just call it 2 phase



And then there were syncrho-tranmistters that used single phase on the rotor and three 'phases' of output to drive receiver units whose rotors were excited by the same single-phase supply. If you swapped the single phase supply the receiver would point 180 out and if you swapped the 'three phases' on the stator you could get rotation in the opposite direction (or be off by 120). These may be the remote positioning units you're thinking of.
Of course these were not meant to rotate continuously but rather provide position/orientation information. And in that vein there were all sorts of variations including 'resolvers' that would provide the sin() and cos() functions of a ship's speed and direction and break it down into N-S speed and E-W speed.
Not exactly 'two-phase', but I always found them fascinating. Used for fire-control systems for ship's guns back before electronics. Also used for dead-reckoning plotter with a simple 'bug' under a glass table.
daestrom
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daestrom wrote:

I have a set of these that runs on 120V, 60 cycle single phase. (One side of two phase?) :-), and actually produces useful torque at the receiver. I used them to rotate my amateur radio antenna.

About the only recent use of the Scott-T transformer set is in converting from the 3-phase "synchro" data to the 2-phase "resolver" data. They're still used in some servo systems.
Of course now almost everything is digital. I have a patent on a high-precision "resolver" for machine positioning that used an electrostatic pick-up from a conductive pattern on the rotor. The output was digitized for machine control.

A variation of this is the electromagnetic deflection of the PPI radar display used for aviation traffic control.
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daestrom wrote:

Thanks- synchro is the word that I wanted ( and escaped me completely at the time of writing -so much for long term memory!). In another application, large versions were used in lifting wide "gates" using 2 motors and the transfer was such as to balance the lifting force on the two sides of the "gate" They could rotate continuously but this would be effective at low speeds only.
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I say a variation of that in shipyard cranes (the tall cranes that straddle the pier with trucks/train going under them). They used two wound-rotor motors, one on each 'truck' of the gantry. By tieing the three-phase rotor connections together, the two rotors would turn in locked-step so the gantry would go down the pier straight. Not exactly a synchro, but a neat way to control the motion of both sides of the gantry long before position indicators, digital feedback, or other 'hi-tech' tracking systems.
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says...>

Are you referring to "Selsyn" motors?

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krw wrote:

Selsyn is the name, thanks. There were other motors but the selsyns were fascinating. The same concept was used to transmit speed information from the shaft of a generator to the flyballs of a governor.
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On Thu, 19 Feb 2009 01:23:27 +0000 (UTC) Michael Moroney
| 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).
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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.)
Don Young
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wrote:

Very nice.
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| 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.
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wrote:

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.
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| 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).
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On 18 Feb 2009 23:16:06 GMT, snipped-for-privacy@ipal.net wrote:

Single phase with a grounded center tap at the pole, so ground is indeed the reference.
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On Wed, 18 Feb 2009 18:24:35 -0800 StickThatInYourPipeAndSmokeIt
| 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)?
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On 19 Feb 2009 07:34:32 GMT, snipped-for-privacy@ipal.net wrote:

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. :-)
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On Wed, 18 Feb 2009 23:44:50 -0800 StickThatInYourPipeAndSmokeIt
| On 19 Feb 2009 07:34:32 GMT, snipped-for-privacy@ipal.net wrote: | |>On Wed, 18 Feb 2009 18:24:35 -0800 StickThatInYourPipeAndSmokeIt
|>| |>|>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.
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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).
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wrote:
| 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 :)
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snipped-for-privacy@ipal.net wrote:

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