Purely a choice of representation -- it's either two portions of a single phase with a delay or two phases at that same relative angle each.
The two representations are totally indistinguishable in their physical implications; choose whichever is more convenient for the task at hand.
It's no different than a change of reference from cartesian to cylindrical coordinates, say. The one is much more convenient when dealing with circular motion than the other but you can and will get the same net answer either way (assuming you do the algebra correctly, anyway).
Actually I don't think it's an issue of representation with the folks like Bill. They just refuse to accept that the two hots in a 240V/120V split phase service have a phase relationship at all. That's why I used the example of morphing what everyone calls 3 phase, to two phase, then to what is identical to split phase, just by dropping one phase and changing the phase angle. At the wires entering a building, you can't tell the difference between them. So either something magical happens at 180 deg or else it's just a special case of two phases.
The power industry refers to 240/120V split phase as "single phase", because it originates from one phase of their primary distribution, as opposed to 3 phase power which uses all three. It's an easy way to refer to it and fits their perspective. But that doesn't change the overall definition of phase in electrical engineering, how you analyze it, represent it, etc. 180 deg phase difference is 180 deg phase difference, no matter how you create it. I'd also point out that even in the power industry, it's correctly called split phase. What happens when you split something? I can't think of a single example of something that gets split, and then you still have just one. And even in the power industry, it eventually matters as that IEEE paper delivered at a power conference shows. The author is clearly saying that to correctly model a 240/120V service, you have to treat it like what it actually is, two phases, differing by 180 deg.
I'm aware of that that they're simply ignorant...which is why _I_ used the geometrical interpretation instead of the physical.
Yabbut... :)
You _can_ get the same place in one coordinate system vs the other...it's just __much__ more complicated to carry around the phase shift (where "phase" means the delay angle, not the two legs in this case) between the two original taps as opposed to writing the two phases (here "phase" is each one of the two split legs) but in the end it all works out the same way (again, presuming the algebra is taken care of correctly which is a real pita to do the "wrong" way...
Again, for comparison the latter is like writing the equations of motion for circular motion in cartesian coordinates -- you can do it but it's a lot more of an exercise in futility than if one simply uses theta,r instead of x,y.
For the Bill's of the world that there are two common English uses of "phase" is, imo, much if not all of the problem. There are the separate generator "phases" and then there's the "phase lag" that is simply a coordinate shift of how to look at a time delay for a given physical phase. It's the latter that gives rise to the split-phase 240V from a transformer and the confusion of that use of the term "phase" with the physical leg from the generator that is the problem.
Like so many other colloquial terms, it should have been named differently from the git-go and that nomenclature used religiously and unambiguously and then the confusion could likely have been prevented. But, the two got called by the same name because it is such a convenient shorthand and isn't confusing to the "trained professional" :J) but leads to mass confusion in general usage as we see hear.
Wouldn't happen to be in Philly, would you? That's the only place in the US I'm aware of that actually has any "real" 90-deg phase shift
2-phase power distribution still in the US and I thought it was only available in commercial locations in the center city.
I was also unaware there were any 2-phase motors other than stepper motors in production and a quick search didn't find any.
You sure it's not split-phase 240V (conventional US 240, not actually
2-phase)? AFAICT(hink) you'd have to have a Scott x-frmr or the like to generate the second phase at the 90-deg phase angle instead of the
180-deg of split-phase.
Can you double-check the actual motor nameplate easily? You got me intrigued as to what they actually did install... :)
Wouldn't happen to be in Philly, would you? That's the only place in the US I'm aware of that actually has 90-deg phase shift 2-phase power distribution still in the US and I thought it was only available in commercial locations in the center city. Way-back when (like around
1900 or even slightly earlier) the generators at Niagara Falls were
2-phase but over time it fell out of favor and 3-phase is de rigueur these days.
I was also unaware there were 2-phase motors other than stepper motors in production and a quick search didn't find any.
You sure it's not split-phase 240V (conventional US 240, not actually
2-phase)? AFAICT(hink) otomh you'd have to have a Scott x-frmr or the like to generate the second phase at the 90-deg phase angle instead of the 180-deg of split-phase.
Can you double-check the actual motor nameplate easily? You got me intrigued as to what they actually did install... :)
To clarify absolutely--I'm not saying one doesn't treat the two sides analogously to what your author is; only that it's mathematically possible (at least theoretically, the practical matter of actually solving the resulting mess aside) to write the system simply as a time delay (phase angle) of one compared to the other instead of as two phases.
He asked for the specifics on the blower motor you claimed to have installed. So, that isn;t an answer. If you have a two phase motor, name it. A typical 120 or 240 V residential HVAC motor is single phase. Hook up a scope and all you will see is one 60 hz sine wave. Has nothing to do with the 120V loads and their phase relatioship to each other. Hook up a scope at the panel and look at the two 120V legs and you will see 180 deg difference.
It's also likely that you and Bill are one and the same idiot.
And now you're back to the same problem as outlined above -- a single _generator_ phase, but two separate outputs with a 180-deg phase _angle_ between them. Now you're back to the point of which way one wants to represent them as outlined above.
"Some common arrangements of audio transformer windings are shown in Fig 11 .4.2.
Example a.) shows a centre tapped secondary winding that can be used to pro vide a selection of different turns ratios. Some transformers may also have tapped primaries for an even wider range of ratios. In audio amplifiers, t he phase/anti phase of signals can be important and phase splitting transfo rmers with centre tapped secondary windings can be used to provide two anti phase signals. The dots near the windings on schematic diagrams indicate t he relative polarity of the signals on different windings, and in this exam ple show that the signal from the upper secondary winding (A) will be in ph ase with the primary signal, while the lower secondary winding (B) will pro vide a signal in anti phase with the primary signal."
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See fig 2, which is the phasor diagram for what comes out of the center tap transormer. Note that there are *two* phases, 180 deg apart, shown.
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tapped-transformer.html
"As it can be seen from the figure that this type of configurations gives u s two phases through the two parts of the secondary coil, and a total of th ree wires, in which the middle one, the center tapped wire is the neutral o ne. So this center tapped configuration is also known as a two phase- three wire transformer system. In this way, half the voltage appears across one half of the phase, that is from line 1 to neutral, and the other half of the voltage appears across t he next phase, that is from neutral to Line 2. If the load is connected dir ectly between line 1 and line 2, then we get the total voltage, that is, th e sum of the two voltages. This way, we can get more amperes of current at the same voltage."
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