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Thread: Wye-Delta Grounding Transformer

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    Wye-Delta Grounding Transformer

    Hello, good day! I just want to ask about the ground of the wye-delta grounding transformer. Do we have to connect it to the ground bus of the main switchboard and/or ground it directly through ground rods? Thank you in advance for your help.

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    First you need to differentiate between system grounding and equipment grounding. Are you grounding the secondary system?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    IMHO,
    It should be connected to ground in 3 different places.
    The grounding conductor of the Primary circuit, building steel, and the supply side bonding jumper.
    See article 250.

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    wye-delta is a rare duck in the low voltage world, except for when someone is using a delta-wye in reverse because its laying around and just too temping to not use. May we ask what is the application? Most important thing is to keep the wye point floating - dont connect anything to it.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Also you might see a transformer with a wye primary and a 'floating' delta uses as a 'grounding transformer' to derive a neutral in an otherwise ungrounded system. So yes please to the original poster please describe in more detail what you are doing.

    -Jon

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    Quote Originally Posted by winnie View Post
    Also you might see a transformer with a wye primary and a 'floating' delta uses as a 'grounding transformer' to derive a neutral in an otherwise ungrounded system. So yes please to the original poster please describe in more detail what you are doing.

    -Jon

    Yeah after reading the OP a few times, the wording does correspond with that use.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by jojo View Post
    Hello, good day! I just want to ask about the ground of the wye-delta grounding transformer. Do we have to connect it to the ground bus of the main switchboard and/or ground it directly through ground rods? Thank you in advance for your help.
    Please clarify what you have for a transformer and what it is being used to do.

    Is it a transformer with Wye primary and delta secondary with primary purpose to change voltage, or is is some sort of autotransformer used to create a neutral conductor in a system that has no neutral? makes a big difference in how to answer the question.
    I live for today, I'm just a day behind.

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    Hi all, thank you for the quick replies. The scenario is this: the source to an industrial facility is 2.4kV-460V delta secondary (2000kVA pad-mounted transformer). This goes to the main switchboard in the electrical building. And the main switchboard supplies the (7) seven buildings in the facility. At first I suggested 400Y/230V so there's no problem for the grounding issues. But there's no choice since the motors to be used for the facility are ANSI rated, meaning 460V 3-phase motors. So for the three-phase, it will have 460V, 3-wire plus eqpt ground. For single phase, there will be a 460V-230V step down transformer (we use 230V single phase, not 120V) plus eqpt ground. My concern here is during a ground fault especially for the motors. Since the system is delta, the breakers won't trip. And there might be other issues since the system is ungrounded like prone to transient overvoltages as stated in IEEE Green Book and from other elec references (Beeman, etc). That's why there's a need for a grounding transformer, also that the zero sequence current will have the return path to source. The grounding transformer will be wye-delta, and rated 200kVA or 225kVA 460V three phase (at least 10% from the 2000kVA source). My concern also is about the ground from the grounding transformer, if it should be connected to the main switchboard ground bus and/or connect it directly to the ground through the ground rods.
    Last edited by jojo; 02-05-19 at 05:29 PM.

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    Perhaps others will chime in who have more knowledge on the subject, but have you considered a zig-zag transformer? I wonder if that is a better option.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Hi Ethan, thank you. I think zig-zag transformer is much costly than the standard wye-delta transformer or even wye)delta banked transformer? Not sure if there's readily available zig-zag transformer here.

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