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 Post subject: Ups
PostPosted: Mon Nov 23, 2009 1:40 pm 
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Joined: Mon Nov 05, 2007 10:10 am
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Location: Mid-West
When looking at arc flash in regards to large three phase UPS systems, curious to how others have modeled them in various software's as a UPS output of a 480V or even 208V UPS? there is a time prior to the UPS entering bypass mode? How does the UPS / inverter rectifier handle this?


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PostPosted: Mon Nov 23, 2009 9:22 pm 
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Joined: Mon Jan 26, 2009 5:00 pm
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Location: Midwest
Mike
most modules are pretty soft and have limited, short duration clearing. I would find a value in the specs that the system can put out for 2 sec duration. Use that in all possible combinations of modules in service. it's not enough to trp anything big instantaneous, but smoke a pdu and burn your eyebrows, probably.

For hard faults, the thing is going into bypass real fast, probably fast enough to neglect the half cycle of module and static transfer. Just model that as being hardwired to bypass and utility then repeat for gens.

I'm also going to try not to model the effects of an upstream closed transition transfer. Sorry skm only gives me 10 scenarios and I blew them all on n+1 modules and generators!

Steve


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PostPosted: Tue Nov 24, 2009 6:23 am 
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What about the battery side of a large UPS? A lot of energy is stored in them, and there are no fuses/CB between the cells, or between the of a single cell, so the clearing time can be long even though the voltage can be only 2 VDC.


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