dc arc flash hazard

[trekrider1]

Arc Flash hazard identification has become a high profile topic at our utility. We have been performing studies on most of our AC station service installations but I haven't seen anything concerning a possible arc flash hazard from our DC battery backup systems. Some of our installations have quite large DC systems and this is becoming a concern to our electricians. Is there an arc flash hazard on our 48VDC and 130VDC systems? Does anyone out there know of any engineering papers that have written addressing this topic? Any information would be helpful and greatly appreciated

 

[dpc]

I would think there is a significant hazard at 125V dc. Unfortunately, the IEEE-1584 standard on arc-flash calculations deals only with ac systems.

The use of fuses instead of circuit breakers will probably help reduce the energy released due to higher speed of operation.

I'm not aware of any technical papers on the subject - but I suspect the US Navy must have some data, due their extensive of dc power on submarines and their own arc-flash detection systems. Have you tried a web search?

 

[ruggedscot]

DC arc flashes are very hazardous especially with batteries. You have to be very careful as you know, Batteries produce hydrogen and this when combined with arc faults generates an explosive mix of conditions. You should be looking to employ fast acting type fuses designed for DC circuits. Any fault on a DC will release a high amount of energy being limited only by thr esistance of the fault cable and internal battery resistance. Current on a low voltage system can be in the magnitude of a few hundered amps of so. On the higher voltage this will be even greater.

rugged

 

[ScottyUK]

Your electricians are right to be wary around battery systems. Install HRC fuses as close to the battery as possible. Impose a total ban on the use of uninsulated tools on the battery itself, where the HRC fuse may not be able to provide protection against a direct inter-cell short circuit. If carrying out installation work on a large battery, leave a link out at the midpoint until all other connections are completed. This action effectively makes one high voltage battery into two lower voltage batteries until the final link is installed, reducing both the possibility of a severe shock and limiting the prospective fault current for the majority of the work.

Among the most dangerous DC systems are generator excitation systems for slipring machines, which can combine high voltages in excess of 1kV, current in excess of 4kA, and large inductance in the circuit. Switching these circuits usually employ a make-before-break contact to insert a dump resistor and perhaps a non-linear voltage dependent resistor into the field circuit to dissipate the stored energy prior to opeing the main field contacts and thus prevent a very intense high voltage arc being drawn.

Beware of all inductive circuits carrying DC: motor field windings can cause persistent arcs and very high voltages, even though they may only carry a few amps.






------------------------------

If we learn from our mistakes,
I'm getting a great education!