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ekstra   ara
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PostPosted: Tue Sep 30, 2008 9:43 am 

Joined: Thu Sep 13, 2007 9:28 am
Posts: 12
Location: Kenai, Alaska
CRN Report to Non-Members

Hmmm .... that I don't know. I certainly know we can't post it on here w/o permission.

Got any friends at a coop that's a CRN member?


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PostPosted: Wed Oct 01, 2008 1:23 pm 

Joined: Wed Oct 01, 2008 1:21 pm
Posts: 1
Just a caution after reading this thread:
IEEE 1584 uses a theoretical model for 15kV and above that is extemely conservative and does not approximate actual arc energy at those voltages. You may get 50-100 cal/cm2 for a situation where ArcPro (based on single phase test data) gives a result of 4-8 cal/cm2.

Any time you're looking at 15kV and above, you should probably consider a method other than IEEE 1584.


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PostPosted: Wed Feb 17, 2010 1:14 pm 
Sparks Level

Joined: Tue Feb 17, 2009 8:38 am
Posts: 53
Location: Westminster, MD
haze10 wrote:
I just finished a job with the utility crews working 12.4KV live. All the crew have a normal FR uniform of Level 2. They dress with gloves and sleeves as needed.

The first question I would ask is if Utility Linemen fall under the NFPA70E regulations? Utilities are exempt from following the NEC. They could very well be exempt from NFPA as they constitute special conditions as a utility and linemen receive specific training and supervision.

My first thought is that you maintain the high, longtime setting to avoid nuisance tripping. When you have to work on the line you can reduce settings. Often utilities have reclosers with 2 to 5 recloses after a fault to clear the line. Its typical to disable the recloser when work is being performed. I would be pushing for longterm upgrades to install maintenance switches on reclosers and station breakers that can easily be turned on and off when work is being performed.

As far a PPE, I think you are limited to Level 2. The suits get way to bulky for a lineman at Level 3 and 4.


haze10,

I certainly don't direct this at you, because from the posts I've seen of yours this is stuff you are aware of, but in response to your post I offer:

The IEEE-1584 calculated HRC levels at higher voltages are significantly less than the low voltage (<600V) calcs because the arcing fault current for medium voltage is very close to the bolted fault current, whereas for low voltage it's around 60% of the bolted fault values. So the trip devices act much faster on the MV systems. I would expect that the level 2 suit covers most Utility applications, within reason.

I know it's logical to use maintenance settings for the low voltage gear, where the instantaneous levels are reduced to just allow system operation while working on the equipment. And there may be some merit to using them on the 5-15 kV class as well - certainly limit the recloser operations. But they may already be HRC 2 without doing anything to the settings.

I know from experience that on the unprotected secondary of a 3000 kVA transformer - looking at 480 Volt versus 4160 Volt systems - the 480 Volt system had about 150 cal/sqcm IE and the 4160 Volt system had less than 4 cal/sqcm IE. (HRC1)

John M


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PostPosted: Wed Feb 17, 2010 8:43 pm 
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Joined: Thu Jan 10, 2008 8:49 pm
Posts: 510
Location: New England
Mayanees,
Maybe it I didn't word it well, but I was basically agreeing with you, and offering some ideas to reduce accidents.

I'm not sure if you are saying , no FR PPE at all, as that I would not agree. We should not have lineman in polyester shirts. What I am saying is that a Level of 1 or 2 as a standard uniform is probably a good idea. The local utility I was working with had already established Level 2 as the standard uniform.


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PostPosted: Sat Feb 20, 2010 7:29 pm 
Sparks Level

Joined: Tue Feb 17, 2009 8:38 am
Posts: 53
Location: Westminster, MD
naw haze.. I'm saying HRC 2 PPE fits most of the lineman's requirements.
John M


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PostPosted: Mon Mar 01, 2010 8:40 am 
Sparks Level
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Joined: Sun Jan 04, 2009 5:00 pm
Posts: 286
Location: Louisville, KY
ArcPro vs...

All software systems I know of excluding ArcPro and Duke Heat Flux Calculator are based on IEEE 1584 equations. These are based on emperical data and are 3 phase data up to about 4160V. The majority of the data is in the 480V range.

The limit with IEEE 1584 is that it tends to over estimate >480V. Several reasons are to blame but the main one is that it extrapolates data to 15KV and then above this it reverts to the Ralph Lee equation which made arc energy directly proportional to system voltage (which is close at 480V and NOT close above that).

The other issue with IEEE 1584 is that is assumes 3 phases which is a much rarer event in 15kV systems on up and even when it happens doesn't always translate to more that much more energy to the worker. SKM does have another option in using formula derived from NESC tables (which came from ArcPro). These have a weakness to in that they assume an arc gap of 1-2 inches which is not realistic in many medium voltage events.

Care must be taken when using any model (emperical or theoretical or a combination) beyond it's range. ArcPro can be used safely up to around 33kV but factors would need to be used to account for 3 phase or arc in a box. IEEE 1584 is excellent to 480V but very limited usefulness beyond that. We don't use it past 4160V. Arcs on utility lines tend to travel away from the source and this could be taken into account. So many things to consider. But if your numbers don't make sense. There is help out there. Definitive answers are few and far between but IEEE 1584 is getting better each time and the next version may still have issues with medium voltage but an EPRI study might fill this gap in.


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