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 Post subject: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Wed Jan 07, 2015 1:26 pm 

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Does anyone know the Arc Flash energy calculation equation of ARCPRO software


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Wed Jan 07, 2015 1:35 pm 
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If you have the ArcPro program, Appendix B provides an overview of the calculation method and background equations. There are a number of equations such as an energy conservation equation for a vertical arc column, electrical current continuity,arc resistance, etc.

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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Wed Jan 07, 2015 1:50 pm 

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I do not have the software that's why I am wondering about the equation as OSHA only considers ARCPRO for calculating Arc Flash catagory above 15kV system.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Fri Aug 07, 2015 3:18 am 

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abk453 wrote:
I do not have the software that's why I am wondering about the equation as OSHA only considers ARCPRO for calculating Arc Flash catagory above 15kV system.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Fri Aug 07, 2015 11:21 am 
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abk453 wrote:
I do not have the software that's why I am wondering about the equation as OSHA only considers ARCPRO for calculating Arc Flash catagory above 15kV system.


It is proprietary and based on modeling. They do go over the Theorectical Background for ArcPro Calculations in Appendix B of the manual but do not give the actual equations.

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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Sat Aug 15, 2015 4:29 pm 
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There's no testing above 15 kV so it's all guessing and conjecture anyways. If you read that huge justification document from OSHA it spells it out pretty clearly. There are basically only 4 "methods" available above 15 kV:
1. Lee
2. ArcPro
3. Duke heat flux
4. Equations from EPRI
5. NESC tables.

OSHA didn't look at the 4th case. EPRI has been doing some modelling in this area but there's again no actual test work to compare to.

OSHA also didn't really address the NESC tables but I believe that a later letter of interpretation covers this. Since the NESC tables are calculated using ArcPro, the issue is pretty much moot.

At lower voltages where data is available, Lee consistently overpredicts and Duke heat flux underpredicts. Since ArcPro splits the middle, it gets the green light.

Some comments were made as to using a "black box" method. I think the justification was basically that something was better than nothing and since there was already industry support for ArcPro and since there were no valid alternatives, ArcPro got the gold star. OSHA certainly wouldn't argue against using the Lee method because it produces ridiculous values as the voltage increases. But when Duke heat flux consistently underpredicts even against known test data, it can't be accepted.

I'm sure at some point in the future someone will do the test work/research (probably EPRI or CIGRE sponsored) and this will be incorporated into IEEE 1584. Or perhaps at some point some creative hacker will carefully disassemble and reverse-engineer the ArcPro code or at least "black box" test it against enough test conditions to reverse-engineer formulas. Then since the Annexes are only recommendations and not regulatory, OSHA will issue a letter of interpretation and this will settle the matter once and for all. Until then, suck it up and use ArcPro.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Mon Aug 17, 2015 12:53 pm 
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abk453 wrote:
Does anyone know the Arc Flash energy calculation equation of ARCPRO software


I haven't used ARCPRO but I would have reservations against using this program for arc flash calculations. As an example, the program requires arcing current on its input. You have to calculate it somehow before running analysis or make up the number. Any calcs are questionable if input parameters are not accurate.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Tue Aug 18, 2015 8:04 am 
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arcad wrote:
abk453 wrote:
Does anyone know the Arc Flash energy calculation equation of ARCPRO software


I haven't used ARCPRO but I would have reservations against using this program for arc flash calculations. As an example, the program requires arcing current on its input. You have to calculate it somehow before running analysis or make up the number. Any calcs are questionable if input parameters are not accurate.


Above 1kV the arcing current is essentially the bolted fault current as shown by IEEE 1584.

lgIa = 0.00402 + 0.983lgIbf where Ia is arcing current and Ibf bolted fault current.

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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Tue Aug 18, 2015 8:25 am 
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wbd wrote:
Above 1kV the arcing current is essentially the bolted fault current as shown by IEEE 1584. lgIa = 0.00402 + 0.983lgIbf where Ia is arcing current and Ibf bolted fault current.


First of all, the IEEE 1584 formula you mentioned applies to the 3-phase arcing current, not the single phase arcing current required for input in ARCPRO.

Definitely, arcing current is always less than the bolted current due to the introduced arc resistance. As an example, the IEEE 1584 formula predicts 19kA arcing current for 20kA bolted fault current, and the difference becomes even greater when the bolted fault current is increased.

I wonder why doesn't ARCPRO require bolted fault current on its input instead of arcing current if the difference between them was indeed small and negligible?


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Tue Aug 18, 2015 4:42 pm 
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There is a posting from me in the thread below where Stephen Cress from ArcPro discusses the formulas for ArcPro as well as arcing current.

viewtopic.php?f=15&t=3275

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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Tue Aug 18, 2015 5:07 pm 
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I believe you are referring to Stephen's comment that On medium voltage systems it is reasonable to assume that this is equivalent to the bolted current. What may seem reasonable to some is not necessarily seemingly reasonable to others. If the ARCPRO developer is so confident about the assumption, why does the program require the arcing current and not the bolted fault current on its input?

I don't trust undocumented calculation procedures in first place. All the procedures for arc flash analysis I've seen so far (including Lee and IEEE 1584) are documented, except ARCPRO. The ARCPRO is not documented anywhere, hence the program accuracy is questionable at the least. Perhaps, they have a very good reason to hide it from professional scrutiny.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Sun Aug 30, 2015 12:10 pm 
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The same (lack of documentation) is also true with the Duke heat flux calculation. There is some documentation more or less describing it but not exact details. The same is also true of the Wilkins time-domain model which has been considered by the IEEE 1584 working committee to replace the current non-time series model.

ArcPro (and Duke heat flux) predate IEEE 1584. So it's interesting to describe it as something new and unknown when in fact the opposite is true from a historical perspective.

I was in the other camp but when considering ArcPro as the "annointed model", this is my take:
1. Claims about being anti-competitive. Ontario Hydro/Kinetrics developed a theoretical model and sells it. Quite literally at the moment, anyone else can develop a theoretical model and sell it. Duke even gave theirs away, and OSHA even considered it in their analysis. This doesn't stop anyone else from doing the same. In fact although there may be licensing restrictions against doing so, theoretically I can simply treat it as a black box and pull data out until I can reverse engineer a set of empirical equations that duplicate what ArcPro does. In fact that is exactly how IEEE 1584 empirical equations work except that they are empirically matching real world test data instead of being tested against a theoretical model. In effect in IEEE 1584 terms, the "real world" is a black box. So I see nothing wrong with what Kinetrics is selling as far as being "anti-competitive".
2. OSHA endorsement of a commercial product is anti-competitive. At the moment there are no competitors so the argument is pointless. If a competing software program (or academic/white box model) becomes available then there is teeth to the argument because there may be a general consensus that since OSHA has "endorsed" ArcPro, no competing software would be accepted. Careful reading of OSHA's position is that this is informational/guidance and not enforced but right now, there is no viable competitor except Duke and Lee, both of which were rightly rejected. Even if such a product were to emerge, without test data, we can't say that A is better than B. We can't do this above 15 kV right now. So even if such a product were to emerge, whose to say which is right and which is wrong? For all we know, Duke heat flux might turn out to be right (but this is unlikely).
3. Other software vendors "can't" compete. Huh? Can't develop and retail an arc flash program for >=15 kV? Nothing is stopping them except that coders don't spend money on the fundamental research. If they did and ArcPro is really that bad, they could corner the market quickly.

So until the first competitor or actual test data appears, it's kind of hard to argue against ArcPro except on a pure academic basis.

Further, it is VERY common to see CFD models with scant documentation. Usually the very simple fundamentals are described and then how the model goes from local calculations to a global result is done with a lot of hand waving. It drives me nuts in the computational fluids/finite element/finite volume calculations as well, and that's what this one is.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Mon Aug 31, 2015 7:58 am 
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Is there a link to the OSHA quasi recommendation?


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Mon Aug 31, 2015 10:51 am 
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My personal argument against using ARCPRO is that the program comes with serious limitations you only find out about after paying $$$$ and purchasing the program and suer manual. As an example, the program user manual states that "the ARCPRO program calculates the thermal parameters associated with an electric power arc aligned vertically in air. The program does not consider arcs in any other physical configuration, [...]". The use of ARCPRO for estimating the arc hazard immediately becomes an engineer's best guess because situations where we have arcs "aligned vertically in air" are at best very limited.

Also, the fact the ARCPRO calls for arcing current instead of bolted short circuit fault current on its input promoting the assumption that the arcing current is equal to short circuit current is very alarming.

Assumptions may work in some cases but generally and totally fail otherwise. If something can't be quantified and justified than it is not engineering but only a guess.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Tue Sep 01, 2015 6:11 pm 
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Estimating is fundamental to engineering. Digital communications is based on executing algorithms like maximum likelihood estimates to guess what the inputs are.

IEEE 1584 Empirical model is only for open air conditions above 1 kV but we apply it to medium voltage switchgear all the time. It also models everything as specific sized enclosures and is not general purpose with respect to the enclosure but again, nobody is complaining about that. So it's just a guess, too.

ArcPro is pretty up front with the limitations of the system. I knew that before spending money on it. Furthermore, fundamentally there really isn't a lot of difference between vertical and horizontal arcs except that with extended (>12") arc gaps, gravity and convection have influences on the arc path. Not that it matters. We have a luminous arc producing lots of radiant energy and ArcPro models this at least on a theoretical basis that seems to reasonably match reality at voltages where test data exists.

And as to "guessing", the choice is between going with a specific, quantified, KNOWN, well studied answer that is right now a unicorn...it does not exist, and going with the best available information even though it's not quite perfect.


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 Post subject: Re: Arc Flash energy calculation equation of ARCPRO software
PostPosted: Mon Jan 04, 2016 11:26 am 
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PaulEngr wrote:
The same (lack of documentation) is also true with the Duke heat flux calculation. There is some documentation more or less describing it but not exact details. The same is also true of the Wilkins time-domain model which has been considered by the IEEE 1584 working committee to replace the current non-time series model.

ArcPro (and Duke heat flux) predate IEEE 1584. So it's interesting to describe it as something new and unknown when in fact the opposite is true from a historical perspective.

I was in the other camp but when considering ArcPro as the "annointed model", this is my take:
1. Claims about being anti-competitive. Ontario Hydro/Kinetrics developed a theoretical model and sells it. Quite literally at the moment, anyone else can develop a theoretical model and sell it. Duke even gave theirs away, and OSHA even considered it in their analysis. This doesn't stop anyone else from doing the same. In fact although there may be licensing restrictions against doing so, theoretically I can simply treat it as a black box and pull data out until I can reverse engineer a set of empirical equations that duplicate what ArcPro does. In fact that is exactly how IEEE 1584 empirical equations work except that they are empirically matching real world test data instead of being tested against a theoretical model. In effect in IEEE 1584 terms, the "real world" is a black box. So I see nothing wrong with what Kinetrics is selling as far as being "anti-competitive".
2. OSHA endorsement of a commercial product is anti-competitive. At the moment there are no competitors so the argument is pointless. If a competing software program (or academic/white box model) becomes available then there is teeth to the argument because there may be a general consensus that since OSHA has "endorsed" ArcPro, no competing software would be accepted. Careful reading of OSHA's position is that this is informational/guidance and not enforced but right now, there is no viable competitor except Duke and Lee, both of which were rightly rejected. Even if such a product were to emerge, without test data, we can't say that A is better than B. We can't do this above 15 kV right now. So even if such a product were to emerge, whose to say which is right and which is wrong? For all we know, Duke heat flux might turn out to be right (but this is unlikely).
3. Other software vendors "can't" compete. Huh? Can't develop and retail an arc flash program for >=15 kV? Nothing is stopping them except that coders don't spend money on the fundamental research. If they did and ArcPro is really that bad, they could corner the market quickly.

So until the first competitor or actual test data appears, it's kind of hard to argue against ArcPro except on a pure academic basis.

Further, it is VERY common to see CFD models with scant documentation. Usually the very simple fundamentals are described and then how the model goes from local calculations to a global result is done with a lot of hand waving. It drives me nuts in the computational fluids/finite element/finite volume calculations as well, and that's what this one is.


Since ArcPro and Duke heat flux programs are proprietary and do not reveal the actual equations or computational algorithm, it is impossible to scrutinize the model they are based on and ascertain its validity. You may consider newly released ARCMASTER V1.0 software program for single- and three-phase arc flash hazard analysis and labeling. The program performs comprehensive arc flash calculations by taking into account system voltage, available fault current, the fault power factor, equipment type, working distance, protective device time-current characteristics, and more. ARCMASTER V1.0 program calculation procedure is well documented and can be found online at http://arcadvisor.com/faq/single-phase-arc The program comes at a fraction of cost of the competitor offering. You can also try the program before buying it.


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