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 Post subject: PV DC Arc-FaultPosted: Mon Sep 03, 2012 7:01 pm

Joined: Mon Sep 03, 2012 5:00 pm
Posts: 8
Location: Riverside CA
How do I calculate Arc-Fault for PV DC? In Southern California we are installing systems of 800V and larger
I'am teaching the 2012 70E to IBEW members installing these systems

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 Post subject: Posted: Mon Sep 03, 2012 8:11 pm
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1702
Location: Scottsdale, Arizona
The calculation method for DC arc flash is found in the thread below. The DC short circuit current for PV systems tends to be on the low side, as in 1-2 times full load amps. Also is a recent article about electrical safety with both PV and Wind

The simplest method for DC arc flash is to use the NFPA 70E tables.

[url='http://www.ecmag.com/index.cfm?fa=article&articleID=13705']PV and Wind Article[/url]

Good Luck!

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Jim Phillips, P.E.
Brainfiller.com

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 Post subject: Posted: Tue Sep 04, 2012 6:02 am
 Sparks Level

Joined: Tue Apr 17, 2012 8:19 am
Posts: 253
Location: Charlotte, NC
brainfiller wrote:
The calculation method for DC arc flash is found in the thread below. The DC short circuit current for PV systems tends to be on the low side, as in 1-2 times full load amps. Also is a recent article about electrical safety with both PV and Wind

The simplest method for DC arc flash is to use the NFPA 70E tables.

[url='http://www.ecmag.com/index.cfm?fa=article&articleID=13705']PV and Wind Article[/url]

Good Luck!

That is a very good article.

My concerns have been regarding the L/R ratio of the cables and how that time affects the clearing time. I've done some research, and it appears that the L/R ratio in bigger cable (around 400 to 500 MCM) is 8-11 microseconds which is not a big concern since the DC XL fuses I am looking at are based on a time constant of 1-3 milliseconds. You would have to look at the L/R ratio for the specific cable you are using and take into account how the cable was routed.

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 Post subject: Posted: Tue Sep 04, 2012 6:54 am
 Sparks Level

Joined: Tue Apr 17, 2012 8:19 am
Posts: 253
Location: Charlotte, NC
The article also makes a good point about incident energy from the grid.

In my calculations for a 1.25 MW inverter, there was 1.77 cal/cm2 from the PV to the inverter and 20.06 cal/cm2 from the inverter to the isolation transformer, but there is 52 cal/cm2 from the grid where the grid ties to the inverter which pretty much means no live work.

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 Post subject: Posted: Tue Sep 04, 2012 6:55 am
 Sparks Level

Joined: Wed Jun 10, 2009 5:00 pm
Posts: 267
Location: Toronto
Circuit time constant and its impact on the protection device clearing time has been addressed in
the On the Performance of Arc Flash Analysis in DC Power Systems article and implemented in DCAFA V2.0 software for arc flash hazard analysis and labeling.

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Michael Furtak, C.E.T.

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