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ekstra   ara
 Post subject: Derating Factor (X/R ratio)
PostPosted: Wed Mar 04, 2009 12:15 pm 

Joined: Fri Jun 06, 2008 12:59 pm
Posts: 3
Location: Winnipeg, MB Canada
What if the symmetrical fault current is the same as the equipment’s rated current,
but the actual X/R ratio is larger than the tested X/R ratio? (MF=Iasym @ X/Rtestd-:-Iasy @X/Rcalc)


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PostPosted: Wed Mar 04, 2009 12:58 pm 
Sparks Level

Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
Not unless you have the sequence info as well. Unless it is very high then not a big deal anyway since most equipment is designed for x/r>1 per the standards.

If I remember correctly, Vacuum Circuit Breakers are required by the ANSI/IEEE standards to interrupt at rated AIC with an offset associated with an x/r=15.


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