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balajisuguna

Post subject: IEEE 15842018  Annex D Posted: Fri Jan 18, 2019 12:04 pm 

Joined: Fri Jan 18, 2019 11:47 am Posts: 2

Hello all,
I have a specific question in context to the new IEEE 15842018  IEEE Guide for Performing ArcFlash Hazard Calculations’ standard.
There are a couple of equations in Appendix  D, equation numbers "(D.101)" and "(D.104)" in pdf page number 74.
In both these equations (D.101 and D.104), they specify a term 'k3*Iarc_600' in the numerator and calculated the final values with respect to it, whereas I believe that it should actually be calculated with respect to "k3*Iarc_600_min".
If someone, who has already looked into the standard or willing to look into it now, comment on my understanding, it will be very useful.
Regards, Balaji Prabhakaran (MIET)  Senior Power Systems Engineer British Power International
Last edited by wbd on Sat Jan 19, 2019 5:38 am, edited 1 time in total. 
removed personal contact info 


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Jim Phillips (brainfiller)

Post subject: Re: IEEE 15842018  Annex D Posted: Sun Jan 20, 2019 3:48 pm 

Plasma Level 

Joined: Mon Sep 17, 2007 5:00 pm Posts: 1543 Location: Scottsdale, Arizona

The 2018 Edition of IEEE 1584 has quite a bit there. Nothing like the 2002 Edition.
D.101 is equation 6 from 4.6 of the standard. D.104 is equation 10 from 4.7 of the standard.
I hope that helps clarify a bit.
Best Regards, Jim


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balajisuguna

Post subject: Re: IEEE 15842018  Annex D Posted: Tue Jan 22, 2019 3:37 am 

Joined: Fri Jan 18, 2019 11:47 am Posts: 2

Hello Jim,
Thanks very much for your response.
However, 4.6 mentions about a general equation '(6)' that must be used for both intermediate and minimum 'E' calculation. However, '(D.101)' is specific to calculating minimum 'E' and hence you will notice 'K13*log(Iarc_min)' used in '(D.101)' in the place of 'K13*lg*Iarc' in equation '(6)'. Therefore, I still believe that it should actually be calculated with respect to "k3*Iarc_600_min".
Please comment/clarify.
Regards, Balaji Prabhakaran (MIET)  Senior Power Systems Engineer British Power International
_________________ Let Peace Be! Balaji


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Ph. Aupetit

Post subject: Re: IEEE 15842018  Annex D Posted: Thu Nov 26, 2020 3:34 am 

Joined: Thu Nov 26, 2020 2:45 am Posts: 4

Hello all,
I am developing an arc flash calculator and I have the same question as Balaji: Why in equation D101, "k3*Iarc_600" is used in place of "k3*Iarc_600_min" which is not complying with the title of Step 10 "Repeat Step 4 using the reduced arcing current"? Thanks for your answer. Regards Philippe Aupetit


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Jim Phillips (brainfiller)

Post subject: Re: IEEE 15842018  Annex D Posted: Sun Nov 29, 2020 4:27 pm 

Plasma Level 

Joined: Mon Sep 17, 2007 5:00 pm Posts: 1543 Location: Scottsdale, Arizona

For less than 600 volts, Iarc600 is used in the numerator of BOTH the 100 percent arcing current and the minimum arcing current (multiplying times k3)
The adjustment to the specific voltage is accounted for with Iarc for 100% and Iarc_min for minimum. Where both are at the specific nominal voltage (Voc)
This is quite different than the medium voltage solution where you calculated everything at two voltages (often 2.7 and 14.3 kV) and interpolate between the two values.


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Ph. Aupetit

Post subject: Re: IEEE 15842018  Annex D Posted: Tue Dec 01, 2020 4:09 am 

Joined: Thu Nov 26, 2020 2:45 am Posts: 4

Hello Jim, Thank you very much for your quick answer. I understood the need to use Iarc600 in the numerator for the calculation of IE and AFD for both the 100% arcing current and the reduced arcing current when Voc ≤ 600 V.
But this leads me to ask another question: Why use, as in the D1 example, the currents Iarc_600/2700/14300_min in this same numerator for the calculation of IE and AFD with the reduced arcing current?
Let's take an example:
Let's use the same system as in the D2 example but with a Voc=600 V. For the reduced arcing current (28.65 kA), with the equations D101 and D104 we find (keeping T=319 ms) IE=14.34 cal/cm2 and AFB=2879 mm.
Let's repeat the same example with a Voc=601 V. The equations D53, D55, D57 of the D1 example must then be used. It is then found (keeping T=319 ms) Iarc_min=28.66 kA, IE=9.95 cal/cm2 and AFB=2290 mm.
So for a Voc variation of 1 V, IE drops 30% and AFB drops 20% which does not seem to me very consistent.
If we replace in the equations D53, D55, D57 the numerator values Iarc_600/2700/14300_min per Iarc_600/2700/14300, then we get the following results: Iarc_min=28.66 kA, IE=14.35 cal/cm2 and AFB=2880 mm, which is more consistent.
On the other hand, if we redo the D1 example by replacing the numerator value Iarc_600/2700/14300_min by Iarc_600/2700/14300 for equations D53, D55, D57 the results become IE=3.21 cal/cm2 (instead of 3.19) and AFB=1712 mm (instead of 1704). The difference is small, which is normal since the influence of the reduced arcing current decreases as the voltage increases.
It should also be noted that the Excel calculator available on the "https://ieeedataport.org/openaccess/arcflashieandiarccalculators" website uses the numerator value Iarc_600/2700/14300 for the equations D53, D55, D57.
Do you not think that a clarification would be useful on this problem? This may be important in Europe where 690V voltage is commonly used in industrial facilities and where the use of the numerator value Iarc_600/2700/14300_min in equations D53, D55, D57 could lead to calculated values of IE and AFB underestimated in relation to reality.
At your disposal to discuss it more precisely if necessary. Regards Philippe


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Ph. Aupetit

Post subject: Re: IEEE 15842018  Annex D Posted: Mon Dec 21, 2020 2:46 am 

Joined: Thu Nov 26, 2020 2:45 am Posts: 4

No comment on my previous post ???


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Jim Phillips (brainfiller)

Post subject: Re: IEEE 15842018  Annex D Posted: Tue Dec 22, 2020 10:18 am 

Plasma Level 

Joined: Mon Sep 17, 2007 5:00 pm Posts: 1543 Location: Scottsdale, Arizona

Ph. Aupetit wrote: No comment on my previous post ??? I've been digging into this and have several people involved. We should have a response after the holidays since most are winding down now (me included). Happy Holidays.


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Ph. Aupetit

Post subject: Re: IEEE 15842018  Annex D Posted: Tue Dec 22, 2020 10:23 am 

Joined: Thu Nov 26, 2020 2:45 am Posts: 4

Super ! Have happy holidays too !


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