UPS Modeling

I'm doing an arc flash study for a data center. This is the first time I've modeled UPSs in a system and am trying to determine the important and superfluous information. The component model in SKM is pretty simple and it appears I only need kVA, voltage, and pf to include it in my study. Should I ignore the static by-pass and internal switches in my model. Do the characteristics of the UPS prohibit a fault from passing thru it?

Eric-

Check your UPS specs. Most UPS systems have very limited fault clearing capability, 300-500% of UPS output, for just a few cycles. If you have multiple modules, this may become significant as a low level type arcing fault, but only if you assume it continues for the entire 2 seconds (or whatever duration), even though it isn't capable of producing that much current, for that long. In reality, it may only sustain an overload ~150% for that long.

Since the UPS has solid state components, it will not directly couple a fault from the utility or generator through to the load side.

For any decent fault, the UPS will go to bypass in less than a cycle, but I'm not sure how to model this in SKM. I don't think there is a reasonable way to approximate a static switch firing either.

I believe at a minimum, you should model the UPS for low level faults as a stand alone source. This may require multiple scenarios if there are multiple modules.

Scenarios should also be run in bypass mode. Again, this may require multiple scenarios based on utility variables, and additional scenarios for generator(s) in operation.

Good luck

Are you modeling the battery side (DC) as well? Those need working on also (and live, since there's no disconnect on a cell itself).

We aren't modelling the DC side until IEEE-1584 provides a method. This is the subject of some research that is in progress.

I agree that UPS's are inherently current limiting. 300 to 500% would be an upper limit and I would model closer to the 300% level.

If you have a static (manual) bypass switch, then I would recommend that you base you arc flash calcs with the UPS bypassed. This would basically be the line fault current and the highest value. Granted its not in bypass often, but thats the time most likely for live work.

As an alternative, the Electrical Safety Program could prohibit live work while the UPS is bypassed.