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4160 Delta Secondary Grounded or Ungrounded

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    4160 Delta Secondary Grounded or Ungrounded

    We have several 3Ø, 208-4160 WYE/Delta step-up transformers. How are these typically grounded, corner ground or are they typically installed as an ungrounded Delta?
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

    #2
    Bump, have I finally stumped the engineers on this forum?
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

    Comment


      #3
      Originally posted by infinity View Post
      Bump, have I finally stumped the engineers on this forum?
      I’ve never seen this before nor have I researched it - but why couldn’t you do either or? Personally I think you’d be better off with a corner grounded delta; at least you’d have reference point - plus we rarely see ungrounded deltas these days.


      Sent from my iPhone using Tapatalk

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        #4
        IMHO a lot depends on whether the voltage will be stepped back down again after a long run (motivation was VD) or whether the 4160 will be utilization voltage for equipment (and if so, what kind.)

        If just a distribution run to step-down transformer, the risk of high voltage to ground caused by restriking arc fault may not be catastrophic. But no disadvantage to corner grounding either.
        If run to utilization equipment, unless it is an industrial process where unplanned shutdown is problematic, I would avoid ungrounded operation.
        Would the difference in max line to ground voltage be a safety issue for your environment?

        Comment


          #5
          The service voltage of 208Y/120 is stepped up to 4160 and then run vertically up through the building where it is stepped back down to 208Y/120. Right now the design calls for a ungrounded Delta, I was just wondering if ungrounded is the typical set up for these types of systems.
          Rob

          Moderator

          All responses based on the 2017 NEC unless otherwise noted

          Comment


            #6
            weird set-up

            why not take the service at 4160 wye?
            how many floors?
            how many 208 taps/xfmrs?

            Comment


              #7
              There are 4-4000 amp services in the building all 208Y/120. There are about 10-208 to 4160 step up and another 10-4160 to 208y/120 step down tranformers, all step ups are setup as ungrounded. The step ups are Wye/Delta and the step downs are Delta/Wye.
              Rob

              Moderator

              All responses based on the 2017 NEC unless otherwise noted

              Comment


                #8
                Originally posted by infinity View Post
                There are 4-4000 amp services in the building all 208Y/120. There are about 10-208 to 4160 step up and another 10-4160 to 208y/120 step down tranformers, all step ups are setup as ungrounded. The step ups are Wye/Delta and the step downs are Delta/Wye.
                Wow
                Ethan Brush - East West Electric. NY, WA. MA

                "You can't generalize"

                Comment


                  #9
                  I think ungrounded would be fine. You already have ungrounded stuff there, keeps it all the same. Also it sounds like there will be people maintaining this stuff that know what they are doing. Finally, regarding the potential over voltage issue from restriking faults, I would think pretty much everything you would install nowadays would be 15KV class so you have plenty of headroom if something along those lines were to happen.
                  Ethan Brush - East West Electric. NY, WA. MA

                  "You can't generalize"

                  Comment


                    #10
                    Originally posted by infinity View Post
                    We have several 3Ø, 208-4160 WYE/Delta step-up transformers. How are these typically grounded, corner ground or are they typically installed as an ungrounded Delta?
                    250.20(C) permits such systems to be grounded, but does not require them to be grounded.

                    (C) Alternating-Current Systems of over 1000 Volts.
                    Alternating-current systems supplying mobile or portable
                    equipment shall be grounded as specified in 250.188. Where
                    supplying other than mobile or portable equipment, such
                    systems shall be permitted to be grounded.

                    Comment


                      #11
                      In years gone past, I used to recommend that delta secondaries be ungrounded when they feed a single circuit and corner-grounded when they feed multiple circuits.

                      What are you planning to do for a ground detection scheme? Will you have any protective relaying on the 4160V?
                      Just because you can, doesn't mean you should.

                      Comment


                        #12
                        Originally posted by jim dungar View Post
                        In years gone past, I used to recommend that delta secondaries be ungrounded when they feed a single circuit and corner-grounded when they feed multiple circuits.

                        What are you planning to do for a ground detection scheme? Will you have any protective relaying on the 4160V?
                        The 4160 secondary feeds a fused disconnect and as far as I can see that's it. Is ground detection required?
                        Rob

                        Moderator

                        All responses based on the 2017 NEC unless otherwise noted

                        Comment


                          #13
                          Originally posted by infinity View Post
                          The 4160 secondary feeds a fused disconnect and as far as I can see that's it. Is ground detection required?
                          250.21(B) only requires ground detection for systems operating at 1000 volts or less. I don't see anything in Part X of 250 requiring ground detection for the higher voltage systems.
                          Don, Illinois
                          (All code citations are 2017 unless otherwise noted)

                          Comment


                            #14
                            Originally posted by don_resqcapt19 View Post
                            250.21(B) only requires ground detection for systems operating at 1000 volts or less. I don't see anything in Part X of 250 requiring ground detection for the higher voltage systems.
                            That's what I thought as well, seems to be a design issue not a code issue
                            Rob

                            Moderator

                            All responses based on the 2017 NEC unless otherwise noted

                            Comment


                              #15
                              Originally posted by infinity View Post
                              That's what I thought as well, seems to be a design issue not a code issue
                              You are correct, this is a design choice.

                              One I did like this was for a Scout camp, the MV was run through the woods (buried) and across a river. With all of the 'critters' out there we were concerned a ground fault would not be noticed until it was catastrophic.
                              Just because you can, doesn't mean you should.

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