David Nebenzahl wrote:

On 1/28/2011 6:38 AM William Sommerwerck spake thus:

How does a center-tapped transformer secondary WHERE
THE OUTPUT IS REFERENCED TO THE CENTER TAP
(ie, the center tap is grounded) NOT generate two separate
phases?

After thinking about this, I've come to the conclusion that it doesn't.

"Phase" implies a relative-timing relationship. Simply inverting polarity
doesn't change the timing between the two waveforms.

That can't be correct.

Let's test the hypothesis. If we had two signals that were 179° out of
phase, would you not say that we had two separate phases? There is a
definite, though small, timing difference.

Let's say the signals were 181° out of phase: two phases again, correct?

So what's "special" or magic about 180° that it wouldn't be considered a
completely separate and distinct phase? Why would phase have a "hole" at
180°? (And for any wisenheimers who will say "well, you must consider 0°
to be a separate phase too!" I say nonsense: that's just a phase
"identity" which we can ignore as being identical to the original phase.)

Repeat the hypothesis a 0º and you will find a hole in there, much the same
as there must be one at 180º.

To understand what is "magical" about that you will need to know phasors and
the math related to that. Once you understand the math that support phasors,
you clearly see why 0º and 180º are the same phasor.

http://en.wikipedia.org/wiki/Phasor

People seem to be tripped up by the fact that it's trivially easy to
produce the 180° phase, and that it is, as you say, a mirror image of
its respective phase. But this doesn't make it any less of a separate
phase.

The other fallacy here is that because we don't actually use 2-phase
electrical power, there cannot be any such thing as 2-phase power. It is
true that two phase power (0° - 180°) is not very useful; that's why we
don't have any 2-phase motors. But technically, a system with two legs
of 0° and 180° is, in fact, a 2-phase system.

Even if it's not called that. Even if it is not used *as a phased
system* (it's used to derive two legs from a step-down transformer in a
120-0-120 arrangement). It's still 2-phase power.

So whaddya say now?

No, it isn't.

--
Mark Cross
If Linux doesn't have the solution, you have the wrong problem.