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 Post subject: Longest arcing time at 130 VAC
PostPosted: Fri Aug 29, 2014 7:49 am 
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What is the longest arcing time that has been recorded experimentally at 130 VAC, and under what conditions (arc gap, voltage)?

I'm really asking the question about 120 VAC but 130 VAC considers the range for nominal voltages.


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 Post subject: Re: Longest arcing time at 130 VAC
PostPosted: Wed Oct 01, 2014 5:51 am 
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Depends on whether you're interested in arcing in a real world environment or artificial conditions in a lab when folks are trying as hard as possible to get a sustaining arc.

At low energy levels in the lab (208V and below, 10 kA and below) it's difficult to get an arc to sustain past the first zero crossing. The challenge is getting energy to both melt the starter wire and create the plasma field before the first zero crossing. Too small of a starter wire and the impedance is too high to get enough current to flow and enough energy to create the plasma field. Too large of starter wire and it takes much of the available energy to melt the wire and there's not enough energy left to create the plasma field before the zero crossing. In tests where the objective was simply to create a sustainable arc at low energy levels they were able to get an arc to sustain past the first zero crossing about 1 time in 6 tries. For those arcs that sustained past the first zero crossing they still self-extinguished within a few cycles. Note that this is at 208 and 240, not 120/130.

The best real world data we have is from the folks who have developed arc resistant equipment and done the associated testing. Very little of this testing has been done at 120 or 208 though - common equipment designs are used and the testing is conducted at 600V or 480V and the arc resistant rating is valid at lower voltages. Anecdotal data from folks who do real world testing, rather than laboratory testing where they are trying to get an arc to sustain, is that arcs at 208 and below very rarely last longer than the first zero crossing.

If you are an IEEE IAS member and have access to the IEEE Xplore digital library look at the papers that Jim Bowen and John Nelson presented at the 2012 PCIC and the 2014 PCIC. They don't specifically address the 130V question, but this is some of the minimal data that has been published on real world arcing faults. There's also the EPRI 208V study, but that doesn't exactly answer your question either.


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 Post subject: Re: Longest arcing time at 130 VAC
PostPosted: Tue Oct 07, 2014 6:37 am 
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Don't know about the 2012 paper. But NEI put the 2014 paper out there:

http://www.neiengineering.com/wp-conten ... esting.pdf

Have the EPRI data as well. Yep, same "issues".

It seems like the only way to get a stable arc in the first place at <250 V at a minimum is (1) small bus gaps, (2) excesively high available fault currents, and (3) 3 phase arcing. Violate any of the 3 and it becomes almost impossible. Considering that published test data at DC for 130 V was only able to sustain an arc with 20 kA and 1/4" bus gap for 0.8 seconds, it seems that single phase AC arcs would be all but impossible to sustain for even 1 or 2 cycles.


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