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DC Arc Flash Incident Energy Calculations

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    DC Arc Flash Incident Energy Calculations

    I realize there isn't a lot of official information out there on DC arc flash, and the latest IEEE-1584 does not yet officially address it either, I am just hoping there are some users here who can share their experience and see if my calculations at least make sense. This is my first attempt at doing DC arc flash calculations, and work will be done on the DC bus when it is not powered, but I would like to know if these numbers sound reasonable. I am using ETAP 19, which has DC calculations built in now.

    What I have is a 250VDC bus, it is powered by a 400A Battery Charger, which is also constantly keeping a 116 Cell Battery charged at all times in case the charger goes down, in which case a switch closes and the battery will be able to power the bus. The 400A Battery Charger is fed from a 600VAC bus.

    When running the Arc Flash scenario as a normal setup, the IE on the 250V Bus is about 60cal/cm2. When disconnecting the battery from the charger and only having the Battery Charger on and powering the bus, the IE drops all the way down to about 6.5. Ignoring the specifics of the values, does it seem reasonable that just by disconnecting the battery the IE level would drop by a factor of 10? I have worked with AC systems almost exclusively, so the DC side is relatively new to me. It doesn't seem completely reasonable to me that the difference would be so much when the battery isn't even supplying power to the bus under normal conditions and is only there as a backup. If this does make sense, can anyone help with explaining maybe how a DC system such as this works and why the difference in supplied IE is so high from the battery but not the charger?

    #2
    See NFPA 70E Appendix D for a description of various DC AF calculations methods.
    What you describe makes sense since the charger has very limited ability to contribute instantaneous energy and the batteries can contribute almost infinity for a very short period of time.
    https://www.lamarchemfg.com/info/cha...rc-flashl.html
    and
    https://www.cedengineering.com/userf...%20Systems.pdf
    Last edited by ron; 09-16-19, 01:00 PM.
    Ron

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      #3
      See some of the Battcon articles. The engineering equations are theoretical and grossly overestimate it by 2 to 10 times.’240 V is just barely sustainable.

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        #4
        Thanks so much guys I read up on what you provided and I have a much better understanding now

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