On Wed, 8 Aug 2018 10:12:36 -0700 (PDT), trader_4
wrote:

On Wednesday, August 8, 2018 at 12:49:45 PM UTC-4, wrote:
On Wed, 8 Aug 2018 06:28:57 -0700 (PDT), trader_4
wrote:
So the
problem I posed is where I morph that into 240/120 service, one step
at a time. Looks like we're stuck on step one, Fretwell says if I
have those two windings that are 90 apart share a common neutral return,
it's no longer two phase, that two phase has to have 4 wires. Which
of course is bizarre. Why would two phases require 4 wires, when we
have 3 phase all over the place with with just 3?


Quite simple grasshopper
You need 4 wires because the 2 phases are not connected together.

If you connect 2 out of phase sources together you get 3 phase. Think
triangle.

OK, let's go through this one step at a time. I take two windings
and put them on a generator shaft, with a difference of N degrees.
I connect on end of each winding to one end of the other winding.
That point is the system neutral. I connect a scope to the neutral.
I look at each of the two conductors coming from the so far unconnected
ends of the two windings. Do I see not see two voltage waveforms
that differ by N degrees?


If I do see that, then how by connecting two loads, let's say a resistor
between the conductor from one winding and and the neutral and another
resistor between the other winding and neutral, do I not still have
two phases and the same waveforms? What magic just happened to make 3 phases? And if I put a resistor between the two conductors, I
don't see how that creates a third phase either. Following that logic,
putting a resistor between two phases of our 3 phase system would
create another phase too, wouldn't it and I'd then have 4 phases?
If I put three resistors between phases, I'd have 6 phases?

As soon as you connect them together, you get 3 phase delta.
If you don't see that, you have no business in this conversation.
Three phase delta is most commonly produced with two "sources"
(transformer secondaries)
It could be done with 2 windings in a generator but why would you
spend all of that money on rotating machinery and not add the 3d
winding to get 100% instead of 66.6% of the output?
In the case of transformers the economy is there so they do it.
In fact I have only seen 3p delta with 3 transformers once, in Key
West and I assume they grew into it.