Single Phase or Polyphase?

[mivey]

That sounds like something mivey would say.

Only because it is true. A single voltage by itself is a single phase. If we start trying to group them into systems of voltages then we start comparing the relative phase angle between the voltages. "Phase" has more than one meaning.

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.

Great. You at least agree in part and recognize that there are three voltages. Oops, that means the "something mivey would say" above is also something jim dungar would say. The concept is the same.

As for in-phase voltages, I would agree: we have three single-phase voltages.

When two or more of the windings are connected in series, the result is still a single phase voltage, although of a different magnitude.

Now you are back to denying there are separate voltages. It looks like you are saying the wiring method is changing the number of voltages. Say it ain't so because you might find yourself saying something like mivey would say.

Why are you saying the two voltages across the windings disappear when the windings are connected in series? The series connection made a 3rd voltage available, it did not dissolve the original two voltages.

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.

If the neutral point has a wire that is a conductor, it makes a whole lot of difference.

Without the neutral conductor, the current in both halves of the winding must be the same and you have only one voltage you can use. With a neutral conductor, the circuits using the winding halves can be different. Without the neutral conductor, we have one voltage to use. With the neutral conductor, we have two more voltages we can use.

Add: My methodology did not change. You can still apply the original rules and get the answer. Your method requires you to change the rules for specifically-identified cases.

 

[mivey]

Now you are back to denying there are separate voltages. It looks like you are saying the wiring method is changing the number of voltages. Say it ain't so because you might find yourself saying something like mivey would say.

Why are you saying the two voltages across the windings disappear when the windings are connected in series? The series connection made a 3rd voltage available, it did not dissolve the original two voltages.

After reading again: maybe you were saying that the series combination created a higher-magnitude single-phase voltage in addition to the two original voltages. If so, I agree.

If that is what you meant: the higher-magnitude single-phase voltage can be created by two in-phase voltage sources or two phase-opposed voltage sources, depending on how they are connected together.

I'm saying the 3-wire secondary can take the place of either combination of sources and the supply voltages we have would be exactly the same.

 

[jim dungar]

A single voltage by itself is a single phase.

Now you saying every possible voltage is its own phase.

two in-phase voltage sources or two phase-opposed voltage sources, depending on how they are connected together.

You have been telling me that the way the sources are connected is immaterial and should not be a consideration.
I have been saying the industry convention is the addition of in-phase voltages, using any other connection should be acknowledged.

 

[mivey]

Now you saying every possible voltage is its own phase.

That is one of the uses of the term "phase". That does not mean it can be counted as a unique voltage when counting the voltages in a particular poly-phase system.

You have been telling me that the way the sources are connected is immaterial and should not be a consideration.

That is mis-representing what I said. If you try to push two opposing fluxes through a single winding, they will cancel. I discussed this in an earlier post.

The stuff in the box does not matter if the voltages at the secondary are the same. The choice of a reference on the primary does not dictate the choice of my reference on the secondary.

I have been saying the industry convention is the addition of in-phase voltages, using any other connection should be acknowledged.

The industry convention shows the relative relationship of the voltages, not specifically how you have to use them. Besides, who has said we should not acknowledge the connection? One of the main discussion points has been talking about the differences in the connections you can take from the secondary.

What needs acknowledging is the fact that a voltage is defined by the reference point we pick for the system we are constructing, not a relative reference point picked by someone in a transformer factory.

 

[jim dungar]

What needs acknowledging is the fact that a voltage is defined by the reference point we pick for the system we are constructing, not a relative reference point picked by someone in a transformer factory.

This is why I have been saying that, with all other things being identical, a center tap reference gives the appearance of 2 out of phase waveforms, but an end point reference give the appearance of 2 in phase waveforms.

Our industry has standards for transformer terminals and connections, why not use those as defaults and then acknowledge any deviation?

You have been telling me that the way the sources are connected is immaterial and should not be a consideration.

That is mis-representing what I said.

These are all statements you made in post 130.

That is why I have tried to get you to quit focusing on the mechanism. It is a black box that has delivered you some voltages.

The voltages are what they are, regardless of the source.

The primary does not dicate how we use the secondary. It does not define the voltage references on the secondary.

And in #138

The voltages are what defines a system of voltages, not how they were derived or created.

 

[mivey]

This is why I have been saying that, with all other things being identical, a center tap reference gives the appearance of 2 out of phase waveforms, but an end point reference give the appearance of 2 in phase waveforms.

These are not just appearances. That is what the voltages really are. Once again, a voltage is defined by the reference you pick.

Our industry has standards for transformer terminals and connections, why not use those as defaults and then acknowledge any deviation?

Why do you feel it is imperative to use a polarity dot as a reference point for your circuit? A polarity dot is just a polarity dot. It does not tell you which terminal you must use as a reference point for your circuit.

These are all statements you made in post 130....and in #138

I'll say it once again since you must have missed the point:

If I have a set of voltages from a box, it does not matter if they were created using two in-phase sources or two phase-opposed sources or a DC source with inverters, etc. I have never said you could take some primary conductors and some transformers and throw them all into a blender and get the voltages you want.

The point is that there is more than one way to create a set of voltages. How they were created does not matter because the outputs will be the same.

If I have a 120 volt sinusoidal voltage, I have a 120 volt sinusoidal voltage regardless of what is in the source box. The polarity markings in the box can't tell me which peak is positive or which peak is negative, etc. for the voltage I take from the secondaries. I decide that when I choose my reference point. The polarity markings in the box can tell me which terminal will be positive or negative relative to my voltage configuration.

A single box can deliver different combinations of voltages. The voltages we take from it determine the system of voltages we are using.

 

[LarryFine]

If I have a 120 volt sinusoidal voltage, I have a 120 volt sinusoidal voltage regardless of what is in the source box.

A single box can deliver different combinations of voltages. The voltages we take from it determine the system of voltages we are using.

If I have two of those black boxes, and I connect the two outputs in series, and total new voltage is exactly twice that of each original voltage, then I can say that the two sources are in phase, and the new center-tapped source is single phase.

 

[jim dungar]

Why do you feel it is imperative to use a polarity dot as a reference point for your circuit?

All ANSI standard transformer windings have polarity dots, why not be consistent and use them? Protective relaying circuits, power measurements, and delta and wye power transformer connections all require consistency in the use of polarity dots, so why not also circuit analysis of known sources?

While it is physically possible to connect the two secondary windings of a standard single primary winding transformer in a series subtractive connection, it is not an industry standard. Following industry standard identification practices, the windings X1->X2 and X3->X4 are in phase, when series connected following standard practices they are additive.

 

[mivey]

If I have two of those black boxes, and I connect the two outputs in series, and total new voltage is exactly twice that of each original voltage, then I can say that the two sources are in phase, and the new center-tapped source is single phase.

Which is exactly how we label the system. What must be recognized is that the secondary voltages are exactly the same as those we would get from two phase-opposed voltages. Not just in appearance, but physically exactly the same.

That brings us back full-circle to the beginning of the whole discussion where people's common-sense runs into the labels we use. If two voltages with a 90 degree phase difference is two-phase, then common sense would say that two voltages with a 180 degree phase difference is two-phase.

From a physical standpoint that is technically correct. But it also is the exact same voltages we get from using two series voltages that we label single-phase. We prefer using the single-phase label even though the set of voltages could represent either.

If people understand the physical reality, they can then understand there has been no change in the rules for poly-phase systems, only a preference for one label over another. If they can understand the reasoning behind the use of the single-phase label, they can accept the single-phase label for a set of voltages that also matches the voltages from a poly-phase system.

 

[mivey]

All ANSI standard transformer windings have polarity dots, why not be consistent and use them? Protective relaying circuits, power measurements, and delta and wye power transformer connections all require consistency in the use of polarity dots, so why not also circuit analysis of known sources?

While it is physically possible to connect the two secondary windings of a standard single primary winding transformer in a series subtractive connection, it is not an industry standard. Following industry standard identification practices, the windings X1->X2 and X3->X4 are in phase, when series connected following standard practices they are additive.

Nothing wrong with that as long as we recognize that a phase-opposed connection is a physical reality and not just a math trick. It will have the same secondary and the set of voltages could represent either. Because we have an alternating current, there is no universal designation of the positive peak and negative peak. It all ties back to a choice of a reference point.

From a physical standpoint, calling it a single-phase set of voltages only tells 1/2 the story and is why people's common sense makes them wonder what is really going on. What is really going on is that we have a labeling preference.

 

[jim dungar]

Nothing wrong with that as long as we recognize that a phase-opposed connection is a physical reality and not just a math trick.

The math trick comes when the connection is really and truly additive, but the choice is made to ignore that fact and call it subtractive instead, simply because a neutral point exists.

Following industry standard marking conventions allows consistency when analyzing circuits with known source connections such as: single winding center taps, series connected windings, high-leg 4-wire deltas, open delta-open wyes.

 

[mivey]

Sorry for the delayed response but I've been vacationing.

The math trick comes when the connection is really and truly additive, but the choice is made to ignore that fact and call it subtractive instead, simply because a neutral point exists.

You seem to be implying that the physical characteristics of the transformer are being ignored. They are not being ignored. It is impossible to ignore them and make the proper connections. What you are ignoring is that the voltages we take from the transformer can be a source for more than one type configuration.

You also continue to ignore the fact that voltages are not voltages without a reference point and there is NO universal designation for a reference point. We can have a standard for how we label relative voltages, but it does not mean these voltages are constrained to be used in only one polarity. Forgetting the mid-point for a moment on a transformer with equal bushing ratings, why do you think X1 is any more special than X4 (or H1 vs H2?)? We could just have easily swapped the 1 & 4. The 1 & 4 are just RELATIVE voltage indicators, NOT UNIVERSAL connection indicators and we could easily ground X1 or X4.

Just because we use one transformer instead of two does not change the system of voltages. Why use two separate transformers if we can get the exact same source voltages from one transformer? If it makes it easier to picture, look at the system of voltages you want and work your way back to see what transformer combinations & types can supply those voltages. Just because a transformer can supply one set of voltages does not mean it can't also be a source for a different set of voltages. It is quite simple to see that a 3-phase transformer can be a source for single-phase or three-phase voltages. It should not be difficult to see that it can also be a source for two-phase voltages.

Following industry standard marking conventions allows consistency when analyzing circuits with known source connections such as: single winding center taps, series connected windings, high-leg 4-wire deltas, open delta-open wyes.

As I said before, the industry standard used for numbering the transformer terminals is NOT an industry standard for how we must "sequence" our connections to the transformer or what reference point we must use. We must use the relative voltage information shown by the "dots" to determine how we make our connections, but the circuit we feed may or may not use the conductor from X1 as a reference and it may not have the voltages oriented using the X1-X2-X3-X4 sequence.

The numbering sequence of the terminals may not be the same as what we use in our circuit. In fact, while I would hesitate to call it an industry standard, more often than not you will find the neutral point used as the reference point. Look at metering voltage phasor diagrams and power quality meter connections and you will find that to be true.

We even have some transformer banking connections that use 1/2 of the winding with the reference in one direction and 1/2 in the other direction. This is not in conflict with any industry standard terminal markings on the transformer as they must be used to make the proper connection. But the voltages we take from the transformer are definitely different than the voltage sequence of X1-X2-X3-X4.

Again, how we use the output voltages and the system of voltages we take from the source are not dictated by the polarity dots and the X1-X2-X3-X4 terminal labeling conventions.

The choice of using the voltages in an X1-X2-X3-X4 sequence is NOT an industry standard but a preference. Analyzing the circuit using an X1-X2-X3-X4 sequence is NOT an industry standard but a preference. The one who uses the voltages makes the connections and reference points they need for their application and analysis.

I will say that for some circuit analysis, using X1-X23 and X23-X4 instead of X1-X23 and X4-X23 makes for much cleaner calculations. But no matter how simple it makes it, it does not invalidate the other method, nor does it mean the other voltages do not exist.

 

[gar]

100408-1844 EST

On the subject of --- Definition of In-Phase" --- from a slightly different field, but still electromagnetic. The following quote is from "Introduction to Physical Optics", John K. Robertson, 1929, 1935, 1941, Chapter II, Study of Wave-Motion, p24.

At any instant, two particles whose times of vibration differ by an integral multiple of the periodic time are said to be in phase. Two consecutive particles in the same phase are separated by a wave-length.

This clearly does not define a half-wave shift as being in phase. If a half-wave shift is not in phase, then there are two phases when the signals are displaced by a half-wavelength.

When you take two signals, one phase displaced by 1/2 wavelength relative to the other, and add these there is a minimum signal resultant. Important in diffraction grating theory, and acoustics.

.

 

[jim dungar]

You seem to be implying that the physical characteristics of the transformer are being ignored. They are not being ignored. It is impossible to ignore them and make the proper connections.

I have been saying to discuss the actual, real life, physical connection of a single center tapped transformer winding. There is absolutely no possible way for this source to be anything other than an additive set of in-phase voltages, V1->ct and Vct->2 with a resultant V12.

What you are ignoring is that the voltages we take from the transformer can be a source for more than one type configuration.

How we connect loads to this 3-wire source cannot change the physical relationship of these (2) additive in-phase voltages.

The only thing that can change is how we view/see/describe, or any other word you want to use, the voltages and the currents.
For example, we can:
(a) fix one probe at terminal #1 and measure the voltages to the CT and #2, or
(b) fix one probe at terminal #2 and measure the voltages to the CT and #1, or
(c) fix one probe at the #CT and measure the voltages to #1 and #2, or
(d) fix the relationship between the probes and measure the voltages from terminal #1-CT, CT-#2, and #1-#2.

As soon as we ignore the real world fact of the voltages being additive, and instead call them subtractive, we are doing nothing more than 'playing math tricks'. We can up with the difference between voltage and current being greater than +/-90?. We can end up with different results for current directions depending on load unbalance {try a 1A load connected L1-N and a 1A load connected L1-L2, what are the currents into and out of each terminal? Now try a 1A load connected L1-N, a 1A load connected L2-N, and a 1A load connected L1-L2, what are the currents into and out of each terminal?}.

 

[LarryFine]

as soon as we ignore the real world fact of the voltages being additive, and instead call them subtractive, we are doing nothing more than 'playing math tricks'.

100%!

 

[mivey]

I have been saying to discuss the actual, real life, physical connection of a single center tapped transformer winding.

Real life physical voltages need real life physical references. Your selection of a reference is a preference, not a universal constant. Letting the manufacturer's numbering represent a reference for you does not mean you did not make a choice. In your case, you are choosing to use the manufacturer's terminal numbers as a pre-determined choice and calling it a universal given. Your OPINION is that this reference is the only correct choice but the fact is that there are other choices available.

There is absolutely no possible way for this source to be anything other than an additive set of in-phase voltages, V1->ct and Vct->2 with a resultant V12.

In your enthusiasm to use the manufacturer's terminal number sequence, you are neglecting basic engineering fundamentals for how a voltage is defined. There can also be two voltages in phase opposition. This is common stuff in audio engineering and signal processing but our tendency to hang onto simple terms in the EC world may make some of us forget what really makes a voltage a voltage. Here are a few quotes for you from other experts that say the real life physical voltages are really 180 degrees out of phase:

Dranetz-BMI
M-I-C-K-E-Wye:
...A "delta" circuit looks like the delta symbol, which is an equal-sided triangle. There are numerous variations of the delta circuit, such as: grounded deltas (one corner of the triangle is connected to a grounded conductor); open-leg delta (only two elements instead of three are used); or, crazy-leg (where one leg is center-tapped to produce two voltages that are 180 degrees out of phase from each other).

SandiaNationalLaboratories
Photovoltaic Power Systems:
...In a utility connected system or with a 120/240-volt stacked pair of inverters, where the 120 /240-volt power consists of two 120-volt lines that are 180 degrees out of phase, the currents in the common neutral in the multiwire branch circuit are limited to the difference currents from any unbalanced load.

U.S. Navy
Navy Electricity and Electronics Training Series-Module 8?Introduction to Amplifiers-NAVEDTRA 14180 pg 1-7:
One way in which a phase splitter can be made is to use a center-tapped transformer. As you may remember from your study of transformers, when the transformer secondary winding is center-tapped, two equal amplitude signals are produced. These signals will be 180? out of phase with each other. So a transformer with a center-tapped secondary fulfills the definition of a phase splitter.

How we connect loads to this 3-wire source cannot change the physical relationship of these (2) additive in-phase voltages.

We do not change the RELATIVE relationship, but saying the voltages between the terminals must be additive is just your opinion based on your choice of a reference.

As soon as we ignore the real world fact of the voltages being additive, and instead call them subtractive, we are doing nothing more than 'playing math tricks'.

Just your opinion/preference, not fact.

Also, additive and subtractive usually refers to the relative orientation of the secondary and primary.

 

[jim dungar]

We do not change the RELATIVE relationship, but saying the voltages between the terminals must be additive is just your opinion based on your choice of a reference. Just your opinion/preference, not fact.

Are you saying the possible voltage rises across a single conductor are not additive? Are you saying it is physically possible to have both voltage rises and voltage drops in the same conductor?

I have not been arguing whether you can measure two different voltage directions, by using the neutral as a reference. I have been saying the definition of 1-phase voltages or 2-phase voltages should not change if a neutral is or is not used.

 

[Hameedulla-Ekhlas]

you two guys ( mivey and jim ) are very smart and experience and I am trying to catch you two but can not.

Ok anyway, regarding to additive and subtractive see below

Although the polartity is known when the sysmbol H1, H2, X1 and X2 are given. In case of the four terminals on the transformer tank in a standard way so that the transformer has either additive or subtractive polarity.
A transformer is said to have additive polarity when terminal H1 is diagonally opposite terminal X1. Similary, a transformer has subtractive polarity when terminal H1 is adjacent to terminal X1 . If we know that a power transformer has additive ( or subtractive) polarity. we do not have to identify the terminals by symbols.

subtractive polarity is standard for all single phase transformers above 200kVA, provided the high-voltage winding is rated above 8660V. All other transformers have additive polarity.

 

[Hameedulla-Ekhlas]

some more information..



transformer voltages were either in phase or 180 degrees out of phase. Voltages, there fore either added or subtracted arithmetically from each other.

see link
http://books.google.com/books?id=kf...&resnum=1&ved=0CDYQ6AEwAA#v=onepage&q&f=false


The primaries or the secondaries are connected in such a way that the AC voltage output of one secondary is upside down relative to the other. Another way of putting it is to say that the two secondaries are bucking each other, and that they are 180 degree out of phase with each other. The easies way to understand this phenomenon is to look at an instantaneous point of time in the transformer's operation.

Please see the attached file. Not the transformer secondaries shown in the left side of the ullustration. Although you do not normally associate any polarity with AC voltages, assume this drawing to represent an instant of time when both secondaries are at a peak voltage output. The polarity of the secondary voltages shown would add to each other- in the same way flashlight batteries add to each other ni a flashlight. Positive to negative positive to negative and so on.

 

[mivey]

Are you saying the possible voltage rises across a single conductor are not additive? Are you saying it is physically possible to have both voltage rises and voltage drops in the same conductor?

Refer back to your physics, e-mag, or whatever text you studied under and see what makes a voltage a voltage. At some point you have to pick a reference point. A rise in one frame can be a fall in another frame. Both are valid frames of reference. The existence of a real voltage in one frame does not mean the voltage does not really exist in a different frame.

Both are valid reference frames but you are trying to say that only one frame is the "real" universal frame of reference and that all others are "math tricks". If you want to see it that way, all of the frames are "math tricks" even the first one you pick.

I have not been arguing whether you can measure two different voltage directions, by using the neutral as a reference. I have been saying the definition of 1-phase voltages or 2-phase voltages should not change if a neutral is or is not used.

If I only bring two wires into a circuit, I can only bring one voltage (one phase). Changing the polarity between these two terminals does not derive a second emf because we still have the same two terminals.

The neutral is a conductor. Bringing three conductors into the circuit gives me three voltages I can use. I now have an option that includes phase-opposed emfs.

You have one problem in that you think 120? is physically somehow treated different than 90? in that one angle means you have two phases while the other doesn't. I think you would eventually be able to work past that flaw in logic.

As for the phase-opposed case: It is going to come down to the wall I discussed many posts back that you will always hit. In order for you to hold your position, you must hold to the belief that when two voltages have a 180? phase difference, they must be the same phase. This position must be held while also saying that any other phase angle difference means they can be different phases.

I contend that this discontinuity in logic is what causes people to get confused when using the labels we have adopted. I think if people understand the physics of the situation, they can accept the labels, understand why we use them, and see that there is not really a discontinuity in logic.

What we really have is a set of voltages that can be used for two different system configurations and we have made a preference choice on which name we will use.