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In article ,
says...

The direction of the power flow through the phantom phase
link then depends on the relative mechanical loading on the two
rotors. In the two limiting conditions of both motors idling or
both motors loaded to the same fraction of their rated HP, each
motor is self sufficient and little or no third phase power flows
through the link.

They don't really have to both be loaded to the same fraction,
it only has to be a very small loading in each case. Then you
see no current flowing on the third line, IF there are no
tuning capacitors, as in my system. Then a mechanical load
on the machine causes the current in that line to spike upwards.

The current in the third leg is *not* zero under all idling
conditions I believe if one installs tuning capacitors though.
Anyway that's my understanding as balancing those currents
seems to be one of the 'figures of merit' for tuining a
converter like that, aside from voltage balancing.

By current here I mean all currents of course, reactive and real.

The currents I see on my L1, L2 connections to my lathe
are mostly out-of-phase. They're not real, they don't represent
real work being done. The current flowing in the generated L3
connection only becomes noticeable when there's mechanical load
so I suspect it is mostly in-phase by its nature.

When I load the lathe, the L1, L2 currents shift in phase towards
real power, and the L3 one simply grows.

Jim

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