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 Post subject: Minimum E higher than maximum E for equal clearing times HVPosted: Sat Nov 02, 2019 9:11 am

Joined: Sat Nov 02, 2019 8:42 am
Posts: 4
Hi guys!

Thanks for an excellent forum to discuss! It's good to see that it's not only me who's struggling wiht the peculiarities of the arc-flash art.

I've chrushed some numbers with the new IEEE 1584-2018 standard, and I get the exact results as the Annex D sample calculations.

However, it seems that when the voltage is increased to e.g. 11 kV and the clearing time for the minimum calculation is equal to the clearing time of the maximum calculation then the minimum calculation gives the highest incident energy, which doesn't make sense.

I've tried to "smoke out" a possible error in my calculation, but honestly can't find it. I'm starting to suspect that this may be a peculiarity with the new 2018-standard. It would be useful to check if any of you other guys get the same result with other software or hand calculation.

Here are my numbers (basically the IEEE 4.16 kV example with voltage adjusted to 11 kV and 197 ms clearing time for both minimum and maximum):

Input data:
Ik = 15 kA
Electrode config.: VCB
G = 104 mm
V_OC = 11 kV
Height = 1143 mm
Width = 762 mm
Depth = 762 mm (although this value is N/A)
Clearing time max current = 197 ms
Clearing time min current = 197 ms

Intermediate results:
E600 max: 8.596 J/cm2
E600 min: 8.204 J/cm2
E2700 max: 11.899 J/cm2
E2700 min: 11.642 J/cm2
E14300 max: 13.280 J/cm2
E14300 min: 13.502 J/cm2

E1 max: 24.953 J/cm2
E1 min: 25.232 J/cm2
E2 max: 12.887 J/cm2
E2 min: 12.973 J/cm2
E3 max: -34.802 J/cm2
E3 min: -35.479 J/cm2

End result:
Max: 12.887 J/cm2
Min: 12.973 J/cm2

Any feedback would be much appreciated! Thanks!

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 Post subject: Re: Minimum E higher than maximum E for equal clearing timesPosted: Sat Nov 02, 2019 12:59 pm
 Sparks Level

Joined: Wed Jun 10, 2009 5:00 pm
Posts: 267
Location: Toronto
what working distance are your calcs based on?

_________________
Michael Furtak, C.E.T.

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 Post subject: Re: Minimum E higher than maximum E for equal clearing timesPosted: Sun Nov 03, 2019 12:38 pm

Joined: Sat Nov 02, 2019 8:42 am
Posts: 4
Oh, sorry, I forgot to list that...

Working distance 914.4 mm

Thanks!

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 Post subject: Re: Minimum E higher than maximum E for equal clearing timesPosted: Sun Nov 03, 2019 7:01 pm
 Sparks Level

Joined: Wed Jun 10, 2009 5:00 pm
Posts: 267
Location: Toronto
electrical-bbq wrote:
Oh, sorry, I forgot to list that...

Working distance 914.4 mm

Thanks!

Indeed I get same results by using ARCAD universal arc flash analysis app as well as Arc Flash Analytic software program (see screenshots below). For all practical means and purpose the observed minimum and maximum incident energies in this case scenario are equal so I wouldn't worry much about the reported discrepancy.

_________________
Michael Furtak, C.E.T.

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 Post subject: Re: Minimum E higher than maximum E for equal clearing timesPosted: Sat Nov 09, 2019 8:04 am

Joined: Sat Nov 02, 2019 8:42 am
Posts: 4
Excellent, thanks arcad! Good to see that the results match. I agree that the discrepancy is practically negligible

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