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SKM PTW Miscoordination

Discussion in 'Software for Arc Flash Studies' started by ZeroSeq, Feb 2, 2009.

  1. ZeroSeq Member

    Miscoordination is not necessarily a bad thing.

    I struggled to eliminate miscoordination errors from my Arc Flash Studies until I spoke with Jim Babcock at SKM. Jim teaches their Arc Flash seminars.

    Traditional protective relay studies are based on Isc, three phase bolted fault currents. In reality most real life faults are less than Isc, especially arcing faults. IEEE 1584 uses 85% of Isc. NFPA 70E uses 38% of Isc.

    What the "(*N5) Miscoordination, Upstream Device Tripped" message indicates is that an upstream device (fuse or relay/CB combination) interrupts the fault before the device closest to the faulted bus. That's good, compared to not clearing the fault at all. It's a situation you may want to address with your protective relay specialist. There may not be a perfect solution that properly protects for both Isc and arcing faults.
    ZeroSeq, Feb 2, 2009
    #1

  2. Noah Member

    Thanks for sharing!
    Noah, Feb 5, 2009
    #2

  3. Gary B Well-Known Member

    Nice to have a reality check.

    Because we are calculation for worse case exposure it is compelling to get swept up in worse case fault thinking which may not be realistic.
    Gary B, Feb 5, 2009
    #3

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