Re: Nice power pole jacobs ladder
Posted by Bert Hickman on 1/1/2008, 5:54 pm, in reply to "Nice power pole jacobs ladder"
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: Hi Bert,
: Here is that link to a nice jacobs ladder happening on one phase of a
: disconnect. This looks to be 33kV to 45kV, on a tall cement pole. Video
: starts with a phase-to-phase arc, quickly extinguished by an upstream
: reconnect. You can then see the persistant arc forming between the red-hot
: elements of the disconnect switch. A breeze blows the arc out to several
: feet long, this happening over and over again. Finally the arc rises up to
: the phase above it and there is a phase-to-phase flashover and shower of
: sparks. Great stuff. Much though I am impressed with our members and their
: Tesla coils, I still believe the ultilties have us all licked when it
: comes to impressive arcing, super jacobs ladders and long sparks!!
: On another note, I see that most of these Youtube videos, done by regular
: people in the right place at the right time, the blame goes to
: "exploding transformers". Whenever there is a ground or phase to
: phase fault, locals blame it on exploding transformers. Rarely have I ever
: seen or known a pole-pig to explode...ocassionaly there might be a bad
: bushing or a flashover caused by a sweet little squirrel, but pole-pigs
: are usually well protected by expulsion fuses which would blow before the
BTW, I have a collection of videos you might like to see in my YouTube Playlists area - these cover Tesla Coils, Arcs and Sparks, High Voltage videos, explosions, etc. I'll be continuing to update the list as I find (or other folks find and send me) other "interesting" video clips. See:
Oil-filled pole transformers can, and do, explode on occasion. One of the more common scenarios is a lightning strike that induces an internal insulation fault within the transformer that initially blows the transformer's HV fuse. Utility linemen see that the HV fuse is blown, and (usually) try replacing it. If the particular fault is not really a "hard" short, but instead is an internal arcing fault (underneath the oil), the new fuse may not blow quickly enough to prevent gas pressure from explosively blowing the top off the transformer and, sometimes, setting the mineral oil on fire. A real risk for linemen. One of the gases that is "cracked" by an under-oil arc is acetylene and, when combined with oxygen in the air space above, can also add to the explosive potential.
There are some companies that produce safety devices that can detect the sudden pulse of internal pressure during an arcing fault in smaller distribution transformers. This triggers an external indicator that tells the lineman NOT to re-power that particular transformer since it had a previous high pressure (arcing) event. There are other devices for larger transformers which detect the pressure pulse from an internal arc. These rapidly cut power to the transformer (Google "Buchholz relay" for more info). One of the companies that makes pressure indicating warning devices had an interesting picture of an exploding distribution transformer - see: