Re: HV Wire - electrical tape?

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Original poster: "Godfrey Loudner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <ggreen-at-gwtc-dot-net>

Hello Daniel

I'm using the two original primaries which are wrapped around the outer legs
of the square core. Each primaries is rated at 115 volts and the wire is
insulated with a rubber like coating. The insulation between each primary
and the core consist of a couple of layers of brown paper (not much at all).
The insulation on the outside of each primary consist of a 1/8 inch thick
wrapping of mica like paper. I had just enough room to wrap an additional
five layers of polyethylene sheet on each primary. Each secondary coil is
rated at 35 kV and 10 to 15 mA. I should get 70 kV with the HV coils in
series. The inner lead of each HV coil comes from an inside soldering
contract point. This was done because the bottom of HV coils intended for
x-ray transformers are grounded to the core. I installed stiff polyethylene
plates on the top and bottom of each HV coil. On top of each plate is 1/2
inch thick ring of acid free artist Kraft paper, painted with polyurethane
as it was wrapped. My idea here was to increase the flashover distance
between the outside of a HV coil to the primary or the core. I had thought
of using vinyl foam weatherstrip for the rings. The outfit will be submerged
under transformer oil and operated at 60 Hz. The HV coils were not intended
for one of those high frequency dental tubeheads.

I have a problem area. I thought I understood these matters, but I'm not
sure.

1. Suppose I ground the inner leads of the HV coils to the core, without
earth grounding the core. Do I have to worry about arcing between those
soldering stress points and the primaries or between the core and the
primaries?

2. Suppose I ground the inner leads of the HV coils to the core and earth
ground the core. Again the same question as above.
Certainly the service line is grounded. If I ground the core to the service
line, then I will be placing a lot of HV stress between the core and the
primaries. But if I ground the core to a homemade earth ground, keeping in
mind that there should be a lot of resistance through the earth to the
service ground, it seems like there would be less  HV stress between the
core and the primaries.

Because of my uncertainties, I decided to isolate the HV coils the best I
could without breaking down the primaries and starting anew. But with the
inner leads of the HV coils connected and isolated from the core, do I still
have to worry about HV breakdown between the bottom of the HV coils to the
primary or the core. There are those high stress soldering contact points,
but there is room for the transformer oil to flow into and around the
primaries.

Also I performed a test with low volts into the primaries (no oil). With the
inner leads of the HV coils isolated from the core and connected in series,
I connected the primaries in parallel. A hot arc (like a NST) jumped a one
inch needle gap between the outer leads of the HV coils. I figured that the
phasing was hit just right on the first attempt, so I marked the primary
leads. Just to be sure, I reversed the phasing. I expected to see little
potential between the outer leads of the HV coils, but now a weak purple arc
jumped the same gap. I'm so sure that the primaries and HV coils are for the
most part identical. Maybe there is something about phasing on square core
that I don't know about. Thanks for your offer of good wire, but I don't
feel like breaking the whole transformer down to wind new primaries.

Godfrey Loudner






----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, January 02, 2003 2:16 PM
Subject: RE: HV Wire - electrical tape?


 > Original poster: "Mccauley, Daniel H by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 >
 >
 > First off, how many turns are you planning on putting on the primaries???
 > If its a small number, i have some
 > excellent quality 60kV high voltage wire which I'd be willing to part
with.
 > We typically use this wire to
 > make prototype high voltage inductors.  Also, what frequency are you
 > planning on using this transformer for??
 >
 > Dan
 >
 >
 >
 >
 >
 > I took the square core from a large filament transformer for a two tube
 > x-ray system and removed the two secondary coils. Leaving the two
primaries
 > in place, I replaced the two secondary coils with two new high voltage
 > coils, which were originally intended for a dental x-ray transformer. My
 > intention is to place the two primaries in parallel and series the high
 > voltage coils, without center grounding to the core. To cut the labor
 > involved in insulating the HV coils from the core, I decided I'll use
vinyl
 > foam weatherstrip, soaked in polyurethane. Using an x-ray transformer, I
 > tested the idea. There was an immediate arc through at the glue seam. Bad
 > Idea! Now its back to proven methods. Now I don't feel bad at losing ten
 > rolls of that 69 kV splicing tape on ebay.
 >
 > Godfrey Loudner