On Friday, September 13, 2019 at 1:37:55 PM UTC-4, Dean Hoffman wrote:
On 9/13/19 8:37 AM, trader_4 wrote:

A bunch cut.

Simple fact, the example Ralph provided is two phase power. And phase
is not limited to 90 deg, you can make it anything you want, just
rotate the second winding. Of course in physics and engineering, we
don't need to create it physically at all to analyze it, we can do
that on a piece of paper. We take two voltage sources:

120 Sine(wt)
120 Sine (wt+O) where O is 0 to 359

Connect them on a common return, we have three wires, the same thing as
Ralph's example. Set O=180, what you have is another version of Ralph's
two phase power, the same thing as 240/120 into your house, two voltage
sources, 180 deg out of phase with each other.

But isn't there a point where two phase ceases to exist and
becomes single
phase? Wouldn't that be the point where capacitors or a start winding
are needed to start motors? Practically speaking. That's what I was
trying to get around to earlier.

No, because phase is simply the relationship of one periodic waveform
to another. If you look at the two waveforms on a scope, with Ralph's
example of two phases on three wires, you'd see two sine waves offset
by 90 degrees, one quarter of a period. If you rotate the winding by
ten degrees, you'd see it shifted by 100 degrees. If you rotate it
to 180 degrees, you see it shifted by 180 degrees, one the opposite
of the other. How practical any of them are to do anything in particular,
what we would or could use them for,
is a separate issue. Theoretically you could start and run a motor
with any phase difference other than 180, but that doesn't mean that
the 180 phase shift isn't there, isn't real, just because it can't
start a motor.






Someone you know really well wrote this at 8:19 am on 9/12.

"There are two phases internally when the cap is in the circuit.
That's why it's there, to give a phase shift.
We call the motor single phase, because they run off a single phase
circuit."

And there are no contradictions there. If you look inside the motor,
look at the voltage waveforms, you'll see two sine waves, one shifted in
phase with the other. Take a look at the three wires in your 240/120V
service, connect the scope probe to the neutral which is the system
reference point and you'll see two 120V sine wave voltage sources,
one 180 deg out of phase with the other. It's the same thing, only
180 deg, instead of 90 or whatever.

I'm the only one here who can give a definition of N phase power:

Power delivered from N voltage sources that are of the same frequency,
differing in phase.

Sine(wt) one phase

Sine(wt)
Sine(wt+O) two phase

Sine (wt)
Sine (wt+O)
Sine (wt+P) three phase

That covers Ralph's two phase (O=90), three phase (O=120,P=240),
240/120V (O=180)into your house,
on up to N phases. That's the beauty, it's consistent, uniform,
I'm not stuck with but it was 90 deg in Philly, those phase shifts
are weird, it's not mechanically balanced, IDK what happens....
That center tapped transformer is two 120V voltage sources 180
deg out of phase with each other. That's the only way 240/120
works.