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.
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.
One thing that sets the "2 phases at 180 degrees" power separate from all the others is that you CANNOT generate polyphase power from it using a clever set of tapped transformers. Scott-T converts between 90 degree
2 phase and 3 phase. You yourself have posted how to get 3 phase power from 120 degree 2 phases with transformers. With enough transformers I can generate 19 phase power from 3 phase if I really wanted to, but not from the split phase to my house.
If you look at the resistive power (square the voltage) you can see there is no difference between single phase and Edison style 180 degree split phase. Both legs have the same power waveform. Not true for any of the other systems you mentioned, or 3 phase.
To me, the problem is that "2 phase power" seems to refer to 90 degree systems and 120/240 is called "single phase" in all of the literature and engineering discussions I recall. It is definitely true that many people, including very competent electricians, refer to "2 phases", "opposite phases", "the other phase", etc. when referring to 120/240V systems. There are other problems in this nomenclature. For example, in a 3 wire system it takes 2 of the "phases" (conductors) to get "single phase". For 120/240V, I prefer the term "leg" rather than "phase". It is also true that many people use the terms "energy" and "power" interchangeabily, although they differ in their engineering meanings. It's all about clear communication of ideas and I prefer to call 120/240V "single phase" along with most of what I hear and read. I spent a number of years an instructor in both electrical power and electronics and know how easy it is to say something that confuses rather than clarifies. Try explaining how two opposing vectors can sum to twice the value of one!! (It's all about reference points.)
It is the output of a transformer winding. Regardless of the 'phase' of the primary side, the SECONDARY side is what feeds us, and it carries with is a GROUNDED center tapped secondary which means it IS single phase (only one wave movin' thru) The center tap allows us to provide protection paths. In a faulty system, they *can* provide just the opposite, but our design does make that a rare instance (San Diego Bus Stop electrocution, 2005). I think that was a 600 volt street lamp feed though. He didn't have a chance.
Technically speaking, it is actually two phase - phases are 360/2 degrees apart. 3 phase 360/3 degrees apart, 4 phase
360/4 etc. Also the power relationships are the same as for balanced 3 phase etc (number of phases)*Vphase*Iphase and for balanced conditions, the neutral current is 0 as in the other systems with n phases and n+1 conductors.
The statement regarding "power waveform" is meaningless- could you clarify your reasoning?
HOWEVER---- This is referred to as 2 phase ONLY in countries which don't use it. In countries that do use it - it is described as the Edison system or
120/240 single phase center tapped and Doug Young has dealt with this quite well. There is no confusion where this system is actually used
(There is what is called, in the motor world, 2 phase where the two phases are ideally 90 degrees apart. but balanced phase currents don't result in 0 neutral current )
The distinction between calling two lines 180 degrees apart and any other phase angle is the ability of two or more phases at other than 180 degrees to produce a rotating flux vector in a motor or other similar electromagnetic machine (without the use of phase lagging caps or other means).
| 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?
| One thing that sets the "2 phases at 180 degrees" power separate from all | the others is that you CANNOT generate polyphase power from it using a | clever set of tapped transformers. Scott-T converts between 90 degree | 2 phase and 3 phase. You yourself have posted how to get 3 phase power | from 120 degree 2 phases with transformers. With enough transformers I | can generate 19 phase power from 3 phase if I really wanted to, but not | from the split phase to my house.
I don't know why 19 phase power would do anyone any good when as 12 phases is all anyone would ever need at home :)
Yes, I know you can't get polyphase out of 2 phase at 180 degrees. You can't get polyphase out of 1 phase (degrees don't apply). So?
| If you look at the resistive power (square the voltage) you can see there | is no difference between single phase and Edison style 180 degree split | phase. Both legs have the same power waveform. Not true for any of the | other systems you mentioned, or 3 phase.
How does this apply to using "phase" as the short designation for the number of hot wires that have different (whether 180 or 120 or 90 or any other) phase angles?
I'm not saying not to use "single phase" as a broad category of all systems that cannot be used to derive "poly phase". But in this case "single phase" and "poly phase" are the disjoint sets the union of which includes all AC systems. Obviously a "1 phase" system is only able to be in the "single phase" category. A "2 phase" system could be in either "single phase" or in "poly phase". Is this what confuses people?
I want to label the wires coming into my home as "phase A" and "phase B". There are 2 phases coming in. And I know they are 180 degrees because they are fed from a pad mount transformer with just one 7200 V primary (I watched it being installed).
| 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.
| To me, the problem is that "2 phase power" seems to refer to 90 degree | systems and 120/240 is called "single phase" in all of the literature and
What do you call a system with 2 hot wires that are 120 degrees apart? What do you call a system with 2 hot wires that are 60 degrees apart? What do you call a system with 2 hot wires that are 30 degrees apart? What do you call a system with 2 hot wires that are 105 degrees apart?
Sure, some of them would be labeled "weird". I would call them all "2 phase" in reference to a category of any system with 2 phases. If I need to qualify the phase angle, I can do that. "90 degree 2 phase" vs. "180 degree 2 phase" and that should be understood.
| engineering discussions I recall. It is definitely true that many people, | including very competent electricians, refer to "2 phases", "opposite | phases", "the other phase", etc. when referring to 120/240V systems. There | are other problems in this nomenclature. For example, in a 3 wire system it | takes 2 of the "phases" (conductors) to get "single phase". For 120/240V, I | prefer the term "leg" rather than "phase". It is also true that many people
"leg" seems such an odd term to me. But then, I think about these things in a more mathematical way. I tried using "vector" once but no one seemed to understand that one at all.
| use the terms "energy" and "power" interchangeabily, although they differ in
Oh, now THAT is a whole other thread waiting to happen.
| their engineering meanings. It's all about clear communication of ideas and | I prefer to call 120/240V "single phase" along with most of what I hear and | read. I spent a number of years an instructor in both electrical power and | electronics and know how easy it is to say something that confuses rather | than clarifies. Try explaining how two opposing vectors can sum to twice the | value of one!! (It's all about reference points.)
"single phase" has always been an area of NON-clarity to me, because it means "1 phase" to some and "2 phase" to others.
On Wed, 18 Feb 2009 18:24:35 -0800 StickThatInYourPipeAndSmokeIt wrote: | On 18 Feb 2009 23:16:06 GMT, 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. | | | Single phase with a grounded center tap at the pole, so ground is indeed | the reference.
Start with a 6 phase system, with phases labeled A,B,C,D,E,F at 60 degree intervals. Tap a branch circuit at A and D. Is this not 2 phases (of 6)?
I only see three lines up there and one ground on the high side. That would be 120 degree shifts by three lines. Take ONE of those lines to feed a single HV branch line down a sub-division street. Use that line to feed the primaries of the pole transformers, the secondary side output of which feeds a certain number of homes each.
Feeding a farm house a quarter mile down the path? Set the output on a plus 5 or plus 10 percent tap. If the distance gets too long, you have to send the HV line, and hang the transformer where it should have been anyway, near the house. :-)
On Wed, 18 Feb 2009 23:44:50 -0800 StickThatInYourPipeAndSmokeIt wrote: | On 19 Feb 2009 07:34:32 GMT, snipped-for-privacy@ipal.net wrote: | |>On Wed, 18 Feb 2009 18:24:35 -0800 StickThatInYourPipeAndSmokeIt wrote: |>| On 18 Feb 2009 23:16:06 GMT, 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. |>| |>| |>| Single phase with a grounded center tap at the pole, so ground is indeed |>| the reference. |>
|>Start with a 6 phase system, with phases labeled A,B,C,D,E,F at 60 degree |>intervals. Tap a branch circuit at A and D. Is this not 2 phases (of 6)? | | | I only see three lines up there and one ground on the high side. That | would be 120 degree shifts by three lines. Take ONE of those lines to | feed a single HV branch line down a sub-division street. Use that line | to feed the primaries of the pole transformers, the secondary side output | of which feeds a certain number of homes each. | | Feeding a farm house a quarter mile down the path? Set the output on a | plus 5 or plus 10 percent tap. If the distance gets too long, you have to | send the HV line, and hang the transformer where it should have been | anyway, near the house. :-)
Were you answering some other question about voltage drop?
I described a 6 phase system. What you see out on the street distribution is not 6 phase. It might be 3 phase and if so would generally be at 120 degree intervals. But I'm not talking about that system as the reference for counting phases in a system. I was talking about a system where there are 6 phase lines at 60 degree intervals. If you don't know what kind of system that is, let me know and I can describe more details for you.
| The distinction between calling two lines 180 degrees apart and any | other phase angle is the ability of two or more phases at other than 180 | degrees to produce a rotating flux vector in a motor or other similar | electromagnetic machine (without the use of phase lagging caps or other | means).
To make that distinction I would use the terms "single phase" (not the same as "1 phase") or maybe "mono phase" ... vs. "poly phase" (since any kind of poly phase system could be used to make a 2D rotating flux in a motor, even a 2 phase system at 90 degrees or even 120 degrees).
"single phase" - systems that cannot develop rotating flux "mono phase" - alias for single phase, to match "poly" "poly phase" - systems that can develop rotating flux "balanced phase" - systems with contant power, and when balance loaded will have no neutral current
"1 phase" a system with only a single phase line, can only be single phase "2 phase" a system with 2 phase lines, can be single phase or poly phase depending on phase angles. If balanced, will always be single. "3 phase" a syetem with 3 phase lines, can be balanced or unbalanced (e.g. corner grounded delta). Can also be single if we count separate lines at 0 degree difference (but that's cheating). We can extrapolate "N phase" from here.
The Edison style 3-wire center tapped split system is BOTH "single phase" and "2 phase" at the same time (although Edison would argue that it cannot be named after him since it's not DC :)
Maybe I should post next about my scheme to identify the _polarity_ of transformer connections :)
Not when you look at the delivered power to an ideal resistive load.
Polyphase power is almost always taught by plotting the voltage waveform of each leg. All EEs are familiar with 3 phase power where one phase has a voltage sinewave with a positive zero crossing at 0 degrees, a second phase has the same voltage waveform with a positive zero crossing at 120 degrees, the third identical but at 240 degrees. IMO, this is a mistake that leads to the "is-the-Edison-system-single-phase-or-2-phase" flamewars.
If, instead, we hook up N identical ideal resistors to the polyphase system and plot the power delivered to each of them, we also get sinewaves, but at twice the frequency, and shifted up so that the negative most excusion is at 0. (it goes negative for reactive loads but let's ignore them)
If we plot 3 phase power this way we still get 3 power waveforms shifted at 0, 120, 240 degrees (when using the double frequency, or at 0, 60, 120 degrees if we use the original frequency scale). If we plot 90 degree 2 phase we still get two power waveforms at 90 degrees. However, the Edison system produces 2 /identical/ power waveforms, completely different from the other polyphase systems. There's only one power phase.
This makes any any even number of phase system questionable. For example, the "six phase" system mentioned by others. It's really three phase in disguise. You could produce a /different/ six phase system with each of the 6 power waveforms shifted by equal amounts, just like you can produce
90 degree two phase by shifting the power by 90 degrees. Like 90 degree 2 phase, it's not symmetrical (you can't plot the 6 voltage waveforms symmetrically, just like with 90 degree 2 phase there's a neutral current for a balanced load. For each of them you can connect the center tap of the transformer secondaries as the neutral and bring out the 180 degree voltage waveform/"the other leg", and you'd probably call it "12 phase" (or "4 phase" for the 90 degree 2 phase system) and get the symmetrical voltages. It's still only 6 power phases (2 for "4 phase"/90 degree 2 phase) I've heard the "4 phase" system called 4 or 5 wire 90 degree 2 phase, depending on whether the neutral is supplied to the load. For 4 wire the center tap can be omitted and we have 2 independent 2 wire circuits.
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.
How the system is grounded has a lot to do with the count on the number of phases. If you have three isolated center-tapped winding on an alternator or transformer bank, you can get either three or six phases very easily without changing the alternators or transformers. I worked at a place that had three-phase distribution using a V connection with the V apex grounded. That made it difficult to use unbalanced loads including those producing unbalanced harmonics arising from rectification. There was no neutral that could be used for Y connected loads.
In particular, this problem reaches into what is called two-phase. Again, with suitable windings, you could get either two-phase or four=phase. Two-phase could be looked at as four-phase with two phases missing.
This all goes to show that a true professional EE should understand what is going on without relying just upon what he learned in class.
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