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just call it 2 phase

Discussion in 'Electrical Engineering' started by [email protected], Feb 18, 2009.

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  1. Guest

    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.
     

  2. Single phase with a grounded center tap at the pole, so ground is indeed
    the reference.
     
  3. 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.
     
  4. Very nice.
     
  5. Don Kelly

    Don Kelly Guest

    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 )
     
  6. Guest

    | 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?
     
  7. Guest

    | 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).
     
  8. Guest

    | 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.
     
  9. Guest

    | 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.
     
  10. Guest

    | On 18 Feb 2009 23:16:06 GMT, 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)?
     

  11. 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. :)
     
  12. Guest

    | On 19 Feb 2009 07:34:32 GMT, wrote:
    |
    |>| On 18 Feb 2009 23:16:06 GMT, 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.
     
  13. Guest

    | 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 :)
     
  14. daestrom

    daestrom Guest

    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.

    I even had the 'privledge' in my early years of working on a shipboard DC
    generator with this third neutral leg brush set up.

    daestrom
     
  15. Guest

    | 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.
     
  16. Guest

    | 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?
     
  17. Guest

    | 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).
     

  18. Ithought it started at 100 and crept up over several years.
     
  19. Guest

    | On 20 Feb 2009 04:13:20 GMT, wrote:
    |
    |>
    |>My understanding is that his DC system was 110/220 volts, not 120/240.
    |
    |
    | Ithought it started at 100 and crept up over several years.

    It was at 110 volts when Edison started running his DC service in NYC.
    I also know 220 volts was being used in Europe by that time. I suspect
    he decided to start with that 220 volts, but determined that light bulb
    filaments last longer when designed for lower voltages, because they are
    thicker and shorter (or maybe just that when he designed them to last
    longer, they just used a lower voltage) ... so he decided to split the
    system in half to accomodate the light bulb on a lower voltage.

    If only he had accepted AC then we might have universally ended up with
    all incandescent lights operating at perhaps 12 volts or so, stepped down
    near the point of use, with a higher voltage going into the building.
     
  20. Guest

    | writes:
    |
    |
    |>| 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.
     
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