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    solar farm transformer grounding

    I guess this can be in grounding and bonding forum but since I have solar panels I placed here. We are still in NEC 2014 so please only references from NEC 2014.

    I have solar farm in which CPS SCH125KTL-DO/US-600 inverters are being used. The outputs of inverters is 600VAC goes to 600V, 3000A, switchboard which is service rated, has 3000A main breaker and is grounded. The switchboard feeds 600V wye to 13.2kV wye 2000kVA bio oil filled transformer. The output of transformer 13.2kV side feeds utility switchboard.

    My questions are following:

    1. Does NEC 2014 talk about medium voltage transformer 600VAC wye to 13.2kV wye grounding and bonding and if so then which section and article?
    2. Does both the 600 VAC wye and 13.2kV wye have to be grounded?
    3. Does system bonding jumper be at which side 600VAC or 13.2kV side for solar panels?
    4. The 3000A, 600VAC switchboard should it be service rated with grounding?

    #2
    Is this a utility or customer transformer? Where is the service point?

    See 250.30 for grounding SDS's

    See 250.20 for systems required to be grounded.

    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

    Comment


      #3
      2000kVA transformer is customer owned. Would both wyes have to be grounded? How does that work?

      Comment


        #4
        Usually the primary and secondary wyes are bonded and grounded. I would guess the MV system is a MGN but ask the POCO what kind of system it is. The NEC addresses MGN's .See part x of article 250, I believe 250.184.
        Ethan Brush - East West Electric. NY, WA. MA

        "You can't generalize"

        Comment


          #5
          Originally posted by hhsting View Post
          I guess this can be in grounding and bonding forum but since I have solar panels I placed here. We are still in NEC 2014 so please only references from NEC 2014.

          I have solar farm in which CPS SCH125KTL-DO/US-600 inverters are being used. The outputs of inverters is 600VAC goes to 600V, 3000A, switchboard which is service rated, has 3000A main breaker and is grounded. The switchboard feeds 600V wye to 13.2kV wye 2000kVA bio oil filled transformer. The output of transformer 13.2kV side feeds utility switchboard.

          My questions are following:
          1. Does NEC 2014 talk about medium voltage transformer 600VAC wye to 13.2kV wye grounding and bonding and if so then which section and article?
          NEC 250.20. Grounding is not specific to transformer wiring.

          2. Does both the 600 VAC wye and 13.2kV wye have to be grounded?
          At these voltages neither has to be grounded, 250.20(B) & (C). An ungrounded system will require ground fault detection.

          3. Does system bonding jumper be at which side 600VAC or 13.2kV side for solar panels?
          Since the 600V side goes to the PV inverters and there is a neutral it could be bonded at the transformer. If the 3000A SWBD was 4 wire run the neutral there and then you can bond at the transformer, at the SWBD, or at both. Or it can be an ungrounded AC system, what does the inverter require?

          What happens on the 13.2kV side is what the POCO wants. It can be grounded or ungrounded. Typically the only reason to have a WYE on the utility side is if the utility requires it and they would also require a specific grounding setup. If a why is not required WYE would you want to use one?

          4. The 3000A, 600VAC switchboard should it be service rated with grounding?
          Not required if that is not the service entrance. I'm kind of getting the feeling the service entrance is at MV.

          Comment


            #6
            One more comment for the OP's #2 and #3: Note that when a system is connected to the primary of a transformer, you dont choose to ground a conductor. That decision has already been made and you have to stick with that scheme. If it is ungrounded, you wouldn't try to be the decider and ground a conductor. If it is grounded, it is already grounded and you wouldnt ground it again.....unless it is a MV MGN system where in fact you would be required to "ground it again". See 250.184(C).
            Ethan Brush - East West Electric. NY, WA. MA

            "You can't generalize"

            Comment


              #7
              Originally posted by electrofelon View Post
              One more comment for the OP's #2 and #3: Note that when a system is connected to the primary of a transformer, you dont choose to ground a conductor. That decision has already been made and you have to stick with that scheme. If it is ungrounded, you wouldn't try to be the decider and ground a conductor. If it is grounded, it is already grounded and you wouldnt ground it again.....unless it is a MV MGN system where in fact you would be required to "ground it again". See 250.184(C).
              One question NEC 2014 Article 250.184(C) MGN can their be any EGC run from service disconnect or everything is grounded and bonded thru neutral only?

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