 3 story building before the arc resistance is
> sufficient for the ionized gas to quit conducting.  This is the only failure
> I have ever seen where the arc lasted so long and grew so large without
> first going phase-to-phase or phase-to-ground taking the circuit out of
> service.  It just keeps growing straight up where it contacts nothing.
> 
> Check out the guy on the right by the truck.  The taller the arc gets, the
> more he crouches down behind the truck.
> 
> Here's the link
> http://www.wiseguysynth.com/larry/misc/LugoSWR.mpg
> 
> Larry Hendry
> 
>