Afraid or frying another winding

[AndreiRS]

Hi all. I will post the same text I just posted on facebook. I'm still having connection problems...

I built a hv transformer, pole style, no current limiting inside, I use an external ballast. First time I tried to turn it on without a spark gap on the insulators, it just fried the secondary. Now I rebuilt it. But this time it is under oil. Still, I only put insulation paper each 8 layers of 120 turns, or 960 turns. I'm trying to make my Tesla coil work, but the safety gap at the insulators keep firing all time and I have almost no sparks at the rotary gap. I just don't know what to do. If I open the safety gap a little more, I'm afraid it will fry it again.

Not sure if the oil will hold things up, since there is no paper between each wire layer, any idea? I know NSTs don't have any paper at all, but this thing can output some 300mA in a short circuit. Would the load from rotary spark gap and capacitors, prevent the internal arcing and destruction?

[profdc9]

You need to put a Terry filter between your transformer and the spark gap.   RF spikes are probably feeding back into your transformer and frying it.  I use MOTs and I had to do this to protect my doubling diode.

This is a good reference.

http://www.laushaus.com/tesla/protection.htm

Don't use the Chokes!!  You're better off using just simple RC snubbers and metal-oxide varistors (MOVs), as well as the safety gap.

Dan

[AndreiRS]

Hi Dan. Thanks for your reply. I have that filter. I didn't explain it well, sorry. When I fried it, it was not connected to anything. There was no load, so it just created an arc inside.

[MRMILSTAR]

If you're going to make your own HV transformer, there are a couple of things that must be done to avoid failure. You need Kraft paper between the winding layers on the secondary coil. This is to provide some spacing between the layers. You also need to immerse the transformer in oil. You then need to pull a partial vacuum on the transformer container to remove the trapped air bubbles within the secondary windings. The Kraft paper provides spacing for the oil. The paper itself provides only negligible insulation. If you don't remove the trapped air bubbles, it will fail.

[shrad]

Kapton has also some advantages there, in that you can order a roll of the width you want, and will insulate well enough for interlayer