Hello all,

I have a specific question in context to the new IEEE 1584-2018 - IEEE Guide for Performing Arc-Flash 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

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

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

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

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.

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://ieee-dataport.org/open-access/arc-flash-ie-and-iarc-calculators" 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

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.

Super !
Have happy holidays too !

Hello,
Was the digging profitable and is there an answer to my question?
Thank you very much for your involvement.

Best regards
Philippe

Thank you for your patience.

After discussing this with various people, the reference to the examples in Annex D that use Iarc-min in the numerator of equations D53, D55 and D57 should be Iarc without the “min� This is consistent with the equations in Clause 4 of the body of 2018 IEEE 1584.

Have a great day!

Hello Jim,
Thanks a lot for your answer.
It's now quite clear and consistent.
We'll be able to finalize our arc flash calculation module in our software.
Best regards
Philippe Aupetit
Trace Software International

Great! Glad to help. Check back here if you have any other questions.

Hi Jim,

I missed this discussion at the time, but stumbled across the issue very recently when using the IEEE DataPort spreadsheet calculators to perform some result validation. I noticed that the Incident Energy and Arc Flash Boundary values calculated via the spreadsheet for the Annex D.1 case, were a little higher than those given in (D.62) and (D.72).

I've since read your advice regarding the (D.53), (D.55) and (D.57) equations. To clarify, am I correct in understanding that...

• the Iarc value which is multiplied by k3 (i.e. the numerator) should be Iarc_Voc and NOT Iarc_Voc_min?
• the Iarc value which is multiplied by k13 should remain as log(Iarc_Voc_min) and NOT log(Iarc_Voc)?
• the above would apply to the (D.63), (D.65) and (D.67) equations for Arc Flash Boundary too?

Is this published in Errata anywhere? It's not mentioned in the official IEEE 1584-2018 Errata document found here.

I think it is important for this information to be published, as the Annex D examples are the only means of correctly interpreting how to apply the Iarc_min values to the Clause 4 equations: (3), (4), (5), (7), (8) and (9).

I think that Clause 4 would benefit from this interpretation being made more explicit too.

Many thanks,
Clive