A mindbender : you never seen this before

Discussion in 'The Projects Forum' started by simeonz11, Feb 11, 2010.

  1. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    So I have studied 3 phase systems before at school , we got a 3 phase power supply and everything there , I understand it perfectly when it comes from the wall plugs but this is a bit "mindbending" to me .

    This is a solid state version of a 3 phase AC system , as you can see this is strange . I have made an very good 3 phase pure sine solid state driver with some pretty powerful amplification . Phase A,B,C are 120 degs out of phase and have same common ground , they all use same power supply .

    I basicly wish to connect this as a Y source , delta load configuration .

    http://www.mhhe.com/engcs/electrical/hkd/tutorials/images/t13-3.gif

    I have spent much mental energy trying to figure out how I should connect it , it is very strange to me . I have much experience @ school as I just connect the alternator leads properly for this type of connection but this seems strange to me .

    It seems to me like I already have my common source point , ( ground ) , is this the right connection ? Can this even be done ? I know it can be done via a transformer Y on the primary to delta on the secondary where neutral is my ground but I wanna try with no transformer . See the pic .


     
    Last edited: Feb 11, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
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    I don't see the problem. Eliminate the load resistors and replace them with a Y configuration and ground. What am I missing? You already have a ± power source, so ground is a true ground.
     
  3. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    Hi Bill , thx for the reply .

    What do you mean Bill ? Connect them in Y connection and remove resistors ?

    My load is a delta load , it has no ground .
     
  4. Wendy

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    Mar 24, 2008
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    I guess I don't understand the question. You already show a Delta load from what I can see, diagram what you want.
     
  5. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    Is this what you mean bill ?

    Yes this connection is easier on the mind and would work but I will not be using Y load . Plz ignore the 30 amps , this is just for example purpose .

    So my Diagram for delta load is good ?
     
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    Last edited: Feb 11, 2010
  6. Wendy

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    Mar 24, 2008
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    If you can call using 30A through an analog design good. :D

    I'd go with MOSFETs and PWM, or at least with PWM, it would be alot more efficient on the transistor side.
     
  7. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    O that was just for showing the schem , its an image I found on google , ignore all about that 30 amps I wont be using anything near that .
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    are you trying to make the secondary of the tranformer a delta connection?
     
  9. Wendy

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    Mar 24, 2008
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    I was thrown by the transformerless designation. I'm a bit confused by the specs.
     
  10. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    Yeah , the image is not very insightful but thats what I would do , Y on the primary and delta on the secondary .

    But I would wish to use no transformer here if possible .
     
  11. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    I put up a new pic for everybody to see what I meant by the transformer
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    ok, you want a wye generator and delta load.

    do you have a three phase generator?

    on the attached simulation, to get it to work, I added 0.1 ohms to the generator, otherwise the simulation would not work properly.
     
  13. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    I am producing 3 x AC sine wave using 3 x pnp/npn pairs , sine waves are out of phase by 120 degrees and use the same power supply and have the same voltage .

    http://hades.mech.northwestern.edu/images/2/20/Transistor_push_pull_follower.gif

    When operating each phase seperatly they all share common ground , I know they can be connected to a Y load but I wanna connect them to a delta load , this becomes confusing as I do not know what to do with the source ground , I believe it is simply not connected to anything just as my diagram in my first post , it is already connected since they all share the same ground of the power supply .
     
  14. Wendy

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    Mar 24, 2008
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    You have all the basic requirements. The ground is irrelevant, but potentially useful. If they are 120° apart then you are already there.

    Just ignore the ground if you don't need it.
     
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    None of the resistors will be tied to the ground in a delta configuration.
     
    Last edited: Feb 11, 2010
  16. eblc1388

    Senior Member

    Nov 28, 2008
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    In a delta connected load, you don't need the ground(common) connection as there isn't any on the load.

    Think of the situation in two phase as in using a two channel audio amplifier in bridge configuration. The speaker is connected across the two outputs of each channel. The common of the amplifier output is not used.
     
  17. williamj

    Active Member

    Sep 3, 2009
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    SIMEONZ11,

    In industry, on a Delta configuration any corner connection of two windings is grounded and the center tap of any Y configuration is always grounded (as shown in the attachments). The ungrounded coil of the Delta configuration is (was) considered or labeled as the "wild leg" or phase.

    On the face of it, it looks as if there is a direct short on the Y configuration to ground, and there is. But bear in mind that the earth ground actually offers quite a bit of resistance between the two points (and there is generally a large distance between the two points). Current flow always follows the path of least resistance and the path of least resistance here is through the windings of the Delta configuration there by avoiding the "short' circuit as it where. (I think) LOLOL!

    Hope this helps,

    williamj
     
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