Single Phase or Polyphase?

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LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
See graphic.
All you're doing is proving that 1 + 1 = 1 - (-1).

Regardless of labeling, the voltages must be in phase in order to add to twice one of them. This applies whether the source is two separate transformers or one with two secondaries.

However, with a single, center-tapped secondary, you can't invert anything; nor do you need to.
 

mivey

Senior Member
Have you devolved into personal attacks?
Pardon me for being so blunt. I get tired sometimes and tend to lower my diplomatic guard. I was stating what I thought appeared to be your trouble-spot in understanding the voltages I have been discussing. It appears to me you seem to have issues of some sort in this area. I'm basing my statements on what you post.

We have been discussing practically forever that one voltage from the center-tap to end is 180 degrees out of phase with the voltage from the the center-tap to the other end. I connect two voltages together where one has a rise from the center to the end and the other has a fall from the center to end and you say that is not what is there. :-?

You should understand that one voltage rise from end to center in series with a second voltage rise from center to end must have different reference points than the two voltages described in the previous paragraph.

There is no question in my mind that this concept is an issue in the communication. It is a simple voltage vector concept that we learned decades ago, and I'm sure you long before me. But I'll try to be more diplomatic in the future when pointing out communication trouble-spots.

The fact remains, if you are not following the voltage vector for X1-X2 vs. X1'-X2', then it seems to me that is why you can't follow the points I have made about a voltage reference. I don't know how else to explain why you are not following the voltage vectors unless you are just not reading close enough or something.
You admit that 'phase-opposed' voltages can not be directly connected, your drawings clearly indicate you are actually adding the opposite of your 'phase-opposed' voltage. This contradicts what you have said in previous posts.
The diagram does show them connected at the neutral and it is exactly what I have said in the past. The phase-opposed voltages have always been discussed as being connected at the neutral point (both have their "X1" points directly connected together at the neutral).
But you say I am wrong for wanting to describe the number of phases based on the actual connections of the voltages.
You are wrong for saying that the voltage between two points can only have one reference. You are choosing your references so both voltages are in phase with the high-side of the transformer. Saying that this is the only choice is simply ignoring the other reference options.

Again, discussion of a potential difference has no significance until a reference is chosen. The voltages are defined by their reference. Saying that we must use the line-side voltage as a reference for both load-side voltages is defining the reference frame for both of the load-side voltages. But it is not a universal reference.
 

mivey

Senior Member
All you're doing is proving that 1 + 1 = 1 - (-1).

Regardless of labeling, the voltages must be in phase in order to add to twice one of them. This applies whether the source is two separate transformers or one with two secondaries.
The difference is the reference point of the voltages. The idea of a voltage being in phase or out of phase with another is going to depend on the reference frame. A voltage does not have a "default" reference.

As for getting twice the voltage: For in-phase voltages, we connect so the vectors are head to tail. For phase-opposed voltages we connect so the vectors are tail to tail. This works on paper, and it works in the physical world when we are deriving different voltages using transformer banks.
However, with a single, center-tapped secondary, you can't invert anything; nor do you need to.
Of course you can. And we make use of this very fact in some of the transformer banks we have in the utility industry.

We can't saw the winding in half and flip it around. That is like saying to change rotation we have to re-wire the motor.

But getting two voltages with opposite phases is simply a matter of how you wire the circuit tied to the secondary.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Pardon me for being so blunt.
I get tired sometimes and tend to lower my diplomatic guard. I was stating what I thought appeared to be your trouble-spot in understanding the voltages I have been discussing. It appears to me you seem to have issues of some sort in this area. I'm basing my statements on what you post.
I will not pardon you.

There is no room on this forum for personal attacks.

mivey said:
You are wrong for saying that the voltage between two points can only have one reference. You are choosing your references so both voltages are in phase with the high-side of the transformer. Saying that this is the only choice is simply ignoring the other reference options.
You are the person insisting on always using a single point (i.e. the neutral) as your reference.

I have stated repeatedly that describing the number of phases should not depend on if the neutral is or is not used.

You took two separate single-phase voltages and defined them as being 'phase-opposed', but you used two unrelated reference points to do so.
Next you inverted one of these sources so that it was no longer 'phase-opposed'.
Then you connected the two now in-phase single phase voltages so they would add.
Finally you choose the common connection point as your reference and called the output voltages as being 'phase-opposed'.

All I have been doing, is asking for the physical connection of the voltage sources to be considered, (2) in-phase voltages connected in series so that they add = 1-phase. The number of phases is not subject to an arbitrary reference choice.

Simply installing an unused tap anywhere along the length of a single conductor does not change the actual voltage rise, or drop, direction from the beginning to the end of that conductor. The tap does however give you the ability to see two different directions when it is used as a new reference point (one of the end points was originally used as a reference to establish the 'base' direction).
 

roger

Moderator
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Location
Fl
Occupation
Retired Electrician
Since I'm not in this disscussion I feel I am neutral enough to close it before it goes any further south.

Roger
 
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