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Thread: 4160 Delta Secondary Grounded or Ungrounded

  1. #31
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    Quote Originally Posted by Wire-Smith View Post
    you've never seen a three phase transformer that you can configure the primary anyway you want? i know there not as common as they used to be.
    Well yes, but they are not intended to be changed as the voltage would change and it would be useless..
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by electrofelon View Post
    Well yes, but they are not intended to be changed as the voltage would change and it would be useless..


    i think your looking at what i'm asking different than what i mean by it. i'm asking if it is really wye(configured primary) delta transformer or if he is just calling it wye delta because he has 208.

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    Quote Originally Posted by Wire-Smith View Post

    i think your looking at what i'm asking different than what i mean by it. i'm asking if it is really wye(configured primary) delta transformer or if he is just calling it wye delta because he has 208.
    Nope the primary is definitely Wye as stated in the OP.

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    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    finally found what i was thinking of

    https://www.eng-tips.com/viewthread.cfm?qid=431498

    waross (Electrical)25 Oct 17 04:02History, not speculation.
    Back one hundred or so years ago, delta:delta transformer banks were the norm.
    After WWII when the use of electricity started to increase greatly many utilities gained a cheap and easy 1.73 increase in distribution line capacity by switching the delta:delta systems to wye:delta. The voltage was often increased from 2300 Volts to 4160 Volts.
    It was found that the wye:delta bank had some serious issues. Overheating and failing due to circulating crrents, and back-feeding into a fault were two issues. Also a ground fault on one phase of the distribution circuit would be back-fed by the wye:delta bank. This could result in the blowing of one of the fuses on the wye:delta bank.
    It was found that these problems could be avoided by floating the primary wye point.
    Leaving the wye point floating eliminated the issues with circulating currents, back-feeding and blown fuses.
    A new issue arose. Over-voltage transients when the bank was energized.
    The solution to this was to connect the wye point to the neutral before energizing the transformer bank. Once the bank was energized, the connection from the wye point to the neutral was opened.
    That is why you occasionally see a wye delta bank with an open fused cut-out or a switch to connect the wye point to the neutral.
    Closed to energize and then opened and left open.
    By the way, I spent over 15 years in a country where the wye:delta connection was popular and I am familiar with most of the issues with wye:delta transformer banks.
    Another issue when a residential circuit had one or more wye:delta banks was the frequent failure of residential refrigerators and freezers.
    I served as system engineer for a small utility for a number of years. It took about three years to get all of the wye delta banks on our system changed over from wye:delta to wye:wye.
    The accepted connection for a wye delta bank is with a floating wye point.
    Been there, done that and got the tee shirt.



  5. #35
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    Quote Originally Posted by Wire-Smith View Post
    finally found what i was thinking of

    https://www.eng-tips.com/viewthread.cfm?qid=431498

    waross (Electrical)25 Oct 17 04:02History, not speculation.
    Back one hundred or so years ago, delta:delta transformer banks were the norm.
    After WWII when the use of electricity started to increase greatly many utilities gained a cheap and easy 1.73 increase in distribution line capacity by switching the delta:delta systems to wye:delta. The voltage was often increased from 2300 Volts to 4160 Volts.
    It was found that the wye:delta bank had some serious issues. Overheating and failing due to circulating crrents, and back-feeding into a fault were two issues. Also a ground fault on one phase of the distribution circuit would be back-fed by the wye:delta bank. This could result in the blowing of one of the fuses on the wye:delta bank.
    It was found that these problems could be avoided by floating the primary wye point.
    Leaving the wye point floating eliminated the issues with circulating currents, back-feeding and blown fuses.
    A new issue arose. Over-voltage transients when the bank was energized.
    The solution to this was to connect the wye point to the neutral before energizing the transformer bank. Once the bank was energized, the connection from the wye point to the neutral was opened.
    That is why you occasionally see a wye delta bank with an open fused cut-out or a switch to connect the wye point to the neutral.
    Closed to energize and then opened and left open.
    By the way, I spent over 15 years in a country where the wye:delta connection was popular and I am familiar with most of the issues with wye:delta transformer banks.
    Another issue when a residential circuit had one or more wye:delta banks was the frequent failure of residential refrigerators and freezers.
    I served as system engineer for a small utility for a number of years. It took about three years to get all of the wye delta banks on our system changed over from wye:delta to wye:wye.
    The accepted connection for a wye delta bank is with a floating wye point.
    Been there, done that and got the tee shirt.


    interesting, thank you. I am very interested in transmission and distribution history. I am familiar with the "trick" of changing to wye systems and feeding things L-N instead of L-L to up capacity. That explains why many distribution voltages are multiples of root 3. Although capacity increase may have been the original reason to go wye, I think now it is preferred because in conjuction with MGN, it is a little cheaper. I think also it has to do with our often illogical obsession with grounding.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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