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Thread: 480V to 240V Transformer

  1. #1
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    Feb 2008
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    480V to 240V Transformer

    new guy here with an, judging fromt the other posts i have read, easy question.

    My electrical history is limited. I worked on the electrical systems of the huey and cobra helicopter in the marines but now i am working as a PLC tech in the modern industry and i am somewhat the quasi electrician here. I am comfortable with household wiring, installing 480V motors and vfd's among other things. The ground i have yet to tread is transformers. I am installing a 3 phase transformer. 480V in and 120/240 out. i will get some more information for you momentarily but where can i start as far as connections go? From what i am told, i need a single leg of 240V out.


    Back with the new info. It is an ACME Transformer Cat. No. T-3-53341-1S

    I found this diagram as well. Is this correct?



    I am thinking it should be wired like this.

    L1-H1-1
    L2-H2-1
    L3-H3-1

    Then X1, X2, and X3 are my three phases of 240? Each one will give me 240 to ground?

    To take this even further, I am going into a VFD after the transformer to give me 220V 50Hz. The VFD accepts single or three phase 240. I am guessing thats 2 or 3 legs of 120?
    Last edited by kurt.brinker; 02-25-08 at 01:37 PM.

  2. #2
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    Xfmr

    The diagram if for 480V delta to 240/120 delta. The X4 is normally grounded and called the neutral. X1-X4-X2 give you 120/240V single phase. X1-X2-X3 give you 240V 3-phase. X3-X4 is only 208V.
    e^(i pi) = -1

  3. #3
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    ok so for my 240V 3 phase vfd input i would wire in X1-X2-X3? I thought 3 phase 240 was 3 legs of 120?

    one more thing. along with the motor, i need to wire in a 220V power strip for foreign power. like this


    how are those wired?
    Last edited by kurt.brinker; 02-25-08 at 01:40 PM.

  4. #4
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    The high-side connection would be correct if you have 480 volts. The other taps can compensate for low highside voltage.

    It would appear that this is a transformer that would normally provide 120/240 (120 volts to ground, 240 volts phase to phase). The X4 would be the neutral/ground with 120 volts at X1-X4/gnd and X2-X4/gnd, 240 volts at X1-X2, X2-X3, and X1-X3. If you had a transformer with changeable taps, you could parallel the secondaries and get 240 to ground (are you sure you need this?)

    I suspect what you need is either one leg of the 120/240 volt configuration (240 volts phase-phase) or all three (240 volt 3 phase). You would have one high leg (208 volts to ground), and two 120 volt-to-ground legs. The 3 phase connection would be the most efficient use of the transformer.

  5. #5
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    X1-X2-X3 is correct. 3 phase 240 volts is 3 legs of 240 volts. I ASSUME they are wired the same way we wire 120 volt strips since they use 240 like we use 120.

  6. #6
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    let me give you a little more info.

    i need the transformer because we have some equipment that runs on 220V 50hz. They were running it at 240V,60Hz with this transformer but they were using it as a steup up transformer. i have no idea how it was wired. they had it plugged into a 120 outlet and it was giving them 240V. I am using the transformer to go from 480V 3 phase and then into a VFD that i will set for 220V/50Hz. does that make sense?

  7. #7
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    Quote Originally Posted by beanland
    The diagram if for 480V delta to 240/120 delta. The X4 is normally grounded and called the neutral. X1-X4-X2 give you 120/240V single phase. X1-X2-X3 give you 240V 3-phase. X3-X4 is only 208V.

    they decided they only needed single phase 240. you say it is X1-X4-X2
    how exactly does that work?

    i need single phase 240 to power the plug i listed earlier.

    i got 120V from X1 to X4 and i go 120 from X2 to X4. but i got 140 from X1 to ground and 140 from X2 to ground. I am guessing i need to place X1 and X2 as my L1 and L2 on the vfd. even though its 140 to ground, its 240 phase to phase so i am ok?
    Last edited by kurt.brinker; 02-25-08 at 04:02 PM.

  8. #8
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    120v-n-120v

    If you only need 120/240V single-phase, there is no reason to pay for and install the 3-phase transformer. Connect 480V 2-wire to a 480-120/240V single-phase transformer.

    Warning: a VFD will generate "50Hz" for a motor but it will be all chopped up and distorted, not a neat sine-wave. If they need 220V 50Hz, a VFD may not be the best choice, if they need it to be clean. You may need to install an output filter on the VFD to clean up the waveform to get it close to sinusoidal.

    Many electronic devices have "universal" power supplies that accept 90-245V and 25-60Hz. Is there a different power supply available for the device they are powering?
    e^(i pi) = -1

  9. #9
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    The couple of times I have been involved with providing 50 Hz it was with a motor generator set.

  10. #10
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    Curiousity question:
    Has anyone looked into a UPS with a 60hz front end and a 50hz output?

    carl
    Using the code for a design guide is a sign of incompetance

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