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 Post subject: Mistake in IEEE 1584:2018 Annex D Example?Posted: Mon Feb 14, 2022 6:13 pm

Joined: Mon Feb 14, 2022 5:48 pm
Posts: 1
Hi All,

Is there a mistake in the IEEE 1584:2018 Annex D example for medium voltage? The results don't appear correct when calculating the Incident Energy and Arc Flash boundary using the reduced arcing currents (Step 11 and Step 13).

For example, if using the formulas shown as per Annex D, consider the following example which is just inside the 0.6 to 2.7kV Voltage band.

Quote:
Three-phase system voltage Voc = 0.601 kV AC (rms)
Three-phase bolted fault current Ibf = 15 kA (symm rms)
Working distance D = 457.2 mm
Electrode Configuration = VCB Vertical in Box
Enclosure Height = 508 mm
Enclosure Width = 508 mm
Enclosure Depth = 508 mm
Gap between conductors (electrodes) G = 32 mm
Arcing Time Iarc =200 ms
Arcing Time for Iarc_min = 200 ms

Results are calculated as follows:
Quote:
Arcing Current Iarc =12.260 kA
Incident Energy = 6.09 cal/cm2
Arc Flash Boundary = 1264 mm
Reduced Arcing Current Iarc_min = 10.826 kA
Reduced Arcing Current Incident Energy = 3.80 cal/cm2
Reduced Arcing Current Arc Flash Boundary = 941 mm

But then re-run the calculation at 0.6kV level (just 1V less) using the <=600V formulas, and the reduced arcing current incident energy and boundary increase significantly:

Results are calculated as follows:
Quote:
Arcing Current Iarc =12.259 kA - Makes sense - slightly less.
Incident Energy = 6.09 cal/cm2 - Makes sense - basically the same
Arc Flash Boundary = 1264 mm - Makes sense - basically the same
Reduced Arcing Current Iarc_min = 10.825 kA - Makes sense - slightly less
Reduced Arcing Current Incident Energy = 5.41 cal/cm2 - much larger incident than compared to using 601V value
Reduced Arcing Current Arc Flash Boundary = 1173 mm - much larger incident than compared to using 601V value

So, if the medium voltage equations in step 11 and 13 are modified to use (k3 x Iarc_600) instead of (k3 x Iarc_600_min) - and likewise for the other intermediate values. The medium voltage results start to look much more normal.
E.g. Re-running the original 0.601V example with these modified intermediate incident energy and arc flash boundary formulas, it yields the following results:
Quote:
Arcing Current Iarc =12.260 kA
Incident Energy = 6.09 cal/cm2
Arc Flash Boundary = 1264 mm
Reduced Arcing Current Iarc_min = 10.826 kA
Reduced Arcing Current Incident Energy = 5.41 cal/cm2 - aligns with 600V example
Reduced Arcing Current Arc Flash Boundary = 1173 mm - aligns with 600V example

So is there a mistake in the formulas in Annex D?

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 Post subject: Re: Mistake in IEEE 1584:2018 Annex D Example?Posted: Wed Mar 02, 2022 12:42 am
 Sparks Level

Joined: Mon Jul 09, 2007 11:43 pm
Posts: 62
Location: Sheffield, England
Yes, I came to the same conclusions as you have some time ago. The fact is that the last time that I checked, which is some months ago now, at least one of the mainstream software manufacturers were interpreting the formulae for >601 volts literally which would lead to the same results that you have experienced. It is of course, up to the IEEE to acknowledge the anomaly and put it right. That being the case, you are correct and the 4.16kV Annexe D example is a mistake.

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