In arc flash calculations can someone explain BRANCH ARC FLASH ? 1

[bdn2004]

I'm confused on why EasyPower outputs this data on an arc flash report. It gives you the Bus Arc Flash current but it also gives the branch arc flash current. What does that refer to and why is it important?

 

[dpc]

"Bus" arc current is the total fault current at the point of the fault, including all sources and all motor contributions. "Branch" arc current is the arcing current through the upstream device that is clearing the fault. The software uses the bus current to calculate the incident energy, and uses the branch arc current to determine the arc duration, based on the time-current curve of the upstream device that is clearing the fault. If there is only one source of fault current, the two values should be the same.

Dave C.

 

[bdn2004]

dpc,

Thanks that makes sense. And when I'm looking at the trip time on the time current curves for that relay - I've got to look at the branch arc fault(kA) to see when it trips. This does have more than one source.

 

[bdn2004]

Taking a closer look at this, according to the drawings this is a paralleled operation, the tie between the busses is NC.
Both main breakers have to be tripped to turn this off. I'm assuming it's taking the slowest one - which in this case is PD-642 in the arc flash calculation. I'm going to check the sequence of events.

 

[dpc]

In the Integrated mode (default) it will figure out the contribution from each source independently, regardless of what the report is showing. The arc time in the report should be for the last device to trip.