Single Phase or Polyphase?

[jim dungar]

No.

X1-X23 and X1-X4:
X1-X23 and X1-X4 are two separate single-phase supply systems because they have different magnitudes.

X23-X1 and X23-X4:
X23-X1 and X23-X4 can be two separate single-phase supply systems because they have different phase angles.

X4-X23 and X4-X1:
X4-X23 and X4-X1 is the same case as X1-X23 and X1-X4 but I'll state it for completeness.

Based on your explanation of X1-X23 and X1-X4, my 240/480V transformer is (1) single phase source because only X1 and X4 are taken to the load, assuming X23 is isolated and insulated.

And if someone connects a 240V load to X1-X23 then it becomes (2) independent single phase supply systems as long as X1 remains the reference point.

But if someone simply the reference from X1 to X23, it becomes a 2-phase system feeding a single phase load.

So doesn't this all still boil down to: The number of phases is dependent on picking the neutral as your reference?

 

[mivey]

Based on your explanation of X1-X23 and X1-X4, my 240/480V transformer is (1) single phase source because only X1 and X4 are taken to the load, assuming X23 is isolated and insulated.

No. The transformer is a source for a single-phase 480 supply, two single-phase 240 volt supplies, and one 240/480 volt two-phase supply. What you have taken from the transformer is a single-phase 480 volt supply. The other options are unused at that point.

And if someone connects a 240V load to X1-X23 then it becomes (2) independent single phase supply systems as long as X1 remains the reference point.

The transformer did not become anything different. You have used another supply option available from the transformer. You have now taken one single-phase supply at 240 volts and one single-phase supply at 480 volts. All supply options are still available at the source.

But if someone simply the reference from X1 to X23, it becomes a 2-phase system feeding a single phase load.

Again, the transformer did not become anything different. It is still a source capable of delivering more than one type of supply.

So doesn't this all still boil down to: The number of phases is dependent on picking the neutral as your reference?

If I pick the neutral as my reference, I have three options:
1) A single-phase 240 volt supply using only X1-X23
2) A single phase 240 volt supply using only X4-X23
3) A two-phase supply using both X1-X23 & X4-X23

Using X1 or X4 as the reference, I only have two options: A single-phase 240 supply or a single-phase 480 volt supply.

What it boils down to is that a source can deliver more than one type supply system. A source can deliver a lower-order supply system. Just because we use only the lower-order system does not mean the source no longer has the higher-order systems available.

For example, there is a tendency to want to label the 3-wire open-wye as single-phase because it usually only serves single-phase loads. The reality is that it is a two-phase supply.

 

[ohmhead]

Wow. Where do you come up with these very explanative answers, so I could study up ( and sound smart, too ) Not to add too much fuel to fire, but I have to ask, then what exactly is Polyphase AC? (since I've yet to come across it.) I apologize if it was defined in prior post, I must have missed it.

Well here it is from a simple electrician with no schooling i just run pipe all day and dig ditches large ones .

Polyphase is more than one phase meaning multiple phases like 3 phase 120/208 volt service .

Yes you can use a 2 pole breaker on 120/ 208V 3 -ph service to get single phase power off it .

Its now 208 volts single phase power .

Poly is more than one in number it can be 2 phase 3 phase 6 phase 12 phase it goes on and on just a word .

Sorry but when they get going theres no stopping .

 

[mivey]

Polyphase is more than one phase meaning multiple phases like 3 phase 120/208 volt service .

Yes you can use a 2 pole breaker on 120/ 208V 3 -ph service to get single phase power off it .

Its now 208 volts single phase power .

Poly is more than one in number it can be 2 phase 3 phase 6 phase 12 phase it goes on and on just a word .

I agree with that. But the question becomes: If you are going to count the # of phases in a system, what constitutes a phase?

 

[ohmhead]

I agree with that. But the question becomes: If you are going to count the # of phases in a system, what constitutes a phase?

Well you have a good point there Mivey my way of thinking is this A -phase is one phase of a multi phase system .

B- phase is also one phase of a multi phase system .

 

[mivey]

Well you have a good point there Mivey my way of thinking is this A -phase is one phase of a multi phase system .

B- phase is also one phase of a multi phase system .

That is the way it was seen as far back as over 100 years ago as well.

 

[ohmhead]

That is the way it was seen as far back as over 100 years ago as well.

Well Mivey now were getting into age here ill be 57 this month on 24 .

 

[jim dungar]

Using X1 or X4 as the reference, I only have two options: A single-phase 240 supply or a single-phase 480 volt supply.

So simply adding a neutral at X23 creates a second phase.

This means the wiring of the load is more important than the source of the waveform and the electric field that created it.

According to the reference I sited from more than 100 years ago, the source was important. when did this change?

 

[mivey]

So simply adding a neutral at X23 creates a second phase.

Just connecting to X23 doesn't create anything on its own. It may be a point that is only used as part of a single-phase supply. The way you configure your system is what defines what kind of system you have. The use of X1, X4, and X23 together with X23 as the reference point is what will allow you to have a two-phase system.

Is it so hard to accept that in the 5-wire 2-phase example that we were able to define a system of four L-L voltages having a 90 degree phase displacement? One configuration is a 2-phase system, the other is a 4-phase system. Both ultimately come from the same source, we merely changed the way we took voltages from the source.

This means the wiring of the load is more important than the source of the waveform and the electric field that created it.

According to the reference I sited from more than 100 years ago, the source was important. when did this change?

The load will always dictate what kind of supply system we need to bring out from whatever source we have.

The load will never dictate what kind of sources might be at our disposal as we can supply multiple-type systems from just one source, or have one source that will only provide the one system we need for our load, or have multiple sources providing what we need.

We can have two pieces of equipment generate two different voltages, used by two different pieces of equipment, to ultimately supply one piece of equipment. If we can consolidate any of the separate pieces of equipment and still get the same two voltages, why does that make any difference?

 

[mivey]

Just connecting to X23 doesn't create anything on its own.

Let me put it another way:
If I had a 2-terminal 480 volt transformer, that source alone does not have the option to provide me with a two-phase supply.

If I open the can, tap into the mid-point of the winding and bring some terminals out, I will have a source that gives me the option of having a two-phase supply where the voltages have a 180 degree phase displacement. It also gives me some additional single-phase options.

 

[jim dungar]

If I open the can, tap into the mid-point of the winding and bring some terminals out, I will have a source that gives me the option of having a two-phase supply where the voltages have a 180 degree phase displacement. It also gives me some additional single-phase options.

There is no way around it, your definition requires me to use the neutral in order to define the number of phases.

You wire a 240V and 480V load using the neutral as your reference and have one 2-phase.

I take the exact same wiring but move my reference to the X1 terminal, and I have two 1-phases.

Then I get rid of the load connected to neutral, and I have one 1-phase.

And all this time, there is a single current flowing through a single transformer winding.

 

[mivey]

There is no way around it, your definition requires me to use the neutral in order to define the number of phases.

The use of the neutral will determine what kind of supply you take from the source. It will not change the source. The presence of the neutral gives me the option to configure my source to be able to provide one two-phase supply and/or multiple single phase supplies. Without the neutral, the only options the source provides are single-phase supplies. It does not mean my load is two-phase. It does not mean I have to configure the supply I take from the source to be two-phase.

You wire a 240V and 480V load using the neutral as your reference and have one 2-phase.

No.

If I wire a 240 volt load and a 480 volt load, I have two different single-phase loads. I am using the single phase-load options available from the source. My loads need two different single-phase supplies.

My loads have not changed the nature of the source. The source is still capable of providing single-phase supplies or a two-phase supply. The source does not care how you define one particular system you take from it, it still has the capability to deliver any of the original options to anyone who wants them.

If you restrict the reference to one particular terminal of the source, then you will not be able to make use of all the systems that the source is capable of delivering. You have applied a filter to the output of the source and have limited the type systems you are going to take from the source.

I take the exact same wiring but move my reference to the X1 terminal, and I have two 1-phases.

You have changed the restricted sets of supplies that you can take from the source. By stipulating that X1 must be the reference, you are defining the system that the source will supply.

You have not restricted the source itself because it still has all of its original capabilities. Your wiring choice is filtering those options. When you change the wiring, you change the filter attached to the delivery side of the source but the source-side system remains the same.

In this case, you have the same two single-phase loads you had before so you are using the single-phase load options available from the source. With the X1 reference, you have filtered out the two-phase option. You only have the 240 volt single-phase option and the 480 volt single-phase option.

The unfiltered source can still be configured to deliver any of the systems it is capable of supplying.

Then I get rid of the load connected to neutral, and I have one 1-phase.

No.
You got rid of one single-phase load. Your filters remain the same. You still have a source filtered to provide a 240 volt single-phase option and the 480 volt single-phase option.

And all this time, there is a single current flowing through a single transformer winding.

It has not been the same all the time because you removed one single-phase load.

All this time the original source remains the same source you had from the beginning. What has changed is the type filter you attached to the output of that source.

 

[jim dungar]

The use of the neutral will determine what kind of supply you take from the source.

So, sources and supplies are not the same thing.

You have changed the restricted sets of supplies that you can take from the source. By stipulating that X1 must be the reference, you are defining the system that the source will supply.

So, again the choice of the reference defines if you have two 1-phase or one 2-phase.

With the X1 reference, you have filtered out the two-phase option. You only have the 240 volt single-phase option and the 480 volt single-phase option.

The unfiltered source can still be configured to deliver any of the systems it is capable of supplying.

Aren't you saying, that the number of phases depends on if the neutral is used or not?

It has not been the same all the time because you removed one single-phase load.

Clearly, this says the way loads are wired defines the number of phases.

All this time the original source remains the same source you had from the beginning. What has changed is the type filter you attached to the output of that source.

The only thing that changes is the use of an arbitrary reference point, but you don't consider that 'a sleight of hand'.

I guess it comes down to:
You are defining 2-phases based on how things are wired/used.
I am defining 2-phases based on how the current is being generated/created based on conductors in magnetic fields.

 

[Volta]

Great discussion. I like the way you have laid this out, Mivey. It is almost easy to follow . Like so many things, though, definitions can make or break agreements. I see the sense in your descriptions, and I now believe that we can technically call a split winding '2-phase'. New to me, I've previously felt that a second source would be needed to rightly call it a second phase.

But that may not be enough of a label to satisfy many of us. It does matter what angle the 'additional' phase(s) is(are) relative to the original, when connecting to equipment. For instance,

Let me put it another way:
If I had a 2-terminal 480 volt transformer, that source alone does not have the option to provide me with a two-phase supply.

If I open the can, tap into the mid-point of the winding and bring some terminals out, I will have a source that gives me the option of having a two-phase supply where the voltages have a 180 degree phase displacement. It also gives me some additional single-phase options.

If we did it twice to the winding, for three equidistant locations you (we) could call it 'three-phase'. I'll buy that, but a common three-phase motor may not, since the 120 degree separation the unit was designed for isn't provided. So I think the terminology of these non-historical sources/supplies should include the info needed to distinguish them from those the industry expects when we hear these phrases.

. . . I guess it comes down to:
You are defining 2-phases based on how things are wired/used.
I am defining 2-phases based on how the current is being generated/created based on conductors in magnetic fields.

Both have a place, but as Jim is saying and I'm sure you agree, the magnetic fields remain important, and at least one term needs a more descriptive label than is being used now.

 

[mivey]

And all this time, there is a single current flowing through a single transformer winding.

Even if you had not removed one of the loads, why would you think both halves of the winding would have the same current?

While the example loads you used were single-phase, consider that a two-phase load could have current phasors that are the same as two unbalanced single-phase loads. Are you saying the X23-X1 current would be the same as the X23-X4 current?

So, sources and supplies are not the same thing.

They are not the same. My source may be a three-phase transformer bank. I may use it to supply single-phase to a load. That does not mean I no longer have a 3-phase source.

I may take out three separate single-phase systems from separate source phases. I am using it as a source of single-phase supplies. That does not mean I no longer have a 3-phase source back at the transformer.

What it means is that I have three separate single-phase sources brought from the transformer. If I have split the single-phase sources out to separate properties, then at the cabinet on the properties I would say I have a single-phase source at the cabinet. If these single-phase sources traveled together and were in a single cabinet on a common property where they could be re-combined, then I would say I have a three-phase source at the cabinet (i.e., three single-phase sources that can combine to make a three-phase source). While you could say you have single and three phase, I have indicated the highest order available which is what we normally do.

You have changed the restricted sets of supplies that you can take from the source. By stipulating that X1 must be the reference, you are defining the system that the source will supply.

So, again the choice of the reference defines if you have two 1-phase or one 2-phase.

It tells me if 2-phase is one of the available choices and determines the highest order available. Without it, the highest order available is single-phase. With it, the highest order available is two=phase.

Aren't you saying, that the number of phases depends on if the neutral is used or not?

The number of phases that can be taken out is dependent on whether or not the center-tap neutral is used

Clearly, this says the way loads are wired defines the number of phases.

It certainly defines what is being used. It does not define what is available at the source

The only thing that changes is the use of an arbitrary reference point, but you don't consider that 'a sleight of hand'.

It is what goes into defining the system. Defining a system is not 'sleight of hand'. We must define a reference frame from which to take measurements. If the load requires both a +V and -V source and the neutral point between them, there is nothing arbitrary about it. If I have some independent loads at V and some at 2V, any reference will do.

I guess it comes down to:
You are defining 2-phases based on how things are wired/used.
I am defining 2-phases based on how the current is being generated/created based on conductors in magnetic fields.

I am defining a 2-phase source based on what kind of voltages are available in the system. A normal n-phase system will have n voltages evenly displaced around 360 degrees. An abnormal n-phase system will have n voltages that are displaced by some angle, but the voltages are not evenly displaced around 360 degrees.

Do you think the currents in a split winding would be any different than the currents in two separate windings using separate but synchronized fields?

 

[mivey]

If we did it twice to the winding, for three equidistant locations you (we) could call it 'three-phase'.

You may have three phases but they would not be the three parts of a system. Every voltage in a system of voltages must have the same magnitude and frequency. It must also have a phase displacement that is different from any other voltage included in the system.

By that, one of the three voltages would have to become part of a different collection of voltages. You would have one two-phase system and one single-phase system. Because of the angles, you could not combine them into a three-phase system.

Both have a place, but as Jim is saying and I'm sure you agree, the magnetic fields remain important, and at least one term needs a more descriptive label than is being used now.

The field produces the voltages we are looking at.

 

[mivey]

New to me, I've previously felt that a second source would be needed to rightly call it a second phase.

The split-winding produces the same voltages that you would get from two separate sources and is a lot more convenient way to do it.

It is much easier to use a center-tapped transformer when building circuits that need +/- supplies than to use two separate transformers.

 

[mivey]

I now believe that we can technically call a split winding '2-phase'.

Technically, yes. But we use it to serve single-phase loads so that is why it gets called single-phase.

But it is important to be able to recognize what is really going on if you want a broader understanding of how things get labeled the way they do and what the limitations are on the labels.

On first contact, our common sense tells us something doesn't quite add up. The traditional labeling methodology is not consistent with the physics of the systems. Many get talked into ignoring what their common sense is trying to tell them. Instead of letting your common sense get buried in jargon, it is better to understand the realities of the systems and the caveats that go with the existing labels.

I'm glad your were able to follow these many pages of text.

 

[Volta]

You may have three phases but they would not be the three parts of a system.

?

Every voltage in a system of voltages must have the same magnitude and frequency.

Wouldn't they be?

It must also have a phase displacement that is different from any other voltage included in the system.

To be considered an 'x-phase' system? Would you call those three windings 'poly-phase', but not three-phase then?

By that, one of the three voltages would have to become part of a different collection of voltages. You would have one two-phase system and one single-phase system.

Tough for me to follow. Is there another way you can state that?

Because of the angles, you could not combine them into a three-phase system.
...

Ok.

 

[mivey]

Maybe the following will be clearer. It is all in the context of counting unique voltages in a "n-phase" system to find out the number for "n".

?

They would not be able to be combined to make a three-phase system

Wouldn't they be?

Yes. I was re-stating part of the definition.

To be considered an 'x-phase' system? Would you call those three windings 'poly-phase', but not three-phase then?

Each voltage by itself could be considered a phase. The voltage all by itself can be a single-phase system. Whether or not the voltage could be considered part of the tally of unique voltages in a larger "n-phase" system count is a different story.

If you want to include a voltage as one of the unique voltages of an "n-phase" system tally, it can not have the same phase angle as another unique voltage in the "n-phase" system.

Tough for me to follow. Is there another way you can state that?

Suppose we have a set of individual voltages. We want to group them into a larger "n-phase" system. When counting unique voltages to find the number "n", we do not want to count identical voltages more than once in any given "n-phase" system. We also want to make sure it is in the same family of voltages (same magnitude & frequency).

To qualify as a unique voltage in the "n-phase" system under consideration, it:

1) Must have the voltage magnitude of the system under study
2) Must have the frequency of the system under study
3) Can't have the same phase angle as any of the other voltages that have been counted.
4) Can't be a voltage measured between a pair of points that have already been used (keeps you from counting the inverse of a voltage already counted).

Any voltage that meets #1 & #2 but fails either #3 or #4 is either identical to a voltage already counted or identical to the inverse of a voltage already counted. It can't be included as part of the count to find "n" because it is not a unique voltage.