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Can electrical curents flow from generator to transformer

  1. Aug 5, 2009 #1
    Hi, got a doubt this mng, when I heard the power will be shutdown in my office tomorrow to repair a faulty circuit b/w transformer and my office.


    when the transformer is shutdown, and generator/ups/battery is used to keep the power supply to critical components, will the current flow into transformer circuit?
     
  2. jcsd
  3. Aug 5, 2009 #2

    russ_watters

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    Staff: Mentor

    Depends on what transformer you're talking about, but I suspect there is a an autotransfer switch between the main building transformer or utility transformer (if there is one) and the main switchgear that switches between utility power and generator power.

    Often, utility power comes in at 480 V (or higher) and is stepped-down to 208/120 after the main switchgear, so that transformer would likely still be powered by a generator.
     
  4. Aug 5, 2009 #3

    negitron

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    I think he's talking about an on-site generator that supplies the building with power when the mains goes offline. That being the case, it should have a transfer switch which keeps the generator from backfeeding the utility supply transformer. This is why you should never plug a generator straight into an outlet to supply backup power--although you can open the main breaker to keep from backfeeding the utility, all it takes is one moment of carelessness to put the lives of utility workers at risk. Have your home backup generators properly wired with a transfer switch!
     
  5. Aug 5, 2009 #4

    russ_watters

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    That's what I was talking about...maybe i wasn't clear.
     
  6. Aug 5, 2009 #5
    Backup power from UPS/battery and generators can (depending on backup) come on in less than 1 power cycle, and as pointed out in an earlier post, disconnects the mains. The other problem is what happens when the mains power comes back on. Ideally, the backup power should synchronize phase with the mains before the mains are smoothly connected; otherwise ther could be a reactive power surge. Many small battery/UPS systems can do this seemlessly, but I don't know how or whether big diesel/electric standby generators do this.
     
    Last edited: Aug 5, 2009
  7. Aug 6, 2009 #6
    thanks everyone....i got what i was looking for. :approve:
     
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