Available fault current calculation for D.C.

[qcroanoke]

Is there such a thing?
I was asked if there is a string of batteries how would we calculate the available fault current.
Obviously it depends on the batteries involved. Is this something the Mfgr. should be able to tell us or is there a calculation we could do?
Thanks.

 

[Carultch]

Is there such a thing?
I was asked if there is a string of batteries how would we calculate the available fault current.
Obviously it depends on the batteries involved. Is this something the Mfgr. should be able to tell us or is there a calculation we could do?
Thanks.

It would be the short circuit current of the battery bank. I'm not sure if manufacturers test for this and publish the results, but if they don't, the calculation I'd recommend for estimating it, would be open circuit voltage / internal resistance at maximum operating load. I wouldn't be surprised if it weren't common to test for this, as it certainly would ruin the battery and likely be dangerous to do a direct test.

This document confirms my suggested calculation:
http://www2.schneider-electric.com/...ve-catalogue/lvped2080006en/pdfs/page_019.pdf

PV modules are tested for DC short circuit current at STC, as these currents are much lower than those for a battery. Typically on the order of 9A. There is the 125% safety factor to account for real life having more irradiance than the nice round number of 1000W/m^2

 

[Phil Corso]

Is there such a thing? I was asked if there is a string of batteries how would we calculate the available fault current. Obviously it depends on the batteries involved. Is this something the Mfgr. should be able to tell us or is there a calculation we could do? Thanks.

It would be wise to contact the Mfgr, especially if there are numerous series-connected cells! Too often the inductance of the interconnecting cables is omitted!

Or do you just have a "need-to-know" mind? If so, I can tell you of my involvement with a football-field of interconnected 24-V truck batteries! Another experience involved a 240V bank supplying suppying power to an inverter!

Regards, Phil Corso

 

[Ingenieur]

Usually published data per cell
as was noted based on internal resistance

common calcs in mining
many types of battery powered mobile equipment

http://arlweb.msha.gov/TECHSUPP/ACC/Approvals/ESD/APOL2165.pdf
at the bottom a program is referenced
it's crude but free lol

 

[qcroanoke]

It would be wise to contact the Mfgr, especially if there are numerous series-connected cells! Too often the inductance of the interconnecting cables is omitted!

Or do you just have a "need-to-know" mind?
Regards, Phil Corso

No, we are installing more and more battery strings for customers that connect to DC power distribution panels and the question has been bought up if the panel can withstand 10,000 amps how much can those batteries deliver to it?
Legitimate question and we need to know how to get an answer to it.

 

[GoldDigger]

Rather than the short circuit current tolerance of the components, I would be more concerned about the DC interrupting capability of switches and OCPD.

Sent from my XT1585 using Tapatalk

 

[qcroanoke]

Rather than the short circuit current tolerance of the components, I would be more concerned about the DC interrupting capability of switches and OCPD.

Sent from my XT1585 using Tapatalk

Please elaborate, If the switches and OCPD's are DC rated for the applied voltage what is there to be concerned about?

 

[GoldDigger]

Please elaborate, If the switches and OCPD's are DC rated for the applied voltage what is there to be concerned about?

Nothing, but people are not always aware that the DC and AC interrupting ratings can be far different. Both for normal current and for AIC.
They need to be rated both for the applied voltage and the applied current.

The insulation breakdown does not differ between DC and low frequency AC, but it is far harder to extinguish a DC arc than an AC arc. And during the arc extinguishing time far more energy may be released inside the switches or OCPD.

Sent from my XT1585 using Tapatalk

 

[wbdvt]

Many battery manufacturers will publish the Short Circuit current for the battery. See attached manufacturer cut sheet.

 

[ron]

This is manuf info. It is now needed even more, not only for short circuit ratings / AIC, but also to use for arc flash calcs, which are now available for DC equipment in 70E-2015