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Machine Riddle No.18 – Generator induced or stray voltage

  • Creator
  • #276

      We have a generator feeding into an incomer, along a distance of about 15m. during ac pressure tests it was fine, all the phases and neutral were tied down to earth, and each one was tested individually.
      Now we have come to power the generators up, we are doing one phase at a time to assure red is red, blue is blue etc through out the system. here we find that when even both sides are disconnected from the generator and the board on say yellow and blue phase and red phases has 11kv on it, about 6.2kv to earth, we find yellow has 4kv and blue has 2kv. we tried different phases it’s about the same.
      will it harm the system and how to get rid of it!

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    • Author
    • #1534

        Please more explain, what is your mean when you say “both sides are disconnected from the generator”, whether your means is the line and neutral disconnection from generator? Where locations have 4 and 2 kV induced voltage? Switchgear buses or generator terminal?

        atiqun nabi

          if i am testing the red phase , i have yellow and blue disconnected at the generator side, but connected to the switchgear buses.


            Ok, I think you front the electrical field coupling phenomenon in step down switchgear. Some high voltage indicator voltage with capacitors can provide that mentioned coupling. Indeed you front the feed-back voltage on disconnected phase via connected phase and load indicator capacitors as shown below. For override that induced capacitive voltage you can remove relevant indicator in switchboard panel.

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