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Re: NST insulations
Hi Alan, all,
> Original Poster: Megavolt121-at-aol-dot-com
>I'm trying to enhance one of my 15/60 Jefferson NSts. Hopefully i
>can get 200ma, but before i get there, I must overcome arcing
>problems. Right now while i cut off shunts(these da#-at-
>Jefferson's don't have those "remove-a-shunts" and i need to cut
>them) it runs dry for testing to make sure it'll run. I usually run it
>dry for about 3-4 secs -at- 75% power on my variac. After i push
>up the power, i get an arcing from my Secondary to my core. Of
>course i turn it off here. What i want to know is if there is anything
>temporary that i can use to prevent arcing during my testing?
You will be increasing the output VA by 333%. While I have beaten
that (467%), I STRONGLY suggest you DO NOT try this in one
step. That is about the best way to fry your xformer. At 467%, my
xformer got pretty hot. It has a duty cycle of only a very few percent,
if it is to survive (although I ran it straight for 30 minutes at this
power level). However, my 7.5kV/75mA NST core is massive (you
can see a picture of it, if you download my MMC calculator) for itīs
rated 562VA. The core is much larger than your 12/60 unit and the
primary wire is "indestructible". Remember, when you double the
output of your NST, the internal (copper) losses go up by a factor
of 4.
I wrote a long mail to Andy Cleary about a similar topic. The subject
was "Various Transformer-questions" and I posted it on the 27 of
February. You might want to read up on it. It contains a few testing
details. If I were you, I would start out with a "modest" increase of
say, 50% (for 90mA). If it survives the tests, go up to 120mA, test
again, then 150mA..... Well, you get the idea. The increase in output
current should not present you with any insulation problems (that is
a question of voltage). As you are getting power arcs at 75% of
120V, I would think about getting a different NST. Otherwise, you
will need to submerge this NST in oil, test it, pull it out of oil,
modify for more power, put it back in oil, retest, etc. You will need
to stop the power arcing in any case, because it will form carbon
and give you headaches later (even when the unit is under oil).
Coiler greets from Germany,
Reinhard