Arc Flash

[Kanu_01]

I have been analysing the arc flash results and I could see fuse on the primary side has tripped before the breaker on the secondary side of T2 transformer. Please find reference photo. Both the buses are seeing the same bolted and arcing fault. LV breaker(C1) on transformer side(T1) is tripping in arc flash results for Bus-1 whereas fuse F2 on transformer primary side is tripping for Bus-2. Also I could see the fuse on transformer T2 primary side is tripping at maximum arcing duration of 2 sec. What could be the reason as breaker, fuse ratings, settings and transformer ratings are similar for both transformers? .

Shouldn’t LV side breaker be tripped first as it is happening for Bus-1?

 

[dpc]

Not information for us to solve this for you. You need to look at the time-current curves for all of the devices and find the operate time at the calculated arcing current. If the fuse is clearing the fault, it probably means the program thinks it is faster at that current than the breaker. Or possibly the breaker is not completely or correctly modeled.

Also look at the actual current through each protective device, not just the total fault current. If all the settings are identical, the time-current curves are identical, and the currents are identical, then the sequence of operation should be similar on both sides.

 

[dpc]

If you are using the IEEE 1584 equations, another long shot is the electrode configuration - the choice of bus configuration (horizontal, vertical, etc) does change the predicted arcing current (slightly). It's possible that a difference in the electrode configuration could cause enough change in arc current to change which upstream device is fastest.

If you post the complete arc-flash report data for the two buses, that would help a lot.