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Jensaugust12

Post subject: Question about table 4102 ieee.c2. vs arcpro Posted: Thu Mar 15, 2018 2:02 am 

Joined: Wed Nov 01, 2017 6:09 am Posts: 27

For my understanding of this tables: It is used some kind of distance from arc:"Calculated by using minimum approach from Table 4412 and subtracting two times the assumed arc gap length" Does this mean that for instance the 161 to 169 kV calculation is done wirth the following input: Ik= 20kA(assumed single phase) Arc Gap distance 161kV/10=16.1 inch Distance to gap: (From table 4412): 51 inches(10ft3inch,use T=3)2*16.1 inches=19 inches If I do calculation with arcpro(is was told that this tables where made by using arcpro?), input shown in picture. I get a result of 11.9 cal/cm2 and not 4cal
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stevenal

Post subject: Re: Question about table 4102 ieee.c2. vs arcpro Posted: Thu Mar 15, 2018 8:27 am 

Joined: Tue Jan 13, 2009 5:00 pm Posts: 543

The table uses line to line voltage, but when finding arc length the note 1 says to divide the line to ground kV by 10. Your calculated arc gap should be divided by sqrt(3).
When I've looked at this in the past, I found the tables did not necessarily correspond to the MADs in the same revision of the NESC. Looking back a revision or two produced better results.
Why 9.3 cycles? Tabulated value is 11.9.
Might try changing the electrodes; I forget which gave better results.


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