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 Post subject: DC Arc Flash Calcs and Table categories for 600+ VoltsPosted: Mon Jul 23, 2012 8:39 am

Joined: Wed May 23, 2012 11:59 am
Posts: 19
Location: Massachusetts
Hello everyone,

What do you assume for Hazard/Risk category for DC equipment over 600 Volts?

Also, how do you calculate DC Arc Flash hazards "D.8.1 Direct-Current Arc Flash Calculations" for voltages over 1000 Volts?

I'm currently working on an above 1000V system and trying to figure out what AF hazard level does this system pose.

Thank for you responses,

Marek

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 Post subject: Posted: Tue Jul 31, 2012 12:06 pm
 Sparks Level

Joined: Wed Jun 10, 2009 5:00 pm
Posts: 263
Location: Toronto
DCAFA V2.0 software is applicable for systems with voltages in the range of 125 to 2000VDC, short circuit currents from 1 to 50kA, circuit time constants from 0 to 50msec.

_________________
Michael Furtak, C.E.T.

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 Post subject: Posted: Sat Aug 18, 2012 5:20 am
 Plasma Level

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
You mean like those of us with electrostatic precipitators? I tried it a couple different ways. I used the formula in D.8.1 which is pretty simple. I also tried looking at the case of a drive and using the microfarads in the DC link capacitor, calculated the amount of energy stored in the drive under the assumption that the capacitor explodes for some reason (it does happen occasionally).

In all cases what I'm finding is that the assumptions used in the table (kA, fault time) are vastly higher than you ever encounter in real world cases. Even when I have DC motors in a Ward-Leonard loop with 8000 A maximum DC current outputs at 90 V DC, a full blown generator flashover never gets above 1.2 cal/cm^2 with the trip time that exists in this system. So what I'm finding is that the table is worthless...ignore it and do the real DC calculation. There was additional material presented at the IEEE ESW and PES conferences on this for quite some time but even if you assume silly stuff like battery series resistance of 0.01 ohms, you just can't get to 1.2 cal/cm^2 if you assume 2 second arcing time using the same logic which is clearly published in IEEE 1584.

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