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1000 second clearing time

Discussion in 'System Modeling and Calculations' started by deprico, Feb 9, 2009.

  1. deprico Member

    Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?
    deprico, Feb 9, 2009
    #1

  2. jghrist Well-Known Member

    Rated current on a 700 kVA (odd size!) transformer is 842A at 480V. The fault current is not reasonable.
    jghrist, Feb 9, 2009
    #2

  3. haze10 Well-Known Member

    1600A MCB is a bit oversized. Does it have a rating plug by which you can change the trip value. A trip value of 1200 or even 1000 amps would shift your trip curve. Even without this, your transformer should be 5 to 6% impedance, which means your fault current should be 15,000 amps. With a finite bus around 10 to 12 thousand amps. So you have something wrong.
    haze10, Feb 10, 2009
    #3

  4. jghrist Well-Known Member

    Maybe the software is looking at the incident energy on the line side of the MCB and is reporting the current in a protective device on the primary of the transformer.
    jghrist, Feb 10, 2009
    #4

  5. Gary B Well-Known Member

    If the software is saying 350A fault, I assume there is a length of feeder cable that should be protected by a small circuit breaker. I suspect you are missing a circuit breaker from your study (just guessing).

    Gary B
    Gary B, Feb 26, 2009
    #5

  6. JPEG New Member

    Deprico: If you're using Easypower, jghrist found your problem. That's just how it presents the results.

    See the report «Upstream Trip Device Name».
    JPEG, Feb 27, 2009
    #6

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