You could use a 220/440 rotary converter as a transformer, but it is REAL
inefficient. The 220/440 motors use the windings in a series or parallel
configuration to make the voltage/current change so none of the wires have
to be large enough to carry a current twice as large as the HP rating
requires. This means you would have to have a idler motor rated twice of
what you normally need to power the same load - i.e. 7.5 HP idler for a 5 HP
load becomes a 15 HP idler for the same load. Starting becomes tricky (now
a 20X current inrush or greater rather than a 10X inrush), and the starting
cap requirements grow exponentially (expensive). There are a couple of
other concerns with this technique, but I think you get the idea. It's not
the easiest, cheapest, or quickest technique.
I don't know of any motors which are specifically made as rotary converters
and step up converters at the same time, but if they were available you
would probably want to consider that as a way to go.

"William B Noble (don't reply to this address)" wrote
in message ...
thanks guys - sounds like there is no brilliant secret, although I'm
still not convinced that there isn't some way that doesn't involve
moving parts to geerate 440AC 3 phase from 220 single phase - but I'm
going to wait until I get the machine and then see what it really has
in it - if I can get it to run on 220, then VFDs are the obvious
answer - small ones are cheap, and for this application I don't need
the fancy vector drives. I wonder if a 220/440 motor can be both a
transformer and a phase converter at the same time - there's something
to think about


On Thu, 24 Nov 2005 10:03:42 -0500, "Jim Reed"
wrote:

Stan, the reason your transformer burned up when you had a VFD in front of
it is the transformer is made for relatively clean sinusoidal power. The
VFDs put out very "dirty" (sometimes actually square wave) power. The
harmonics created by this dirty power cause losses within the transformer
that it is not designed to take. You should always use a VFD after your
final transformer, and not before, if you're going to use one.
Mr. Noble, if you're intending to stay with the original motor, I would
recommend a 220 VAC 3 phase slave motor of 15 HP driving a 3 phase
transformer stepping the 220 VAC up to 440 VAC. Then, if you still want a
variable speed drive, put it on the 440 side. The 15 HP motor will need
to
be started/run by a static phase converter. There's a lot of info on this
out on the net, and if you need more information, I can find some good
people in Indianapolis who can help further. Good luck with your new
machine.
"stanley baer" wrote in message
...
william_b_noble wrote: