Taps on Transformers

Do the tap settings on power transformers affect the ARCFLASH study enough for us to be concerned with them?

Voltage is a variable in the ieee formula for calculating arcing current. So it would have some effect. You'd have to run the equation with the different tab positions to see how much. My gut feeling is that it won't have a big difference, but not sure.

The problem with accounting for taps is that there is no formula to determine impedance at different taps. Unless you have the test data on different taps, you can't accurately calculate the fault current.

Large power transformers generally are sold with impedance at tap settings, but that information is probably long gone by the time an arc flash study is being conducted. One could theoretically include both extremes and study the effects at each location on downstream distribution system, but managing such a study will point out that perhaps the methods should include a little compromise for sake of practicality.