Two phase to three phase transformation

Discussion in 'General Electronics Chat' started by ersch, Sep 7, 2014.

  1. ersch

    Thread Starter New Member

    Sep 6, 2014
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    I need to convert a two phase three wire system to a three phase four wire system. I can do this with a Scott T transformer but I am not sure where to connect the neutral on the three phase secondary windings to achieve the four wire output that I need.
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Welcome to AAC.

    1) It would help to know in what country you are.
    2) Are you committed to using the Scott T transformer, or will you consider other approaches (e.g., rotary or solid state)?
    3) How much power (voltage and current) do you need for the three-phase?
    4) Do you need the conversion to run a motor? If so, do you want variable speed too?

    John
     
  3. ersch

    Thread Starter New Member

    Sep 6, 2014
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    1) US
    2) Yes. I am committed to use a Scott T transformer.
    3) Total power will be 45 kVA with an input of 240 V, two phase, three wire and an output of 208/120 V three phase, four wire.
    4) The load is general power and not a motor so no variable frequency is necessary.
    ersch
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Where in the USA do you have two phase power and not a full three phase power?

    If you are thinking that the common 120/240 VAC that is present in the vast majority of home is two phase you're already wrong. It's simply a single phase 240 VAC supply that has it's center tap connected as the common/ground reference point.
     
  5. Electric Al

    Member

    Nov 6, 2013
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    Are you sure it is 2 phase , and not single phase 120 or 240 ?

    You can do it with a roto- phase unit and a step up 3 phase transformer , which will have a neutral connection !




     
  6. ersch

    Thread Starter New Member

    Sep 6, 2014
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  7. ersch

    Thread Starter New Member

    Sep 6, 2014
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    I appreciate your help but it is counterproductive to assume that I don't know the difference between a single phase common three wire system and a two phase (displaced 90 degrees) input connected in an L fashion with the corner as the neutral. Please try to help me by answering the original question as stated.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Here we go...
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    In the USA, two phase with just a common (white wire) is no longer code. Two phase/single phase 220/240V with green (safety ground) is code and two-phase with green and a white (four wires) -- from which you can get two, single phase circuits -- is also code. At least, that is as I remember it. My NEC book is in another city, so I cannot check it now. Basically, you are not allowed to use the grounded wire (i.e., the white/com) as a ground. If the third wire is white, then you don't have a safety ground.

    Are the wire colors non-white or non-green X 2 (e.g., a black and a red) with a white or a green wire . Is the third wire white or green? If the third wire is green, that can only be used as the safety ground, not as a common. Is this wiring in metal conduit or plastic?

    John

    Edit: Sorry, I was writing while post #7 was made and didn't see it. Good luck. I would and do use a rotary converter.
     
  10. ersch

    Thread Starter New Member

    Sep 6, 2014
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    I am interested in your complete reply. All I got is "Here we go..."
     
  11. BR-549

    Well-Known Member

    Sep 22, 2013
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    Thank you ersch. I had never heard of a Scott T transformer. Very interesting. I wasn't aware of early 2 phase history.
    Do you have a print of the scott t? I want to compare it to the one I reviewed.
     
  12. Brownout

    Well-Known Member

    Jan 10, 2012
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    That's all you're gonna get. You're experiencing Pennsylvania (USA) humor.

    From the little bit of reading I did, a Scott T transformer converts between 4 wire two phase and 3-wire 3 phase. But you said you wanted to go from 3-wire two phase to 4-wire 3 phase. Maybe more details would help us to help you for figure it out. Seems there are no Scott T transformer experts in here.
     
    Last edited: Sep 7, 2014
    GopherT likes this.
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Are you operating an antique generator of some sort? Or are you running 3-phase into a Scott T transformer to get the 2-phase power.
    No US utility is running 90-degree generators any more. Without a 90-degree generator, or 3-phase into a Scott T, you have no 2-phase power source (90-degrees out of phase).

    Until we have an answer, it doesn't sound like anyone around here is motivated to give you an answer.
     
  14. BR-549

    Well-Known Member

    Sep 22, 2013
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    I read Philly does.
     
  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I stand corrected.

    Only city center area of Philadelphia is running 90-degree 2-phase power. Unless you live there, or you are running an antique 90-degree generator, or you are running 3-phase into a Scott T, you have no 2-phase power source (90-degrees out of phase).

    Until we have an answer, it doesn't sound like anyone around here is motivated to give you an answer.
     
  16. BR-549

    Well-Known Member

    Sep 22, 2013
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    Oh I am motivated, but I don't have the knowledge. That's quite a circuit. From what I can find, I think Brownout is right though.
    I think Philly uses these to supply 2 phase to their customers.
     
  17. Lestraveled

    Well-Known Member

    May 19, 2014
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    ersch
    You have to expect a little skepticism? This is your first post on this forum. You pose a question based on a highly unusual power form as if everyone has it available in their backyard. You present no schematics, no wave forms. You have asked a complex question involving a very unusual waveform. We are not mind readers, and you appear resistant to provide information needed for a meaningful exchange.
     
    Last edited: Sep 8, 2014
    inwo likes this.
  18. ersch

    Thread Starter New Member

    Sep 6, 2014
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    Not a very friendly answer. If everybody had it in their backyard I probably would not have to pose the question. No schematics are required. Waveforms are not unusual: The two phase input has a garden variety sine wave each displaced by 90 degrees and the output likewise has garden variety sine wave each of three displaced by 120 degrees. I do not require mind readers: a simple knowledgeable person will do. I can do the transformer conversion but I was asking how to establish a neutral connection in the output. When I get my answer, and I will, I will forward it to you so you can help someone else.
     
  19. BR-549

    Well-Known Member

    Sep 22, 2013
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    From what I see, it looks like a delta out...so I don't think your gonna get a neutral.

    And you guys thought I was bad.
     
  20. inwo

    Well-Known Member

    Nov 7, 2013
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    So it may require a second transformer set to get 208/120.

    I haven't seen a connection for star out.
     
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