Increased Arc Flash rating on transformer secondary

[MinnDakEng]

Can anyone explain the reasoning the Arc Flash rating is higher on the secondary side of a transformer than the primary side?

 

[jghrist]

Higher fault current. Slower clearing time.

 

[ElectricalPhil]

absolutely right (higher current + longer time).

At my facility, we've found the secondary of our station service transformers to be consistently one of the worst places for arc flash hazard.

We've added fusing on every transformer secondary to reduce the clearing time and/or limit fault current.

 

[rockman7892]

Will there be more fault current on the secondary side of a 4.16kV Delta - 480V wye 1500kVA transformer then on the primary side when served from a utility transformer rated at 4.16kV secondary and 20MVA. I would think there would be more avaliable current on the primary side considering the impedanceds are roughly the same.