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| 1000 second clearing time https://brainfiller.com/arcflashforum/viewtopic.php?f=23&t=328 |
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| Author: | deprico [ Mon Feb 09, 2009 11:49 am ] |
| Post subject: | 1000 second clearing time |
Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this? |
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| Author: | jghrist [ Mon Feb 09, 2009 1:14 pm ] |
| Post subject: | |
deprico wrote: Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?
Rated current on a 700 kVA (odd size!) transformer is 842A at 480V. The fault current is not reasonable. |
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| Author: | haze10 [ Tue Feb 10, 2009 5:53 pm ] |
| Post subject: | |
1600A MCB is a bit oversized. Does it have a rating plug by which you can change the trip value. A trip value of 1200 or even 1000 amps would shift your trip curve. Even without this, your transformer should be 5 to 6% impedance, which means your fault current should be 15,000 amps. With a finite bus around 10 to 12 thousand amps. So you have something wrong. |
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| Author: | jghrist [ Tue Feb 10, 2009 8:37 pm ] |
| Post subject: | |
Maybe the software is looking at the incident energy on the line side of the MCB and is reporting the current in a protective device on the primary of the transformer. |
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| Author: | Gary B [ Thu Feb 26, 2009 8:03 pm ] |
| Post subject: | |
deprico wrote: Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?
If the software is saying 350A fault, I assume there is a length of feeder cable that should be protected by a small circuit breaker. I suspect you are missing a circuit breaker from your study (just guessing). Gary B |
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| Author: | JPEG [ Fri Feb 27, 2009 7:20 am ] |
| Post subject: | |
jghrist wrote: Maybe the software is looking at the incident energy on the line side of the MCB and is reporting the current in a protective device on the primary of the transformer.
Deprico: If you're using Easypower, jghrist found your problem. That's just how it presents the results. See the report «Upstream Trip Device Name». |
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