I have a 3000kVA utility transformer with its secondary connected directly to the main switchgear bus. When I run the arc flash it produces an incident energy of 150 cal/cm^2. Any recommendations as to how I can lower that incident energy? With the transformer connected directly to the bus there doesn't appear to be a place to install a main circuit breaker or anything. I am kind of stumped on this one. Any help would be greatly appreciated.

Thanks in advance!

You have a common problem and thee are a few mitigation solutions, In fact I am presenting mitigation mitigation solutions at a conference in 2 hours on this very issue. First thing to look at is your primary fuse, there may be some older types that will work much better. If not you can replace your primary fuse with a mini VCB that uses current inputs from the secondary side of the transformer.

Remote racking and switchnig may be the right solution too, depending on your needs.

I think S&C was making electronic fuses that have programable trip points. You could try to work in a CB on the primary but have the CTs on the secondary. Also, check the fuse catalogs to see if there is a faster one.

Here is a link to S/C fault fiter electronic fuse arrangement.I plugged this into our arc flash program and it reduced the main board from 170 cal to 48 cal.


http://www.sandc.com/products/faultfiter/default.asp