4800V system questions

On a 4800V system with 15Kv class gear when running a arc-flash study based on IEEE-1584-2002, the gap distance for 15Kv gear is 153mm as opposed to 102mm for 5Kv class gear, however when you run the serino of a 4800V system on 5Kv gear with 153mm gap distance the category increases 1 class in most cases why is this if the clearing time does not change and the available fault current remains the same??

Mike,

With the calcs that I have done for medium and low voltage, the levels do rise with an increase in arc length. With all other factors being equal and as long as the system is able to sustain the arc with the larger gaps, one would expect to get more radiated heat energy from a larger, or in this case longer source.

Hope this helps.

Alan