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ekstra   ara
 Post subject: Does this make sense? If so, then how?
PostPosted: Thu Apr 29, 2010 10:55 am 
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Joined: Thu Apr 29, 2010 10:49 am
Posts: 7
If I have a 225kVA 4.16kv/480V xfmr in my model and I run arc-flash using ETAP.

Is it possible that the high side gets a lower HRC than the secondary side?

Let's say there is a 50E fuse on the primary side.

The results come back as Cat 0 for the primary side and Cat 1 on the secondary side.

I am hesistant to put a Cat 0 stick on the primary side. Is there something wrong with my calculations or is this normal? I have seen this in a few other studies as well.


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PostPosted: Thu Apr 29, 2010 1:36 pm 
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Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
Yes. Arc flash is current Dependant, and you have much less on the primary side.


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PostPosted: Thu Apr 29, 2010 1:45 pm 
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Joined: Wed Jun 04, 2008 9:17 am
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Location: Spartanburg, South Carolina
And probably faster clearing.


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PostPosted: Fri May 14, 2010 6:41 am 
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I just found that to be kind of strange to have a low primary side but a really high secondary side when I am dealing with transformers in ETAP


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PostPosted: Fri May 14, 2010 6:46 am 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
titan wrote:
I just found that to be kind of strange to have a low primary side but a really high secondary side when I am dealing with transformers in ETAP


Normal to see that. A fault on the secondary side before the OCPD will rely on the primary fuses to clear the fault, but they will see much lower current levels on the other side of the transformer and have a long clearing time.


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PostPosted: Thu May 20, 2010 1:56 pm 
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Wouldn't the current levels be higher?


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PostPosted: Thu May 20, 2010 6:28 pm 
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Location: Spartanburg, South Carolina
titan wrote:
Wouldn't the current levels be higher?


Current level is inversely proportional to voltage level.


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PostPosted: Thu May 20, 2010 7:45 pm 
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Joined: Mon Jan 18, 2010 11:35 am
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Location: Wisconsin
titan wrote:
I just found that to be kind of strange to have a low primary side but a really high secondary side when I am dealing with transformers in ETAP


Most people are surprised that the secondary AFIE is so high compared to the primary. This is the reason that service entrance locations are usually aove 40 cal/cm┬▓. And why the 'task table' should not be used for these locations.


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