Me either!
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| Motor Contribution Too High https://brainfiller.com/arcflashforum/viewtopic.php?f=2&t=1645 |
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| Author: | blane [ Wed Mar 30, 2011 1:20 pm ] |
| Post subject: | Motor Contribution Too High |
I'm using SKM Power Tools in a study. The facility has 15 Motors over 50hp. The Isc 3P feed back to the main breaker is calculated at 69,390 A. This seems way to high when the main feed is only 38,157 A. Is this normal? |
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| Author: | jghrist [ Wed Mar 30, 2011 1:47 pm ] |
| Post subject: | |
Total HP? Voltage? |
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| Author: | blane [ Thu Mar 31, 2011 4:19 am ] |
| Post subject: | |
1200 HP Total, 480V |
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| Author: | jghrist [ Thu Mar 31, 2011 7:50 am ] |
| Post subject: | |
A rough approximation of motor contribution would be to assume 6 times FLA and HP = kVA, so 1200 HP would have 6*1200/0.48/sqrt(3) = 8,660 A fault contribution. There is a problem with the 69,390 A value. |
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| Author: | BCR_1962 [ Thu Mar 31, 2011 8:43 am ] |
| Post subject: | |
If you are using SKM, in your motor data pages check what you have in the LRA/FLA field (locked rotor to full load, the default is 5.88). Did you accidentally enter a HP value in one of these fields for a motor? Bob Ragsdale P.E. |
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| Author: | blane [ Fri Apr 01, 2011 4:51 am ] |
| Post subject: | |
Thank you both for your help. I entered the FLA in the LRA/FLA field for the motors. Once changed, it looks much better. Thanks |
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| Author: | BCR_1962 [ Fri Apr 01, 2011 6:29 am ] |
| Post subject: | |
Not that I've ever done that. |
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| Author: | Ex twidget [ Fri Apr 01, 2011 11:13 am ] |
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Me either! |
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