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Sub Boards or Incomer??

tonydon

Hi

We have a large commercial site fed by 2 onsite substations…

The substations feed panel boards in our side of the subs  i.e. Incomer

The panel boards then feed sub boards within the site, some of which will feed other downstream boards

Our questions are (for condition reporting)

  1. section i… Is the supply characteristic always referring to the incoming supply
  2. when testing a board is the supply protective device the supply feeding this particular board i.e. potentially an mcb in another upstream board that supply's this board … or  is the supply protective device the device on the incoming supply to the site  i.e this will then be the device listed on each board (the same throughout the site)
  3. Is the supply characteristic the supply to the whole site or the supply to just this board
  4. the ZE cannot be reasonably ascertained by test,  but, we also cannot get our supplier to give us this reading by inquiry  What should we do?

 

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    If distances are short, then you may be able to use the rating plate on the transformer, and maybe add a small correction for the length of cable to it .

    You can assume for PSSC that for example a 5% 1MW transformer droops 100% at 20MW, and that that associated current per phase would define the Zs at the terminals.

    In a complex nested system and this sounds like it is, you may be better reporting Zdb at each board, so Zdb 1 is the Zs reading taken at the main switch of board 1. 

    mike

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  • 0

    If distances are short, then you may be able to use the rating plate on the transformer, and maybe add a small correction for the length of cable to it .

    You can assume for PSSC that for example a 5% 1MW transformer droops 100% at 20MW, and that that associated current per phase would define the Zs at the terminals.

    In a complex nested system and this sounds like it is, you may be better reporting Zdb at each board, so Zdb 1 is the Zs reading taken at the main switch of board 1. 

    mike

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