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 Post subject: Solving for IE
PostPosted: Tue Jul 17, 2018 10:08 am 

Joined: Tue Jul 17, 2018 9:47 am
Posts: 1
I am a Mechanical Engineer conducting an Arc-Flash Study for my plant to become 70e compliant. I am demoing the Easypower system and created a 1-line diagram of one of my systems that is fed from the utility to a transformer and then into a 480V 3000A Switchgear that feeds the rest of the system. I've played around with the numbers manually and in Easypower, but I think I'm more confused by my discrepancies. According to my manual calculations, the closing time is no more than .08 seconds, and after figuring the Incident Energy of the main, the switchgear IE should be 8.2 cal/cm2. Easypower didn't label it and claimed it didn't have any upstream protection. If that is the case how would I label the switchgear, if at all?

Thanks.


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 Post subject: Re: Solving for IE
PostPosted: Wed Jul 18, 2018 12:01 pm 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 822
Location: Rutland, VT
Hello,

I will be very honest with you and say that you are above your head in this endeavor. One needs to have a good understanding of electrical systems, arc flash studies and the software being used.

You refer to closing time but it should be opening time. Where did the 0.08s come from? Were you using arcing current on a tcc to determine? If you have the software set to ignore Main, then there is no main to trip. Can the main be used as if it is not separated from the bus, then it cannot be used.

You may be setting up employees to be underprotected if you do not have an thorough understanding of the subject matter.

Since you are just demoing the software, you might want to obtain some proposals to do the study. It may be less than you think.

I haven't even begun to tell you about the data collection.

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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 Post subject: Re: Solving for IE
PostPosted: Wed Jul 18, 2018 3:21 pm 
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Joined: Sat May 17, 2008 5:00 pm
Posts: 85
I agree with WBD's comment. This study is not just a calculation exercise or "plug and chug" People's live's are at stake and the studies can be quite complex. For your question, it is likely that the software was searching for the next device upstream which is a common approach. The concern is a local arc flash could escalate above the protective device so the 0.08 second clearing time wouldn't be the determining factor for the arc duration.


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 Post subject: Re: Solving for IE
PostPosted: Wed Jul 18, 2018 4:29 pm 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 822
Location: Rutland, VT
I feel compelled to go farther to comment on the complexities of a study.
Do you know what an overdutied breaker is? What do you do when there are overdutied breakers/buses/switches are found? Do you know how to do protective device coordination? Do you know about techniques to reduce incident energy and not compromise coordination? Do you know how to do TCCs. What do youdo about motors with vfds?
Who is going to do the data collection? Do you know what data is needed? Do you know how to make a reasonable engineering judgment if data can’t be ontained? Do you know what data to ask the utility for?
And then there is labeling...what gets labeled? Are there muliple scenarios withemergency generatorsetc

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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