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 Post subject: Impedance Tx Grounding-SKM Arc Flash Study Effects
PostPosted: Tue Apr 13, 2021 8:24 pm 
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Joined: Tue Sep 03, 2019 4:08 pm
Posts: 1
I am currently taking Jim's Arc Flash class via the On-Line video's; and the class is excellent and well worth the $ 495.
One of the early lectures talks about how impedance grounding limits the single-phase to ground fault current, and therefore limits the arc flash incident energy. I had an past SKM study and I added impedance grounding to the delta-wye transformer, and the SKM study DID NOT show lower arc flash incident energies. I assume this is based on the arc flash study being based on the 3-phase fault current, which would not be affected by the impedance grounding of the transformer.

Does anyone have any ideas on how to show the affects of impedance grounding in an Arc Flash study, or using SKM software, or other software?

Thanks,
Gabe Paoletti, P.E.
Paoletti Engineering PLLC


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 Post subject: Re: Impedance Tx Grounding-SKM Arc Flash Study Effects
PostPosted: Sat Apr 17, 2021 3:12 pm 
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Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1620
Location: Scottsdale, Arizona
Thanks for your kind comments about the On Demand Arc Flash / IEEE 1584 Class

The IEEE 1584 incident energy equations are based on a three phase arc flash so the direct effect of impedance grounding would not be seen. Here are a few points regarding impedance grounding and arc flash.

- Most faults originate as L-G so with impedance grounding it would limit the current and incident energy and not escalate into a three phase event. i.e. it would stop a large number of faults from becoming a three phase arc flash.

- Since IEEE 1584 is based on three phase arc flash, modeling single phase is not addressed and impedance grounding is not an issue in the calculations.

- The 2002 Edition of IEEE 1584 equations gave slightly different results for the three phase incident energy depending on whether the system was grounded or ungrounded/impedance grounded

- The 2018 IEEE 1584 equations did away with that difference. It had to do with the erratic nature of the arc during initiation which was filtered out be removing 2 cycles.

Hope that helps!


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