Re: HV Wire - electrical tape?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Godfrey,

Since you don't have robust insulation between the core and primary or 
between the primary and inner portion of the secondaries, I'd recommend 
connecting the inner leads of your HV windings to the core AND to the mains 
ground. This will keep the voltage stress seen by the inside and outside 
portions of the primary controlled and low (i.e., line voltage). Your RF 
ground can still be used for the center electrode in the safety gap and to 
ground the base of the TC secondary. Do not connect the RF ground to the 
transformer core.

Best regards,

-- Bert --
-- 
Bert Hickman
"Electromagically" (TM) Shrunken Coins
Stoneridge Engineering's Teslamania
http://www.teslamania-dot-com

Tesla list wrote:
>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
>