just call it 2 phase

These discussions seem to me to make my point. Most everyone seems to have the correct concepts in mind. It just boils down to how we describe them. In other words: "We agree on what it is but what do we call it?" Sometimes you have to describe something in several different ways, all of which can be correct, to make it understandable to some who does not understand it. One idea I used in describing leading and lagging phase concepts is riders on a merry-go-round. If two are exactly opposite (180 degrees apart) , who is leading? Maybe it would be clearer if we kept phase and polarity separate. For fun, shift from sine waves to pulses to see how you can confuse the issue.

The power issue is also important to understanding. It took a long time for me to see how 3 phases at 120 degrees provided more uniform power than 2 phases at 90 degrees. Of course the 3 phase system provides power peaks every 60 degrees and the 2 phase system only every 90 degrees!! That can be clear as mud for a student. I also think it's important to keep in mind that a voltage never appears on or at 1 conductor, but only between 2. In a 3 wire system it is correct to refer to phase A, B, or C current but the voltages have to be A-B, B-C, and C-A. It often helps if we are clear whether we are referring to voltage, current, or power.

Don Young

On Thu, 19 Feb 2009 17:23:49 -0500 daestrom wrote: | snipped-for-privacy@ipal.net wrote: |> On Wed, 18 Feb 2009 18:28:10 -0600 operator jay |> wrote: |>

|>> There are three phases of distribution running around your city. A |>> single phase goes into your neighborhood to power your home. Really |>> I |>> do not think there is any true difficulty caused by current |>> nomenclature; there has not been for me. And I suspect I could come |>> up with shortcomings and ambiguities using your proposed system as |>> well. So, better the devil we know, because at least everyone knows |>> it. |>>

|>> Have you tried using terminology like "240V, single phase, two wire, |>> plus ground", or "240V, single phase, three wire, plus ground", or |>> "347/600V, three phase, four wire, plus bond". Those can be |>> shortened |>> to "240/1phs/3W" etc. Substitute the greek 'phi' phase symbol (or a |>> capital P in a real pinch) instead of 'phs' and it's pretty compact |>> and explicit. 120/240V,1Phs,3W+G is not too bad. |>

|> These terms are too long. |>

|> Note that I am not saying "single phase" is out. But when |> distinguishing between "three wire circuit where 2 wires are hot at |> 120 volts and are 180 degrees apart" vs. "two wire circuit where 1 |> wire is hot at 120 volts and degrees apart are irrelevant", I would |> say "2 phase" and "1 phase" (not the same as "single phase"). |>

|> Got alternative SHORT names for these two systems that are clear? |>

| | Why not just 'Edison connection'. He started a lot of this with his | three-wire DC power system. It had 240 VDC between the two outside legs and | 120VDC between each of those and the neutral.

But *HE* despised AC. Additionally, what he did doesn't match all cases of what I would call "2 phase", which includes a service derived from just 2 of the 3 phases in "3 phase" that is balanced at 120 degrees.

My understanding is that his DC system was 110/220 volts, not 120/240. The exact history of electrical service and system voltages is something I am still trying to figure out. Apparently much of Europe was operating on a three phase 220/127 system, with most things connected L-L, for many years long ago. Some remnants reportedly remain in parts of Spain and Norway. So did Edison pick the voltages? Or did Tesla? Or Westinghouse? Siemens?

| These discussions seem to me to make my point. Most everyone seems to have | the correct concepts in mind. It just boils down to how we describe them. In | other words: "We agree on what it is but what do we call it?" Sometimes you | have to describe something in several different ways, all of which can be | correct, to make it understandable to some who does not understand it. One | idea I used in describing leading and lagging phase concepts is riders on a | merry-go-round. If two are exactly opposite (180 degrees apart) , who is | leading? Maybe it would be clearer if we kept phase and polarity separate. | For fun, shift from sine waves to pulses to see how you can confuse the | issue. | | The power issue is also important to understanding. It took a long time for | me to see how 3 phases at 120 degrees provided more uniform power than 2 | phases at 90 degrees. Of course the 3 phase system provides power peaks | every 60 degrees and the 2 phase system only every 90 degrees!! That can be | clear as mud for a student. I also think it's important to keep in mind that | a voltage never appears on or at 1 conductor, but only between 2. In a 3 | wire system it is correct to refer to phase A, B, or C current but the | voltages have to be A-B, B-C, and C-A. It often helps if we are clear | whether we are referring to voltage, current, or power.

4 phase at 0,90,180,270 is uniform power. You can get that with just two transformers with 120/240 volt secondaries (the "2 phase" "Edison split"). One of them has a 277 volt primary connected A-N. The other has a 480 volt primary connected B-C (or C-B to reverse the rotation). Bond both center taps together and to ground. I believe it is not the most efficient way to transmit power, however, even if the neutral is omitted (e.g. the "square" configuration instead of "triangle" which is more commonly known as delta).

90 degree 2 phase delivers a balanced power waveform. A sine wave shifted 90 degrees is a cosine wave, and you may remember from math sin^2(x)+cos^2(x)=1 for any x. 90 degree 2 phase (the 3 wire version, anyway) does not, however, have a zero neutral current when balanced.

On Fri, 20 Feb 2009 20:05:18 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>On Thu, 19 Feb 2009 19:28:38 +0000 (UTC) Michael Moroney wrote: | |>| What I've called the 3 wire version of 90 degree 2 phase. Two hots and the |>| neutral. The 5 wire variant needs no neutral current (the 4 wire variant |>| doesn't even have a neutral), but, of course, uses more copper. | |>There is the distinction between an unbalanced polyphase system and a balanced |>polyphase system. The balanced polyphase system (3 or more phases) delivers |>the uniform power waveform. As long as the system is balanced, this works. | | 90 degree 2 phase delivers a balanced power waveform. A sine wave shifted | 90 degrees is a cosine wave, and you may remember from math | sin^2(x)+cos^2(x)=1 for any x.

You're right. This will work down to 2 phases when the angles are correct. Ironically, the mathematics is identical to 4 phases, or generalized is identical to 2x phases for any N phase system. And that means the 2 phase

180 degree system (also known as Edison split) is the equivalent in terms of power waveform as 1 phase.

| 90 degree 2 phase (the 3 wire version, anyway) does not, however, have a | zero neutral current when balanced.

The optimal system design that has both a flat power waveform and is balanced with zero neutral current is 3 phase. Mr. Tesla figured that out a while back.

Or just call it Split Phase as everyone in the industry does, and be done with it.

On Sat, 21 Feb 2009 16:09:14 -0500 Twayne wrote: | snipped-for-privacy@ipal.net wrote: |> You can have 2 phases at 90 degrees. Or you can have 2 phases at 120 |> degrees. Or you can have 2 phases at 109.70519 degrees. Or you can |> have 2 phases at 180 degrees. It's still 2 vector angles relative to |> the reference point, which is generally the grounded conductor. |> Trying to avoid referring to two phases as two phases just because |> their angle happens to be 180 degrees is just stubbornheadedness. If |> you need to specifically say what the angles are because the angles |> matter, then say it. But there's really no reason we can't refer to |> the type of power system supplying most homes in the USA as two phase |> power. |>

|>> WARNING: Due to extreme spam, googlegroups.com is blocked. Due to |>> ignorance | by the abuse department, bellsouth.net is |>> blocked. If you post to | Usenet from these places, find |>> another Usenet provider ASAP. | |>> Phil Howard KA9WGN (email for humans: first name in lower case at |>> ipal.net) | | | Or just call it Split Phase as everyone in the industry does, and be | done with it.

What I have encountered is that fewer than half understand this term. Lots of people already call it 2 phase. In a purely technical aspect, it really is 2 phases. Sometimes the phase angle is 180 degrees. And sometimes it is 120 degrees. When it is 120 degrees do you still call it Split Phase?

I'm suggest "2 phase" for all cases of having 2 phases regardless of the degree angle. This includes not only the "Edison style split single phase" but also the "Got only 2 phases out of the 3 phase service" which is just "2 phases at 120 degrees", as well as "corner grounded open delta" which is "2 phases at 60 degrees" and can mimic 3 phase delta for many purposes. There is also "2 phase at 90 degrees". If it's a 3 wire system where one is a grounded conductor or otherwise considered to be the neutral reference point, and the other 2 have a phase angle other than 0 degrees, I call it a "2 phase" system. That's a broad classification. It can be narrowed down by describing it further, such as the number of degrees.

Lots of people do NOT understand "split phase". This number seems to be greater than the number that do NOT understand "2 phase".

Yes. That's why everything is 3 phase today.

On Sun, 22 Feb 2009 01:30:25 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>| 90 degree 2 phase (the 3 wire version, anyway) does not, however, have a |>| zero neutral current when balanced. | |>The optimal system design that has both a flat power waveform and is balanced |>with zero neutral current is 3 phase. Mr. Tesla figured that out a while back. | | Yes. That's why everything is 3 phase today.

Except for the places that have certain forms of 2 phase (180 or 120 degree) or just 1 phase.

That depends on how you look at it- if you bring out only the two terminals A,D you have a single voltage between them. It is then indistinguishable from a single phase 2 wire supply. With a single voltage, phase, as a relative term, becomes a problem. as what do you relate this single voltage to? If the 6 phase system is a Y rather than a polygon (super delta) then you have a neutral and then you can consider that you have a 2 phase system where the voltages Van and Vbn are 180 degrees apart. You then have 3 terminals. This is indistinguishable from the center tapped single phase system which fits what the Europeans refer to as 2 phase. Neither are distinguishable from a 2 wire single phase system if you ignore the neutral.

we are getting into "Yah, But.." territory here.

Not really- remembering that we consider the power delivered to be the average power.

----- If one has been through single phase AC analysis and phasor relationships, this plotting is nice but not at all necessary. polyphase voltage relationships- not power relationships are often shown that way-and this is useful-. but then one gets into application of phasors as previously learned in single phase analysis.

So far what you say is also valid for single phase. Normally, however, one goes from this presentation of the instantaneous power to a mathematical formulation and from this to average power per cycle- which is what is generally referred to as "power" and the relationship of this average power to rms voltages and currents is shown. Power factor is related to this as well. When we consider a 240V 60Hz source, the voltage is then generally expressed as an rms voltage and the power delivered to a resistive load as calculated from (Vrms^2)/R is the average power- which is also what a wattmeter measures..

I see what you are getting at. It is not something fundamentally different because the instantaneous power in this case is proportional to the square of the instantaneous voltage so that the power waveform is always positive, even when the voltage is negative. So when you have two voltages 180 degrees out of phase (as you have in the Edison system- measuring with respect to the neutral), the power waveforms will peak at the same time for equal loads on each leg. Now consider a two phase system with the voltages measured with respect to a neutral which are x degrees apart, Now let x approach 180 degrees and there will be a phase difference between the instantaneous power waveforms that gets progressively smaller until it becomes 0 when the voltages are exactly 180 degrees apart. There is no fundamental change that takes place. In terms of average power per phase and total power- no change exists. Note also that if you look at the total power waveform rather than the individual legs- then the waveform that you will get will be indistiguishable from the single phase or the 2 phase case except for magnitudes for the same phase voltages and resistive loads per phase. In terms of average powers (using rms voltages) the average power will be directly proportional to the number of phases for equal phase voltages and loads.

It is true that 6 phase, 12 phase, etc are are derived from 3 phase systems and provide no net power advantage over 3 phase. 6 phase has some advantages in compact transmission lines because the interphase voltage is the same as the voltage to neutral and this allows lower clearances. 6 and 12 phase rectifier supplies offer better smoothing of the DC. Other than these advantages -nothing. Balanced 3 phase does have an advantage over balanced 2 phase (that is, single phase, center tapped, as we both prefer to call it) in terms of transmission, transformation, generation, and motors. This advantage has nothing to do with power waveforms.

A n phase system is nothing more than n single phase systems that are interconnected in Y or as a polygon (super delta). Certain advantages accrue but these generally boil down to $ advantages.

OK 3 wire 90 degree 2 phase- which is not "balanced" in the sense of 0 neutral current- only the 180 degree version can be balanced- and that balance is the reason that the Edison system is so useful.

I have just come up with a magic box. I connect its to a three-phase source. I ask a technician to measure the voltages between pairs of wires leaving the output of the box. She comes up with two measurements of 120V and one of 170V. Should the Tech be fired?

The box is a Scott T transformer.

What is the point. Once you have two phases, you can build equipment that gives you anything you want. Actually, one phase (and retiurn is enough, although more complicated.

All this talk is garbage. Just stick to fundamentals!

Bill

On Sun, 22 Feb 2009 17:32:47 -0800 Don Kelly wrote: | snipped-for-privacy@ipal.net wrote: |> On Wed, 18 Feb 2009 20:10:15 -0800 Don Kelly wrote: |>

|> | phases are 360/2 degrees apart. 3 phase 360/3 degrees apart, 4 phase |> | 360/4 etc. |>

|> That would be the normal way of thinking of it. It gets interesting when the |> number of phases is any even number. For example 6 phase. I have mentioned |> the concept of 6 phase before and some people get confused. If a 6 phase |> system with phases labeled A,B,C,D,E,F (going around the circle) with phase |> angles of 360/6 degrees each, gives you 240 volts between A and D, then why |> can't a subsystem tapped from just A and D alone be called 2 phase? They are |> counted as 2 phases. |>

|> | That depends on how you look at it- if you bring out only the two | terminals A,D you have a single voltage between them. It is then | indistinguishable from a single phase 2 wire supply. With a single | voltage, phase, as a relative term, becomes a problem. as what do you | relate this single voltage to?

If you have a neutral or ground or some kind of ground reference, even if high impedance, then you have 3 points, 2 or 3 vectors, and can determine an angle. If you don't, all you have is the voltage difference.

| If the 6 phase system is a Y rather than a polygon (super delta) then | you have a neutral and then you can consider that you have a 2 phase | system where the voltages Van and Vbn are 180 degrees apart. You then | have 3 terminals. This is indistinguishable from the center tapped | single phase system which fits what the Europeans refer to as 2 phase. | Neither are distinguishable from a 2 wire single phase system if you | ignore the neutral.

Is it standard in Europe to use "2 phase" to refer to what Americans mostly use some variation of "Edison style split single phase"?

I don't like to call any AC system based on Edison in any way. Edison did not design around AC. He did DC. Thus he didn't split his power system in any way considering angles, because there were no angles. Edison would not recognize the power system coming into my home. Tesla might.

And Edison is quite far from being my favorite inventor/scientist/engineer.

On Sun, 22 Feb 2009 21:01:46 -0800 Salmon Egg wrote: | In article , | Don Kelly wrote: | |> That depends on how you look at it- if you bring out only the two |> terminals A,D you have a single voltage between them. It is then |> indistinguishable from a single phase 2 wire supply. With a single |> voltage, phase, as a relative term, becomes a problem. as what do you |> relate this single voltage to? |> If the 6 phase system is a Y rather than a polygon (super delta) then |> you have a neutral and then you can consider that you have a 2 phase |> system where the voltages Van and Vbn are 180 degrees apart. You then |> have 3 terminals. This is indistinguishable from the center tapped |> single phase system which fits what the Europeans refer to as 2 phase. |> Neither are distinguishable from a 2 wire single phase system if you |> ignore the neutral. | | I have just come up with a magic box. I connect its to a three-phase | source. I ask a technician to measure the voltages between pairs of | wires leaving the output of the box. She comes up with two measurements | of 120V and one of 170V. Should the Tech be fired? | | The box is a Scott T transformer. | | What is the point. Once you have two phases, you can build equipment | that gives you anything you want. Actually, one phase (and retiurn is | enough, although more complicated. | | All this talk is garbage. Just stick to fundamentals!

Fundamnetally, Edison did not contribute to AC.

Fundamentally, you can have a reference terminal, and 2 power terminals with AC output at some fixed frequency. If you have controls to change their phase angles, you still have 2 of them, even if you happen to adjust them to exactly

180 degrees apart.

I'm not talking about the average power. I'm talking about the instantaneous power over a complete cycle.

Again, I am not talking about average power. I had more in mind a polyphase AC motor, which consumes a fixed amout of power, no matter what the instantaneous phase relationship is at any moment in time. It delivers a fixed power to its load, without vibrations from the power line frequency under ideal conditions. It also has a rotating field allowing for automatic start. Contrast with a single phase induction motor, whose power consumption at any point in time varies with the input waveform.

This just goes to show that an unbalanced polyphase source can be made to degrade until it becomes almost as bad as a single phase source, yet there still is something fundamental that happens at 180 degrees and nowhere else (except 0 degrees). You can still generate a constant power draw, even if it becomes absurdly difficult, by, for example, extracting two outputs derived from the sum and the difference between the two voltages, and scaling them (with transformer turns ratio) - as long as the phase isn't 180 or 0 degrees. When, for example the angle is 179 degrees, and the voltage is 100V, the difference voltage is nearly

200V and nearly in phase with the two legs, but the sum voltage is less than 1% of that, ~1.75 volts, but at about 90 degrees to the first. You could step it up to almost 100:1, but now we increase the current 100 times, and it's a horribly reactive load, a power factor of near 0. But it's still possible. Not at exactly 180 degrees, however, since to get the 90 degree phase you'd have to divide by 0 since the sum is now a constant 0. But in this case (only) you can use one transformer instead of two.

Saying that "there is no fundamental change" that happens at this angle is not true. It's like saying that if you plot the graph y=1/x, there is no fundamental change that happens at x=0.

Au contrarie, Edison might look at the three wires, measure 120/120 and 240 and say, "Gee, that's pretty much how I did it except you're using that 'deadly' AC crap!"

daestrom

Correct you look at the voltages with respect to the T junction- assuming it is available external to the box-there is no reason for it to be so. There is another set of terminals so 3 more voltage pairs can be measured- the 3 phase input. The technician should be fired for not measuring the voltages between the supply terminals but more importantly not measuring the voltage as specified. The voltages from the T junction are not the output. If you look at the terminals, you will have two sets of voltages in quadrature -2 phase- and the result will be two equal voltages in quadrature.

OK we are now getting down to something I said in error regarding the instantaneous power in the different cases- I did my math this morning and OOPS was the result. . Yes, the single phase and 2 phase,180 degree system which we both prefer to call a 3 wire single phase system will have a net pulsating power and will not inherently produce a rotating field while the 3 phase and 2 phase 90 degree systems have constant instantaneous power and can inherently produce a rotating field.

Here we run into a conflict between two definitions of "balanced"

One definition uses the balanced set of voltages each shifted 360/n degrees from the adjacent phases so that the sum of phase to neutral voltages and phase currents are each 0. That is the the neutral current =0. This is not fully spelled out in Gross, "Power System Analysis" but is implied in the first chapter which is the only place that he makes a comparison between alternative transmission schemes. The 180 degree apart single phase 3 wire system fits this.

On the other hand, Krause and Wasynczuk "Electromechanical Motion Devices" define the "balanced 2 phase system as you do, equal voltages in quadrature- as you have done. This is a machines perspective as only this form produces constant instantaneous power and a single rotating field.

It is not as drastic as that. Actually, the magnitude of the double frequency component will change in a well behaved manner-as the magnitude of the cosine of the relative phase angle. so it will be 1 at 180 and 0 at 90 degrees while the magnitude of the average power happily remains at 1 throughout. Nothing drastic happens at 180 degrees- all that happens is that the neutral current is 0 (a bonus) and that the pulsating component of the instantaneous power is at a maximum (not a bonus).

So while the total instantaneous power will have a double frequency component dependent on the relative phase of the two voltages, the total average power will be the same at all phase angles between the legs, corresponding to the sum of the average power in each leg-taken individually. I'm not sure what you are trying to do by using the sum and difference approach (particularly if you are using phasors as it appears when you talk about 100V, 1.75V at nearly 90 degrees etc as power calculated from phasors will be the average power, not instantaneous power) Why bother- just consider what the situation is for different angles between the legs. No horrible reactive problems or scaling needed. Surely you are not proposing such an exercise just in order to keep the total instantaneous power constant- it isn't worth the effort and time domain, not phasor analysis would be needed.

Now, for a induction motor, certainly the double frequency term is a nuisance and at the 0 and 180 degree points, there will be no starting torque and running torque will be pulsating. Hence the desire for a 90 degree shift. Single phase motors are definitely inferior to a polyphase motor, including a two phase machine- but two phase systems of any consequence died before either of us saw daylight - some recovered during the 40's as low power control motors and tachometers (phase fixed but voltage magnitudes variable).

**************** Apologies- my statements above are arrant nonsense. The only excuse that I have is that I was distracted by the wind whistling between my ears as when I went to bed and blocked the wind with a pillow, it became obvious that I blew it.