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 Post subject: Coordination Studies - where is the Standard reference?
PostPosted: Wed Nov 25, 2009 7:19 am 
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Where is the reference (OSHA, IEEE, NFPA70E) that says our arc flash studies need to include a coordination study? I know (we all know here) that we need to do coordination to have a full arc flash picture, but I have some customers who are trying to cut corners (and costs). I'd like to have a reference to bolster my case.


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PostPosted: Wed Nov 25, 2009 8:28 am 
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While selective device operation is a desired result for operations don't know that it is necessary for arc flash calcs. If the upstream device ends up being faster, the IE you calculated for the downstream device based on it's clearing time just became lower.

Helps from an arc flash standpoint, hurts from an operation point of view.

However, if you do the coordination in concert and end up lowering the trip time for the downstream device for proper operations, it will get better for the arc flash study.

I guess you could do the arc flash study, then the coordination, and then go back and redo the arc flash study. :)

While I do believe they should be done together, don't know that it is necessarily required for arc flash calcs.

Others?


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PostPosted: Wed Nov 25, 2009 9:57 am 
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Alan, did you just talk around a circle? :)

If no PDCS is done and you just use the settings they have, I would make sure you have a disclaimer stating so. And chances are they have some settings "cranked way up" so you AF results will be higher in most cases than they need to be. In the long run, IMO, this "shortcut" will end up costing your customer more in the long run.


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PostPosted: Wed Nov 25, 2009 10:07 am 
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Coordination is not needed for arc flash, use the fastest clearing device.

Best solution may be the maintenance instantaneous setting which throws coordination out the window.


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PostPosted: Wed Nov 25, 2009 10:13 am 
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re: coordination

clarification (maybe): All the arc flash studies I've seen from consulting firms include short circuit analysis, coordination, and arc flash anlysis. Is there a standard that says we need to include all these (particularly coordination) in our studies?


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PostPosted: Wed Nov 25, 2009 12:00 pm 
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uriah1 wrote:
clarification (maybe): All the arc flash studies I've seen from consulting firms include short circuit analysis, coordination, and arc flash anlysis. Is there a standard that says we need to include all these (particularly coordination) in our studies?


I dont know any standard that says you must do a coordination study, but if you dont, you will simply get a "picture" of the plant hazard levels, without the possibility to use the easiest solution to several cases, wich is the coordination study...

This and Zog comment usually convince most customers that a coordination study is needed.


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PostPosted: Wed Nov 25, 2009 12:06 pm 
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Alan, did you just talk around a circle?

Sure did! Just summing up the difference in the requirements of the standards and opinion......with some fun as well.

Happy Thanksgiving to all.


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PostPosted: Wed Nov 25, 2009 12:35 pm 
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mandatory selective coordination

I found this, so I thought I'd share it...

The NEC® has mandatory selective coordination requirements for the following systems.
Emergency Systems- Article 700

700.27
Legally Required Standby Systems- Article 701

701.18
Critical Operations Power Systems- Article 708

708.54
Healthcare Article 517

517.26 Required for Essential Electrical Systems
(In addition, selective coordination is required in elevator circuits (620.62), which is not discussed in depth in this paper.)


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PostPosted: Mon Nov 30, 2009 8:44 am 
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uriah1 wrote:
clarification (maybe): All the arc flash studies I've seen from consulting firms include short circuit analysis, coordination, and arc flash anlysis. Is there a standard that says we need to include all these (particularly coordination) in our studies?


There is no standard that says what is to be included in an arc flash study at all.
Yet.

Our host is working with the IEEE 1584 committee to develop an arc flash study standard, and maybe he included these others in the arc flash standard.
Jim?


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PostPosted: Wed Dec 02, 2009 5:08 pm 
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WDeanN wrote:
Our host is working with the IEEE 1584 committee to develop an arc flash study standard, and maybe he included these others in the arc flash standard.
Jim?


... you rang?

NEC Article 620 also references coordination. Elevators and emergency power system coordination both have a lot of politics behind it that I won't go into here. I was interviewd by EC & M magazine in 2007 about it all since I have performed hundreds of them and teach the stuff. For better or worse, I was pretty direct about what was going on.

Several organizations also have their own mandates for coordination, I know the Veteran's Administration used to mandate studies, I imagine they still do. I believe the Army Corp and FAA also do. I'm pretty sure the state of Florida, may also require it - they were one of the first back in the 1980's - Friends from Florida, please correct me if I missed that one. I have taught many people from several of these agencies/organizations over the years about how to perform coordination studies.

There is a draft of IEEE 1584.1 which is a document that can be used for specifying studies. I co-authored it and just completed a total re write earlier this year. A new draft was just sent to a few people for comments this week.

It is being developed to create a more level playing field in the area of studies since there are quite a few "snake oil salesman" providing studies that are not truly arc flash calculation studies.

The draft does reference the need for protective device clearing times as part of the calculations and states they need to be obtained from a coordination study but stops short of requiring the coordination study as part of the arc flash study.

I wanted it included but our official scope dictates that we focus on the arc flash calculations and study rather than expand it to included other studies.

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PostPosted: Fri Dec 04, 2009 9:02 am 
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thank you very much, Jim


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PostPosted: Wed Dec 09, 2009 6:45 am 
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I'll put in my 25cents, it used to be 2cents.

I deal with older plants and find that equipment duty study is also important to note while doing a power analysis study. I do not call any study just Arc Flash, you can but your not looking at the big picture. I have found several bad applications of protective devices.
Again, like coordination, equipment duty is not a necessary part of the study. But all the study components make for a great model of the systems safe and reliable operation.

IMO, I believe many companies are looking at the quickest, cheapest method to show compliance but lack the knowledge of all the factors involved in electrical safety and reliability. Again IMO, unless someone shows me different a significant error in equipment duty ratings poses a hazard, while coordination is a reliability issue.


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PostPosted: Wed Dec 09, 2009 8:07 am 
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Exactly! I see this as a very big problem. There are many people that understand parts of the overall problem but not the total picture, i.e. they understand PPE but not the other very important areas of the power systems such as short circuit and coordination or how important correct system modeling can be.

I agree coordination is a desired outcome but unless it is a matter of life safety or similar issue it is usually just a realiability issue. However since incident energy is directly related to a protective device clearing time, coordination now plays a critical role in ALL power systems where an arc flash study is being performed. Often a simple solution for lowering the incident energy is to use the coordination study to determine setting changes (ususally temporary) to lower the clearing time.

Short circuit studies are very much a safety issue. Even NEC Article 110.9 and 110.10 spell this out. Overdutied equipment can presesnt a very serious hazard.

Unfortunately, I have seen many cases where the owner does not want to hear this. "Just use typical data" or "we already had a short circuit study performed....... ... in 1972" or "if you are going to make me include the other studies I will find someone else" are all very common and very incorrect responses.

A complete arc flash calculation study needs to include both the short circuit and coordination study as well as proper system modeling of utility contributions, conductors, transformers etc. This is one of the primary reasons why a "complete" arc flash calculation study can be quite a lengthy and expensive process. If a person is attempting the arc flash study without a good understanding of power system analysis, there could be trouble ahead.

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PostPosted: Wed Dec 09, 2009 9:26 am 
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Thanks Jim,
Okay, you converted me on coordination from a reliability tool to include coordination as a tool to reduce Ie. :o Thanks for guiding me from that foggy state of mind. I new that about coordination, but was focusing on the importance of a total study to include equipment duty ratings and opened mouth for the foot.

I must emphasis to all newbie’s that all cannot be learned from the NEC, NFPA 70E & IEEE-1584. Jim has started a great forum to learn from. There is so much more to consider then just the AF. Newer facilities may not have the concerns that a plant >10 years old may have. For me its better to consider and look at everything possible during a study.


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