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Thread: 480 Delta - 480 Wye

  1. #1
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    Exclamation 480 Delta - 480 Wye

    I have a design with 480VAC Wye with two UPS systems (300kVA each) on this configuration, as well as a 150kVA transformer 480Y/120-208Y. Unfortunately, the local energy company installed a 2MVA - 480VAC Delta configuration transformer.
    What can I do?
    I really appreciate your coop.
    Yours truly.

  2. #2
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    Quote Originally Posted by rebf1203 View Post
    I have a design with 480VAC Wye with two UPS systems (300kVA each) on this configuration, as well as a 150kVA transformer 480Y/120-208Y. Unfortunately, the local energy company installed a 2MVA - 480VAC Delta configuration transformer.
    What can I do?
    I really appreciate your coop.
    Yours truly.
    Have the utility change their transformer.

    Seriously, what is your problem? Are you running all of these sources in parallel? Or, is the utility transformer a 480V delta configuration that you will be using as a by-pass of your UPS?

    How you are interconnecting these devices will influence the solution.
    Just because you can, doesn't mean you should.

  3. #3
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    Thank you

    No. For your information the 2MVA 480VAC Delta transformer is the main feeder for the installation, and both UPS (480VAC Wye) will be connected to the main breaker panel, as well as the 150kVA tranformer (480VAC Wye).
    Therefore my problem. The load will be feeded out of the UPS system.

  4. #4
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    Quote Originally Posted by rebf1203 View Post
    No. For your information the 2MVA 480VAC Delta transformer is the main feeder for the installation, and both UPS (480VAC Wye) will be connected to the main breaker panel, as well as the 150kVA tranformer (480VAC Wye).
    Therefore my problem. The load will be feeded out of the UPS system.
    I'm no engineer but it sounds like you need 480 delta/480 wye
    transformers for your UPS's and a 480 delta/120/208 wye for your other loads.

  5. #5
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    Quote Originally Posted by rebf1203 View Post
    No. For your information the 2MVA 480VAC Delta transformer is the main feeder for the installation, and both UPS (480VAC Wye) will be connected to the main breaker panel, as well as the 150kVA tranformer (480VAC Wye).
    Therefore my problem. The load will be feeded out of the UPS system.
    If the utility will not change their transformer, you will need to supply your own 480 delta to 480V wye transformer for each UPS input and for each UPS bypass circuit.

    Supplying the UPS with 480V delta instead of 480Y/277 means that the components on the input side (ie. filters) may see a higher Line-Ground voltage than they were designed for. With a 480Y/277V output the UPS can never be bypassed to the 480V delta supply.

    If the 150kVA transformer is to provide 208Y/120 output, it does not make a difference if its input is from a delta or wye source.
    Just because you can, doesn't mean you should.

  6. #6
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    Thank you again.

    Yeah, the utility won't change the transformer, so we will have to look for a 1 Ratio transformer (480 Delta - 480 Wye) to feed each UPS.
    Thank you for the tip about the transformer that doesn't have a problem with the Delta feeding, which will feed the 120/208VAC load.
    Yours Cordially.

  7. #7
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    Quote Originally Posted by rebf1203 View Post
    Yeah, the utility won't change the transformer, so we will have to look for a 1 Ratio transformer (480 Delta - 480 Wye) to feed each UPS.
    Technically speaking, a 480D-480Y transformer doesn't have a 1:1 turns ratio. It is made up of three 480-277v transformers.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  8. #8
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    Have you thought about a D-Y with a Z-Z secondary?

  9. #9
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    Mar 2009
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    Guatemala
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    Thanks

    I have done some thinking about a D-W transformer but it is so strange in our country, and takes couple of weeks to arrive. We will be working with the the Delta output of the transformer with a logical neutral.
    Sincerely yours.

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