Dan sez: "Suppose I take a three phase motor and use some method to get it
running on a single phase source, and then connect the three leads of
the motor to a three phase rectifier bridge. Do I not have three phase
power going to the rectifier bridge? Is my ripple current not pretty
much what I would expect if I had the rectifier bridge connected to the
output of a three phase generator? It seems to me that a RPC does not
need a load motor to work."

Yes, Dan (I think) you'd have 3-phase current going to the rectifier
bridge. This is true by virtue of the fact a 3-phase motor running on
single-phase delivers 3 phase currents to a resistive load. Notice, I did
not say "generates" 3-phase current because the original single-phase line
terminals are connected through to the resistive load and the other "phase",
if you will, is derived via transformer action within the 3-phase motor.
The 3rd. leg voltage, and current, into the rectifier will (obviously) be
less than the single-phase line voltage suplied directly to the rectifier.

Now, stop at this point and forget the rectifier. The description above
would apply equally well if the load on the idler was composed of 3 light
bulbs, also a resistive load. In that case, the light connected directly
across the single-phase line would burn at full brilliance while the other 2
bulbs connected from the 3rd leg to L1 and L2 respectively would burn at
less than full brilliance.

IMO, your other point re. a RPC needing a load motor to work is moot. This
because an idler motor alone is not a RPC.

Bob Swinney


wrote in message
oups.com...

Dan


Robert Swinney wrote:


No. A RPC is not a three-phase device in the classical sense; It isn't
fed
with 3-phases and it does not "generate" 3 phases as would, say a 3-phase
alternator. True, the currents circulating in the load motor may make
you
think they are 3-phase but that is because they are the products of a
special network. That network is *not* comprised of motors having all 3
sets of leads connected in parallel. Because of the way it is connected,
that network has the capability of taking single-phase current into two
3-phase motors and delivering currents that emulates true 3 phase
current.
Key to accomplishing this is the non-parallel connection between the 3rd
legs.

Bob Swinney