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mcgee9t2

Post subject: Short Circuit Calculation as part of AF study Posted: Thu Aug 08, 2019 3:54 am 

Joined: Fri Jun 14, 2019 5:51 am Posts: 13

have recently had this conversation a few times with my colleages, when performing an arc flash study on SKM PTW there are 2x options for the short circuit calculation used within the arc flash calc; IEC60909 & Comprehensive.
from my understanding  Comprehensive is a basic Ohms Law type calculation, IEC60909 ultimately is also ohms law, however, also makes allowances such as the Voltage Factor which adds an additional 5% (if memory serves my correct) onto the calculated fault current. etc.
in my mind; IEC60909 is the method to use when specifying equipment/undertaking fault level studies as this will increase the fault level and therefore ensure equipment is rated worse case (could also increase cost as you may need to "over rate" equipment  but we wont get into that) Comprehensive (ohms law) is the method to use when completing arc flash studies as this is going to produce a slightly lower fault current (although still correct and accurate) which will increase trip times and produce a higher incident energy and therefore worse case arc flash calculation.
i have discussed this will other engineers in the company, however, their issue is that the fault level study is not to a standard (although to me ohms law is a given and as good as a standard  afterall, standards are based on laws such as Ohms law etc.).
therefore there is a bit of a conflict over which method to use, i have spoken to engineers who i know that work at other consultancies and they are all in agreement with me.
please could i request your opinions and also if anybody knows of a section within the IEEE1584 guide which states something to the effect of "60909 may produce lower results due to voltage factors", sadly the only information i can find in IEEE1584 states 'calculate the fault current' and also provides a reference to IEEE551 (which sadly i do not have a copy of).


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mcgee9t2

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Thu Aug 08, 2019 3:55 am 

Joined: Fri Jun 14, 2019 5:51 am Posts: 13

P.S i had a search to see if this has already been covered but couldnt find anything on here/on google, if anybody knows of any papers/references/websites etc. please let me know.


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arcad

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Fri Aug 09, 2019 6:59 pm 

Sparks Level 

Joined: Wed Jun 10, 2009 5:00 pm Posts: 263 Location: Toronto

mcgee9t2 wrote: P.S i had a search to see if this has already been covered but couldnt find anything on here/on google, if anybody knows of any papers/references/websites etc. please let me know. Make sure the program/method you are using is taking into account both active and reactive parts of equipment impedance when calculating available fault current. Run away from any that don't. How do you know it does? The program would require all the equipment X/R ratio on its input (resistance and reactance for calbles) and would calculate the equivalent source X/R along with the available fault current at the point of fault. Also, many programs and procedures of this type do not properly account for motor loads as they simply have the user add the motor contribution to the utility source KVA. Some programs make short circuit fault current assumptions based on transformer size etc. This inadvertently distorts short circuit fault current values and blurs the safety margin. As far as papers/references, I strongly encourage you to check links below: 1. simplified MVA method for short circuit analysis: http://arcadvisor.com/files/ShortCircuitABC.pdf2. comprehensive MVA method: http://arcadvisor.com/faq/mvamethodshortcircuitfaultcurrentcalculations
_________________ Michael Furtak, C.E.T. http://arcadvisor.com


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mcgee9t2

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 12, 2019 1:50 am 

Joined: Fri Jun 14, 2019 5:51 am Posts: 13

Power tools does take into consideration both resistance and reactence when completing calculations, all equipment is modelled with X and R Components.


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Jim Phillips (brainfiller)

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 12, 2019 7:15 am 

Plasma Level 

Joined: Mon Sep 17, 2007 5:00 pm Posts: 1492 Location: Scottsdale, Arizona

I was one of the coauthors of a paper that addressed this topic. It was presented in 2018 at the IEEE PCIC Conference and was a comparison of ANSI and IEC short circuit calculations and how they affect IEEE 1584 calculations. The paper is titled: "Comprehensive Overview, and Comparison of ANSI vs. IEC Short Circuit Calculations  Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations," You can obtain it at: IEEE Transactions on Industry Applications On page(s): 13 Print ISSN: 00939994 Online ISSN: 19399367 Digital Object Identifier: 10.1109/TIA.2019.2919479 LINK to IEEE Xplore: https://ieeexplore.ieee.org/document/8723616


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SteveA

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 12, 2019 8:23 am 

Joined: Mon Dec 07, 2015 9:45 am Posts: 33 Location: Massachusetts

SKM's "Comprehensive" Method is their own method of calculating the Short Circuit currents. It is the method they use in calculating the SC currents for the arc flash analysis. It is also more "comprehensive" than the ANSI method, which ignores many relevant factors, such as current limiting devices such as CL fuses.


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mayanees

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 12, 2019 9:33 am 

Joined: Tue Feb 17, 2009 8:38 am Posts: 46 Location: Westminster, MD

Jim Phillips (brainfiller) wrote: I was one of the coauthors of a paper that addressed this topic. It was presented in 2018 at the IEEE PCIC Conference and was a comparison of ANSI and IEC short circuit calculations and how they affect IEEE 1584 calculations. The paper is titled: "Comprehensive Overview, and Comparison of ANSI vs. IEC Short Circuit Calculations  Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations," You can obtain it at: IEEE Transactions on Industry Applications On page(s): 13 Print ISSN: 00939994 Online ISSN: 19399367 Digital Object Identifier: 10.1109/TIA.2019.2919479 LINK to IEEE Xplore: https://ieeexplore.ieee.org/document/8723616… and on a related topic! I'm interested in that document, and I thought that for the first time ever my IEEE membership is going to provide me with a free useful document. OOPS. My bad. I followed the links. I was logged in right away, but this requested an institutional password which must've been different. So I followed the link to change the institutional password and ten minutes later the password arrived and still didn't open the Institutional membership. I'm an IEEE member because my company pays for it. And I think I've been an active member for 30+ years, but still no free useful information.


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SteveA

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 12, 2019 1:33 pm 

Joined: Mon Dec 07, 2015 9:45 am Posts: 33 Location: Massachusetts

mayanees wrote: Jim Phillips (brainfiller) wrote: I was one of the coauthors of a paper that addressed this topic. It was presented in 2018 at the IEEE PCIC Conference and was a comparison of ANSI and IEC short circuit calculations and how they affect IEEE 1584 calculations. The paper is titled: "Comprehensive Overview, and Comparison of ANSI vs. IEC Short Circuit Calculations  Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations," You can obtain it at: IEEE Transactions on Industry Applications On page(s): 13 Print ISSN: 00939994 Online ISSN: 19399367 Digital Object Identifier: 10.1109/TIA.2019.2919479 LINK to IEEE Xplore: https://ieeexplore.ieee.org/document/8723616… and on a related topic! I'm interested in that document, and I thought that for the first time ever my IEEE membership is going to provide me with a free useful document. OOPS. My bad. I followed the links. I was logged in right away, but this requested an institutional password which must've been different. So I followed the link to change the institutional password and ten minutes later the password arrived and still didn't open the Institutional membership. I'm an IEEE member because my company pays for it. And I think I've been an active member for 30+ years, but still no free useful information. for an institution filled with engineers the IEEE website is horrifically bad.


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mcgee9t2

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Thu Aug 15, 2019 1:14 am 

Joined: Fri Jun 14, 2019 5:51 am Posts: 13

SteveA wrote: mayanees wrote: Jim Phillips (brainfiller) wrote: I was one of the coauthors of a paper that addressed this topic. It was presented in 2018 at the IEEE PCIC Conference and was a comparison of ANSI and IEC short circuit calculations and how they affect IEEE 1584 calculations. The paper is titled: "Comprehensive Overview, and Comparison of ANSI vs. IEC Short Circuit Calculations  Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations," You can obtain it at: IEEE Transactions on Industry Applications On page(s): 13 Print ISSN: 00939994 Online ISSN: 19399367 Digital Object Identifier: 10.1109/TIA.2019.2919479 LINK to IEEE Xplore: https://ieeexplore.ieee.org/document/8723616… and on a related topic! I'm interested in that document, and I thought that for the first time ever my IEEE membership is going to provide me with a free useful document. OOPS. My bad. I followed the links. I was logged in right away, but this requested an institutional password which must've been different. So I followed the link to change the institutional password and ten minutes later the password arrived and still didn't open the Institutional membership. I'm an IEEE member because my company pays for it. And I think I've been an active member for 30+ years, but still no free useful information. for an institution filled with engineers the IEEE website is horrifically bad. also cant get the document to open. doh


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Jim Phillips (brainfiller)

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 19, 2019 4:35 am 

Plasma Level 

Joined: Mon Sep 17, 2007 5:00 pm Posts: 1492 Location: Scottsdale, Arizona

Not sure what the download issues are. I can download without problems but sounds like something is wrong for some. Maybe try "Get Help > Technical Support" at the top. Agreed the website can be frustrating from my own past experience.


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cflatters

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 19, 2019 5:55 am 

Joined: Wed Jul 18, 2018 12:35 am Posts: 3 Location: UK

The UK and Europe use IEC 60909 widely and IEC 609091 Table 1 does give recommended values for Cmin and Cmax for 'Prefault voltage' which above 1kV is typically 1.0 and 1.10 respectively whilst for LV values of 0.9 and 1.1 are commonly used and applied to the nominal system voltage at each bus.
They do tend to yield slightly higher values but this is intended to factor some areas of the model where data may be subject to some degree of uncertainty. I believe that the SKM 'Comprehensive' calculation method also allows voltage factors to be applied to applied in a similar manner and arguably doing so is eminently sensible.
As far as I am aware, the IEEE1584 SKM Arcflash evaluation module uses bolted fault current from the 'Comprehensive' calculation model unless I have missed an option ??
OK  Just found the option to use IEC 60909 or Comprehensive Fault currents ….. I do tend to use the 'Comprehensive' method however I have found that using 'Comprehensive' method with identical voltage factors to IEC 60909 shows a high degree of correlation to the latter as I would expect.


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Gary B

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 19, 2019 7:03 am 

Joined: Thu Oct 18, 2007 7:10 pm Posts: 261 Location: NW USA

Regarding the original question, if one method of calculating gives accurate results by adjusting for voltage drop, that would seem to be the one for Arc Flash Calculations. If this is some field variable that could actually change, then you cannot assume lower fault current provides lower arc flash values, because oftentimes just the opposite is the case when instantaneous protection is not triggerd because of the lower fault current.
In a perfect world you would have enough time to calculate worst case arc flash results using both methods. Then you would discover that arc flash exposure might be heavily governed by what ever contact resistance or air contamination existed that day. Bottom line is these are approximations and because of that is it important to stick to some industry standard (or be prepared to defend all of physical science).
Regarding IEEE: downloading documents seems to be controlled by the same swell folks that designed programmable VCR's (a joke from 30 years ago). I no longer attempt this, but my business partner/ wife seems to do well.


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Robertefuhr

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Mon Aug 19, 2019 7:53 am 

Sparks Level 

Joined: Tue Oct 26, 2010 5:00 pm Posts: 187 Location: Maple Valley, WA.

For EU projects, we use the IEC method. For all US and Canadian projects, we use the comprehensive calculations and apply the appropriate X/R tested multiplier.
_________________ Robert Fuhr, P.E.; P.Eng. PowerStudies


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mcgee9t2

Post subject: Re: Short Circuit Calculation as part of AF study Posted: Tue Aug 20, 2019 8:46 am 

Joined: Fri Jun 14, 2019 5:51 am Posts: 13

cflatters wrote: As far as I am aware, the IEEE1584 SKM Arcflash evaluation module uses bolted fault current from the 'Comprehensive' calculation model unless I have missed an option ??
Yes SKM used Comprehensive to calculate BF, hence if you select IEC60909 the Bolted Fault section of the datablock remains 0.0kA. (unless you run a comprehensive calculation at which point it will show the calculated bf current, however if you then run it as IEC60909 again the datablock BF remains as the comprehensive calculated BF, but the calculation table shows the BF as the IEC60909 break current therefore calculation results and the SLD do not align).


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