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ekstra   ara
 Post subject: Can someone explain to me....?
PostPosted: Tue Dec 01, 2009 3:59 pm 
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Joined: Sat Nov 21, 2009 3:10 pm
Posts: 25
When running the short-circuit analysis portion of the analysis, the program I am using shows a higher Isc current at a MCC bus then it does at the utility xfmr that is feeding this particular MCC. Can someone explain this to me?

Typically when I have done short circuit analysis by hand it has always been lower do to the distance between buses, equipment, etc. So, I am a little caught off guard here.

Thanks in advance for anyone's help!


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PostPosted: Tue Dec 01, 2009 6:57 pm 
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Joined: Mon Jan 26, 2009 5:00 pm
Posts: 46
Location: Midwest
bruinfan-

Your motor contribution be offsetting the reduction in utility current from the impedance between the transformer and the MCC.

Try reducing motor contribution by taking them out of service or reducing the contribution to 0 cycles.

a hawksfan


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PostPosted: Wed Dec 02, 2009 9:08 am 
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Location: Kansas city
The bus you are referring to at the utility transformer: is it on the primary or the secondary side of the transformer?


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PostPosted: Wed Dec 02, 2009 9:44 am 
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It is on the secondary. The transformer feeds the MCC bus.


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PostPosted: Wed Dec 02, 2009 8:19 pm 
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Joined: Thu Jan 10, 2008 8:49 pm
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Location: New England
Motor contribution is highest at the MCC bus, because there is cable impedance to get back to the secondary xfrm terminals.


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