OT: Help with three phase transformer function

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Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>

With Terry's indulgence, I'd like to ask a question of the list's EE types 
about the function of an unusual three power phase transformer I salvaged 
recently.  I can't figure out the way the fields work in the core.
This transformer was rated at 3 KVA, and has a massive "O" shaped core, 
nearly 2.5" thick in cross section.  The primary side was marked for 200 
VAC input, three phase, and there are two secondaries, each rated at 100 
volts, single phase (this was from a Japanese SONY IC parts placer).
On side of the "O" is a first primary which connects to two of the input 
three phases.  On the side is a second primary connected between the third 
phase and an apparent center tap of the first primary.  There are two 
isolated secondaries, each wound outside one of the individual primaries.
My question is what is the voltage and current wave form on the two output 
secondaries?  Since there is only one flux path in the core, it seems to me 
that the two secondaries have to have outputs that are in phase with each 
other.  Would not all the output power come from the third input phase, or 
would there be a contribution from the two lines feeding the center tapped 
first winding?

I don't have an immediate application for this transformer, but after all 
the work I did to salvage it, I'm just trying to figure out how it 
worked.  I could probably use it as a beauty of an isolation transformer, 
just by backfeeding one of the secondaries and drawing power from the other.

Thanks in advance for your assistance.

Dave Speck