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Re: Finished with Isolation Transformer.



Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Steve C,

I tried that.
The laminations I used meant a core center leg measuring 2.25" x 6.5". The
coils were an oval shape and not round. Notice the Isolation transformer
pictured. The laminations are the ones I used to construct my first HV
transformer so the coils in this transformer are also oval shaped but with
much heavier wire and a lot less layers.

The reason the HV transformer failed was the shape of the coils. During
winding insulation had to be used between each layer. This formed a
"cushion" as more layers were wound. Without my knowing it as more layers
were added the forces were unequal and caused the long sides of the coil
(wire layers) to buckle deep inside in an "S" pattern, the first 5 or 6
layers. What this did was it brought the edge of the layers much closer to
the edge of the extra insulation  i used to guard against flashover. During
ramp up all was well until I reached a little over 6KV then there was a
yellow-red flash and a huge bubble erupted in the oil. Flashover had reared
it's ugly head since the edges of the inside layers were much closer to each
other than the design called for.

Lesson learned:
Be sure to wind ROUND coils for homebrew HV transformers. And use
laminations to allow room for round coils.
Square coils should be OK too but the idea is to be sure the forces applied
to the first few layers aren't unequal and not great enough to deform them
as more layers are added.

Since I had no such laminations to wind round are square coils I decided to
go with MOTs and wind an isolation transformer to eliminate the possiblity
arcs within the MOTs. The 4 pairs of secondaries are insulated from each
other, the core and primary. The thinest insulation is the 2 sheets of 1/16"
polypropylene. That's 1/8" of poly.

Here's a pic to explain how an isolation transformer helps when adding MOTs
in series.


ftp://ftp.xmission-dot-com/pub/users/p/potluck/pics/primaryiso.jpg

Rick W.
SLC



----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, February 24, 2003 4:21 PM
Subject: Re: Finished with Isolation Transformer.


 > Original poster: "Stephen Conner by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > At 07:48 24/02/03 -0700, you wrote:
 > >Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > ><potluck-at-xmission-dot-com>
 > >
 > >Hi all,
 > >
 > >Finally finished the isolation transformer I've been working on.
 >
 > That sounds like one awesome transformer. I have just one question: You
 > obviously know how to build transformers, and you seem confident with HV
 > isolation and vacuum impregnation techniques, so why didn't you just wind
 > an 11kV secondary on your transformer and forget about the MOTs
altogether?
 > Future generations would remember you as "The Man who built his own Pole
Pig"
 >
 > Steve C.
 >
 >
 >
 >
 >