Transformer Simulation Help Needed

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

Hi All,
       I recently built an NST farm consisting of five 15/60s and two 15/30s
all in parallel.  They were checked to make sure none were connected in
opposition. These are all 120v 60HZ units. I made them selectable by putting a
switch on each primary, but since I don't have any 15KV contactors, the
secondaries were wired in the circuit all the time. After on-off testing over a
few days with switchable PFCs and a resistive load (800ohm-at-800Watt), three of
the 15/60 transformers had failed (open secondaries). I suspect that the
stresses on secondaries in the circuit with some of them idle may have ca! used
the problem. I don't know if the idle ones stressed the active ones or vice
versa. Then again, maybe it was just their time to die.  
       Would it be possible for someone skilled in the art of transformer
simulation to provide insight before I do any more damage, or unnecessarily
tear out all the select switches? What more data would be needed? The 15/60s
are all rated 8.23A primary and both 15/30s are rated 3.85A. If this problem is
not of general interest, would someone RSVP off-list? 
TIA,
Matt D.