[BC] Re: SF6

[Bruce Doerle]

Jeff,

The Marconi 600kW mediumwave transmitter used a cap filled with SF6. It
was about the size of 55 gallon drum.  I thought it was a Comet.  I
don't remember the details (it was over ten years ago), but I do
remember J. Fred telling us that if we have an arc in the cap, it had to
be removed and taken outside to be purged of the SF6 which turns into a
poisonous gas when arc occurs.  

I found this interesting SF6 tidbit on YOUTUBE:
http://www.youtube.com/watch?v=HIXEzj08MwE

Bruce
>>> <Xmitters at aol.com> 2/19/2007 8:21:19 PM >>>
In a message dated 2/19/2007 4:51:11 PM Central Standard Time, 
broadcast-request at radiolists.net writes:


> SF6 insulation was one way of making 345 kV underground cable work
for 
> power transmission.
> 
> Not many places have the high power density which requires that kind
of 
> insulation, but NYC does.
> 
> In L.A., which has the second highest power density, we just used 
> multiple 230 kV lines, sometimes three or four in parallel.


Peter:

SF6 is also used in transmission line circuit breakers. That type of
breaker 
is called a "puffer" and it is much smaller than the traditional oil
filled 
circuit breaker. My local power company, Commonwealth Edison Company,
has some 
puffers on the 138 kV side of their transmission substation that's not
to far 
from me. We also have a great deal of 34.5 kV transmission feeding
distribution 
substations. Along the way, they have line circuit breakers that look
much 
like (but are not) Jennings air switches for RF. I do not know if these
are 
Puffer type circuit breakers or not. Would you happen to know? These
things 
replaced some very old open air line switches. SOP was to drop the line
at the 
transmission substation then open these field switches after the 34.5
kV system was 
dead. I don't know if this is still SOP with these new switches or not.


Sorry for the thread drift but this is a very interesting topic :-)

Jeff Glass
Northern Illinois University



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