Estimating transformer in rush.

[haze10]

Because of the age and make of my transformers I can no longer get information from the manufacturer. I'm installing some new protective relays on the feeders to my building transformers. I'd like to set Inst at 2x no load inrush current. But I can't find what the in rush is. Is there a way to estimate it. The transformers are 1500 KVA padmount 5.0% impd, 4.16kv to 480V, delat/wye. Any best way to guess at the inrush?

 

[ElectricRob]

Potential inrush problems aren't just limited to tripping feeder breakers. You should also take a look at the source impedance and estimate the likely voltage dip that will result from the inrush current.
Several months ago, we connected a new industrial customer to a 69 kV radial transmission line - the line already served two other industrial customers and a retail substation. When the new customer's 20 MVA transformer was energized, one of the other industrial customers called to let us know that they experienced a voltage dip that caused some of their equipment to drop offline (and they didn't seem very happy about it).