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Re: safety gaps at high power



Original poster: "Edward Wingate by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ewing7-at-rochester.rr-dot-com>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Tesla729-at-cs-dot-com>
> 
> Hi all,
> I've got a quick question for y'all. I have a safety gap that I installed
> on my 10 kVA pole pig. The problem that I have with this SG is that
> when it is set to where it does occasionally fire, it immediately power
> arcs, when it fires, due to the heavy current, and will only extenguish
> when I turn the power control variac way down. If I set it where it dosen't
> fire at all, then I am defeating the purpose of having it in the first place.
> I was wondering if any of you other "pig" coilers had noticed this pro-
> blem. I remeber reading an article by Richard Hull in one of the TCBA
> volumes, and he stated that he didn't even use safety gaps at power
> levels over 5 kVA due to this problem. BTW, my pig is externally bal-
> lasted with an arc welder. Comments anyone?
> 
> David Rieben

David,

My magnifier uses a 14400 volt pole transformer ballasted with an arc
welder alone and will exhibit the same tendency to power arc the
transformer safety gap when I slow rotary gap to approximately 7000 RPM
or less from the normal 7500 to 8000 RPM operating range when the
voltage input to the system is at the maximum 235 volts. The safety gap,
which I would NEVER operate the system without, is protecting the system
components from possibly damaging overvoltages when I experiment with
varying gap speeds, which I do frequently, and their effect on spark
appearance. Lower gap speeds make the arcs "slower" and less "frantic"
and faster gap speeds cause the opposite effect. I would much rather
deal with the occasional power arc than risk component damage from
overvoltages! Even if you opt for opening up the safety gap to a wider
setting you still have more protection than having no safety gap at all!
I also run safety gaps set to 1" on the capacitors in this system, but
since the two tank capacitors are rated at 45 KV each and they are
running in series (equidrive) for a total combined rating of 90KV the
safety gaps on the capacitors have never fired, but they are there
nonetheless. Safety gaps are cheap, components are not!!

Happy New Millennium to you and all on the list! (Yes, this is the real
one!)

Ed Wingate RATCB