Averagesupernova said:
If you search, you will find that I have argued many times that what some people call 2-phase is more correctly just single phase.
Agreed. There
does exist a thing called 2-phase power, but it doesn't apply here.
Averagesupernova said:
I don't see how you say that when referencing the scope ground to the center tap of a transformer and measuring each end with separate probes on a dual channel scope that the observed voltages are not 180 degrees out of phase.
What I said was that if you placed the ground clips of 2 channels both on the center tap and the probes to each end, you would, in effect, be reversing the orientation of one of the channels in relation to the other and, therefore the waveforms would
appear to be 180 degrees out of phase.
Averagesupernova said:
Do you feel that two totally different secondary windings are required in order to be considered 180 degrees out of phase? Just exactly what do you consider a requirement before you can say two signals are 180 degrees out of phase?
Yes. Let's start with the simplest of transformers having a turns ratio of, say 2:1. This xfmr will have a high voltage primary coil with 2 leads (one at each end of the coil), labeled H1 and H2 and a low voltage secondary coil, also with 2 leads (one at each end of the coil), labeled X1 and X2. If you apply a standard (sinusoidal) AC voltage to the primary coil, a voltage of 1/2 the value will be induced on the secondary coil. When the primary voltage rises, so will the induced voltage (and vice-versa), so you can see that the induced secondary voltage will be in phase with the primary voltage (but at 1/2 the amplitude). Now, if you were to reverse the leads measuring that voltage, it would appear to be 180 degrees out of phase with the primary. Agreed?
Now, let's take a 2nd transformer that is identical to the 1st one, except that it has a "center-tapped" secondary (let's label this lead as X0). This is a single coil with a lead attached to each end (X1 and X2) and one attached to the center of the coil (X0). There would be 1/2 the number of turns in the secondary coil as there are in the primary (just as in the 1st xfmr). The center tap will have half that number of turns (or 1/4 the number of turns in the primary) on either side (between X0 and X1 and between X0 and X2). If you were to apply the same AC voltage to the primary coil and measure the voltage from one of the end leads, say X1 to the center tap X0 (ignoring X2 for now), you would in effect have a xfmr with a turns ratio of 4:1. Again, the induced secondary voltage will rise when the primary voltage rises (and vice-versa), so it, too, is in phase with the primary. Agreed?
No matter how many times a single secondary coil is tapped, a voltage measured from any 2 leads connected to different points on the coil will rise and fall with the inducing primary voltage.
This supports why we correctly refer to 240/120V systems as "split phase" rather than "2-phase" ... there are not 2 different phases, but rather a single phase that has been split in two parts.
To repeat an earlier example, I can make a D-cell battery look as though it supplies negative 1.5 volts merely by reversing the leads of my voltmeter. This is what we're doing with the scope. So, in effect, what we end up with is a single primary coil and 2 secondary coils connected end-to-end. Imagine then there are actually 2 separate secondary coils, each with leads connected at both ends (only). The secondary induced voltages will both rise and fall in time with the source (primary) voltage. These voltages are both in phase with the primary voltage and, therefore in phase with each other.
Using vectors to illustrate: We know that the two 120V voltages of split-phase 240/120V add up to 240V. So if we take the voltage between X0 and X1, and assume its angle to be 0 degrees (it's not in reference to anything, so we can choose any angle), we would have a vector of length 120 pointing directly to the right. Now, take the voltage between X0 and X2 and let's assume that it is 180 degrees out of phase from the first voltage. We would then have a vector of length 120 pointing directly to the left. I you add these 2 vectors, you can see that they would cancel each other out. Alternatively, if we have 2 vectors both of length 120 pointing in the same direction and add them together, we would have a resultant vector of length 240 pointing in the same direction as the original 2 vectors.
Remember, too, that split-phase power (3-wire 240/120V power) is considered single phase, not 2-phase (you said it, too).
Averagesupernova said:
Question for you: Suppose I had 3-phase delta 240 volts with a center tapped transformer for the neutral to provide the 120 volt circuits coming into a room (all 4 wires). Lets call this power source A. Suppose I also have a standard 3-wire 240 volt (typical residential in the U.S.) coming into the same room. Lets call this power source B. I then 'manufacture' a new signal from power source B. Never mind the method I use to do it. This new signals phase and voltage are adjusted relative to the two 'hot' wires from power source B to form the third leg of a 'new 3-phase system'. I now run out of this room power source A, and power source B along with power source B's newly 'manufactured' signal. I just keep them separate with no indication which is which. Could you tell the difference? And if so, why?
I'm not really sure what the point of this question is. Especially since you don't disclose how you derived 3-phases from the standard 3-wire 240 volt source.