Single Phase or Polyphase?

[gar]

100327-0950 EST

jim:

The two 240V voltages are X1->X2 and X3->X4. They are in phase, based on industry convention.

When they are connected in series they remain two in phase voltages of X1->X23->X4, with a single resultant additive voltage of 480V.

If X1 and X3 are reference points, then X2 and X4 are in phase.

Therefore, if X1 is connected to X3, then X2 and X4 are in phase and the voltage difference between X2 and X4 is zero.

If X2 is connected to X3, then because of the known phase relationship the X4 to X3 voltage is added to X2 to X1 producing an X4 to X1 voltage double the voltage X2 to X1.

Because of the series connection you used, X1 to X2-X3 to X4, and the known phase relationship the voltages added, meaning got larger.

I agree.

But if you were to use the series connection X1 to X2-X4 to X3, then the voltages subtract, and the difference between X1 and X3 is zero.


Consider:

V2 = V1*sin t + V1*sin t = 2*V1*sin t
V2 = V1*sin t - V1*sin (t+180) = 2*V1*sin t

V3 = V1*sin t - V1*sin t = 0
V3 = V1*sin t + V1*sin (t+180) = 0

So if adding produces a larger result, then subtracting and doing a 180 deg phase shift of one sin function produces the same result.

Definition of reference points and and voltage points is all important in defining phase relationship.

What is the maximum possible phase shift with an RC network?

Consider this:
A center tapped secondary, a first diode anode connected to X1 and a second diode anode connected to X4, both cathodes are connected together, and a load resistor from the cathodes to X2-X3. What is the output?

Next a single diode from X1 to a load resistor to either the center tap or X4. What is the output?

After this change the transformer so X2 and X4 are the "center tap". Now what is the result?

With two diodes and a load resistor I have created a circuit that can tell if there is a phase difference between two sine waves of equal amplitude and frequency.

It is also possible to build a phase measurement circuit using zero crossing and slope detection components.

A phase is a description of the relationship of one waveform to another not a particular transformer connection.

I can build a transformer with single phase input that produces an output that is phase shifted from the input by an angle that is not simply 180 deg out of phase. Simply by adding a shading coil to the transformer core.

.

 

[mivey]

Your number of phases change when you move your reference, but you say I am being inconsistent.

Take our example of two identically connected 240 series connected windings with a (1) 240V load and (1) 480V load. For you to define the number of phases requires you to know which terminal of the transformer is the reference point, but you say we should ignore how it is connected.

The transformer remains capable of delivering:
A) one single-phase 240 volt supply
B) one single-phase 480 volt supply
C) two single-phase 240 volt supplies, both having the same phase angle. By definition, these two voltages can't be classified into a single poly-phase system of voltages because they have the same phase angle.
D) two single-phase 240 volt supplies in phase opposition. By definition, these two voltages can be classified into a single poly-phase system of voltages because they have different phase angles.

So the way we wire our circuit does make a difference in what voltages we take from the supply. No matter what we take away for a specific application, the transformer is still a source capable of delivering A, B, C or D.

The "industry standard" you keep referring to only tells use the relative relationship between the terminals. It does not tell us we have to connect to the terminals in only one way.

 

[mivey]

The two 240V voltages are X1->X2 and X3->X4. They are in phase, based on industry convention.

And that same convention tells you X1->X2 is in phase opposition to X4->X3. The convention shows the relative relationship, not how you have to connect.

An industry convention might say: B is higher than A and C is higher than B. Since it is a relative indicator, we can also say A is lower than B and B is lower than C. Or we can say A is lower than B and C is higher than B.

The industry convention gives us the relative positions for a specific case but does not dictate that the other valid relationships based on the specific case are not true.

When they are connected in series they remain two in phase voltages of X1->X23->X4, with a single resultant additive voltage of 480V.

Yes, two in-phase voltages connected in series to produce a third phase of 480 volts (phases add). The same 480 volt phase you get by using a common connection for two voltages in phase opposition (phases subtract). It can be seen either way. Both are valid connections. The center-tap can satisfy either type supply need.

So the transformer is connect using industry standards of X1->X23->X4. Now you come along and connect your o-scope to X23 and see 2 out of phase waveforms of X1->X23 and X4->X23, so you say they are out of phase.

We have two phases. The system reference allows them to be grouped into a single system designation. They can also keep separate system designations if they are used as separate systems.

I connect my scope to X1 and I see 2 waveforms in phase of X1->X23 and X1->X4.

We still have two phases (X1->X23 and X23->X4). The system reference does not allow them to be grouped into a single system designation so they keep separate system designations.

The only change to the relationship of the two waveforms X1->X2 and X3->X4 has been how we connect the scope.

Chicken & Egg: Just because someone else started with one reference first does not make a different reference invalid. One connection method to the phases allows them to be grouped into a single system designation, the other doesn't.

Or, are you saying that as soon as I connect two voltages in series a second phase is created because the magnitude of the sum of the voltages (X1-X4) is different than magnitude of each individual (X1-X23)?

A third phase is created. Without the two 240 volt phases connected in series, you would not have the 480 volt phase.

 

[jim dungar]

If X2 is connected to X3, then because of the known phase relationship the X4 to X3 voltage is added to X2 to X1 producing an X4 to X1 voltage double the voltage X2 to X1.

Because of the series connection you used, X1 to X2-X3 to X4, and the known phase relationship the voltages added, meaning got larger.

I agree.

But if you were to use the series connection X1 to X2-X4 to X3, then the voltages subtract, and the difference between X1 and X3 is zero.

Definition of reference points and and voltage points is all important in defining phase relationship.

We are in agreement.
I have never said the reference point is unimportant when performing an analysis. I have said that the number of phases should not change just because the reference point changes.

A phase is a description of the relationship of one waveform to another not a particular transformer connection.

I use the number of Line-Line waveforms to define the number of phases in a power system. This methodology allows me to be consistent with more than 100yrs of our industry's terminologies and not be concerned with the presence or absence of a neutral.

I can build a transformer with single phase input that produces an output that is phase shifted from the input by an angle that is not simply 180 deg out of phase. Simply by adding a shading coil to the transformer core.

Yes, but the 'direction' of the output is still dependent on the physics of the transformer.

 

[jim dungar]

A third phase is created. Without the two 240 volt phases connected in series, you would not have the 480 volt phase.

So now you say, a 240/480 3-wire transformer secondary (that every transformer manufacturer calls single-phase) is actually three-phase.

How stupid of me to define 3-phase power systems in a manner that is consistent with the terms used by our electric industry.

 

[gar]

100327-1523 EST

jim:

If I did not have two different phases from a center tapped secondary I could not do full wave rectification with two diodes.

I am happy to call this transformer with a center tapped secondary a single phase transformer, but it has two different output phases.

.

 

[jim dungar]

100327-1523 EST

jim:

If I did not have two different phases from a center tapped secondary I could not do full wave rectification with two diodes.

You have 2 single-phase voltages added in series to create a single L-L waveform. You choose to wire them into a circuit that uses the neural as a reference point and therefore views them as being 'out of phase' yet there is still only a single L-L waveform. The actual/physical connection of the 2 source voltages has not changed just because your circuit does or does not use a neutral.

I am happy to call this transformer with a center tapped secondary a single phase transformer, but it has two different output phases.

And I want a clarifying statement added, "it appears to have two different output phases when viewed from the neutral."

 

[mivey]

I have never said the reference point is unimportant when performing an analysis. I have said that the number of phases should not change just because the reference point changes.

The same number of phases (voltages). But how those phases can be classified into a system of voltages depends on the system reference.

I use the number of Line-Line waveforms to define the number of phases in a power system. This methodology allows me to be consistent with more than 100yrs of our industry's terminologies and not be concerned with the presence or absence of a neutral.

You are not consistent with terminology from more than 100 years ago that called a 5-wire 90-degree displaced set of voltages a four-phase system. Also, when you ignore the common connection, you are not consistent with industry terminology that calls a 3-wire open-wye two-phase.

Yes, but the 'direction' of the output is still dependent on the physics of the transformer.

And is consistent with what you get when you join the two phase-opposed voltages such that their fluxes will combine.

 

[mivey]

So now you say, a 240/480 3-wire transformer secondary (that every transformer manufacturer calls single-phase) is actually three-phase.

Read my previous post again. I did not say it made a 3-phase system. There are 3 different phases (voltages). The 480 volt phase can't join the 240 volt phases in a count of system voltages because it is a different voltage magnitude. It is in a single-phase classification by itself.

The 240 volt phases may or may not be able to be classed together in a system, depending on the system reference. If not classified together, they are classified in separate single-phase systems.

Once again, with a regular poly-phase system, an n-phase system will have n voltages of equal magnitude with different phase angles evenly displaced by 360/n degrees. If the angles are not evenly displaced, you have an irregular poly-phase system.

How stupid of me to define 3-phase power systems in a manner that is consistent with the terms used by our electric industry.

Again, I have already shown you the inconsistencies in your method.

 

[mivey]

You have 2 single-phase voltages added in series to create a single L-L waveform.

Where is the requirement that these two voltages must be joined to create only one voltage? These two voltages can be used independently.

You choose to wire them into a circuit that uses the neural as a reference point and therefore views them as being 'out of phase' yet there is still only a single L-L waveform.

Then you are ignoring the other two available waveforms.

The actual/physical connection of the 2 source voltages has not changed just because your circuit does or does not use a neutral.

We have made more voltages available.

And I want a clarifying statement added, "it appears to have two different output phases when viewed from the neutral."

I want a statement that says voltages that use the neutral can be used as series in-phase voltages or opposed-phase voltages connected at a common point because the center-tap can represent both and without going back to the time of creation it is impossible to tell the difference.

While we are at it, I also want a statement that says a neutral gives us the option of taking two more voltages from the transformer.

 

[mivey]

...I am happy to call this transformer with a center tapped secondary a single phase transformer, but it has two different output phases.

I do call it a single-phase transformer. But I also recognize that that term is based on the historic use and the type systems it can supply may not be consistent with the general definition of a poly-phase system under certain conditions.


Add: I believe I said earlier that it is a single-phase load to its source.

 

[jim dungar]

The same number of phases (voltages). But how those phases can be classified into a system of voltages depends on the system reference.

You treat the source as a black box, which is an acceptable practice and makes for convenient math. A person should not have to know if a neutral is involved before they define the number of phases.

You are not consistent with terminology from more than 100 years ago that called a 5-wire 90-degree displaced set of voltages a four-phase system.

We called it a 2-phase 5-wire system. The Lx-Lx' connections were not valid L-L voltages. Cooper Power Systems does not mention a 4-phase 5-wire system when they discuss 'historic' power distribution systems (http://www.cooperpower.com/library/pdf/R201902.pdf). The website http://www.3phasepower.org/2phasesystems.htm does mention some people referring to it as a 4-phase 5-wire system, but they include the statement "The ability of the two-phase, five-wire distribution system to supply the standard voltages of 115/230 V was a main feature in a lengthy article published in the AIEE Transactions in 1925 by an engineer associated with the Philadelphia Electric Company in Pennsylvania."

Also, when you ignore the common connection, you are not consistent with industry terminology that calls a 3-wire open-wye two-phase.

I have been trying to keep the discussion to a simple single winding primary transformer with a center tap. And, there is not agreement even among utilities on what to call a 120/208 3-wire circuit, although single-phase and 'network' seem to be the most predominant terms. The term open-wye is usually used with the primary connection of a transformer bank (see the above Cooper reference), and seems to almost always be paired with a delta secondary.

 

[LarryFine]

I am happy to call this transformer with a center tapped secondary a single phase transformer, but it has two different output phases.

To me, it's more accurate to say two polarities rather than two phases.

Because the two peaks occur at the same time, there's only one phase.

 

[mivey]

You treat the source as a black box, which is an acceptable practice and makes for convenient math. A person should not have to know if a neutral is involved before they define the number of phases.

What is inside the black box and how it is labeled can be different than the label for the system of voltages I take from the black box. What is in the black box is still a source for whatever I take from it.

If you want to know how many voltages you have taken from the source, you have to know how many pairings you have.

We called it a 2-phase 5-wire system. The Lx-Lx' connections were not valid L-L voltages.

Of course they were valid. Not used perhaps, but valid nonetheless.

Cooper Power Systems does not mention a 4-phase 5-wire system when they discuss 'historic' power distribution systems (http://www.cooperpower.com/library/pdf/R201902.pdf). The website http://www.3phasepower.org/2phasesystems.htm does mention some people referring to it as a 4-phase 5-wire system, but they include the statement "The ability of the two-phase, five-wire distribution system to supply the standard voltages of 115/230 V was a main feature in a lengthy article published in the AIEE Transactions in 1925 by an engineer associated with the Philadelphia Electric Company in Pennsylvania."

That nice, but I have shown other sources that did call it that. It was known that a 3-wire 2-phase system was a sub-set of a 4-phase system. And it is still known that way today. And a 5-wire system was known to be a 4-phase system even though it could just be used for a 2-phase load.

I have been trying to keep the discussion to a simple single winding primary transformer with a center tap. And, there is not agreement even among utilities on what to call a 120/208 3-wire circuit, although single-phase and 'network' seem to be the most predominant terms.

Predominant depends on where you look. A 3-wire wye distribution is commonly called 2-phase in the utility industry. The 3-wire wye services are more commonly called network services. I guess to distinguish them from the the historic 2-phase service. I don't know why they do not call the distribution a network distribution but they do call it v-phase as well. There again, why not call the service a v-phase service? Who knows, but history it is what it is. As long as we understand the nature of the voltages, we can label it what we want without confusion.

The term open-wye is usually used with the primary connection of a transformer bank (see the above Cooper reference), and seems to almost always be paired with a delta secondary.

True. It just seemed descriptive but with a lot less typing.

 

[mivey]

To me, it's more accurate to say two polarities rather than two phases.

Polarity is where you take one pair of wires and swap them. Here we have two different pairings. Not quite the same thing.

I'm pretty sure gar made that same point earlier.

Because the two peaks occur at the same time, there's only one phase.

If the maximum peaks occur at the same time there is only one phase. If one is at a max peak while the other at a min peak they are in phase opposition.

I'm pretty sure gar made that same point earlier too.

 

[mivey]

If the maximum peaks occur at the same time there is only one phase.

Only one phase per system, that is. There are still two voltages.

 

[LarryFine]

Only one phase per system, that is. There are still two voltages.

Sure, just as with two batteries in series if the center is available. Then you have a bi-polar supply and multiple voltages.

 

[mivey]

Sure, just as with two batteries in series if the center is available. Then you have a bi-polar supply and multiple voltages.

That was covered back in post #84 but I'll re-cap:

A circuit with ICs that requires a ?V supply would need a positive and a negative supply (dual-voltage, analogous to 2-phase AC).

The battery stack can be used for positive voltages as well as negative voltages and can be a source for both. The center-tap can be used for series connected in-phase voltages as well as for common-connected phase-opposed voltages and can be a source for both.

The positive battery stack can substitute for two positive batteries or a combination of a positive and negative battery. The single-phase center-tap can substitute for two in-phase voltages or two phase-opposed voltages..

 

[gar]

100328-0802 EST

jim:

From my post:

A phase is a description of the relationship of one waveform to another not a particular transformer connection.

You replied with the post:

I use the number of Line-Line waveforms to define the number of phases in a power system. This methodology allows me to be consistent with more than 100yrs of our industry's terminologies and not be concerned with the presence or absence of a neutral.

By your definition in this quote, if I have a transformer with a single primary, and three isolated secondaries, then I have three phases.

Or six isolated secondaries is six phases.

.

 

[jim dungar]

By your definition in this quote, if I have a transformer with a single primary, and three isolated secondaries, then I have three phases.

That sounds like something mivey would say.

A third phase is created. Without the two 240 volt phases connected in series, you would not have the 480 volt phase.

Just like I said about a two winding transformer which has two in-phase voltages, your transformer would have three single-phase voltages but not any poly-phase voltage. When two or more of the windings are connected in series, the result is still a single phase voltage, although of a different magnitude. And if we care about the terminal relationships in order to connect these multiple windings together, then there is nothing wrong with using those terminal relationships when analyzing the resultant circuit, we should not need to change our methodology simply because a neutral point is created.