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Thread: zig zag transformer

  1. #11
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    Quote Originally Posted by kwired View Post
    There is no neutral conductor running to it on the drawing though, just indicates a ground connection at the midpoint.
    To me, it looks like the midpoint is the artificial neutral, and the only purpose of it is to provide a balanced connection to the earth.
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  2. #12
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    Quote Originally Posted by K8MHZ View Post
    To me, it looks like the midpoint is the artificial neutral, and the only purpose of it is to provide a balanced connection to the earth.
    Yet the source ahead of this appears to already be a grounded wye, which should already fulfill that purpose.

  3. #13
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    Quote Originally Posted by kwired View Post
    Yet the source ahead of this appears to already be a grounded wye, which should already fulfill that purpose.
    Looking hard at the drawing, I renew my comment that the source grounding is only seen when the disconnect is closed, since there is no neutral connection to the inverters. I do not see why floating the inverter output (when not operating, because of anti-islanding) should be harmful, but it still might be the motivation.

    Sent from my XT1585 using Tapatalk

  4. #14
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    Quote Originally Posted by GoldDigger View Post
    Looking hard at the drawing, I renew my comment that the source grounding is only seen when the disconnect is closed, since there is no neutral connection to the inverters. I do not see why floating the inverter output (when not operating, because of anti-islanding) should be harmful, but it still might be the motivation.
    While it's a little hard to say for sure with the photo cutting things off, it does look to me like the neutral goes to the inverters. It seems like the drafter just omitted the neutrals inside the switchboard for clarity.

    Not saying you are wrong about the motivation, we've heard about demands for source grounding (which to my knowledge is unnecessary). I also wonder what you think of my 705.32 comment though.

  5. #15
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    Also notice the cutting off. It looks like the breaker is a normally open breaker that closes upon activation of the "S" on the right side of the page. Perhaps seeing the rest of the drawing would give some clue as to the intention. I don find it interesting that this is odd enough that no one here with the vast knowledge represented, has yet said, "Oh that is a ..."


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  6. #16
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    It is a grounding xfmr for the 480
    the assoc cb looks like it is tripped by a 0 seq on the 13.2 kv prim?
    why I do not know
    it does gnd the load side of the 3000 fused sw if open



  7. #17
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    Quote Originally Posted by Strathead View Post
    Also notice the cutting off. It looks like the breaker is a normally open breaker that closes upon activation of the "S" on the right side of the page. Perhaps seeing the rest of the drawing would give some clue as to the intention. I don find it interesting that this is odd enough that no one here with the vast knowledge represented, has yet said, "Oh that is a ..."
    Here is a more complete picture. I am confused by the logic of the kirk key. Here is what the note 11 says:

    "Direct trip. If 480V 1200A circuit breaker is open, trip sent to 13.2KV 1200A VCB."
    So if the Zig Zag or its supply circuit fails, in such a way that causes the breaker to trip (or someone manually turns it off for that matter), they want the MV supply to also open. The 480 system is already grounded, so why is the zig zag needed, and not only that, why do they see it as so important that the MV supply opens if the zig zag goes offline? Is this just perhaps a silly utility requirement based on grounding myths that system grounding is of paramount importance and that "more" is better?
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  8. #18
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    Quote Originally Posted by GoldDigger View Post
    Looking hard at the drawing, I renew my comment that the source grounding is only seen when the disconnect is closed, since there is no neutral connection to the inverters. I do not see why floating the inverter output (when not operating, because of anti-islanding) should be harmful, but it still might be the motivation.

    Sent from my XT1585 using Tapatalk
    The inverters are SMA sunny tripower, 30KW and do have a neutral. But I do agree that the motivation is likely to do with some (irrational) fear that the inverters will lose their reference to ground and float. Not only do I see that is very imnprobably, but even if it did I dont see that as that big a deal really.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #19
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    Quote Originally Posted by electrofelon View Post
    Here is what the note 11 says:
    "Direct trip. If 480V 1200A circuit breaker is open, trip sent to 13.2KV 1200A VCB."
    1200A at 13.2KV ??? That can't be right.

    (Is this when an RFI becomes a WTF?)

  10. #20
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    Quote Originally Posted by zbang View Post
    1200A at 13.2KV ??? That can't be right.

    (Is this when an RFI becomes a WTF?)
    Why? A 25MVA, 13.2kV Transformer would be about 1100A full load. The system is being supplied by National Grid and this may be a large manufacturing facility supplied off of a 115kV transmission line.

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