Transformer Design

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

Original poster: "Ben McMillen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <spoonman534-at-yahoo-dot-com>

Hello all,
  Yesterday evening I took some time to begin the design of
a new power supply for TC work. I'm planning on using the
core from an old power transformer that was being thrown
out. It's a 3 phase tranny rated at 240/260/280V input 3
phase. Output is 17 -at- roughly 280 amps. The name plate is
marked 4.8KVA. I went to this site for design information:

http://members.tripod-dot-com/~schematics/xform/xformer10.htm

After working through some of the numbers, I got rather
confused working out the VA ratings of the core. Accordint
to the chart given on the webpage, for a core area of
6in^2, I should get a VA of about 900VA. Since there were
three secondaries and primaries, I multipy that by 3 to
come up with 2.7KVA. So where does the 4.8KVA marked on the
name plate come from? If I divide that by 3 I come up with
1.6KVA per core. Is something different for 3 phase? How
does core area relate (in mathematical terms) to VA
ratings? Could someone direct me to a webpage with
appropriate formulas? I want to do this by the numbers.. 

The core of this beast measures 9 1/2 inches by 11 inches
and weighs about 80lbs.(quite hefty) Each leg has a core
area of 6 in^2. I was hoping to wind the primary for
120/240V operation and place it on the center leg. The
secondaries will each be 7.2KV (on the outer 2 legs of the
E core) (center grounded to core) for a total of 14.4KV.
Does anyone see a problem with this? How would I go about
configuring the primary for 120/240V operation? (in the US)

Thanks for any help! I'm hoping to use this PS with an 8"
coil ;)

Coiling In Pittsburgh
Ben McMillen


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