Re: 1256 variacs + questions

["Kevin R Eldredge" <kreld-at-juno-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

>
>Is Kevin on this list?  If so:
>
>Kevin, would you be willing to share your transformer design with us 
>(me) 
>as I am in California and having trouble finding pigs without $300 
>shipping 
>on top of the price.
>

Hi Chris, all

  I could have bought a pole pig locally, but I buy them at scrap value
so most of them are 7200 volt units as that distribution voltage is being
phased out around here.   I tend to "want" to build all the components
that I can, so I built this 23000 volt 15 kVA transformer.  This was not
my first rewind of a transformer, and would not recommend it without
reading some material on transformer designs, especially high voltage
units.

   The secret is finding a suitable core for rewinding.   There happens
to be a surplus electrical supply here that lets me have oddball voltage
dry type power transformers for cheap.   They had a nice open core 15 kVA
transformer in a metal case rated 240/480 to 2400 volt.   I simply tore
one end of the core off & removed the 2 windings.  The low voltage
windings were to be reused as is with a new high voltage winding wound
over them.  This makes rewinding sooo much easier as the large primary
wires are very difficult to wind.   Spacers were installed between the
old primary & new secondary as did the old primary windings for good oil
flow.  It is important to keep adequate clearance in the windings from
the core and inter layer windings.

   Two 11.5 kV windings were wound using Kraft paper for layer
insulation.  Calculations on output voltage was based on the fact that
one turn around the primary equaled 2.6 volts with 240 volts in.  Simple
math provided the amount of turns needed.   The core is rated 15 kVA,
this does not change as long as the new  secondary winding can handle it.
  The original metal plate case was welded up to hold oil ( no easy task
with a plain stick welder), an aluminum top was fabricated as well as
high voltage output terminals.  The 240 volt input terminals were
salvaged pig low voltage bushings.   I filled it with Exxon mineral based
transformer oil & fed it power checking for proper operation, (no
bubbles, smoke or arcing in the core).  Tests were done with up to 150
amps input with rewarding output arcs.

  Other transformer I have built just for Tesla Coils are a 13 kV 10 kW
unit, a rewound 7200 volt pig to 14 kV 10 kVA, and several 10 & 12 kV 1 &
2 kVA units built into 30 LB freon containers filled with oil.  These are
all still working as intended.
  Also, you might try calling a transformer shop out of State to keep
from building one, close enough for a trip to pick it up yourself to save
shipping charges.

Kevin E.


>Another question:
>
>Has anyone built any of their secondary structures with wood.  I am 
>designing a large coil and would like to make it an open air design 
>(like 
>Greg Leyh's monster) but I am having trouble finding good strong 
>materials 
>to build the framework.  If anyone has any wisdom in this area it 
>would be 
>greatly appreciated.
>
>Thanks,
>
>Chris
>
>

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