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 Post subject: AF level at synch. gen breaker
PostPosted: Mon Mar 11, 2013 9:23 am 

Joined: Mon Mar 11, 2013 9:16 am
Posts: 4
Hi all,
I'm trying to determine the AF level at the breaker for a 4.5 MVA synchrounous generator.

With the utility isolated, I can calculate the level on the gen side of the breaker by using the generator decrement curve and fixing the time at 2 seconds, however, if I then connect the utility, I get significantly more fault current for the full two seconds even though differential protection would remove the utility contribution in a few cycles.

Is there a way to combine contributions from a decrement curve for two seconds and a utility source for a specified duration when calculating an arc flash level?

I'm using ETAP 12.

Thanks


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PostPosted: Wed Mar 13, 2013 8:30 am 

Joined: Mon Mar 11, 2013 9:16 am
Posts: 4
Can anyone help me with this?

The short version of the question is can ETAP calculate incident energy and boundaries based on different clearing times from multiple sources, and if not, is it permissible to do it by hand and how.


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PostPosted: Wed Mar 13, 2013 2:06 pm 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 822
Location: Rutland, VT
I don't know if ETAP has a feature like EasyPower that is called the Integrated method. The Integrated method takes into account the decreasing currents from motors and generators and also from multiple sources being switched out through protective devices tripping. Did you ask ETAP or look at the Help file?

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PostPosted: Thu Mar 14, 2013 2:11 pm 

Joined: Mon Mar 11, 2013 9:16 am
Posts: 4
I know it can integrate decrements curves from generators, but the multiple sources is the question. I haven't seen anything in the help file.
I might have to contact ETAP.


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PostPosted: Fri Mar 15, 2013 11:01 am 

Joined: Mon Mar 11, 2013 9:16 am
Posts: 4
ETAP recommended to create a dummy relay/breaker to set the clearing time on the generator side of the breaker to 2 seconds, then enable the subtraction of incident energy for multiple sources in the preferences menu.

This did the trick. Now I've got 2 seconds of contribution from the generator, and 0.103 seconds of contribution from the utility combined.


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