Does anyone know if there are any Arc Flash requirements for the DC side of a PV system? Or if there are no requirements what NFPA70E states in regards to Arc Flash on DC systems? I've done several studies before where I provided an Arc Flash analysis on the AC side of a PV system but am now being asked if any analysis is needed on teh DC side of the system?
Arc Flash requirements for DC side of PV system
- Thread starter philly
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- Placerville, CA, USA
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- Retired PV System Designer
On the DC side of a PV system, there is a rigid fault current limit which is not much, if at all, higher than the normal operating current.
There could well be a DC arc, but the energy available would be only the maximum normal power from the array elements, for the duration until a protective device tripped or the arc stopped on its own as the wires melted back.
No high Short Circuit Current potential. So the analysis would be somewhat different. Low power but very long duration, so still a lot of energy. The analysis might indicate that the hazard rating is low because of that, but I would still do it to find out. Needed: yes. Required: I don't know.PS: If there are batteries involved, then the fault currents could be much higher than normal operating currents.
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zog
Senior Member
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- Charlotte, NC
Yes you still need to do the analysis, the problem is DC arc flash analysis procedures are still in thier early stages. SKM has a DC module for the fault current part but for the most part the 70E has advised to use the AC equations for the analysis until further research is complete.
Some guidance for you, you can google the "Cline method" and/or refer to Annex D in the 2012 NFPA 70E
D.8.1.1 Maximum power method. The following method
of estimating DC arc flash incident energy was presented at
the 2007 IEEE Electrical Safety Workshop (see reference 2
below). This method is based on the concept that the maximum
power possible in a DC arc will occur when the arcing
voltage is one half of the system voltage. Testing completed
for Bruce Power (reference 3 below) has shown that
this calculation is conservatively high in estimating the arc
flash value. This method applies to DC systems rated up to
1000 VDC.
I I
IE V I T D
arc bf
m sys arc arc
= ∗
= ∗ ∗ ∗
0 5
0 01 2
.
.
where:
Vsys = the system voltage, in volts
Ibf = the system bolted fault current, in amperes
Iarc = the arcing current, in amperes
Tarc = the arcing time in seconds
D = the working distance, in centimeters
IEm = the estimated DC arc flash incident energy at
the maximum power point, in cal/cm2
For exposures where the arc is in a box or enclosure, it
would be prudent to use a 3? multiplying
zog
Senior Member
- Location
- Charlotte, NC
Sorry, that didn't transfer well, just look in annex D
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