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 Post subject: Arc Flash Documentation
PostPosted: Thu Nov 13, 2008 8:54 am 
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Location: CA
How should Arc Flash studies be documented?

After the labels have been applied, how should the all the equipment data and software options that went into defining the labels be documented?
Has anyone come-up with a policy for maintaining all of these records and up-dating them as required?


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PostPosted: Mon Nov 17, 2008 10:20 am 
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We have issued an electronic format copy of the model that may be maintained by the customer using the same software we did (actually we matched their coorporate standard). We also issue a full short circuit report and arc flash analysis report that is the standard printout from the software. That is the standard stuff I am aware of.

In addition to this, we issued a label schedule with a serial number for each location that may be referenced to a marked up single line diagram. The acompanying report has disclaimers about the calcs only being valid in normal configuration and at this point in time, given the understood distribution system as per the single line diagram.

Having issued all that as a benchmark, we have been employed to update the study with new construction projects. Theoretically we have given the customer enough information that others could revise the work but so far they have chosen to come back to us.


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PostPosted: Wed Nov 19, 2008 11:27 am 
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Gary B,
Thank you for your reply.
Our facility has about 50 buildings, 13.8/7.2kV, and 115kV. We are using SKM's PTW software to do our own calculations and labels.

I like the idea of matching label serial numbers to the single line diagrams.

The software files, you mentioned, define the exact values used for the study, but that my not be useful five years from now when the software may change. Did you also provide printed reports showing all relay settings, cable impedances, etc...?

How did you handle various operating modes? We have many large motors and some unusually large motors. Two facilities draw 180MW each at full load. PG&E, our utility, has provided us with both max and min MVA ratings for their various operating modes. The permutations are mind-boggling.

Are there other AF Forum members who are plant operators doing their own calculations and labels? How have you modified you documentation control to include arc flash?


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PostPosted: Wed Nov 19, 2008 12:12 pm 
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ZeroSeq -

I did a arc flash analysis for a company in PG&E territory some years back and I must have been the first to request actual short circuit data at a specific location. I had to exchange numerous emails with their engineer as he kept replying to use an infinite bus methodology. After much education on my part, he finally provided a range. I got a range of 7 to 100 MVA. I ran several scenarios and since 7 MVA produced worst case, that was used. It was unfortunate as it led to many areas that were Category #3 and #4, which under a more reasonable scenario were #1 and #2.

I usually provide a hard copy printout of the data used (cables, protective devices and their settings) with the report, along with the AFH by bus location to back up label placement. Also in the report is a recommendation to contact the utility on a yearly basis to verify that the system has not changed. A sample letter is included for that.

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PostPosted: Tue Jan 06, 2009 10:37 pm 
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ZeroSeq wrote:
Gary B,
Thank you for your reply.
Our facility has about 50 buildings, 13.8/7.2kV, and 115kV. We are using SKM's PTW software to do our own calculations and labels.

I like the idea of matching label serial numbers to the single line diagrams.

The software files, you mentioned, define the exact values used for the study, but that my not be useful five years from now when the software may change. Did you also provide printed reports showing all relay settings, cable impedances, etc...?

How did you handle various operating modes? We have many large motors and some unusually large motors. Two facilities draw 180MW each at full load. PG&E, our utility, has provided us with both max and min MVA ratings for their various operating modes. The permutations are mind-boggling.

Are there other AF Forum members who are plant operators doing their own calculations and labels? How have you modified you documentation control to include arc flash?


Some executive decisions were made to simplify this:

1) it is assumed the distribution system was in "normal" configuration. If alternate feeders were in use etc. hot work was not to be performed. This facility had most motors on at one time, with an off line spare, so it was not difficult to estimate or consider 'normal'.

2) We printed out tables of relay protective settings. This was simplified to only include instantaneous, short term and long term settings etc. and not the multitude of other little logic function inherent in modern relays. THAT EXERCISE ALONE probably paid for our study in operating reliability, because so many anomolies were hidden in the previously too detailed files.

3) cable impedances were not documented but the modeled cables are in the software model and are supposed to match the single line diagrams. Most cable lengths were estimated.

4) At some point we had to make practical assumptions, and noted those, rather than getting stuck in perpetual academic thinking. For example if one calculates 12,000A max available and the instantaneous can be set at 4,000A, arc flash exposure will probably not suffer even if the utility is not up to maximum duty.


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PostPosted: Wed Jan 07, 2009 6:26 am 
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ZeroSeq,
I am performing the in-house study for my facility. It sounds like we are in similar situations. I have to use five separate SKM models to keep my facilities straight and stay within the 2000 bus limit. (granted, many of these are node buses between impedences.)

The utility contribution at my location is generally so large that most changes don't affect equipment downstream. We are being fed 161kV from the utility.

I've used the SKM scenario manager to keep up with operating modes, and have been able to isolate most transfer switches so that I have a minimum number of scenarios to go through. After running several case studies, I've been able to figure out what provides worst case fairly quickly.

So far, the project files are our largest documentation source. I have added many "user defined fields" to the components to be able to keep up with my notes on various buses and switches, etc. I keep the projects backed up, and GOD HELP who ever tries to take my SKM away! (I really should get some of the data exported, but have not found a good method that I like that I won't still have to go through and straighten to my liking afterward.)

As far as internal controls go, I am pretty well it. I try to keep everything documented so that the next poor sap won't have to figure out what I did and why, but there is no "official" methodology as of yet. We are still refining, and as SKM revizes, that opens up new methods for us. It's really a bit of a mess. There are others involved in the process, and there is a separate "design" department that does not use SKM as far as I know, so the whole process is a bit convoluted, as well as a few other "administrative" departments thrown in.
Bottom line, I try to keep good notes and files and stay informed of ongoing internal projects that modify my results...


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PostPosted: Sun Jan 13, 2013 5:17 pm 
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Hi every one,
I am conducting my first arc flash study for a substation.
I read a lot including IEEE Std, so I know what it is about.
However, I still need a hint by somebody who does it frequently. I need to know what equipment should I include in the study, and also i will be happy if somebody can provide me with a template of the final report.
Thanks on advance,
Eagle.


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PostPosted: Sun Jan 13, 2013 5:26 pm 
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Hello,
First off, please understand that I don't think you will receive a template report from anyone one this forum. I think that is beyond what the purpose of this forum is and their are many consulting engineers on this site who would consider that proprietary information.
That said, in your report you need to convey your assumptions, results and recommendations. Additionally, since you are doing it for a substation that makes a difference. Is the substation utility owned or customer owned? If utility, then the NESC applies.

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PostPosted: Mon Jan 14, 2013 4:01 pm 
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In addition to the concerns that wbd made, I believe liability would also be a concern for someone offering their template. Probably best to just think about how you perform the study, what goes into it, how do you present the data (what is available from the software etc.) and start building your model. Good luck!


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PostPosted: Sat Jan 19, 2013 12:28 pm 
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I have been doing our generating plant arc flash studies as part of my job for about 3 or 4 years now, and have completed about 15 of them. (Almost done! Now time to start reviewing the studies for the 5 year rule and fixing the mistakes I made in the past). Documentation has been one of the biggest challenges. Right now this is my method:
-I provide a report to the plant. Most of it is boiler plate, but I describe the various scenarios that I run - bas case, high fault, low fault, standby high fault, standby low fault etc. I also include an appendix with the oneline, protective relay settings and all of the input data. These are easily run in the data visualizer in SKM and don't take significant amounts of time, although they do take significant amounts of paper.
-Each report has a project binder. I put every scrap of hard copy information that I gathered into this - drawings, hand calcs, utility fault studies, distribution circuit maps, you name it. Field notes are probably the most important thing I keep, and I make sure I intial and date the notes.
-I also include a CD with the binder that includes the PTW files and all the electronic data I gathered including emails.

Most of this is in response to finding contractors studies terribly lacking in data. I remember when I first started this work I was trying to mimic a previously performed study to ensure I was doing the work properly. I couldn't do it, not enough data was provided.

I'm sure my method is not perfect, but it certainly has been useful. I often use data from previous studies in subsequent studies, and I'm pretty sure it'll make the next round of verification studies after 5 years a lot smoother. If nothing else seeing the documentation will make me trust the data that is in SKM, even if I don't review it in detail. I'll have to completely redo some earlier studies partly because I didn't save the documentation, and partly because my methods have become much more advanced and thorough.


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PostPosted: Sun Jan 20, 2013 2:25 pm 
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Part of a study too are assumptions. For instance it is normal to establish certain cutoffs (e.g. <1.2 cal/cm2 if not marked) and assumptions such as about the utility, various scenarios (e.g. bus tie closed), when you use line vs. load faults, recommended settings, and when you deviate from the standard such as changing working distance when appropriate.It is also very important to document software settings. Simply telling SKM to ignore line/load side, changing the simulation time limit, or how the software deals with subtransient and transient reactances can matter a great deal.


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PostPosted: Tue Mar 05, 2013 9:25 am 
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Hopefully I am not posting this question to the wrong forum, if so, please correct me. In observing the NFPA 2012 requirements, can we still use the tables provided to do our calculations? Thank you for any input on this you can provide.

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PostPosted: Thu Mar 07, 2013 3:36 pm 
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Yes you can as long as you meet the conditions of the table. For example Table 130.7(C)(15)(a), for Panelboards or other equipment rated >240V and up to 600V the parameters are: max of 25 kA short circuit current available; maximum of 2 cycle fault clearing time, so some analysis is needed.

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PostPosted: Thu Mar 28, 2013 1:52 am 
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That makes the tables almost useless. You need to perform a short-circuit calculation. Then you need to know the time-current response of the OCPD. You have to enter the calculated short-circuit in the TCC graph and determine the opening time of the OCPD. Then you have to compare these two results against the maximum values permitted by the table. You might as well perform the calculated incident energy analysis.


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