Luc wrote:
Thanks for the replies Jim and Paul!
Paul I have a question for you: you say that the piecewise approach is supposed to get a mention in the next edition, but where do you read things like this?
Because if I tell people about this at my company I do want to have something to fall back on so to say.
I mean that I can say ‘this and that will probably come in the next edition because it is on the IEEE1584 website’. Not to be insulting but I can’t say ‘this and that will probably come in the next edition because someone on the internet told me’. I know you guys are not random people but the person I tell this to will think that either way.
Hope I did not insult you guys, because that is not my intension.
Nothing published. With both IEEE and NFPA the only way to get "official" information is when they publish draft editions of an upcoming standard for public comment. If you communicate with the various committee/subcommittee members though they will frequently reveal privately some direction as to where the conversation is going.
IEEE 1584 currently does not really address the input (current) at all. What we have is that several tests were performed and incident energy was measured. The data was then curve fitted to a formula, resulting in an empirical equation. The tests were performed in the lab with a controlled (or at least measured) level of fault current. It has nothing at all to do with the power system analysis side of things. It is simply based on empirically derived equations that match roughly a 300 test database.
When applying this to an actual power system, you need to determine an available fault current. In the lab, the current source is a constant and there is only one source. In an actual power system it is not constant and there are multiple power sources. Thus one should do piece-wise fitting of the current to the arc flash calculation to arrive at an accurate estimate. As I said...IEEE 1584 does not mention this but it is implicit in the analysis.
Both SKM and ETAP (the two I'm familiar with) do SOME modelling of motors and generators. There are specific settings for this in both systems. However it is not all that sophisticated in implementation.