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 Post subject: Electric Utilities and the NESC
PostPosted: Thu Dec 27, 2007 7:24 am 
Sparks Level

Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
Anyone out there looking at this from a utility perspective? I have done some calcs using the Duke Flux program and the values are much lower (as expected) than with attempts to use the IEEE equations. Overhead distribution lines obviously exceed the range of the parameters (6" phase spacing...etc.) used in the IEEE studies. I am also investigating the use of Arcpro. Does anyone have experience with this software? The NESC folks were not as thorough as others and left us with "ballpark" tables or the use of commercially available software.


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PostPosted: Fri Jan 04, 2008 7:11 am 
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Joined: Thu Jul 19, 2007 7:54 am
Posts: 201
Location: St. Louis, MO
I've heard that the NESC uses ArcPro for the tables.


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PostPosted: Fri Jan 04, 2008 9:39 am 

Joined: Wed Jul 04, 2007 7:57 am
Posts: 6
Hey WDN do you know if anyone has backchecked the NESC tables against Arc Pro, i.e. has anyone out there run the numbers on their own?


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PostPosted: Fri Jan 04, 2008 10:10 am 

Joined: Wed Dec 12, 2007 6:54 am
Posts: 9
I am leading my company's efforts to comply with the NESC requirements effective 1/1/09. A significant percentage of our OH and UG distribution and OH transmission system has fault currents and clearing times that preclude using the tables in NESC C-2. We also have two underground network systems that present their own problems. We have not yet determined what methodology to use for determining the arc flash energies. Also since the distribution system configuration frequently changes we have concerns about actual values at the time work is to be performed.

I would be interested to hear how other utilities are approaching these issues.


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PostPosted: Fri Jan 04, 2008 10:53 am 
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Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1630
Location: Scottsdale, Arizona
I think everyone is beginng to take a good look at this in advance of the January 1, 2009 deadline. I just spoke at an electric utility workshop several weeks ago and this became a major topic of discussion. Many of the utilites were pondering the "what do we do" question. There are three methods that make up the basis for the utility analysis. For equipment i.e. switchgear, etc. where the phases can be close enough for a single phase flash to become a three phase flash, people are using commercial programs based on IEEE 1584. i.e. EasyPower, SKM, ETAP etc. For overhead lines, they were using programs like Arc Pro that has been mentioned in the forum a few times. The final method is some were holding their breath and using the tables as a first iteration and will move on to calculations later. For changing system configurations, people are running multiple "what if" cases to see if any of the cases cause a serious increase in the hazard. As you and many utility people are aware, the problem that most people had in common is that unlike industrial and commercial systems where the emphasis is on placing the equipment into an "electrically safe" working condition, you can't exactly de energize a transmission or distribution line. Over the past month there seems to have been an increase in NESC discussion. There is an NESC section in the forum also. Probably a good idea to check back from time to time to see where this discussion goes.

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PostPosted: Mon Jan 07, 2008 6:47 am 
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Joined: Thu Jul 19, 2007 7:54 am
Posts: 201
Location: St. Louis, MO
Steve Linford wrote:
Hey WDN do you know if anyone has backchecked the NESC tables against Arc Pro, i.e. has anyone out there run the numbers on their own?


Steve,
I saw someone on EngTips about a month back that was back checking the tables using ArcPro. He indicated he ran into some problems above 65kV, however, and could not find the anomaly. He thought it may be in the working distance. He said it checked until that point.

I found the thread on Eng-Tips. There are few details. http://www.eng-tips.com/viewthread.cfm?qid=204472&page=1


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PostPosted: Wed Jan 14, 2009 11:39 am 
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Joined: Tue Jan 13, 2009 5:00 pm
Posts: 576
That was me. Thanks to gobblerhuntr's recent post at Eng-tips, I've found this forum.
Table 2 was problematic. The [url="http://grouper.ieee.org/groups/nesc/TIA_5Sept2008.pdf"]TIA[/url] fixed the problem.


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PostPosted: Wed Jan 14, 2009 4:02 pm 

Joined: Mon Dec 29, 2008 10:14 am
Posts: 2
Location: Calgary, AB
You have to be very careful with Arc Pro. Its only been validated up to 35kV. However, EPRI is currently working on research for both Transmission and Distribution open air arc models which hopefully will be incorporated into Arc Pro or another software program over the next couple of years.


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