
How does your arc flash calculator deal with single phase faults? 
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"I'm dealing with a number of single phase transformers and considering the possiblity of arcing faults at the secondary terminals. I'm not sure how to handle this."
The Duke Power Heat Flux Calculator is most oftent cited when single phase arc incident energies are to be determined. The Duke Power Flux Calculator guide also explains how to calculate 3 phase arc using single phase arc data (see page 9). The calculator assumes the arc incident is being sustained by a single phase source. The Guide says To correct for the involvement of all three phases, multiply the incident energy value from the Heat Flux Calculator by a factor of 2.8. I do not know the calculation procedure behind the the Duke program. However, if you trust the factor, you can use it to calculate single phase arc using three phase arc data obtained using the IEEE 1584 procedure and dividing the resulting value by 2.8.
If you are using the ArcAd online short circuit calculator for fault current analysis, you need to "convert" your single phase transformers to three phase by multiplying their KVA ratings by 3, run the analysis, use obtained 3 phase bolted fault current values to calculate incident energies using the IEEE 1584 based online arcflash calculator, and divide the resulting values by the Duke's factor of 2.8
I run some numbers using the Duke software and suggested procedure. From my prospective there is quite a good correlation between the resulting values. Personally, I find IEEE procedure more advanced because it calculates arc current based on prospective bolted fault current value, geometry and configuration of the equipment. Unfortunately, there is no help screen in the Duke software  my problem with using the Duke tool is how to calculate single phase arc current using single phase short circuit current value?
