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 Post subject: arc flash in matlab
PostPosted: Thu Jun 09, 2011 7:22 am 

Joined: Wed Jun 08, 2011 10:52 am
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i am planing to implement arc flash analysis in matlab with 2 different guy, one is charge of doing short circuit analysis, other guy will make protective device coordination analysis, then i will combine their result and implement arc flash analysis on matlab. i download IEEE standard book and got formulas from it. i got confused, if i know short circuit result from other guy, this short circuit results are the same as bolted phase currents?

other question is formula for arc current contains bolted current as well, they also ask for K (open configuration or box configuration) what does it mean open configuration or box configuration?

what are the necessary information i should get from the guy who did protective device coordination. clearing time or arcing time? because inside the incident energy formula t=arcing time, which comes from protective device coordination? and also inside the formula there is a x(distance component) what is that x?

thanks for advanced.


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PostPosted: Thu Jun 09, 2011 10:05 am 
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I think you need to read the text of the IEEE guide in addition to getting the formulas. This will answer many of your questions.


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PostPosted: Thu Jun 09, 2011 12:12 pm 
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Are you doing this for a project in school or is this for a real world application?

If this is for school, do you need a complete 'ready to be defended in a court of law' application, or one that simply proves your skills with Matlab?

If this is for a real world application, how much confidence do you have in the values being provided to you?

Regardless, the opening times of the protective devices must be based on the arcing fault currents determined by the IEEE formulas including applicable tolerances.


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PostPosted: Thu Jun 09, 2011 12:22 pm 

Joined: Wed Jun 08, 2011 10:52 am
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two other friends do short circuit study and protective device coordination. we have sample circuit. one friends write codes in matlab to find short circuits on every bus and equipment. other friends did protective device coordination analysis for same circuit(i am not sure how he did that). i am supposed to do arc flash analysis using data from other two guys analysis.

so i am asking you, what is the necessary data i should ask from other two guys to do arc flash analysis. right now, i know all short circuit for every bus and equipment.

all i am gonna do, i will get necessary information from short circuit analysis and protective device coordination analysis, then implement arc flash formula with matlab.

should i ask guys, short circuit current? buses voltages? then what else?


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PostPosted: Thu Jun 09, 2011 12:53 pm 

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it is for school and education purpose and i dont know 'ready to be defended in a court of law'


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PostPosted: Thu Jun 09, 2011 1:00 pm 
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We can't teach you everything there is to know about doing an arc hazard analysis on this forum. There are multiple resources available, however. Start with NFPA-70E and IEEE-1485. Also see the following articles:
http://www.brainfiller.com/documents/ArcFlashJimPhillipsPart1.pdf
http://www.brainfiller.com/documents/ArcFlashJimPhillipsPart2.pdf
http://www.brainfiller.com/documents/ArcFlashJimPhillipsPart3.pdf


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PostPosted: Thu Jun 09, 2011 2:30 pm 

Joined: Wed Jun 08, 2011 10:52 am
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thank you sharing with a nice material,

i finished it, and some point i need to ask.
q1)i think system mode is very important, because we can come up with different worst case scenarios, how can we decide which one is worst one? where is the stop point?
q2) it says bolted there phase current is the same as traditional short current current? is it true?
q3)why do we calculate 85 and 100% of arcing current to determine clearing time?
q4)is arcing time the same as clearing time? to calculate incident energy, i need to know arcing time or clearing time?
q5) what is the way of calculation working distance? it says generally 18 inches?


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PostPosted: Thu Jun 09, 2011 7:51 pm 
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cooldesign wrote:
thank you sharing with a nice material,

i finished it, and some point i need to ask.
q1)i think system mode is very important, because we can come up with different worst case scenarios, how can we decide which one is worst one? where is the stop point?
q2) it says bolted there phase current is the same as traditional short current current? is it true?
q3)why do we calculate 85 and 100% of arcing current to determine clearing time?
q4)is arcing time the same as clearing time? to calculate incident energy, i need to know arcing time or clearing time?
q5) what is the way of calculation working distance? it says generally 18 inches?


q1) Calculate incident energy (IE) for each possible mode.
q2) Yes.
q3) Actual arcing current depends on arc resistance which cannot be determined precisely. Using 85% provides for the possibility of arc currents being lower than calculated.
q4) arcing time must include both relay operating time and breaker clearing time. For fuses and low voltage breakers, it is generally the same.
q5) Working distance depends on equipment design (where is the arcing point with relation to where the worker has access?) and working practice. The values shown in the IEEE guide are typical, but if you know that your situation is different, document it and use the actual distance.


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PostPosted: Fri Jun 10, 2011 2:51 pm 

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calculation of arcing time is not clear for me? how do we calculate arcing time? do we need to always to look at upstream protective device?


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PostPosted: Fri Jun 10, 2011 3:52 pm 

Joined: Wed Jun 08, 2011 10:52 am
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jghrist, do you have a nice document to understand it?


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PostPosted: Fri Jun 10, 2011 9:00 pm 

Joined: Wed Jun 08, 2011 10:52 am
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for example, i wanna calculate incident energy for one equipment or one bus in the circuit, i need to calculate bolted fault current on that equipment and arcing time. this arcing time is for this equipment or equipment before that equipment?

for example if fault happens then recloser operates after that in 0.2 sec, so this 0.2 sec is arcing time?

can you give me numeric information like that?

thanks in advanced.


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PostPosted: Sat Jun 11, 2011 7:55 pm 
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The arcing time is determined by the time-current characteristics of the upstream protective device and the magnitude of the arcing current that flows through the protective device.

If fault happens and a recloser interrupts the current in 0.2 sec, then the arcing time is 0.2 seconds. If the circuit recloses, then you could have a second arc with possibly a different arcing time. I'd add both arcing times together. Also consider using a "maintenance switch" that would disable reclosing.


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PostPosted: Wed Jul 13, 2011 9:06 am 
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Joined: Thu Oct 18, 2007 7:10 pm
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cooldesign wrote:
calculation of arcing time is not clear for me? how do we calculate arcing time? do we need to always to look at upstream protective device?


Simple answer is yes, the clearing time will depend on upstream protective device, HOWEVER; it is a major concern that the arc flash calculations integrate the energy from all possible sources including downstream motors, and sum the energy from each source based on independent clearing times of all devices.


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