Transformer connection

Discussion in 'General Electronics Chat' started by TAC480, Nov 28, 2013.

  1. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    I'm trying to make sense of this,

    Consider a 480 Delta primary / 208 Y secondary transformer used in reverse order so that the 208 side is used as the primary and the 480 used as the secondary.

    If one leg of the 480 is connected to a 277 volt load using the center tap of the 208 Y for the neutral connection, what would be the expected effect on the transformer?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    How can you use one phase of the 480 what is now the secondary and the Y connection of the primary?
    Max.
     
  3. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    The 208 Y center tap was bonded to the transformer enclosure. One leg of the 480 D was connected to the 277v load (HID lighting) and the neutral side of the load connected at the bonding termination of the transformer.
    I'm not saying this is right, just how it was connected!
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    For the most part if I am reading this correctly nothing will happen.

    Going from a connection on a 480 volt delta, which I am guessing has on common or earth ground point, to a common earth point doesn't give you anything.
     
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One phase of the delta secondary Must be referenced to earth ground or a neutral somewhere in order to complete the circuit, IOW it is not enough for the load neutral to be connected to earth ground. .
    A drawing would make it clear as I feel something is missing?
    Max.
     
  6. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    I don't recall seeing a ground reference on the delta. It would seem that it would have been made through the HID ballast (grounded at location ?) and the bonding termination at the transformer.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Often with delta supplies, one corner of where two phases connect is taken to earth ground as a neutral.
    There is also a 'High leg' or 'Wild leg' configuration where one phase has a C.T. and this is taken to earth as a neutral, for a split supply, simulating the familiar C.T. transformer secondary.
    Max.
     
  8. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    So essentially this is a corner grounded delta with an in line resistor.
     
  9. MaxHeadRoom

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    Jul 18, 2013
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    It could be, but I am not sure what you mean by inline resistor?
    The phase junctions would be connected directly to earth ground if this is what you have.
    Max.
     
  10. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Three phase delta doesn't have to be grounded, we use floating delta for critical life-safety systems where power continuity is critical so we can detect a single phase ground and correct it without tripping circuits.
    http://static.schneider-electric.us/assets/consultingengineer/appguidedocs/section6_0307.pdf

    I'm not sure that the OP configuration is doing without a drawing either.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That I realize, but he mentioned that the load was referenced to ground?
    Need a picture!;)
    Max.
     
  12. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    By in line resistor I mean the HID ballast (load). I guess if I were to measure from one of the other phases to ground I would get some oddball voltage as opposed to the 480 that would be expected.
     
  13. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    Going back to my original question I'm now thinking the transformer would not be affected but the HID ballast would not perform properly since the 277v connection is being supplied with 480v!?
     
  14. MaxHeadRoom

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    If one corner is earth grounded, apart from the load phase that only leaves one other phase and that would also read the same to ground as your 'Load' phase.
    IF this is how I assume it is configured.
    Max.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I think there are too many suppositions here, so it definitely requires confirmation before any more concrete answers can be given?
    Max.
     
  16. TAC480

    Thread Starter New Member

    Nov 28, 2013
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    Thanks to all for helping me think this through.

    Happy Thanksgiving
     
  17. inwo

    Well-Known Member

    Nov 7, 2013
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    Think you meant no ground.

    Then that's correct.
    You would just have an un-allowed connection from a floating system to earth.
    From center tapped delta you have 240/240/415 to ground
    Corner grounded 480/480/0
    Need 480 Y to get 277/277/277
    Won't get 277 from 480 Delta.

    I believe that you can center ground 480 v delta by adding three small transformers that give 277 to ground, BUT then you can't use the 277 volts to supply load.

    Will have to regroup for a 277 load. Most lighting now is multi voltage.
     
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