Re: Potential Transformers

Tesla List wrote:
> >From MSR7-at-PO.CWRU.EDUMon Jun  3 22:22:09 1996
> Date: Mon, 3 Jun 1996 07:49:24 -0400
> From: MSR7-at-PO.CWRU.EDU
> To: tesla-at-pupman-dot-com
> Subject: Re: Potential Transformers
> Hello Coilers,
>         Earlier, i wrote:
> >>My search for a suitable potential transformer continues.....
>         My rationale for choosing a potential transformer is based primarily
> on space limitations.  I have a "sensitive" neighbor, so outdoor firings are
> not something I can do routinely.  (He likes to call the police for anything
> out of the ordinary, which places constraints on a number of my hobbies!)
> That leaves me with a garage and basement, limiting my sparks to about 6
> feet or so.  I have a nice RF ground in my basement, so most of the work is
> done there.  I will also probably stick with 120 volt A.C. for input using
> 1-2 kVA.  Thus, the decision for a potential transformer instead of a pole pig.
>         On another note, that 9 kV 150 mA neon transformer I blew last week
> spent a couple days in my freezer over the weekend.  I then proceeded to
> chip away the tar quite easily using a small hammer and screwdriver.
> Warning: Lots of tar shards everywhere, and lifting a cold 60 pound
> transformer out of the bottom of a freezer is not recommended.  One winding
> shows signs of overheating.  Still have to strip off the remaining tar near
> the windings.  May soak it in a solvent for a few days.  Suggestions?
> Regards,
> Mark S. Rzeszotarski, Ph.D.

I have done this many, many times to neon transformers over the years.
It's messy, but the results are worth it. Several things happen when
a transformer of this type is used in Tesla service: 1) the transformer
'shorts', but not as one might think...what can happen is a conductive
path is formed through the tar, thus appearing as a low-impendence
current path, effectively shunting all current. 2) the tar, while
being a good noise eliminator, unfortunately makes a lousy heatsink,
allowing the windings to get rather warm.

What you should do after letting the unit soak for a few days is to
take the core apart if at all possible and coat the high-voltage
windings (there will be two of them on either side of the primary)
with high-quality corona dope. Replace the 'U'-shaped mica pieces
between the coils and the core with equally-shaped pieces cut from
a clear plastic 2-liter soda bottle. (The bottle is made from HD
polyethylene, which has an incredibly high dielectric strength rating.)
Reassemble the unit.

The end result is now an air-cooled transformer that is almost short-
proof. If you want to really go all the way, you can place the unit
in a sealed box filled with high-voltage mineral oil.

- Brent Turner